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Impact analysis of fiber reinforced polymer honeycomb composite sandwich beams
Abstract
Large scale fiber reinforced polymer (FRP) composite structures have been used in highway bridge and building construction. Recent applications have demonstrated that FRP honeycomb sandwich panels can be effectively and economically applied for both new construction and rehabilitation and replacement of existing structures. This paper is concerned with impact analysis of an as-manufactured FRP honeycomb sandwich system with sinusoidal core geometry in the plane and extending vertically between face laminates. The analyses of the honeycomb structure and components including: (1) constituent materials and ply properties, (2) face laminates and core wall engineering properties, and (3) equivalent core material properties, are first introduced, and these properties for the face laminates and equivalent core are later used in dynamic analysis of sandwich beams. A higher-order impact sandwich beam theory by the authors [Yang MJ, Qiao P. Higher-order impact modeling of sandwich beams with flexible core. Int J Solids Struct 2005;42(20):5460–90] is adopted to carry out the free vibration and impact analyses of the FRP honeycomb sandwich system, from which the full elastic field (e.g., deformation and stress) under impact is predicted. The higher order vibration analysis of the FRP sandwich beams is conducted, and its accuracy is validated with the finite element Eigenvalue analysis using ABAQUS; while the predicted impact responses (e.g., contact force and central deflection) are compared with the finite element simulations by LS-DYNA. A parametric study with respect to projectile mass and velocity is performed, and the similar prediction trends with the linear solution are observed. Furthermore, the predicted stress fields are compared with the available strength data to predict the impact damage in the FRP sandwich system. The present impact analysis demonstrates the accuracy and capability of the higher order impact sandwich beam theory, and it can be used effectively in analysis, design applications and optimization of efficient FRP honeycomb composite sandwich structures for impact protection and mitigation.
... Several studies have found that the energy absorption and dissipation during the vibration of a complex sandwich structure are highly influenced by the structure, material properties, and dimensions of the outer layers and core [124][125][126][127][128][129][130]. Sandwich beams are generally more effective than homogenous ones on reducing vibrations [125]. ...
... It has been found that the energy absorption and dissipation (i.e. vibrations response) of such structures is influenced by their structure, material properties, and dimensions of the outer layers and core [128][129][130]. In fact, research has shown that complex beams are generally more effective than homogenous ones for vibration reduction applications [125]. ...
... Several studies have found that the energy absorption and dissipation during the vibration of a complex sandwich structure, as in Figure 3-3, is highly influenced by the structure, material properties, and dimensions of the outer layers and core [124][125][126][127][128][129][130][131]. The conductor vibration behaviour at low frequencies is dependent on the weight of both components, but it is dominated by the properties of the most tensioned one [152]. ...
The electricity generation and demand have increased rapidly in recent years due to the improved quality of life, developed renewable energy strategies (RES), and electrification of traditional heat and transport energy sectors to replace fossil fuels. To accommodate this trend, electric utilities try to avoid the expensive traditional solution of building new overhead lines (OHLs) and reinforce existing networks through re-tensioning old conductors or re-conductoring with High-Temperature Low-Sag (HTLS) conductor technologies. The effect of conductor structure and material properties of its individual components (core and aluminium) on the vibrations response have not yet been captured thoroughly in the literature. This thesis investigates the possibility of increasing the electrical network power capacity by constraining the OHL-Conductor system design to aeolian vibrations and therefore evaluates the appropriateness of existing conductor vibrations methods for the various conventional conductor sizes and new conductor technologies. In this respect, a vibrations model is developed based on the standard method known as the Energy Balance Method (EBM) which permits evaluating conductor vibration response in terms of vibration amplitudes and bending stresses for all expected wind-excitation frequencies and mitigating their performance with vibration dampers. An effort towards improving the existing models within the EBM to predict the vibrations response of HTLS conductors has been achieved by incorporating the tension-temperature characteristics within the damping system formulation to form the so-called STARcol-EBM. To validate the developed model, the obtained analytical solutions are compared with field recorded measurements available in CIGRE and collated by ESB. The analytical solutions showed that CIGRE-EBM does not account for the structure and material properties, while STARcol-EBM provides more accurate predictions of conductor vibrations response. However, there are inaccuracies in low frequencies which requires further investigation. Moreover, a Finite Element Model (FEM) has been established in COMSOL to study the free and forced wind-induced vibrations and the resultant fatigue on single multi-layer conductors considering their complex round and trapezoidal stranding patterns. The FEM analysis is based on Multiphysics accounting for the conductor’s thermal and mechanical aspects as well as material and geometry properties. Consequently, the fatigue is quantified for both inter-layer and inter-wire interactions. The simulations show that free conductor vibrations are dictated by the conductor materials and tension distribution between the core and aluminium strands. Forced vibration simulations identified non-linear fatigue stresses for round and trapezoidal designs, which is more pronounced in larger conductor sizes. Furthermore, CFD simulations developed for wind flow around single OHL conductors with different outer layer stranding shape and sizes utilising COMSOL. Thus, an equation was established numerically to quantify the induced forces into the conductor, permitting the feasibility of using FEM solutions to develop the wind-induced forces into the OHL conductor span. The proposed FEM is limited to the efficiency of used computers and consumed time.
... The effectiveness of the technique was successfully verified by comparing with numerical and experimental results. A limited number of theoretical studies on wave propagation in sandwich structures have also been reported which investigate the dispersion characteristics and elastic response of the propagating GWs due to transient surface loading [31][32][33][34]. More efficient 2D semi-analytical models with limited applications have been developed for GW propagation in sandwich plates [35][36][37]. ...
... The effectiveness of the technique was successfully verified by comparing with numerical and experimental results. A limited number of theoretical studies on wave propagation in sandwich structures have also been reported which investigate the dispersion characteristics and elastic response of the propagating GWs due to transient surface loading [31][32][33][34]. More efficient 2D semi-analytical models with limited applications have been developed for GW propagation in sandwich plates [18,35,36]. ...
... This is because only the implicit solver is not sufficient to accurately handle the simulation of wave propagation. Moreover, the piezoelectric elements are not available in the explicit code but it is available in the implicit code in ABAQUS [31]. Therefore, the 3DCSCS (500 mm × 500 mm × 7 mm) plate is modeled using the explicit code and the PTDs (10 mm diameter and 0.4 mm thin) are modeled using the implicit code. ...
3D-core sandwich composites are novel lightweight construction materials being used heavily in defense,
aerospace, marine, and automobile industries. In spite of the many commendable advantages, the 3D-core
sandwich composite structures are prone to barely visible low-speed impact damages that may significantly
jeopardize the safety and integrity of the structural assembly. The aim of this paper is to develop an advanced
structural health monitoring framework to efficiently identify such damages in the sandwich structure using
ultrasonic guided wave propagation. Theoretical analysis, numerical simulations and laboratory experiments of
guided wave propagation in 3DCSCS have been carried out to demonstrate the effectiveness of the identification
of barely visible impact damages. It is found that the presence of such damage regions significantly magnifies the
fundamental antisymmetric mode of the propagating signals. The 3D numerical simulation gives physical insight
and a good agreement has been observed with experimental results which affirms our understanding of the effect
of damage on the propagating waves. The impact damage regions in the sandwich structure are experimentally
identified using a modified signal difference algorithm based health monitoring framework. The proposed
structural monitoring framework is found to be significantly efficient for the detection of impact damages in a
sandwich structure.
... Frostig et al. 25 integrated classical thin plate theory with three-dimensional elasticity theory to propose a novel higher-order theory capable of addressing various types of loading and distinguishing loads applied on different skins. Qiao et al. 26 proposed a high-order impact sandwich beam theory for modeling sandwich beams with a flexible core. This model is capable of predicting the fully elastic field and high-order vibration analysis under impact. ...
... 6g, 8g, and 10g increase from 172.41 Hz, 170.8 Hz, 168.9 Hz, 166.3 Hz, and 164.5 Hz to 201.1 Hz, 194.8 Hz, 187.2 Hz, 178.9 Hz, and 171.6 Hz, respectively. The main reason for this phenomenon is that the increase in the thickness of the honeycomb layer leads to an increase in the stiffness matrix K and mass matrix M in Eq.(26). ...
This study investigates the nonlinear vibration characteristics of all-composite honeycomb core sandwich panes (ACHCSPs) based on high-order shear deformation theory, Gibson equivalent theory, and Jones–Nelson–Hui nonlinear theory. In this model, the intermediate honeycomb layer is equivalently represented as a single layer of orthotropic material. The energy equation is established using the energy method, and the nonlinear vibration characteristics are determined using the Newton–Raphson method. To validate the model, experimental specimens of ACHCSPs are prepared, and an experimental platform is constructed for nonlinear vibration testing. Finally, the influence of honeycomb layer thickness, honeycomb unit wall thickness, and wall length on its nonlinear vibration characteristics is discussed. The results indicate that the proposed theoretical model can effectively predict the nonlinear vibration characteristics of ACHCSP. Additionally, within the allowable range, it is possible to appropriately increase the honeycomb unit wall thickness or decrease the wall length.
... Consequently, the impact performances were evaluated to study the effect of low-velocity impact on the electromagnetic performances of 3DWS-MAs, as shown in Fig. 6. The impact experiments were carried out under the energies of 2, 4, 6, and 8 J, respectively, in order to contrast with other antennas [49][50][51]. Fig. 6a-h showed that the dent of structure gradually deepened in radiating patch as the impact energy increases from 2 to 8 J for both 3DWS-MA-F and 3DWS-MA-T. However, for the 3DWS-MA-F, when subjected to the impact energy of more than 4 J, delamination was gradually occurred in the ground plane, and when the impact energy reached 8 J, both patch and ground plane were delaminated, proving that delamination is the major failure mode for glued antennas. ...
... However, when the antenna was under the impact energy of 8 J, S 11 curve was obviously changed, while the resonant frequency was shifted from 2.42 to 2.5 GHz, which was caused by the structure delamination of patch and ground plane. Therefore, the 3DWS-MA-T proposed in this study showed better damage resistance than other composite antennas consisting of sandwich panels and glass fiber composites, which malfunctioned under 2 J impact energy due to the delamination of structures [50,51]. ...
