Mechanics of Advanced Materials and Structures

Published by Taylor & Francis
Print ISSN: 1537-6494
A study is made of the effect of mesh distortion on the accuracy of transverse shear stresses and their first-order and second-order sensitivity coefficients in multilayered composite panels subjected to mechanical and thermal loads. The panels are discretized by using a two-field degenerate solid element, with the fundamental unknowns consisting of both displacement and strain components, and the displacement components having a linear variation throughout the thickness of the laminate. A two-step computational procedure is used for evaluating the transverse shear stresses. In the first step, the in-plane stresses in the different layers are calculated at the numerical quadrature points for each element. In the second step, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of transverse shear stresses. Numerical results are presented showing no noticeable degradation in the accuracy of the in-plane stresses and their sensitivity coefficients with mesh distortion. However, such degradation is observed for the transverse shear stresses and their sensitivity coefficients. The standard of comparison is taken to be the exact solution of the three-dimensional thermoelasticity equations of the panel.
The electromechanical characterization of carbon nanotube (CNT) papers, which are immersed in an aqueous electrolyte, is the main focus of this paper. The experimental set up consists of an ordinary three electrode cell, filled with the liquid electrolyte and using the CNT paper as working electrode. The in plain strain of the paper is measured and its quasi static and dynamic response to various electrical potential excitations has been investigated in a series of experiments. Additionally, the influence of different electrolytes, pre-stresses and types of carbon nanotubes (SWNT vs. MWNT) was studied.
Our last studies proposed a model of cortical bone [1], [2] with five architectural levels macroscopic, osteonal, lamellar, fibrous and fibrillar. In order to take into account the complex process of mineralisation, a new entity has been introduced, the EVMC (Elementary Volume of Mineral Content), which is made by hydroxyapatite cristals and fluid containing mineral ions. Each cristal is made on a solid part and on surounding gel. The modeling of the EVMC architecture is very important for the construction of bony properties at each level of its architecture and of course at the macroscopic level. In this paper, investigations are pursued on the possible geometrical organisation of these EVMC and their elastic properties are computed. Model is made by taking successively into account spatial organization of hydroxyapatite crystals, different mineralizations, a new behaviour’s law, motion of fluid containing ions in each of architectural levels and homogenization of complex composite structures (lamellae, osteons, and cortical bone). On a mathematically point of view, asymptotic developments method in a new piezoelectric framework (with threshold) is used. Developed computational methods have been packed into the software called SiNuPrOs (Numerical Simulations of Cortical Bone’s Properties). On a biomechanical point of view, it has been established that human cortical bone is a non piezoelectric orthotropic medium for which anisotropy is essentially involved by the nanoscopic architecture. For a given organisation of EVMC, mechanical properties are found at macroscopic level and under a standard loading, the obtained mechanical fields induce nanoscopic fields (strain, stress, electrical potentiel) in these EVMC. This process could be seen as an iterative process or a feedback phenomenon and represents an interesting approach of bone remodeling.
A finite-element model for the analysis of thermal stresses in oxidation-protecting coatings on carbon-carbon composites is developed. The model is based on an incremental formulation of the generalized plane deformation theory and allows for temperature-dependent material properties, and the application of coatings at different temperatures. Emphasis is on the determination of stresses in the coatings near a geometric discontinuity, such as the corner radius of a rectangular cross section. The model is used to study the St. Venant effect associated with the discontinuity and the effect of the orthotropy of the carbon-carbon substrate on the stresses in the coatings. The importance of using temperature-dependent material properties is demonstrated.
We employ an evolutionary algorithm to investigate the optimal design of composite protectors using one-dimensional granular chains composed of beads of various sizes, masses, and stiffnesses. We define a fitness function using the maximum force transmitted from the protector to a "wall" that represents the body to be protected and accordingly optimize the {topology} (arrangement), {size}, and {material} of the chain. We obtain optimally randomized granular protectors characterized by high-energy equipartition and the transformation of incident waves into interacting solitary pulses. We consistently observe that the pulses traveling to the wall combine to form an extended (long-wavelength), small-amplitude pulse.