Wireless communication technology plays a crucial role in the development of aviation and aerospace owing to the increasing demand for high performance, lightweight, environmentally adaptability, and structural stability. With these advantages, three-dimensional woven spacer structure becomes a potential platform for microstrip antennas, which is a significant candidate in wireless technology. In this study, we proposed an ultra-light-weight Kevlar/polyimide 3D woven spacer microstrip antenna (3DWS-MA-T) by embedding the conductive copper threads into the fabric to form an integrated structure. The fabricated 3D woven spacer composites (3DWSCs) overcome the conflict between lightweight and strong mechanical properties, exhibiting ultra-low volume density of 0.34 g/cm³ and compressive strength of 3.8 MPa. The resulting all-textile multifunctional 3DWS-MA-T achieved superb electromagnetic performance (gain value > 5 dB) with a good impedance matching (S11 value < −20 dB) and a working frequency near the designed frequency of 2.4 GHz. Furthermore, the antenna demonstrated perfect structural integrity, exhibiting a suitable maintenance of resonant frequency and impedance matching after the impact of 8 J or a treatment in extreme low/high temperature. The 3DWS-MA-T can be readily incorporated into the structural component of the airplane, satellite, or high-speed vehicles without sacrificing its functionality and mechanical performance, signifying great potential in multifunctional composites.
Graphical abstract
Proposed an ultra-light weight antenna with superb structural integrity and stable electromagnetic performance (gain > 5 dB) for aerospace applications
... Many researchers [25][26][27][28][29][30] have presented a theoretical analysis of elastic-wave propagation in layered-structures. A theoretical formulation of wave propagation in the sandwich structure under specified boundary and interface conditions was presented in Ref. [25]. ...
... A theoretical formulation of wave propagation in the sandwich structure under specified boundary and interface conditions was presented in Ref. [25]. Based on predefined prior kinematic assumptions, some researchers [26][27][28][29] presented higher-order wave propagation formulations for sandwich structures. In Ref. [30], a twodimensional (2D) Thomson-Haskell method based theoretical model was proposed to calculate dispersion curves, displacements and energy distributions of different Lamb modes. ...
This paper presents a theoretical, numerical and experimental analysis of Lamb wave propagation and joint-debond identification in an advanced composite structure with core-junction. In the process, the wave modes in the recorded sensor-signals are effectively identified based on the theoretically obtained time-history response and dispersion curves for the sample structure. In order to study the core-junction and joint-debond effects, the finite element based numerical simulations were carried out in ABAQUS and the results verified with laboratory experiments. It was observed that the presence of core-junction in the structure reduces the propagating Lamb wave mode amplitudes, whereas the presence of localized joint-debond significantly increases the modal amplitudes. The study was further extended for the analysis of variable core-junction thickness and joint-debond size effects on the amplitude difference between the baseline and affected Lamb wave signals. Finally, a baseline-free debond detection strategy is proposed for the detection of hidden joint-debond locations in the target structure.
... Stiffness and strength are the most important properties of sandwich structures that should be considered in design together with weight and cost. Researchers used experimental , numerical [1, 2, 5, 10, 14, 16, 17, 19-21, 23, 24, 27-36], and analytical [2, 3, 7, 14-16, 18-20, 22-26, 28, 31, 32-39] methods to investigate mechanical response and failure behavior of sandwich plates with honeycomb [5, 6, 7, 10, 12, 15-17, 19, 25, 30, 33-35], corrugated [1,27,29], foam [1, 2, 7, 8, 9, 11, 13, 17, 21-23, 26-28, 30, 36, 38], truss [3,18,24,39], and web [27,31] cores under static and dynamic [5,12,14,30,34] loads. Several failure modes were investigated by the researchers including core crushing [5,6,10,12,17,25,19,24,25,27,28,35,39], delamination [4,8,18], yielding or fracture of face sheets [3,7,12,25,26,28], face wrinkling [3,7,12,20,22,24,38], buckling [4,11,18,24,25,27,32,33,37,39], indentation [2, 3, 7, 9, 10, 12, 14-16, 21-23, 34, 37, 38], face sheet-core debonding [4,11,27,32,36], and core shear failure [3, 7, 8, 12-15, 18, 19, 22, 24, 26-28, 35, 38, 39]. ...
... For this purpose, three-point bending tests [1, 3, 4, 7-9, 12-16, 21, 22, 25-27, 36, 38, 39], four-point bending tests [7,20,28,31,38], in-plane compression tests [4-7, 11, 24, 27, 29, 32, 33], flatwise compression tests [4,10,17,19,27], and indentation tests [2, 3, 7, 9, 10, 12, 14, 15, 21-23, 34, 37, 38] are conducted. Some researchers [13,15,20,22,25,28,30,34,39] proposed methods to predict failure and its mode. Overall, the core material should have sufficient stiffness to prevent local buckling and sufficient strength not to sustain damage. ...
In this study, a new core design is introduced for sandwich composite structures. Its strength and failure behavior are investigated via three-point bending tests. E-glass-fiber-reinforced epoxy resin is selected as the material for both the core and the face sheets. The core has an egg-crate shape. Acoustic emission (AE) method is used to detect the progression of damage. Signals due to elastic waves caused by activated damage mechanisms are investigated in order to identify the corresponding failure modes. A finite element model of the sandwich structure is developed to predict the failure behavior of the specimens under the loading conditions in the tests. A promising agreement between the results of the finite element model and the experiments is observed. The force-deflection- relation, the failure load as well as the region where damage initiates are accurately predicted.
... The design of a core depends on the application. There are many types of designs for cores such as hexagonal [81], sinusoidal [88,57,58], entangled [10], corrugated [89], egg honeycomb [69], pyramidal [69], square [72,66], and triangular core [72,90]. The most popular design for a honeycomb core is a hexagonal core and sinusoidal core (Table 3). ...
... The failure modes of the aramid fiber cores, density 48 kg/m 3[58]. ...
Researchers have worked on variety of natural fibers reinforced with polymer composites using different parameters to come up with various recommendations. The investigation involved aspects of composition materials and mechanical properties of natural fiber composites. The satisfactory results of natural fiber composites have encouraged researchers to delve deeper into the abilities of natural fiber composite in the form of a core structure. The potentiality of utilizing natural fiber composite in core design has wide potential in modern industries. This paper presents a review on natural fibers and polymer matrices commonly used in core fabrication, core design, fabricating processes of cores, and mechanical properties of cores. Ongoing research of rice husk composites to be fabricated in the form of honeycomb core structures is also discussed.
... The central displacement history of the top face sheet of a simply supported isotropic sandwich beam is computed from the present approach and compared with the one evaluated by Qiao et al [6]. The results reveal that the peaks of the central transverse displacement of the top face sheet based on present theory are higher (Figure 2). ...
... The results reveal that the peaks of the central transverse displacement of the top face sheet based on present theory are higher (Figure 2). This is because that the results of Qiao et al. [6] were achieved based on HSAPT in which the face sheets follow the classical beam theory. ...
The response of sandwich beam with carbon nanotube (CNT) reinforced composite face sheets and soft core when subjected to the action of an impacting mass is analysed theoretically. Contact force between the impactor and the beam is obtained using the conventional Hertz law. The field equations are derived via the Ritz based applied to the total energy of the system. The solution is obtained in the time domain by implementing the well-known Runge–Kutta method. After examining the validity of the present solution, the effects of distribution of CNTs, nanotube volume fraction, core-to-face sheet thickness ratio, initial velocity of the impactor and the impactor mass are studied in detail. Finally, it is concluded that, the highest peak contact force and the lowest indentation of the top face sheet belong to the sandwich beam with V-distribution figure of face sheet, followed by the uniformly distributed and Λ-ones, respectively. Keywords: Carbon nanotube fibers, sandwich beam, soft core.
... A limited number of theoretical studies on wave propagation in sandwich structures have also been reported which investigate the dispersion characteristics and elastic response of the propagating GWs due to transient surface loading [31][32][33][34]. More efficient 2D semi-analytical models with limited applications have been developed for GW propagation in sandwich plates [18,35,36]. ...
... This is because only the implicit solver is not sufficient to accurately handle the simulation of wave propagation. Moreover, the piezoelectric elements are not available in the explicit code but it is available in the implicit code in ABAQUS [31]. Therefore, the 3DCSCS (500 mm × 500 mm × 7 mm) plate is modeled using the explicit code and the PTDs (10 mm diameter and 0.4 mm thin) are modeled using the implicit code. ...
The 3D core sandwich composite structure (3DCSCS) is a recent concept of sandwich
construction with foam core reinforced by composite columns. The combination of thickcore
and thin-skins with higher stiffness, results in a beneficial lightweight structure.
However, low speed impacts can cause barely visible localized damage or disbonds
(BVLIDs) at the core-skin interphase, which may cause a serious loss in stiffness and may
jeopardize the safety and integrity of the whole structural assembly. Therefore, detection
of such BVLIDs are crucial to prevent catastrophic failures. Towards this, a coordinated
theoretical, numerical and experimental study has been carried out using ultrasonic guided
wave (GW) based structural health monitoring (SHM) technique.
... A limited number of theoretical studies on wave propagation in sandwich structures have also been reported which investigate the dispersion characteristics and elastic response of the propagating GWs due to transient surface loading [31][32][33][34]. More efficient 2D semi-analytical models with limited applications have been developed for GW propagation in sandwich plates [18,35,36]. ...
... This is because only the implicit solver is not sufficient to accurately handle the simulation of wave propagation. Moreover, the piezoelectric elements are not available in the explicit code but it is available in the implicit code in ABAQUS [31]. Therefore, the 3DCSCS (500 mm × 500 mm × 7 mm) plate is modeled using the explicit code and the PTDs (10 mm diameter and 0.4 mm thin) are modeled using the implicit code. ...
... Much of the earlier work focused on the behavior of honeycomb core sandwich structures under low velocity impact [9][10][11][12][13][14][15][16][17]. Usually honeycomb cores are made out of aluminium or out of composite materials: Nomex, glass thermoplastic or glass phenolic. ...
... By inserting an additional inter sheet in the core reduces the local crash/buckling. P. Qiao et al. [16] concerned with impact analysis of a FRP Honeycomb sandwich panel with sinusoidal core geometry in the plane and extending vertically between face laminates. The impact responses (e. g., contact force and central deflection) are predicted by softwares ABAQUS and LS-DYNA. ...
... The use of GFRP or glassfibre-reinforced polymer has particularly been growing due to its substantial advantages such as ease of installation, resistance to corrosion, high strength-to-weight ratio, and, most importantly, cost-effectiveness when compared with other composite materials such as CFRPs or carbon-fibre-reinforced polymers [10][11][12][13][14][15][16][17][18][19]. Sandwich structures have been increasingly used in civil engineering applications, which are a type of structure made of two fabricated GFRP face sheets and bonded to a lightweight material called a core [20]. In such structure systems, the face sheet layers provide an enhancement in the strength and bending stiffness, while the core provides the majority of the shear stiffness [21][22][23][24][25]. FRP web-flange sandwich structures have been successfully used in the applications of bridge deck construction [26][27][28][29]. ...
Studies have shown that the proper selection of core materials in sandwich structures improves the overall structural performance in terms of bending stiffness and strength. The core materials used in such systems, such as foam, corrugated, and honeycomb, are frequently applied in aerospace engineering. However, they are a costly option for civil engineering applications. This paper investigates the bending performance of the proposed GFRP softwood sandwich beams assembled using pultruded GFRP with adhesive connection methods for potential applications in prefabricated building construction. The ultimate load capacity, load–deflection responses, failure modes, bending stiffness, load–axial-strain behaviour, and degree of composite action were experimentally evaluated. The effects of varying shear-span-to-depth ratios a/d between 2 and 6.5, as well as different timber fibre directions of the softwood core, on the overall structural performance were clarified. The results showed that changing the timber fibres’ orientation from vertical to longitudinal shifted the failure mode from a brittle to progressive process. Moreover, the adhesive bonding was able to provide full composite action until the failure occurred. Finally, numerical modelling was developed to understand failure loads, deformation, failure modes, and strain responses, and to evaluate bending stiffness and composite action. The results showed satisfactory agreement with the experiments.
... In addition to analytical methods, two or three-dimensional finite element (FE) models of structural elements are frequently used to investigate the impact behavior in more complex cases including concrete [8], reinforced concrete [9][10][11][12], composite [13,14] beams and slabs. The formation of the impact requires determining partial or complete contact state of the two impacting bodies and their separation over time so that the problem is considered primarily as the contact-impact problem [15][16][17]. ...
The aim of this study is to compare the results obtained from analytical and finite element solutions of low velocity transverse impact problem of a sphere onto simply supported beam. Twelve models with various mass ratios were created by keeping the beam dimensions constant and changing the sphere radius. The effect of the element size in the finite element solution was analyzed with five separate meshes whose element size gradually decreases at the impact point. In the solutions, the deflections of the beam and the displacement of the sphere at the impact point were taken into account. To check the validity of the model, a comparison with an experimental study in the literature was also made. Comparisons show that the deflections obtained from the analytical solution are compatible with the finite element solution within the period of repetitive or continuous contact between the sphere and beam. Particularly, as the mass ratio defined for beam and sphere gets smaller, maximum deflection values obtained from analytical and finite elements become closer. For the cases including sub-impact, after the sphere leaves the beam there exist differences in the results mainly because of the sub-impacts.
... Honeycomb sandwich panels are used to render better mechanical characteristics, lower density of the materials, and maximum ability to absorb energy levels in various applications such as automotive, aerospace, and other transportation applications. Hazizan and Cantwell (2003), Li and Crocker (2006), Qiao and Yang (2007), Saha (2008), and Aumjaud et al. (2015) have investigated that VCR engine can operate at varying CRs as per the requirement of the vehicle, and the engine can be modified with suitable volume of combustion chamber. Seepersad et al. (2004) have described that honeycomb structures had replaced most of the metallic structures during the manufacturing of spacecraft and aircrafts because of their maximum specific strength and stiffness values. ...
There are a number of techniques available to reduce the engine vibration, and vibration isolation is one among those techniques. Such vibrations can be isolated using hybrid engine mounts that absorb the forces caused by vibration. Consequently, the present work proposes a hybrid aluminium mount filled with silica gel to isolate the engine vibration. Experiments were carried out on the variable compression ratio engine mounted on the hybrid honeycomb structure, and the free, forced vibrations, and frequency domains were analysed. The test results portrayed that the performance of the engine with a hybrid mount is found to be better than the conventional rubber mount. The hybrid sandwich panel with a honeycomb structure crowded with silica gel as fibrous material was utilized to isolate the engine vibrations. Compared with conventional mount (1.502 m/s²), high amount of vibration was reduced by honeycomb structured mount (0.814 m/s²) using different load conditions and fuel input pressure of 150 bar. Vibration in conventional mount for blower closing condition was 1.546 m/s² and that in honeycomb structured mount was 1.4 m/s².
... The OHL conductors have been modelled using the homogeneous beam theory to study their vibration-induced bending stresses and strains [16]. Literature has reported that the energy absorption and dissipation of complex sandwich structures undergoing vibrations is highly influenced by the composition material properties and dimensions of the outer layers and core [17][18][19][20][21][22][23]. It has also been reported that sandwich beams are generally more effective than homogenous ones on reducing vibrations [18]. ...
Utilities aim to improve asset management strategies and enhance the utilization of their assets through low-risk reliable practices. Overhead lines and conductor designs have been evolving to increase systems’ power capacity and mechanical integrity, which have also extended asset lifetimes. Nevertheless, it is still challenging to predict a conductor’s fatigue stresses due to wind-induced vibrations that can help to estimate its useful life. A finite element model (FEM) has been established in COMSOL to study the free and forced wind-induced vibrations and the resultant fatigue on single multi-layer conductors considering their complex round and trapezoidal stranding patterns. The FEM analysis is based on multi-physics accounting for the conductor’s thermal and mechanical aspects as well as material and geometry properties. Consequently, the fatigue is quantified for both inter-layer and inter-wire interactions. The simulations show that free conductor vibrations are dictated by the conductor materials and tension distribution between the core and aluminum strands. The bigger the difference between the material properties of the core and aluminum, the lesser the conductor vibrations, especially when the aluminum becomes slack. In fact, a conductor equipped with carbon core (ACCC), has the best vibration resistance among other conductors with steel core (ACSR) and homogeneous (AAACs). Forced vibration simulations identified non-linear fatigue stresses for round and trapezoidal designs, which is more pronounced in larger conductor sizes. Larger trapezoidal ACSRs exhibit better fatigue resistance compared to smaller and round stranded AAACs.
... The OHL conductors have been modelled using the homogeneous beam theory to study their vibration-induced bending stresses and strains [16]. Literature has reported that the energy absorption and dissipation of complex sandwich structures undergoing vibrations is highly influenced by the composition material properties and dimensions of the outer layers and core [17][18][19][20][21][22][23]. It has also been reported that sandwich beams are generally more effective than homogenous ones on reducing vibrations [18]. ...
Utilities aim to improve asset management strategies and enhance the utilization of their assets through low-risk reliable practices. Overhead lines and conductor designs have been evolving to increase systems’ power capacity and mechanical integrity, which have also extended asset lifetimes. Nevertheless, it is still challenging to predict a conductor’s fatigue stresses due to wind-induced vibrations that can help to estimate its useful life. A finite element model (FEM) has been established in COMSOL to study the free and forced wind-induced vibrations and the resultant fatigue on single multi-layer conductors considering their complex round and trapezoidal stranding patterns. The FEM analysis is based on multi-physics accounting for the conductor’s thermal and mechanical aspects as well as material and geometry properties. Consequently, the fatigue is quantified for both inter-layer and inter-wire interactions. The simulations show that free conductor vibrations are dictated by the conductor materials and tension distribution between the core and aluminum strands. The bigger the difference between the material properties of the core and aluminum, the lesser the conductor vibrations, especially when the aluminum becomes slack. In fact, a conductor equipped with carbon core (ACCC), has the best vibration resistance among other conductors with steel core (ACSR) and homogeneous (AAACs). Forced vibration simulations identified non-linear fatigue stresses for round and trapezoidal designs, which is more pronounced in larger conductor sizes. Larger trapezoidal ACSRs exhibit better fatigue resistance compared to smaller and round stranded AAACs.
... Zenkour (2004) performed a viscoelastic stability analysis on the FRC plates using both classical and higher-order plate theories. Qiao and Yang (2007) studied the mechanical impact responses of a sandwich beam made of FRPs by the means of ABAQUS commercial software. Moreover, a genetic algorithm (GA) based model is introduced by Roy and Chakraborty (2009) to optimize the vibration control of FRP shells. ...
Application of a newly developed refined higher-order beam theory in the thermal buckling problem of a multiscale hybrid nanocomposite beam is shown here with respect to effect of nanofillers aggregation for the first time. In this research, a mixture of macro and nanoscale fillers will be utilized to be dispersed in an initial matrix to possess a multiscale hybrid nanocomposite. The equivalent material properties are seemed to be calculated coupling the Eshelby-Mori-Tanaka model with the rule of mixture to consider the effects of CNTs inside the probably generated clusters while finding the mechanical properties of such novel hybrid nanocomposites. Furthermore, an energy based approach is implemented to obtain the governing equations of the problem utilizing a refined higher-order plate theorem. Next, the derived equations will be solved in the framework of Galerkin’s well-known analytical method to reach the critical buckling load. It is worth mentioning that influence of various boundary conditions is included. Once the validity of presented results is proven, a set of numerical examples are presented to explain how each variant can affect the buckling behaviors of the structure.