A set of micromechanics equations for the analysis of particulate reinforced composites is developed using the mechanics of materials approach. Simplified equations are used to compute homogenized or equivalent thermal and mechanical properties of particulate reinforced composites in terms of the properties of the constituent materials. The microstress equations are also presented here to decompose the applied stresses on the overall composite to the microstresses in the constituent materials. The properties of a 'generic' particulate composite as well as those of a particle reinforced metal matrix composite are predicted and compared with other theories as well as some experimental data. The micromechanics predictions are in excellent agreement with the measured values.
This paper concerns with mesh restrictions that are needed to satisfy several important mathematical properties -- maximum principles, comparison principles, and the non-negative constraint -- for a general linear second-order elliptic partial differential equation. We critically review some recent developments in the field of discrete maximum principles, derive new results, and discuss some possible future research directions in this area. In particular, we derive restrictions for a three-node triangular (T3) element and a four-node quadrilateral (Q4) element to satisfy comparison principles, maximum principles, and the non-negative constraint under the standard single-field Galerkin formulation. Analysis is restricted to uniformly elliptic linear differential operators in divergence form with Dirichlet boundary conditions specified on the entire boundary of the domain. Various versions of maximum principles and comparison principles are discussed in both continuous and discrete settings. In the literature, it is well-known that an acute-angled triangle is sufficient to satisfy the discrete weak maximum principle for pure isotropic diffusion. An iterative algorithm is developed to construct simplicial meshes that preserves discrete maximum principles using existing open source mesh generators. Various numerical examples based on different types of triangulations are presented to show the pros and cons of placing restrictions on a computational mesh. We also quantify local and global mass conservation errors using representative numerical examples, and illustrate the performance of metric-based meshes with respect to mass conservation.
, the acceptable results will need about 400, 000 DOFs for the nonlinear analysis. 
A rectangular quartz crystal plate with coordinates  
Frequency-shifts at different amplitudes in comparison with nonlinear finite element  
Distributions of TSh vibrations in the central line of a plate with different amplitudes  
A nonlinear analysis of high-frequency thickness-shear vibrations of AT-cut quartz crystal plates is presented with the two-dimensional finite element method. We expanded both kinematic and constitutive nonlinear Mindlin plate equations and then truncated them to the first-order equations as an approximation, which is used later for the formulation of nonlinear finite element analysis with all zeroth- and first-order displacements and electric potentials. The matrix equation of motion is established with the first-order harmonic approximation and the generalized nonlinear eigensystem is solved by a direct iterative procedure. A backbone curve and corresponding mode shapes are obtained and analyzed. The nonlinear finite element program is developed based on earlier linear edition and can be utilized to predict nonlinear characteristics of miniaturized quartz crystal resonators in the design process.
In this article uniaxial constrained recovery is modelled using the theory of generalized plasticity, which was developed by J. Lubliner and F. Auricchio. As a mechanical obstacle that delays free recovery in a shape memory alloy wire, a bias spring made of an ordinary material is used. Two flow rules are used in the modelling: linear and exponential.
This paper compares two optimization strategies used to identify mechanical parameters associated to elasticity and plasticity behaviors of biopolymer materials. The first strategy is based on classical gradient-based methodology. It assumes that the gradient of the error between the finite element and experimental load-deflection curves is proportional to the update of mechanical parameters. The second methodology is an adaptive heuristic technique derived from genetic algorithm. It considers selection of probable solutions from the possible range of mechanical parameters. Both methodologies are used to identify Young's modulus, tangent modulus and yield stress of biopolymer composite materials exhibiting different behaviors.
A sublaminate model for analysis of laminated and sandwich beams is developed that incorporates a general zig-zag approximation within each sublaminate. The displacements are postulated so that the transverse shear and the transverse normal stress and stress gradient continuity conditions are met in the sublaminate. Four variations, respectively with linear or cubic approximation, with and without zig-zag representation, are confronted. The aim is to assess the practical advantages of higher-order approximations of displacements within sublaminates. The numerical applications concern laminated and sandwich beams loaded by a sinusoidally distributed transverse load and a laminated beam thermally loaded. Also, cases with reduced elastic moduli of faces and core, simulating damage or failure, are investigated to assess accuracy when the layers exhibit distinctly different material properties. Comparisons are made with the 3-D elasticity solution and with various models in literature. The present model provides practical advantages when the material properties change abruptly across the thickness and the laminates are thick. A single sublaminate is required for modeling the faces of sandwich beams and solid laminates, contrary to the models with zig-zag terms neglected. This corroborates the capability of zig-zag representation within sublaminates to improve accuracy.