... Zenkour [16] performed a visco-elastic stability analysis on the FRC plates using both classical and higher order plate theories. Qiao and Yang [17] studied the mechanical impact responses of a sandwich beam made of FRPs by the means of ABAQUS commercial software. Moreover, a genetic algorithm (GA)-based model is introduced by Roy and Chakraborty [18] to optimize the vibration control of FRP shells. ...
Present paper is proposed to capture the influences of carbon nanotubes’ agglomeration on the stability behaviors of multi-scale hybrid nanocomposite beams within the frameworks of refined higher order beam theories for the first time. In this research, a mixture of macroscale and nanoscale fillers will be utilized to be dispersed in an initial matrix to possess a multi-scale hybrid nanocomposite. The equivalent material properties are seemed to be calculated coupling the Eshelby–Mori–Tanaka model with the rule of the mixture to consider the effects of carbon nanotubes inside the probably generated clusters while finding the mechanical properties of such novel hybrid nanocomposites. Furthermore, an energy-based approach is implemented to obtain the governing equations of the problem utilizing a refined higher order beam theorem. Next, the derived equations will be solved in the framework of Galerkin’s well-known analytical method to reach the critical buckling load. It is worth mentioning that influence of various boundary conditions is included, too. Once the validity of presented results is proven, a set of numerical examples are presented to explain how each variant can affect the structure’s stability endurance.
... Zenkour (2004) performed a viscoelastic stability analysis on the FRC plates using both classical and higher-order plate theories. Qiao and Yang (2007) studied the mechanical impact responses of a sandwich beam made of FRPs by the means of ABAQUS commercial software. Moreover, a genetic algorithm (GA) based model is introduced by Roy and Chakraborty (2009) to optimize the vibration control of FRP shells. ...
The present article is proposed to capture the influences of carbon nanotubes’ agglomeration on the natural frequency behaviors of multi-scale hybrid nanocomposite plates for the first time. The constituent material, which is a hybrid nanocomposite, is consisted of both macro- and nano-scale reinforcing fibers dispersed in a polymer matrix. The equivalent material properties are seemed to be calculated coupling the Eshelby-Mori-Tanaka model with the rule of the mixture to consider the effects of carbon nanotubes inside the probably generated clusters while finding the mechanical properties of such novel hybrid nanocomposites. Furthermore, an energy-based approach is implemented to obtain the governing equations of the problem utilizing a refined higher-order plate theorem. Next, the derived equations will be solved in the framework of Galerkin's well-known analytical method to reach the fundamental frequency. It is worth mentioning that the influence of various boundary conditions is included. Once the validity of the presented results is proven, a set of numerical examples are presented to explain how each variant can affect the plate’s natural frequency.
Communicated by Wei-Chau Xie.
... Analysis of guided wave dispersion characteristics in each type of target structure is significant for the success of these SHM techniques that uses networks of small, lightweight and cost-effective piezoelectric transducers (PZTs) [23][24][25][26][27][28]. Several studies [29][30][31][32][33][34] proposed the theoretical analysis of propagating elastic-wave in layered-mediums. However, these analyses were mainly based on several predefined kinematic assumptions, restricted to the frequency-wavenumber domain results, and the results suffer from numerical-instabilities at the high operating frequency range. ...
This paper presents a non-destructive analysis of joint-debond effects on propagating guided wave modes under
variable ambient temperature conditions and proposal of an online monitoring strategy for identification of
single as well as multiple joint-debond regions in a sandwich composite structure (SCS). A semi-analytical
analysis of guided wave dispersion in a SCS was carried out to identify different wave modes within the operating
frequency range. An extensive analysis of core-core joint-debond effects on the guided wave modes under
variable temperature conditions was studied by performing experimental investigations and validated finite
element simulations. The analysis results showed that the presence of joint-debond at the core-core interface
significantly increases the wave mode amplitudes and the increase in ambient temperature further increases the
amplitude difference between the bonded and debonded-influenced signals. An online monitoring strategy is
proposed to effectively identify the hidden joint-debonds in SCS based on the extracted differential features of
debond effects in the wave mode amplitudes of the sensor signals.
... Analysis of guided wave dispersion characteristics in each type of target structure is significant for the success of these SHM techniques that uses networks of small, lightweight and cost-effective piezoelectric transducers (PZTs) [23][24][25][26][27][28]. Several studies [29][30][31][32][33][34] proposed the theoretical analysis of propagating elastic-wave in layered-mediums. However, these analyses were mainly based on several predefined kinematic assumptions, restricted to the frequency-wavenumber domain results, and the results suffer from numerical-instabilities at the high operating frequency range. ...
... Zenkour [23] performed a viscoelastic stability analysis on the FRC plates using both classical and higher-order plate theories. Qiao and Yang [24] studied the mechanical impact responses of a sandwich beam made of FRPs by the means of ABAQUS commercial software. Moreover, a genetic algorithm (GA) based model is introduced by Roy and Chakraborty [25] to optimize the vibration control of FRP shells. ...
... Frostig et al. [7] and Frostig and Baruch [8] used the variational principles before introducing the high-order sandwich panel theory (HSAPT), which includes the transverse flexibility of the core. From that point on, HSAPT has been used by various researchers [9][10][11][12], in order to calculate the impact response of sandwich plates and beams. As to Mohammadi et al. [13], they improved the HSAPT model by considering the in-plane stresses of the core. ...
This study tracks the development of an analytical model, designed to investigate the dynamic response of a composite sandwich plate subjected to a low-velocity impact. The model is based on the thick anisotropic plate theory, developed by Reddy and Pagano, which takes into account a through-thickness shear. An indentation law, as proposed by Hertz, is used to model the local response under the impactor. The good correlation between the shock and the simulation results testifies the validity of the method as far as the prediction of the contact force and the shear deformation in the core are concerned.
... Theoretical work on elastic wave propagation in a layered medium is presented by several authors [23][24][25][26][27] . An analytical formulation of elastic wave propagation in sandwich plates under specified conditions was presented in Nilsson (1993) 23. Higher-order theoretical wave propagation models based on some defined kinematic-assumptions are also proposed for sandwich beams [25][26][27] . ...
... Dynamic responses of beams [17] , plates [18] and shells [19] under impact loads have been studied extensively. Mines et al. [20] experimentally studied the low-velocity impact responses of composite sandwich panels and they found that higher impact velocities increase the energy absorption of the panels. ...
This paper presents an analytical study that predicts the low-velocity impact response of a spinning functionally graded (FG) graphene reinforced cylindrical shell subjected to impact, external axial and thermal loads. The nanocomposite cylindrical shell is constructed based on a multiplayer model with graphene platelet (GPL) nanofillers whose weight fraction is constant in each concentric cylindrical layer but follows a layer-wise variation in the thickness direction, resulting in the position-dependent elastic moduli, mass density, Poisson's ratio and thermal expansion coefficient through the shell thickness. With effects of the thermal expansion deformation, external axial loads, centrifugal and Coriolis forces as well as the spin-induced initial hoop tension taken into account, the natural frequency of the cylindrical shell is derived on the base of differential equations of motion which are established according to the Donnell's nonlinear shell theory and the Hamilton's principle. The time-dependent contact force between a foreign impactor and the cylindrical shell is calculated by adopting a single spring-mass model. In addition, on the base of the other second-order differential equation, time-dependent displacements and strains are obtained by using the Duhamel integration. In numerical analyses, validation examples are carried out to verify the present solution, and then comprehensive parametric investigations are given to study effects of the GPL weight fraction, dispersion patterns, spinning speeds, temperature variations, geometrical sizes of the shell, the external axial load, radius of the impactor and the impact velocity on the contact force, contact duration and time histories of displacements and strains of the nanocomposite cylindrical shell.
... In another study, Qiao and Yang (2007) used the HSAPT to study vibration and impact behavior of large scale fiber reinforced polymer structural honeycomb composite sandwich beams with sinusoidal core geometry. Yang and Qiao (2007) also studied the effect of asymmetric lay up of sandwich beams with arbitrary boundary conditions. ...
The Nonlinear dynamic response of a sandwich plate subjected to the low velocity impact is theoretically and experimentally investigated. The Hertz law between the impactor and the plate is taken into account. Using the Extended High Order Sandwich Panel Theory (EHSAPT) and the Ritz energy method, the governing equations are derived. The skins follow the Third order shear deformation theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the three dimensional elasticity is used for the core. The nonlinear Von Karman relations for strains of skins and the core are adopted. Time domain solution of such equations is extracted by means of the well-known fourth-order Runge-Kutta method. The effects of core-to-skin thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that these parameters play significant role in the impact force and dynamic response of the sandwich plate. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The results are compared with experimental data acquired by impact testing on sandwich plates as well as the results of finite element simulation.
... Theoretical study on elastic wave propagation in a layered medium is presented by several authors [23][24][25][26][27]. An analytical formulation of elastic wave propagation in sandwich plates under specified conditions was presented in [23]. ...
Bonded composite structures are the special type of sandwich-like structures in which multiple carbon-fibre laminates are bonded with adhesives, and debonding can appear at the bond-layer due to variable loading and uncertain operating conditions. This study aims to investigate debonding effects on Lamb wave propagation in a bonded composite structure under variable ambient temperature conditions. In the process, a combined theoretical analysis, time-domain spectral element simulation, and experimental analysis of elastic wave propagation in a carbon-fibre reinforced adhesively-bonded composite structure have been carried out. It is shown that theoretical analysis and spectral formulation are effectively able to capture the behaviour of Lamb modes in the healthy structure due to variations in ambient temperature. It is found that the primary anti-symmetric Lamb wave mode amplitude and velocity decrease with an increase in ambient temperature. Further, the spectral formulation accurately captures the effects of debonding on the Lamb wave signals under variable temperature conditions that are consistent with the experimental results. Finally, temperature correction factors are proposed for the primary anti-symmetric mode velocity and amplitude difference calculations and the effectiveness of the factors are verified successfully for selected study cases.