Electro-rheological (ER) fluid devices offer controllable output dynamics at fast speed of response. This ER performance is examined for robotic applications. Given the rapid speed of response of the clutch, this ER clutch is considered as an alternative actuator for the robot arm. In the present paper, the main objective is to validate a mathematical model that predicts the output velocity response of this ER device. The other aim is to develop a suitable engineering technique to activate and de-activate the output response of the ER clutch rapidly for achieving fast start-stop motions of ER–actuated robot arm. Next, a trend study on the ER output velocity response is conducted to determine suitable input parameters for fast robotic performances and also to identify some preliminary ER problems for feasible ER-robotic applications.
A general framework for characterizing the behavior of electroactive heterogeneous media is developed. The governing equations of the coupled electromechanical problem are obtained together with the appropriate boundary and interface continuity conditions. Preliminary calculations for the class of sequentially laminated composites are carried out. These calculations demonstrate that the electromechanical coupling can be improved by considering non-homogeneous electromechanical actuators. In particular, we show that the overall response of a composite actuator can be better than the responses of its constituents. These findings are in agreement with recent experimental work showing that the limitations of these actuators can be overcome by making composites of flexible and high dielectric modulus materials.
Schematic illustration of the layered structure geometry. The film is divided into sublayers when the stress changes with thickness. 
Phase velocity of the fundamental and the first order Love mode in the Cu/Si layered system for wave propagation parallel to the [100] and [110] axis as function of the frequencythickness product f h. 
Theoretical studies are made in order to evaluate the acoustoelastic effect of prestressed layered systems using the ordinary differential equation method (ODE) and the stiffness matrix method (SMM). The modifications for residual stresses consider the change of the density, the influence of residual stress, and the modification of the elastic stiffness tensor by residual strain and by third-order constants. For illustration, we use a layered system of copper deposited on a silicon substrate. The acoustoelastic effect is investigated for both Love and Rayleigh surface acoustic waves. The obtained results demonstrate the importance of the acoustoelasticity studies for the homogeneity examination.
The article focuses on the use of the method of sampling surfaces (SaS) to exact three-dimensional (3D) solutions of the steady-state problem of thermoelectroelasticity for piezoelectric laminated plates subjected to thermal loading. The SaS method is based on selecting inside the nth layer In not equally spaced SaS parallel to the middle surface of the plate in order to choose temperatures, electric potentials, and displacements of these surfaces as basic plate variables. This permits the representation of the proposed thermopiezoelectric plate formulation in a very compact form. The SaS are located inside each layer at Chebyshev polynomial nodes that improves the convergence of the SaS method significantly. As a result, the SaS method can be applied to 3D exact solutions of thermoelectroelasticity for piezoelectric laminated plates with a specified accuracy using the sufficient number of SaS.
The dynamic compressive experiments were performed on 3D braided composites with different braiding parameters using the Split-Hopkinson-Pressure-Bar (SHPB) technique. The dynamic stress versus strain curves and the important mechanical properties were determined. The influence of braiding parameters on the dynamic properties and failure mechanism of composites are analyzed in detail. The results show that the smaller braiding angle and higher fiber volume fraction will contribute to better longitudinal dynamic compression properties. The damage drastically increases with the braiding angle. Moreover, the composites with a higher fiber volume fraction bear a more severe destruction and become more brittle in failure.
Several one-dimensional finite elements for the static analysis of shear actuated piezo-electric three-dimensional beams are presented. A generic expression of stiffness and mass matrices is obtained through a Unified Formulation. The derivation is general regardless of the approximation order of the displacements and the electric potential over the cross-section and the number of nodes along the axial direction. A Lagrange’s polynomials based layer-wise approximation is used. Several mechanical boundary conditions and sensor and actuator configurations are investigated. Results are assessed towards three-dimensional finite element solutions. It is demonstrated that the proposed class of finite elements is able to yield very accurate results.