... The author derived the governing equations by applying the one-dimensional thin plate/beam theory to the laminates and the general 2D field equations to the honeycomb core. Some other higher order theoretical models were also presented by several authors [28][29][30][31] to analyze the dynamic response of sandwich beams. However, these theoretical models utilized several priori kinematic assumptions. ...
"Honeycomb Composite Sandwich Structure" (HCSS), is a novel material that has been adopted globally as a major structural component in aerospace, marine and automotive vehicles due to its high strength to weight ratio and high energy-absorption capability. In this study, a combined numerical and experimental study is carried out in an effort to understand the attributes of the propagating Guided Wave (GW) modes in the presence of a High-Density (HD) core zone in a HCSS. Owing to the complex structural characteristics, the GW propagation study in HCSS with HD-core zone inherently possesses many challenges. Therefore, Two Dimensional (2D) numerical simulations of wave propagation in the HCSS without and with HD-core region are accomplished using surface bonded Piezoelectric Wafer Transducers (PWTs). Results of the numerical study show that the presence of the HD core leads to substantial decrease in the amplitude and the group velocity of the output GW signal. In order to validate the results of the simulation, experiments were conducted, which shows good agreement between the experimental and numerical results is in all the cases considered. In order to study the effect of size of the HD core zone on the group velocity and the amplitude of the propagating wave modes, a parametric study is also carried out for a selected range of the HD core widths. It is observed that the group velocity and the amplitude of the received GW modes are just about inversely proportional to the HD core width.
In this article, an in‐depth investigation into the mechanical response of novel Y‐shaped core sandwich beams under static and dynamic compressive loading conditions is presented. Utilizing deep feed‐forward neural networks (DFNNs) as the primary supervised learning scheme, the compressive behavior of these advanced structures is predicted. The trained DFNN model demonstrates high fidelity in capturing the stress–strain relationships, as evidenced by the close alignment of predicted and experimental results. Key design parameters of the cores of the sandwich beams are varied to understand their influence on the beams’ linear, plateau, and densification regions, where higher values of design parameters contribute to increased stiffness, prolonged plateau regions, and higher densification points. Additionally, the impact of loading rates (1, 7, and 14 mm min⁻¹) on the mechanical performance is analyzed, revealing significant rate‐dependent behaviors. The decision tree algorithm exhibits superior classification performance with a 99.79% accuracy, further validating the robustness of the predictive model. In contrast, the support vector machine algorithm with radial basis function shows moderate accuracy at 75.12%. Through these findings, the potential of DFNNs in predictive modeling and the importance of design parameters and loading rates in optimizing the mechanical performance of novel Y‐shaped core sandwich beams is proposed.
In the realm of nanotechnology, polymer composites, being lightweight and transparent, are used in a multitude of applications. The present work, in particular, focuses on the reinforcement of carbon nanotubes (CNTs) within polymer composites in order to impart conducting properties in a non-conducting polymer. Usually, resistance in the flow of current occurs due to the re-agglomeration of CNTs and in order to overcome this problem, modification of CNTs was carried out through utilization of zinc (Zn) and copper (Cu-Zn) nanoparticles (NPs). Two types of filler: Ⅰ and Ⅱ having Zn/CNTs and Cu-Zn/CNTs were fabricated respectively. In polymethyl methacrylate (PMMA), different wt. % of the fabricated fillers Ⅰ and Ⅱ were dispersed, which corresponds the synthesis of monometallic and bimetallic composites. Methods and techniques like FTIR, XRD, SEM, and LCR meter were used for analyses of these composites. For monometallic and bimetallic composites, the observed conductivity value of filler was 3×10-3 S/cm and 1.67×10-4 S/cm at 0.1 and 0.05 wt. % respectively. It was concluded that in bimetallic composites, a high conductivity value was achieved at low filler concentration. These lightweight composites with significant properties make them useful in for manufacturing panels or casings in the aerospace and automotive industries.
Carbon fiber reinforced polymers (CFRP) are widely used nowadays as primary and secondary bearing structures in the aviation industry. However, CFRP structures are threatened by unpredictable low-velocity impact events (caused by dropped tools, etc.) during the assembly process, which can cause impact damages. To prevent CFRP damage during the assembly process, a rubber layer can be placed on the surface of the CFRP to form a protective hybrid structure. The influence of rubber layer thickness on the protection effect and on the impact response of the hybrid structure were first investigated in this study. The experimental results indicate that the rubber layer significantly improved the CFRP’s impact resistance, with fewer damage modes and less damage area observed. Furthermore, the thicker the rubber layer places, the lower the CFRP delamination position occurs. The whole impact process of this hybrid structure was simulated using the mixed-mode damage criterion for CFRP laminate and the hyperelastic law for the rubber layer. The finite element model was refined with mesh size and contact behavior corresponding to the experiment condition, which showed good agreements with impact response and delamination area experiments. Some internal damage details and damage evolution were also discussed using the finite element model.
Additive manufacturing technologies, well known as three-dimensional printing (3DP) technologies, have been applied in many industrial fields, including aerospace, automobiles, shipbuilding, civil engineering and nuclear power. However, despite the high material utilization and the ability to rapidly construct complex shaped structures of 3D printing technologies, the application of additive manufacturing technologies in railway track infrastructure is still at the exploratory stage. This paper reviews the state-of-the-art research of additive manufacturing technologies related the railway track infrastructure and discusses the challenges and prospects of 3D printing technology in this area. The insights will not only help the development of 3D printing technologies into railway engineering but also enable smarter railway track component design and improve track performance and inspection strategies.
High-Temperature Low-Sag (HTLS) conductor technologies are often implemented, among many approaches, for optimizing the overhead lines utilization. The advancements of HTLS conductors are based on the differences in core and aluminum properties and installation procedures. This non-linear conductor behavior, although considered in the sag-tension calculations, by implementing the knee-point temperature, is often omitted from the aeolian vibration calculations. To understand the implications of the complex HTLS conductor structure on vibrations, a new calculation approach is proposed in this paper to quantify the effect of installation and operating conditions on the performance of any HTLS conductor. The proposed method conceives a prediction lay area that estimates where the actual field data are expected to lay, and is validated with good accuracy against the field data from ACSR, ACCC, and GZTACSR. The developed model enables the prediction of non-homogeneous (composite) conductors and should be implemented at above knee-point operating temperatures with zero aluminum tensions.
Glass Fiber-reinforced plastic (GFRP) sandwich composites are extensively used in various engineering applications owing to their advantageous structural properties such as high specific strength to weight ratio, resistance to shear and compressive forces as well as their cost-effectiveness and manufacturing ease. Machining these composites however is a difficult task. The durability of the material deteriorates due to machining induced meso-damage that accumulate over time, creating the motivation to study what the damage mechanisms depend on. Many Non-Destructive Testing (NDT) techniques are often used to characterize such damages. Acoustic Emissions (AE) has emerged as an important non-destructive method for real-time examination of damage evolution. This study aims to investigate the effects of various acoustic emission features along with force, torque and tool wear on the delamination caused on the GFRP sandwich honeycomb composite during the drilling process. Experiments were conducted and delamination for each hole was measured. Consequently, data-driven models were used to characterize damage in the material.
One of the most important causes of bridge failure is the design and structural deficiencies of bridge bearings. Recently, typical bridge bearings with the reinforcement of steel or fibre have been widely used in base isolation system. Especially for fibre-reinforced rubber bearings, they offer numerous benefits as higher stiffness and strength, more flexibility, and decrease of transport and fabrication costs. Under vibration, common bridge bearings cannot perform well and the materials used in the bearings cannot sustain under environmental conditions. To develop the performance of these common bearings to obtain their superior physical and mechanical properties (e.g. lightweight, higher stiffness, better impact resistence, and vibration attenuation), the use of metamaterials (periodic structures) in the bearings is considered for this reason. The current paper is the world’s first to present a comprehensive, state-of-the-art overview of the development of meta-functional composites for bridge bearing applications, exposed to both static and dynamic conditions. Also, the paper shows an approach to fabricate meta-functional composite bridge bearings via additive manufacturing (AM) technologies. Furthermore, the numerical simulation has been conducted to enable new insights into the behavior of a meta-functional bridge bearing suitable for real-life practial applications. These insights are fundamental to the performance benchmarking including the development of vibration-based condition monitoring and inspection for predictive bridge component maintenance.
The present work investigates the progressive failure in a corrugated core type CFRP composite structure under out-of-plane compression and four-point-bending tests. The structure has a novel geometry where unidirectional prepreg is used for both the corrugated core and the facesheets, which are manufactured together in a single process. AE registration is applied during the four-point-bending test and the k-means++ clustering algorithm is used to group the similar events and provide reliable correlations with failure modes. Test results are complemented with finite elements progressive failure analysis in which Hashin’s failure criterion and Cohesive Zone Model are utilized to predict the intralaminar and interlaminar damage modes respectively. The model is validated by comparing load-displacement curves and observed failure modes during the tests. Analysis of AE results reveals failure modes during four-point bending test and provides reliable evidence which is in good agreement with the predictions of the finite element model.
Due to the multiple dimensional and embeddable characterizations, the three-dimensional woven structure is of great potential as a platform for multifunctional composites. As an example of this concept, we proposed a light-weight and high-gain three-dimensional woven spacer microstrip antenna (3DWS-MA) for the first time by integrating microstrip antenna into 3D woven spacer composites. The single-element 3DWS-MA showed superb electromagnetic performance with the gain value of 7.1 dB, which is more than four orders of magnitude higher than traditional microstrip antenna (2.5 dB). Furthermore, the 3DWS-MA maintained proper resonant frequency and impedance matching after the impact of 18 J, exhibiting excellent structural integrity.