This article presents a unified analytical solution for the anti-plane elastic field in an elliptical inhomogeneity with polynomial eigenstrains in anisotropic materials possessing an elastic plane of symmetry. The elastic field takes the form of a quadratic polynomial, with coefficients determined analytically based on the principle of minimum potential energy. Expressions for the elastic energy are given by means of complex representation and conformal transformation. The resulting solution is verified for the shear stress at the interface between the elliptical inhomogeneity and matrix. Numerical examples are given to illustrate the distributions of shear stress and strains at the interface.
This work presents a new analytical model for constrained layer damping (CLD). CLD is an effective vibration suppression approach. Unfortunately, most of the existing research involving analytical models for constrained layer damped structures considered the simple beam structure and are therefore not applicable for many real systems. As a result, it is important to be able to model the CLD of structures like plates and improve both the accuracy and versatility of the predictions. Most existing research assumes that shear deformation of the damping layer is the dominant source of damping, despite the fact that some research has noted that this assumption is often not valid. To address these needs, this work provides development of an analytical model for a three-layer CLD plate structure. Unlike previous models, this analytical model treats the three-layer plate as not only having shear deformation, but also as having longitudinal extension and transverse compression deformation in the damping layer. Because of these new considerations, all types of damping in the intermediate layer have been taken into account. This newly developed analytical mode is validated by comparing it with experimental data from published literature. Then, a parametric study between this newly developed compression plate analytical model and another newly developed plate analytical model that neglects compression damping is conducted in order to explore the impact of some design parameters on the structure's modal characteristics. For cases when the face layers have different thicknesses, it is shown that it may be necessary to include the transverse compressional damping component to provide an accurate prediction of the natural frequencies and loss factors.
The coupled bending-extensional in-plane vibration of a rotating curved beam is considered. The dynamic system is governed by two coupled differential equations and six boundary conditions. The conventional method of transition matrix is usually used to solve the system composed of one nth order differential equation and n boundary conditions. In this study, the system of a rotating curved beam is different from that of the conventional one. The modified method of a semi-analytical transition matrix is developed to study this system. Finally, several physical observations about the rotating curved beam are manifested.
An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading.
This article is devoted to the evaluation of refined theories for static response analysis of piezoelectric plate. The Carrera Unified Formulation (CUF) is employed to generate the refined plate models. The CUF allows the hierarchical implementation of refined models based on any-order expressions of the unknown variables. Equivalent single layer (ESL) and layerwise (LW) approaches are used to generate the refined models. The governing equations are obtained considering Navier-type, closed-form solutions. The axiomatic/asymptotic technique is employed in order to evaluate the relevance of each model term. This technique computes the relevance of a model term by measuring the error introduced with its deactivation with respect to a reference solution. The axiomatic/asymptotic technique is applied considering the sensor and actuator configurations for piezoelectric plates. Moreover, the analyses are performed taking into account the influence of the length-to-thickness ratio (a/h) and the use of isotropic or orthotropic materials. “Best” models are proposed and the stress/displacement components and electric potential distributions are evaluated by means of these reduced models.
This article proposes a complex application of a refined electro-mechanical beam formulation. Lagrange-type polynomials are used to interpolate the unknowns over the beam cross section. Three- (L3), four- (L4), and nine-point (L9) polynomials, which lead to linear, bi-linear, and quadratic displacement field approximations over the beam cross-section, are considered. Finite elements are obtained by employing the principle of virtual displacement in conjunction with the Carrera unified formulation (CUF). With the CUF application, the finite element matrices and vectors are expressed in terms of fundamental nuclei whose forms do not depend on the assumption made (L3, L4, or L9). Additional refined beam models are implemented by introducing further discretizations over the beam cross-section. Some assessments from the bibliography have been considered in order to validate the electro-mechanical formulation. Complex three-dimensional geometries have been studied in order to demonstrate the capabilities of the present formulation.
An investigation of the free vibration behavior of thin-walled composite box-beams is carried out by considering different assumptions in the constitutive equations. Within the present model some non-classical effects, such as restrained warping and transverse shear, are incorporated. Free vibration results are validated against experimental and numerical results, which are available in the literature. The natural frequencies obtained based on the different assumptions of constitutive equations are compared, and it is revealed that these assumptions play an important role in the proper treatment of the free vibration behavior of torsion-bending coupled composite beams. The results obtained based on the proposed constitutive equations are demonstrated to have a good agreement with the finite element results as far as the lower natural frequencies of the beams are concerned.
This article presents an investigation on the mechanical properties of porous interlayers between fiber bundles and matrix in three-dimensional (3D) carbon/carbon composite. Micro computer tomography systems are employed to observe the microstructures in situ and nondestructively in the porous interlayers. Statistical analyses are utilized to obtain microstructure parameters. Mechanical models are developed to describe the mechanical behavior of these porous interlayers. Using microstructure parameters in the calculation model, mechanical properties of porous interlayers are obtained. The calculation results and experiment results by push out tests are accordant. Results show that the mechanical properties of porous interlayers are inhomogeneous and discrete.
The deflection of multi-layered ceramic capacitors (MLCCs) due to high pressure was investigated. Classical laminated plate theory and linear elastic assumptions were adopted. Three boundary conditions are considered, such as all edges simple-supported, two simple-supported and the other two free, and all free. Four corners fixed and the elastic foundation at the bottom are added. Finite element method (FEM) with software ANSYS was used to obtain the displacements. Compared with numerical results, the analytical solutions of two cases were acceptable, such as four edges free and two edges simple-supported and the others free with the errors 0.1–6.2%.
In this contribution an energetic model for multi-phase materials is developed describing the influence of microstructure on different length scales as well as the evolution of phase changes. Restrictions on the energy functional are discussed. In such a non-convex framework, interfacial contributions serve for relaxing the total energy. Such models can be applied to describe the macroscopic material properties of carbon fiber reinforced carbon where phase transitions between regions of different texture of the carbon matrix are observed on a nanoscale as well as columnar microstructures on microscale.
An experimental-computational procedure is proposed and numerically validated for combined compression and bending tests and for identification of parameters in anisotropic elastic-plastic material models of the mechanical behavior of foils, specifically of paperboards and laminates for liquid containers. From the experimental standpoint, the proposed technique generalizes the instrumentation and “modus operandi” of traditional uni-axial testing with the following novel provisions: the foil specimen is stabilized by two elastic “blocks” of a well known polymeric material (therefore, such system is called “sandwich” herein); “full-field” displacement measurements by a digital image correlation (DIC) technique are envisaged, and examined by sensitivity analyses with respect to the sought parameters; the experimental data provided by DIC might be enriched by the digitalized relationship between external loading and imposed displacements in the test; test simulations (“direct analyses”) are performed by finite element modeling and the sought parameters governing the specimen behavior are assessed by minimization of a discrepancy function (inverse analysis); the minimization by mathematical programming is made fast and economical by radial basis functions (RBF) interpolations based on preliminary proper orthogonal decomposition (POD).
An analytic model was developed to predict the failure strength of pin loaded composite joints using a two-dimensional analysis. The characteristic dimensions, which define the characteristic curve, were obtained by stress analyses associated with no bearing and tensile tests on laminates with and without a hole. The available experimental data in the literature was then used to evaluate the joints’ strength. There was a good agreement between the experimental data and the computed joints’ strength. Additionally, the failure mode that characterizes the failure condition depends on the orientations of the laminas that constitute the laminate used for joint construction.
Effect of varying the number of terms in the Fourier series expansions in the solution
Figure10. Transverse normal stress in the mid-plane of core and at the face sheet /core interface
Transverse deflection of the circular cylindrical composite sandwich shell
In this study, a high-order model for the analysis of circular cylindrical composite sandwich shells subjected to low-velocity impact loads is presented. The sandwich shell is composed of two composite face sheets and a transversely compliant core. The impact behavior of the cylindrical composite sandwich shells is described by a high-order sandwich shell theory. The interaction between the impactor body and the sandwich shell is approximated using a spring mass model. The present analysis is based on an iteration procedure, and yields analytic functions describing the contact force history. The contact force is considered to be distributed uniformly over a contact patch, the size of which depends on the magnitude of the impact load as well as the elastic properties and geometry of the impactor. Finally, the obtained results have been compared with the available experimental results, and a good correlation has been found.