This paper presents the low-velocity impact behavior of sandwich panel with carbon fiber reinforced plastic (CFRP) composite facesheet and Nomex honeycomb core through experimental and numerical methods. Experiments were carried out on two thickness of honeycomb core at various impact energy levels. The dynamic response including contact force history and energy absorption as well as contact duration was recorded. The damage modes were obtained through non-destruction inspection (NDI) C-scan and microscopic observation. A refined three-dimensional finite element model combined with continuum damage mechanics (CDM) was developed with composite plies and detailed honeycomb core. Physically-based Puck’s composite failure criteria and energy based progressive damage model were used to capture the intralaminar damage initiation and evolution, respectively. The interlaminar damage of facesheet and debonding of facesheet/core interface were predicted using cohesive element. The hexagonal honeycomb cells were characterized in FE model with an elasto-plastic constitutive model and damage criterion in detail during impact. The simulation results show good agreements with experiments and the model can be used to predict the low-velocity impact response and impact damage effectively. More detailed responses, such as internal damage details, damage modes and evolution, are observed and discussed with the numerical model proposed.
Application of the Rayleigh-Ritz method for the vibration problem of a porous multi-scale hybrid nanocomposite graphene oxide powder (GOP)/carbon fiber (CF)-reinforced beam is shown here for the first time on the basis of a new refined higher-order shear deformation beam theory. The structure consists of an initial matrix which is strengthened via both macro- and nano-scale reinforcements. Herein, GOPs and CFs are selected to be dispersed inside the resin. Moreover, the influences of porosity are included, too. The governing equations of the problem are achieved in the framework of a new refined higher-order beam model. Afterward, the Rayleigh-Ritz well-known finite-element method (FEM) is implemented to solve the problem for various boundary conditions (BCs). The validity of the presented formulation is checked by comparing the results of the employed FEM with those achieved from the Navier solution. it is shown that hybrid nanocomposites are able to support higher natural frequencies in comparison with either conventional fiber-reinforced composites or common two-phase GOP-reinforced nanocomposites.
Honeycomb sandwich composites are extensively used in military shelters, aerospace structures, ground transportation structures, auto‐racing bodies, ship panels, and other special purpose structures requiring lightweight construction materials. But debondings at the face‐sheet‐to‐core junctions frequently occur due to the variable operating and loading conditions, which may menace the safety and overall integrity of the structural assembly. This paper aims to effectively identify such hidden debonding regions in these advanced structures, using Lamb wave‐based monitoring technique. A semianalytical analysis of Lamb wave dispersion in a healthy sandwich structure is carried out to identify various Lamb modes and to study their propagation phenomenon. A combined finite element‐based simulation and experimental analysis of Lamb wave propagation in sandwich panels (healthy and with debonding) are then carried out using piezoelectric transducer networks. It is observed that the presence of debonding significantly reduces the propagating Lamb wave mode amplitudes. A debonding detection algorithm, which uses the differential changes in Lamb mode amplitudes, is applied to efficiently identify single and multiple debonding regions in the structure.
It is always a big challenge to effectively enhance the impact resistance without sacrificing the processability and thermal stability of thermosetting composites. High performance diallyl bisphenol A modified bimaleimide (BD) thermosetting composites are fabricated by interleaving aminated aligned carbon nanotubes bundle (ACNTB-NH2)/polybenzimidazole (PBI) hybrid films. Because the hybrid film contains −NH2 and −NH− and ACNTB-NH2 protrudes from the film surface, the chemical interfacial interaction can be formed at hybrid film/matrix resulting from the reaction of −NH2 and −NH− in hybrid film and C=C in BD system, and the interface is strengthened by ACNTB-NH2 that can join the polymers together at the bimaterial interface like a rivet. The resultant BD/[5%ACNTB-NH2@PBI]n composites show greatly improved thermal stability and mechanical properties without sacrificing good dielectric property of BD, which can be attributed to the high inherent integrated properties of PBI hybrid films and the interface strengthening action between PBI hybrid film and BD matrix. The carbon fiber reinforced BD composites with PBI hybrid film interleaves are also fabricated, the mechanical properties of resultant composites show increasing trends with the increase of PBI hybrid film layer. Eventually, the flexural strength, impact strength and interlaminar shear strength of CF/BD/[5%ACNTB-NH2@PBI]5 increase by 16%, 42% and 33%, respectively, compared to those of CF/BD composite.
Nonlinear low velocity impact response of sandwich beam with laminated composite face sheets and soft core is studied based on Extended High Order Sandwich Panel Theory (EHSAPT). The face sheets follow the Third order shear deformation beam theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the two dimensional elasticity is used for the core. The nonlinear Von Karman type relations for strains of face sheets and the core are adopted. Contact force between the impactor and the beam is obtained using the modified Hertz law. The field equations are derived via the Ritz based applied to the total energy of the system. The solution is obtained in the time domain by implementing the well-known Runge-Kutta method. The effects of boundary conditions, core-to-face sheet thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that each of these parameters have significant effect on the impact characteristics which should be considered. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The contact force histories predicted by EHSAPT are in good agreement with that obtained by experimental results.
Profiled hollow core sandwich panels (SPs) and their components (outer layers and core) were manufactured with ponderosa and lodgepole pine wood strands to determine the effects of low-velocity impact forces and to observe their energy absorption (EA) capacities and failure modes. An instrumented drop weight impact system was applied and the tests were performed by releasing the impact head from 500 mm for all the specimens while the impactors (IMPs) were equipped with hemispherical and flat head cylindrical heads. SPs with cavities filled with a rigid foam insulation material (SP foam ) were also tested to understand the change in EA behavior and failure mode. Failure modes induced by both IMPs to SPs were found to be splitting, perforating, penetrating, core crushing and debonding between the core and the outer layers. SP foam s absorbed 26% more energy than unfilled SPs. SP foam s with urethane foam suffer less severe failure modes than SPs. SPs in a ridge-loading configuration absorbed more impact energy than those in a valley-loading configuration, especially when impacted by a hemispherical IMP. Based on the results, it is evident that sandwich structure is more efficient than a solid panel concerning impact energy absorption, primarily due to a larger elastic section modulus of the core’s corrugated geometry.
A very low concentration of thermoplastic polybenzimidazole (PBI) film interleaved bismaleimide/diallyl bisphenol A (BMI/DBA) system with sandwich structure was designed for the outstanding impact resistance. The effects of PBI film layers (0∼5) on the mechanical, thermal, dielectric properties and flame retardancy of BMI/DBA were investigated. BMI/DBA interleaved with 5-layer PBI film demonstrates a 274% increase in impact strength relative to BMI/DBA, and exhibits higher fracture toughness, flexural strength and modulus than BMI/DBA. The improvement in the mechanical property for PBI film interleaved BMI/DBA system is mainly attributed to the combined effects of the effective energy dissipation of the sandwich structure and the good interfacial bonding between PBI film and the matrix. Due to the high thermal stability of PBI, the effective thermal insulation and electromagnetic field barrier of PBI film in the sandwich structure and the increase of the reacted CC in resin system, PBI film interleaved BMI/DBA shows better thermal property, much higher flame retardancy and lower dielectric constant compared to BMI/DBA. In addition, when the same amount of PBI is applied, BMI/DBA interleaved with PBI film exhibits much better comprehensive properties than BMI/DBA with PBI particles for the sandwich structure. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers
A three dimensional integrated microstrip antenna (3DIMA) is a novel multifunctional structure, which can perform as a load bearing structure and function as an antenna. In this study, a single-element and a double-element microstrip antenna were integrated into cylindrical three-dimensional woven glass fiber/epoxy composites respectively. Their electromagnetic performance and impact damage were investigated. The results showed that with the decrease of the curvature radii from 75 to 25 mm, the single-element 3DIMAs with the feed direction perpendicular to the curvature showed more stable resonant frequencies and gain values than those of 3DIMAs with the feed direction parallel to the curvature. While the opposite results were observed for the double-element 3DIMAs. The double-element cylindrical 3DIMAs with the feed direction parallel to the curvature showed the best voltage standing wave ratios (VSWR<1.25), resonant frequencies (near 1.5 GHz), gains (from 2.37 to 1.44 dB) and reasonable radiation pattern properties. In addition, impact tests were conducted with the impact energies ranging from 0 to 20 J. The results showed that the VSWRs slightly changed, demonstrating good impact resistance, and structural integrity of cylindrical 3DIMA structure.
A new nonlinear finite element model is proposed for the dynamic analysis of cylindrical sandwich panels with shape memory alloy hybrid composite face sheets and flexible core. In order to present a realistic transient vibration analysis, all the material complexities arising from the instantaneous and spatial martensite phase transformation of the shape memory alloy wires are taken into consideration. The one-dimensional constitutive equation proposed by Boyd and Lagoudas is used for modeling the pseudoelastic behavior of the shape memory alloy wires. Since the martensite volume fraction at each point depends on the stress at that point, the phase transformation kinetic equations and the governing equations are coupled together. Therefore, at each time step, an iterative method should be used to solve the highly nonlinear equations. Moreover, considering that the stress resultants generated by the martensite phase transformation in the wires are path-dependent values, an incremental method is used to estimate the increment of the stress resultants at each time step. The governing equations are derived based on the energy method and Newmark time integration method is used to solve the discretized finite element equations. Finally, several numerical examples are presented to examine the effect of various parameters such as intensity of applied pressure load, operating temperature, location of shape memory alloy wires, volume fraction of the shape memory alloy wires, and also boundary conditions upon the loss factor for panels with different aspect ratios.