The anti-creep capability of metallic foams is important to structural applications at elevated temperatures. Currently, available creep models for opened-cell foam materials are usually derived by rather simplified meso-structural models. Here, we try to predict the creep properties of new fiber-reinforced closed-cell foams with more realistic 3D meso-structures. In the study, three-dimensional Voronoi structures are constructed to describe the inner structure of closed-cell foams, and reinforcing fibers are modeled by line segments penetrating through cell walls. Based on the recommended model, not only the steady creep strain rates of both the unreinforced and the reinforced foam materials are well predicted with considering the effects of temperature, stress, and relative density, but also the creep evolution features of metal foam are revealed from the meso-deformation behaviors. It is found that, at moderate temperature and stress, the creep rate of the fiber-reinforced metallic foam can also be well described by a power law with respect to the foam relative density. The influence of addition of fibers on the creep properties is parametrically studied and it is shown that addition of fibers has a positive effect on restricting the creep rate. It is observed that during creep, the stresses of cell walls are redistributed and become more homogeneous with time. When the creep rate of metallic foam reaches steady state depends on when the stresses of cell walls become homogeneous.
This work deals with the vibration of orthotropic multilayer sandwich structures with viscoelastic core. A finite element model is derived from a classical zigzag model with shear deformation in the viscoelastic layer. The aim of the present work is to establish numerical models and develop numerical tools to design multilayer composites structures with high damping properties. To fulfill this purpose, a finite element model has been developed for vibration analysis of a sandwich plate (elastic orthotropic)/(viscoelastic orthotropic)/(elastic orthotropic). A numerical study from the variation of the damping properties of the structures was performed according to the faces materials fibers orientation.
A general model of the equations of the generalized thermoelasticity for an infinite space weakened by a finite linear opening Mode-I crack is solved. The material is homogeneous isotropic elastic half space. The total deformation of a Mode-I crack in thermoelastic half-space in the context of Lord-Şhulman and Green-Lindsay theories is studied, as well as the coupled theory and the interaction with each other under the influence of gravity. The normal mode analysis is used to obtain the exact expressions for the physical quantities. Comparisons are made with the results between the three theories in the presence and absence of gravity.
The methodology utilized in estimating the residual properties of plies with matrix ply cracks is discussed. The technique involves the use of a laminate unit cell and a volume-averaging scheme to extract stress/strain data from a three-dimensional finite element model. The procedure for developing periodic boundary conditions and their implementation in the unit cell models is explained. The volume-averaging scheme capturing the contribution of the crack to the deformation of the laminate is presented. Residual thermo-mechanical properties of the cracked plies were then estimated and compared with experimental results of cross-ply laminates and were found to be in good agreement.
A numerical study on the indentation and scratch responses of epoxy (EP) and its composites using finite element modeling is presented. This work is motivated by previous experimental results [11. Z.Z. Wang, P. Gu, Z. Zhang, L. Gu, and Y.Z. Xu, Mechanical and tribological behavior of epoxy/silica nanocomposites at the micro/nano scale, Tribol. Lett., vol. 42, pp. 185–191, 2011.[CrossRef], [Web of Science ®]View all references], which show that the addition of silica nanoparticles can obviously increase the hardness and modulus and improve the scratch-resistance of the EP matrix. Simulation results are compared with these experimental ones and show very close agreements. The modification mechanisms of the nanoparticles are also presented. Stress analysis demonstrates that the load transferring from matrix to particles is the direct strengthening mechanism.
The article reports on the design of a novel class of transducers for structural health monitoring and strain sensing designed using a Fourier-based approach. The design procedure formulates the problem considering an arbitrarily shaped distribution of the sensing surface. Interrogation of the sensors is based on the generation of guided and surface acoustic waves generated in the region surrounding the transducers. The representation of the distribution of the sensing material is analyzed and designed in the spatial Fourier domain, where the emission characteristics of the transducer in relation to the interrogating wave can be tailored to a specific application. For structural health monitoring, the sensing material distribution can be defined to provide the transducers with frequency-dependent directional properties, which can be employed as part of an interrogation scheme based on generation and processing of guided waves in the structure. For strain sensing, one-dimensional and two-dimensional grating configurations monitor frequency shifts of radiation associated to local straining of the gratings. These frequency shifts can be related to the local strain components, so that a rosette-like configuration can be implemented. The article illustrates the commonalities of the design procedure, which leads to novel Lamb wave and strain transducers, and suggests the potential integration of the two sensing modalities as a single device for health and usage monitoring of structural components.