A two-step perturbation method is used to study the nonlinear behavior of functionally graded carbon-nanotube-reinforced composite cylindrical shells with different filler distributions. Compared with traditional carbon fibers, carbon nanotubes (CNTs) have remarkable mechanical properties. 1 For this reason, there has been a considerable amount of attention paid to the use of CNTs as reinforcements for polymer composites, and to thus obtain lightweight structural materials with improved thermomechanical characteristics. 2, 3 Damage to such materials from impacts, however, can be a critical issue. This is especially the case for the fabrication of aircraft structural components. Studying the response of thin laminates that are subjected to low-velocity impacts is therefore a significant area of ongoing research. 4 In a previous study, the nonlinear low-velocity impact response of CNT-reinforced composite (CNTRC) single-layer and sandwich plates in a thermal environment have been analyzed. 5 Such CNTRC structures are often used in aerospace and automobile applications because of their favorable properties. In the previous study, the effects of various parameters on the impact response of the plate structures were explored. These parameters included the material property gradient, volume fraction distribution, temperature change, initial stress, initial velocity of the impactor, and core-to-face sheet-thickness ratio. To the best of our knowledge, however, there has not yet been an investigation into the low-velocity impact response of functionally graded (FG) CNTRC cylindrical shells. In this work, 6 we have thus considered two different types of CNT distribution (i.e., uniformly distributed and FG-distributed reinforcements) in CNTRC cylindrical shells. The geometry and coordinate system of the cylindrical shells is illustrated in Figure 1(a). The CNT distributions for our different configurations of FG (in the thickness dimension) cylindrical shells are presented in Figure 1(b). In the uniformly distributed (UD) sample, the CNT volume fraction (V CN) is constant across the shell's thickness. In contrast, for the two FG-distributed samples ('type ' and 'type X'), V CN varies across the Figure 1. (a) The geometry and coordinate system of a carbon-nanotube-reinforced composite (CNTRC) cylindrical shell that is being subjected to a low-velocity impact. V 0 : Initial impactor velocity. L, R, and h represent the shell length, radius, and thickness, respectively. X, Y, and Z: Coordinate axes. (b) The variation in CNT volume distribution (V CN) across the shell thickness (t) for the uniformly distributed (UD) and functionally graded (FG) CNTRC shells. Two different distributions—type and type X—of FG shells were obtained. Continued on next page
Currently, there is strong interest in the effects of impact induced damage to composite structures as evidenced by the large number of articles on this topic that have appeared in the literature in recent years. With laminated composite structures, foreign object impacts, that are expected to occur during the life of the structure, can introduce damage that is often difficult to detect and can significantly reduce the strength of the structure. Research efforts concentrate on monolithic laminates while sandwich structures with laminated facings, which are also used extensively in aerospace and other applications, received less attention. A comprehensive review of the literature dealing with impact on sandwich structures is presented in this review article. The mechanics of contact between a rigid indentor and a sandwich structure is discussed in detail since it is very important to account for the local deformation in the contact zone in developing a model for predicting the contact force history. The mechanical behavior of foam and honeycomb core materials is reviewed along with experimental results and models for predicting the contact law between a smooth indentor and a sandwich structure. The development of mathematical models for predicting the contact force history and the overall response of the structure is also discussed. Finally we review the failure mechanisms involved in impact damage development, the parameters affecting damage size, and the residual properties of sandwich structures. This review article has 85 references.
Based on the zeroth-order approximation of a two-scale asymptotic expansion, equivalent elastic shear coefficients of periodic structures can be evaluated via the solution of a local function and the kl (y), ij homogenization process reduces to solving the local function by invoking local periodic boundary con-kl (y) ij ditions. Then, effective transverse shear stiffness properties can be analytically predicted by reducing a local problem of a given unit cell into a 2D problem. In this paper, an analytical approach with a two-scale asymptotic homogenization technique is developed for evaluation of effective transverse shear stiffness of thin-walled hon-eycomb core structures with general configurations, and the governing 3D partial differential equations are solved with the assumptions of free warping constraints and constant variables through the core wall thickness. The explicit formulas for the effective transverse shear stiffness are presented for a general configuration of hon-eycomb core. A detailed study is given for three typical honeycomb cores consisting of sinusoidal, tubular, and hexagonal configurations, and their solutions are validated with existing equations and numerical analyses. The developed approach with certain modifications can be extended to other sandwich structures, and a summary of explicit solutions for the transverse shear stiffness of common honeycomb core configurations is provided. The lower bound solution provided in this study is a reliable approximation for engineering design and can be efficiently used for quick evaluation and optimization of general core configurations. The upper bound formula, based on the assumption of uniform shear deformation, is also given for comparison. Further, it is expected that with appropriate construction in the displacement field, the more accurate transverse stiffness can be analytically attained by taking into account the effect due to the face-sheet constraints.
In this paper, a combined analytical and experimental study of dynamic characteristics of honeycomb composite sandwich structures in bridge systems is presented, and a relatively simple and reliable dynamic experimental procedure to estimate the beam bending and transverse shear stiffness is proposed. This procedure is especially practicable for estimating the beam transverse shear stiffness, which is primarily contributed by the core and is usually difficult to measure. The composite sandwich beams are made of E-glass fiber and polyester resins, and the core consists of the corrugated cells in a sinusoidal configuration. Based on the modeling of equivalent properties for the face laminates and core elements, analytical predictions of effective flexural and transverse shear stiffness properties of sandwich beams along the longitudinal and transverse to the sinusoidal core wave directions are first obtained. Using piezoelectric sensors, the dynamic response data are collected, and the dynamic characteristics of the sandwich structures are analyzed, from which the flexural and transverse shear stiffness properties are reduced. The experimental stiffness results are then compared to the analytical stiffness properties, and relatively good correlations are obtained. The proposed dynamic tests using piezoelectric sensors can be used effectively to evaluate the dynamic characteristics and stiffness properties of large sandwich structures suitable for highway bridge applications.
Natural motions of sandwich beams with a transversely, flexible- (soft-) core are analyzed based on a higher-order theory formulation. The theory does not resort to the use of presumed displacement patterns and permits imposition of the different support conditions at the same boundary section. Finite differences are used to approximate the governing equations, and the deflated iterative Arnoldi algorithm is applied to solve the algebraic eigenvalue problem. Free vibration predictions of the higher-order theory are shown to be in good agreement with experiments reported in the literature. The face sheet deflections of the sandwich beams with nonidentical support conditions at the same boundary are different in the close vicinity of that boundary. The interaction between the face sheets and the core plays a crucial role in the vibration response of sandwich beams with a soft core. The parametric study shows that the qualitative sequence of the antisymmetric (global) and symmetric (local) vibration modes varies with face sheet thickness and that there are sandwich beam layouts for which some higher vibration modes arise from the interaction of the basic modes.
A comprehensive approach for the analysis and design of pultruded FRP beams in bending is presented. It is shown that the material architecture of pultruded FRP shapes can be efficiently modeled as a layered system. Based on the information provided by the material producers, a detailed procedure is presented for the computation of fiber volume fraction (Vf) of the constituents, including fiber bundles or rovings, continuous strand mats, and cross-ply and angle-ply fabrics. Using the computed Vfs, the ply stiffnesses are evaluated from selected micromechanics models. The wall or panel laminate engineering constants can be computed from the ply stiffnesses and macromechanics, and it is shown that the predictions correlate well with coupon test results. The bending response of various H and box sections is studied experimentally and analytically. The mechanics of laminated beams (MLB) model used in this study can accurately predict displacements and strains, and it can be used in engineering design and manufacturing optimization of cross-sectional shapes and lay-up configurations. The experimental results agree closely with the MLB predictions and finite element verifications.
The stresses and failure maps in a sandwich beam that consists of a transversely flexible compressible core between two laminated composite skins, are presented. The stresses and the failure maps are determined using a general, systematic rigorous, and high-order analysis that is based on variational principles, and includes the flexibility effects of the core on the global and local bending behavior of the beam. The analysis uses closed form solutions for any type of skin construction, symmetric or unsymmetric laminated composite layups, any type of core, compressible or incompressible, any type of loading, concentrated or distributed, and any types of boundary and continuity conditions that may differ from one skin to the other, even in the same section. Failure patterns are determined with the aid of the analytical description of the longitudinal stresses in the skins and the principal stresses through the thickness of the core. The stresses in the core and the skins, along with an appropriate failure criteria, for a specified three point bending beam, are demonstrated in the form of principal stresses, failure and failure load maps, that indicate possible failure patterns and locations.
The bending behavior of a sandwich beam with a “soft” core and unsymmetrical laminated composite skins has been analytically investigated. The effects of the extension-bending coupling caused by the unsymmetrical layups on the bending behavior, are presented. The skins may be made of different materials, different layups, i.e. symmetrical or unsymmetrical, different geometries and may have different boundary conditions (even at the same section). The “soft” core is considered compressible and a change in its height is allowed. The analysis uses variational principles and models the core as a two-dimensional elastic medium, and the skins as one-dimensional composite laminated beams, or a composite panel with cylindrical bending. The analysis is general, rigorous, includes high-order effects and uses closed-form solutions for any type of sandwich construction, for any type of loading and for any combination of boundary conditions. The solutions include the stress and displacement fields along the beam and through the height of the core. Local effects in the vicinity of concentrated loads that consist of dimples and high bending moments in the skins and abrupt changes in the peeling stresses, are studied.
Localized load effects using a high-order theory for the bending behavior of a sandwich panel with a "soft" core (i.e., flexible) in the vertical direction that is based on variational principles are presented. The theory embodies a rigorous approach for the small-deformation analysis of sandwich plates having high-order effects owing to the nonlinear patterns of the in-plane and vertical deformations of the core through its height. Thus, the high-order and local effects are an inherent part of the high-order theory and improve on the available classical and high-order theories. The formulation details the governing equations and associated boundary conditions for a general construction of a sandwich panel with unidentical skins and a "soft" core made of foam or aramid honeycomb. The theory uses a classical thin-plate theory for the skins and a three-dimensional elasticity theory for the core. The behavior is presented in terms of internal resultants and displacements in skins, peeling and shear stresses in skin-core interfaces, and stress and displacement fields in the core, even in the vicinity of localized loads. The analysis handles any type of load and distinguishes among loads applied at different skins. A parametric study has been conducted on a simply supported sandwich panel with identical skins that are subjected to both a concentrated load applied at the middle of the panel with a transversely flexible, stiff core and distributed on a square region with various dimensions for various panel aspect ratios and to a fully uniform distributed load with various modulus of elasticity ratios of skin panel to core (in vertical direction).