In this work, the governing equations of generalized magneto-thermo-viscoelasticity (MTVE) with one relaxation time and variable electrical and thermal conductivity for a one-dimensional problem are formulated into a matrix form using the state space and Laplace transform techniques. The resulting formulation is applied to a half-space medium subjected to ramp-type heating and zero-traction. The inversion of Laplace is carried out using a numerical approach. Numerical results for the dimensionless temperature, the stress, and the displacement distribution are given and illustrated graphically. According to the numerical results, some comparisons have been shown in figures to estimate the effect of some parameters on all variable fields, and discussion has been established.
Nonlocal variational formulation is established for continuum with the internal long-range interactions. Applying this theory, we develop a new microbeam model, which is used to investigate the scale effects of a micro-cantilever in micro-electro-mechanical system (MEMS). The calculations show that when the thickness of a micro-cantilever is on the micron-order of magnitude, the static deflection of the micro-cantilever increases with the thickness decreasing, but the eigenfrequency remains almost constant. The prediction for the static deflection agrees well with the existing experimental data. This new model provides a concise interpretation, distinguished from the strain gradient theory and surface elasticity, for the scale effects in MEMS. In this model, the scale effects are regarded due to the long-range interactions within material.
The active vibration of plates integrated with distributed piezoelectric actuators is studied using control theory. The optimization problem consists of finding the control voltage applied to distributed piezoelectric patch actuators, which suppresses the transient displacements and velocities of plates with the least control effort. An explicit optimal control law is derived by utilizing the maximum principle theory for the structural dynamic systems in two space dimensions. The implementation of the theory is presented in an example, and the effectiveness of the proposed control is investigated by a numerical simulation.
In this study, the analysis of thermal residual stresses in a nickel-alumina bimaterial are studied using finite element analysis. The variation of the normal thermal residual stress and shear stress is evaluated near the interface of the bimaterials. The effect of the temperature gradient, the thickness of the material, and the size of the assembly on the distribution of thermal stresses are highlighted. The mechanical resistance to fracture of this type of assembly mainly depends on these residual stresses, which are initiated after the elaboration process of the bimaterials.
In practice, the element connection may not be clamped perfectly in the manufacturing process. For the safety of a structure in an earthquake, the elastic element connection is helpful for the propagation of energy through all of the structure elements and the prevention of local damage. So far, the theory for a structure with partially clamped joints has not been investigated clearly. The mathematical model is established here. The analytical solution for this system is derived. It is found that the effects of the rotational spring constants, the ratios of the bending rigidities, and the element lengths on the natural frequencies are significant.
Experiments and finite element analysis (FEA) were performed on scarf-patch repaired composite panels. Tensile static tests were performed on pristine and repaired panels to evaluate their tensile strength. The obtained results showed that the repaired panels restored tensile strength by 95% of the pristine value. Subsequently, a verification finite element (FE) model was established. Two additional models, one with homogenized mechanical properties of the laminate and one that considered that the ply-by-ply properties were built to simulate the experimental repairs. The predictions of the two models agreed reasonably well with the experimental results and the optimum scarf angle was found at 2.5°.
Rotating around any axis OA with azimuth angle (, ). 
The central frequency and width of band gap (BG) at N = 3 and N = 4 N = 3 N = 4 Changes 
The geometric configuration of 3D phononic crystal with simple cubic lattice. (a) 3D phononic crystal made of anisotropic sphere embedded in isotropic host in a simple cubic lattice. (b) The project of 3D phononic crystal in the xy coordinate plane when anisotropic spheres rotate around z axis ( is the rotating angle). (c) The project of 3D phononic crystal in the xz coordinate plane when anisotropic spheres rotate around y axis ( is the rotating angle). (d) The project of 3D phononic crystal in the zy coordinate plane when anisotropic spheres rotate around x axis ( is the rotating angle). 
Band gaps of 3D phononic crystal with orthotropic spherical inclusions embedded in the isotropic host are studied in this article. For anisotropic phononic crystal, band gaps are dependent upon not only the periodic lattice but also the orientation of orthotropic spheres. When the orientation changes continuously, for example, rotating these spherical inclusions around a spatial axis, the pass band and the forbidden band change as a result. These changes include the location and width of band gaps, and even appearing and disappearing of band gaps. The plane wave expansion method is used to reduce the band gap problem considered to a mathematical eigenvalue problem. The numerical simulation is given for YBCO/Epoxy composite. The location and the width of band gaps are estimated for different rotating angles and filling fractions. The influence of orientation of anisotropic spheres on band gaps is discussed based on these numerical results.
In this article, an analytical method is applied to investigate the local buckling of a lemniscate delimitated shape near the surface of piezoelectric laminated shells subjected to coupled thermal, electric, and mechanical loadings. Here, the Young's modulus and the thermal expansion coefficients of the material are treated as functions of temperature change in the piezoelectric cylindrical laminated shells, and the geometrical axes of local lemniscate delamination are inconsistent with the geometrical main axes of piezoelectric laminated base-shells. In examples, the effects of thermal and electric environments, geometrical parameters, and material properties on the local buckling for lemniscate delamination near the surface of piezoelectric laminated base-shells are described and discussed.
This investigation aims at designing and fabricating rigid polyurethane foam core/glass fabric-epoxy and carbon-glass fabric-epoxy sandwich composites with and without design optimization. Optimization of design was done for the sandwich beams using modified beam equations so as to obtain maximum strength in bending. Parameters like deflection, flexural rigidity, bending and shear stress, normal stress, and shear strain were determined for the sandwich composites and due comparison was made with the results evaluated for samples without design optimization. The above-mentioned sandwich composites with different low foam density values were fabricated using the conventional hand lay-up technique. Test samples were machined and the testing was carried out keeping the existing ASTM standard guidelines in mind, using a three-point bend test apparatus. It was observed that, though only the normal stress, bending stress, and shear stress were design optimized, the flexural rigidity also showed a considerable increase when compared with the results of the investigation where no design optimization was done. The observed failure modes of the specimens indicate that the true design optimized values for strength were not obtained despite considerable gains due to optimization. More insight towards achieving a closer optimization can be obtained by conducting the studies using higher densities of rigid foams of various materials and better epoxy resins keeping cost in mind. The existing standard regulations in the testing of sandwich specimens also deserve another look. The highlight of the work is in comparison of the optimized sandwich properties with the shape factors.
Carbon-based composites are known to possess excellent tribo properties coupled with high temperature stability. These requirements can be met using carbon-ceramic composites (CCC). CCC have been developed using different types of reinforcements in the form of particulate and fibers with phenolic resin as carbon matrix precursor. In particulate composites, calcined petroleum coke (CPC), fly ash, silicon carbide, and boron carbide were used as reinforcements, whereas in the category of fibrous composites, carbon fibers were used as an additional reinforcement. A comparison of fly ash-based carbon-ceramic composites (FACCC), carbon fiber-based carbon-ceramic composites (FCCC), and other particulate carbon-ceramic composites (OPCCC) has been studied.
Nanofibrous interconnected networks have been fabricated from PLA and PET using two different techniques, namely, electrospinning and the concept of microfibrillar composite (MFC), to compare the morphology, production methods, costs, and, to an extent, their potential as scaffolds. Both methods of production create a three-dimensional network, with the electrospun scaffolds being comprised of a fibrillar, cross-plyed structure compared to the extruded scaffolds that consist of an interconnected porous network. The average diameter of the fibers ranged from 125–145 nm and 70–75 nm for the electrospun and extruded scaffolds, respectively. Mouse osteoblastic MC3T3-E1 cells have been used to test the biocompatibility of the electrospun scaffolds. A live/dead stain indicated that cells could attach and grow on the PLA and PET scaffolds. A preliminary cost analysis demonstrates that electrospinning is substantially more time and cost effective for larger quantities produced; however, the MFC technique can potentially produce totally solvent-free scaffolds.
Top-cited authors
Erasmo Carrera
  • Politecnico di Torino
Farzad Ebrahimi
  • Imam Khomeini International University
Mohammad Reza Barati
  • Amirkabir University of Technology
Ashraf Zenkour
  • Kafrelsheikh University
Antonio Ferreira
  • University of Porto