A general, high-order theory based on variational principles is presented for the bending behavior of a sandwich beam with a core that is vertically flexible. The theory embodies a rigorous and systematic approach to the analysis of such structurs, which have high-order effects caused by the nonlinearity of the longitudinal and the transverse deformations of the core through the height. As such, it improves on the available classical and superposition theories. Beam construction consists of the upper and lower skin, metallic or composite laminated symmetric, with nonidentical mechanical and geometrical properties, and a soft core made of foam or honeycomb. The formulation uses a beam theory for the skins and a two-dimensional elasticity theory for the core. The behavior is presented in terms of internal resultants and displacements in skins, peeling and shear stresses in skin-core interfaces, and stress and displacement fields in the core, even in the vicinity of concentrated loads. The method is applicable to any type of loading exerted on the skins and to any type of boundary or continuity conditions, including cases in which at the same section the conditions at the upper skin are different from those at the lower. Some typical cases are studied numerically.
The consistent higher-order dynamic equations and the corresponding continuity and boundary conditions for sandwich beams with a transversely flexible core are derived, with nonlinear acceleration fields in the core taken into account. A discretized formulation based on an efficient implicit finite difference scheme is presented and numerically validated. The higher-order analysis reveals that the dynamic magnitudes of normal stresses between the face sheets and the core increase dramatically at the boundaries of a sandwich beam, whereas the values remain at the level of response to quasi-static loading through the span, including the points of application of localized loads. The present work provides an accurate and efficient tool for the analysis of sandwich beams with a transversely flexible core subject to dynamic loads of arbitrary type, including the practical case of localized dynamic excitation.
The analysis presented embodies a general rigorous approach including high order effects owing to the non-linearity of the displacement fields of the core caused by its flexibility in the vertical direction. In the high order approach beam theory is used for the skins and a two-dimensional elasticity theory for the core, and it is applicable to any type of sandwich construction, including non-symmetrical ones, and to any type of boundary conditions, including cases in which the conditions at the upper skin differ from those at the lower one. The results are described in terms of displacements in the various skins, longitudinal and vertical, and shear stresses in the core. Typical cases of a simply supported beam are numerically studied.
Free vibration analysis of sandwich panels with a flexible core based on the high-order sandwich panel theory approach is presented. The mathematical formulation uses the Hamilton principle and includes derivation of the governing equations along with the appropriate boundary conditions. The formulation embodies a rigorous approach for the free vibration analysis of sandwich plates with a general construction, having high-order effects owing to the non-linear patterns of the in-plane and the vertical displacements of the core through its height. As such, it improves on the available classical and high-order theories. The formulation uses the classical thin plate theory for the face sheets and a three-dimensional elasticity theory or equivalent one for the core. The analyses are valid for any type of loading scheme, localized as well as distributed, and distinguish between loads applied at the upper or the lower face. It can also deal with any type of boundary conditions that may be different at the upper and the lower face sheets at the same edge. The effects of the rotary inertia of the various constituents of the sandwich construction are included. Two types of computational models are considered. The first model uses the vertical shear stresses in the core in addition to the displacements of the upper and the lower face sheets as its unknowns. The second model assumes a polynomial description of the displacement fields in the core that is based on the displacement fields of the first model. In this case the unknowns are the coefficients of these polynomials in addition to the displacements of the various face sheets. The two computational models have been validated numerically through a very good comparison with the well known classical and high-order plate theories. The numerical study consists of free vibration eigenmodes of two typical simply-supported panels, including higher modes that cannot be detected by other high-order computational models, and a parametric study that compares the results of the various computational models and the first-order shear deformable results.
Lightweight and heavy-duty fiber-reinforced polymer (FRP) composite honeycomb sandwich structures have been increas-ingly used in civil infrastructure. Unique cellular core configurations, such as sinusoidal core, have been applied in sandwich construction. Due to specific core geometry, the solutions for core effective stiffness properties are not readily available. This paper presents a mechanics of materials approach to evaluate the effective stiffness properties of sinusoidal cores. In particular, the internal forces of a curved wall in a unit cell are expressed in terms of resultant forces, and based on the energy method and principle of equivalence analysis, the in-plane stiffness properties of sinusoidal cores are derived. Both finite-element modeling and experimental testing are carried out to verify the accuracy of the proposed analytical formulation. To illustrate the present analytical approach as an efficient tool in optimal analysis and size selection of sinusoidal cores, several design plots are provided and discussed. The simplified analysis and formulation presented for sinusoidal cores can be used in design application of FRP honeycomb sandwich and optimization of efficient cellular core structures.
In this study, a higher-order impact model is presented to simulate the response of a soft-core sandwich beam sub-jected to a foreign object impact. A free vibration problem of sandwich beams is first solved, and the results are vali-dated by comparing with numerical finite element modeling results of ABAQUS and the solution by Frostig and Baruch [Frostig, Y., Baruch, M., 1994. Free vibration of sandwich beams with a transversely flexible core: a high order approach. Journal of Sound and Vibration 176(2), 195–208]. Then a foreign object impact process is incorporated in the higher-order model, and the contact force and deflection history as well as the propagation of transverse normal, shear, and axial stresses during the impact are analyzed and discussed. The validity of the model in the impact response pre-dictions is demonstrated by comparing with finite element solutions of LS-DYNA. The calculated stresses caused by a foreign object impact are then used to assess failure locations, failure time, and failure modes in sandwich beams, which are shown to compare well with the available experimental results. The effects of impact mass, initial velocity, core stiff-ness, and core height on the impact stresses generated in the beams are discussed. The influences of impact mass and initial velocity on the contact force history are close to those by the linearized impact solution, but the proposed higher-order impact model captures the non-linear impact process and different generated stresses. Compared to the fully backed sandwich case, the core height shows a great influence over the impact process of a simply supported sandwich system, in which the global behavior of the sandwich is dominant; while the core stiffness shows minor effect over the impact process. The higher-order impact model of sandwich beams developed in the study provides accurate predictions of the generated stresses and impact process and can be used effectively in design analysis of anti-impact structures made of sandwich materials.
Fiber-reinforced plastic (FRP) composite decks have been increasingly used in highway bridge applications, both in new construction and rehabilitation and replacement of existing bridge decks. Recent applications have demonstrated that FRP honeycomb panels can be effectively and economically used for highway bridge deck systems. This paper is concerned with design modeling and experimental characterization of a FRP honeycomb panel with sinusoidal core geometry in the plane and extending vertically between face laminates. The analyses of the honeycomb structure and components include: (1) constituent materials and ply properties, (2) face laminates and core wall engineering properties, (3) equivalent core material properties, and (4) apparent stiffness properties for the honeycomb panel and its equivalent orthotropic material properties. A homogenization process is used to obtain the equivalent core material properties for the honeycomb geometry with sinusoidal waves. To verify the accuracy of the analytical solution, several honeycomb sandwich beams with sinusoidal core waves either in the longitudinal or transverse directions are tested in bending. Also, a deck panel is tested under both symmetric and asymmetric patch loading. Finite element (FE) models of the test samples using layered shell elements are further used to correlate results with analytical predictions and experimental values. A brief summary is given of the present and future use of the FRP honeycomb panel for bridge decks. The present simplified analysis procedure can be used in design applications and optimization of efficient honeycomb structures.
This paper presents the results of a combined theoretical and experimental investigation of local bending effects in a clamped circular foam-cored sandwich plate subjected to a central point load. The theoretical investigation was conducted using an approximate method of local bending analysis, where the basic approach is to consider the deflection of the loaded face as being governed by a two-parameter elastic foundation model, which takes into account the existence of shearing interaction effects between the loaded face and the core material. The experimental investigation was conducted using a holographic interferometry technique, from which detailed information about the displacement field of the loaded face was obtained. Comparison between the theoretical and experimental displacement fields revealed a very convincing agreement, thus showing that the simple elastic foundation approach provides a good description of the local bending phenomenon.
Due to increased traffic volumes and incidence of impact damaged to bridge structures, there is a pressing need to develop a collision protection system for highway bridges against over-height truck impact. In this study, a linear elastic model for the impact response of bottom face sheet-rigidly supported sandwich structures including shear-off effect is developed. The solutions for a discrete model and concentrated and distributed loading cases for collision protection I-Lam system are obtained, of which the contact force history and maximum deflection are predicted. Compared to the LS-DYNA finite element analysis (FEA), the relatively simple analytical methods proposed accurately predict the impact response. The discrete model shows a better correlation with FEA predictions, while the model with distributed forces overestimates the deflection of the top face sheet but under-evaluates the peak contact force. The developed models including the shear-off mechanism can be used to approximate the impact response of rigidly supported sandwich structures hit by an over-height truck. The two important impact factors, i.e. the maximal deflection and peak contact force, can be used in primary design and optimization of collision protection sandwich structures.
Impact analysis of fully backed composite sandwich plates is presented, and a shear deformable model of face sheet laminates on a two-parameter elastic foundation is developed, in which the nonlinear contact law is included. The core in the sandwich is modeled as a two-parameter elastic foundation with nonlinear decay of displacement through the thickness. Hertz contact law is adopted to simulate the nonlinear impact response of the face sheet laminates. The proposed model is compared with a solution for simply supported laminated plates, and with experimental and numerical results of fully backed composite sandwich plates. The effects of core stiffness (elastic foundation), transverse stiffness of face sheet laminate, contact stiffness, and tip shape of the projectile on the impact response are investigated. It indicates that the analytical model developed can be used as a versatile and accurate tool to study the nonlinear impact response of composite sandwich structures.
In this paper, the mechanical behavior of composite materials with periodic microstructure is analysed. The corresponding elastic problem is solved by using the Fourier series technique and assuming the homogenization eigenstrain to be piecewise constant. Then, the coefficients of the overall stiffness tensor of the composite material are expressed analytically in terms of the elastic properties of the constituents (fibers and matrix) and as a function of nine triple series which take into account the geometry of the inclusions. In the case of composite materials reinforced by long fibers, simple formulas for evaluating these series are proposed. Close-form expressions for the elastic moduli of the fiber reinforced composite with periodic microstructure and for the equivalent transversely isotropic material are obtained. Finally, several comparisons with experimental results are presented.
Fiber-reinforcement polymer honeycomb short span bridge for rapid installation
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Strength evaluation of honeycomb FRP sandwich panels with sinusoidal core geometry
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