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Mechanical behavior of woven glass fiber reinforced composites under impact compression load
Abstract
Two types of glass fibre-reinforced plastic composite were subjected to compressive impact loading. The effects of the glass processing operation, the matrix type, number of plies and the strain rate on the composite strength have been investigated. The split Hopkinson pressure bar (shpb) technique was used to produce failure strain rates ranging from 100 s−1 to 1000 s−1. The results, obtained as strength vs. strain rate, indicate that the strain rate has a slight effect on the impact compressive strength for all composite variables. The highest strength is obtained for the composite based on a vinyl ester matrix. The glass treatment process does not appear to influence the strength.
... The split Hopkinson bar (SHPB) has been widely used to determine the dynamic properties of materials at high strain rates [3][4][5][6][7][8][9][10][11][12]. Significant efforts have been made to investigate the effect of high strain rate on the dynamic behaviour of polymers adhesives and composites laminates using the Split Hopkinson bar under various loading conditions [13][14][15][16]. Hosur et al. [17] investigated the dynamic response of unidirectional carbon/epoxy composite material subjected to in-plane dynamic compression tests using SHPB with different strain rates of 82, 164 and 817 s −1 . ...
... They demonstrated in their study that the longitudinal compressive strength and failure strain increase however, the longitudinal modulus decreases with increasing strain rate. El-Habak et al. [14] examined the mechanical behaviour of woven glass fibre-reinforced composites at strain rates from 10 2 to 10 3 s −1 for three types of matrix (polyester, vinylester and epoxy). They concluded that the vinyester matrix allows to obtain the highest strength. ...
This study examines the behaviour of adhesively-bonded composite joints under dynamic compression tests. The purpose of this work is to use the split Hopkinson pressure bar (SHPB) for the dynamic characterization of adhesively bonded joints subjected to in-plane compression loading and in particular, the effect of strain rate on the mechanical behaviour and the damage kinetics. These joints are studied using glass/vinylester composite materials which are frequently used in naval applications Compression tests are performed at different strain rates using SHPB and high speed camera has been used to follow the damage progression. The experimental results have shown that the dynamic properties change with respect to the change in strain rate. Fibre buckling and delamination are the main damage criterias seen in the specimens under in-plane compressive tests. Therefore, this study not only allows us to understand the dynamic response of the adhesively bonded joints under dynamic compression but also enables us to establish damage models based on strain rate effect, for structure design purposes.
... The Split Hopkinson Pressure Bar (SHPB) have widely used to describe the dynamic properties of materials at different strain rates [4][5][6][7]. The effect of different strain rates on dynamic behavior in composite laminates were studied using the Split Hopkinson Bar [8][9][10][11]. Hosur et al. [12] investigated the dynamic behavior of uni-directional carbon/epoxy composite laminates under SHPB compression tests related to various strain rates. The dynamic results were compared with static compression tests, and they found that the stiffness and hardness values obtained from dynamic tests are higher than the values obtained in static tests. ...
In this investigation, the dynamic behaviour of glass fibre reinforced poly- mer under in-plane and out-of-plane dynamic compression tests was studied experimentally and numerically under varying the fibres orientation and the loading conditions. The composites consist of unidirectional E-glass fibers reinforced epoxy polymer composites used in modern helicopter blade application as inner surface. Specimens, with a cylindrical shape, are impacted at a constant strain rate subjected to SHPB and Ls Dyna program. The numerical results are in good agreement with experimental results. The results show that the out-of-plane stress values for different fiber orientation are close to each other, but the in-plane stress value is far lower for the fibers direction of ±45◦. This study will facilitate fiber orientation selection for dynamic effects during the helicopter blade production phase. Not only simple tests but also practical ideas make this study stand out. Considering results, the use of ±90◦ fiber direction in helicopter blades seems to be more advantageous against dynamic effects.
... Strength again generally appears to increase with strain rate [97,101] with a rate dependence somewhere between linear and log-linear, although there is some evidence of a weaker rate dependence at very high strain rates due to thermal softening or enhanced damage [102,103]. Different matrix materials have been found to exhibit different degrees of rate-dependence [87,104]. Song et al. noted that while woven CFRPs were generally stronger and stiffer at high rate, the reverse was true for in-plane compression. ...
This review aims to assess publications relevant to understanding the rate-dependent dynamic behaviour of glass- and carbon-fibre reinforced polymer composites (FRPs). FRPs are complex structures composed of fibres embedded in a polymer matrix, making them highly anisotropic. Their properties depend on their constituent materials as well as micro-, meso- and macro-scale structure. Deformation proceeds via a variety of damage mechanisms which degrade them, and failure can occur by one or more different processes. The damage and failure mechanisms may exhibit complex and unpredictable rate-dependence, with certain phenomena only observable under specific loading conditions or geometries. This review focusses on experimental methods for measuring the rate-dependent deformation of fibre composites: it considers high-stain-rate testing of both specimens of ‘simple’ geometry as well as more complex loadings such as joints, ballistic impact and underwater blast. The effects of strain rate on damage and energy-based processes are also considered, and several scenarios identified where strength and toughness may substantially decrease with an increase in strain rate.
... To study the variation of damping with fi-acture toughness, four additional tests were performed to calculate Fracture toughness and impact energy at regular immersion periods. These were analyzed in the previous chapters (5)(6)(7)(8). Fracture toughness and impact energy were calculated fi-om these tests. Further, these test results were used to study the variation of damping with Fracture toughness and impact energy. ...
Glass fibre reinforced polymer composites (GFRP) are being widely used in many applications because of their light weight, high stiffness and good damping properties. Their use in both offshore and onshore applications is becoming inevitable because of their excellent anti corrosive behaviour. These composites are subjected to severe loading and environmental conditions during their service. The conduct of the composites under certain ecological conditions is to be examined for legitimate working and to stay away from conceivable disappointment of the part. Likewise amid the lifetime of the composite there is a plausibility that the composite might be subjected to various situations than that it is as a rule by and by utilized for. Under every one of these conditions it gets to be distinctly basic that the conduct of the composite be considered for safe outline. Damping is one such property that should be contemplated for evaluating the vibrational conduct of the composites.
In the first part of the work, an attempt is made to study the variation of damping of GFRP composite subjected to different environmental conditions. Three distinctive fluid situations; Seawater, saline water, and ordinary water were utilized for the review to evaluate the damping conduct of the composite. The damping variety of the composite was considered for at regular intervals of submersion in the particular medium up to a most extreme of 60 days utilizing free vibration rot technique. Examples treated with seawater show more damping limit than different examples. The most extreme increment was around 37%. Saline and typical water treated examples indicated decrease in the damping great beneath the untreated examples of the request of around 47% and 32% individually. This differentiating conduct is ascribed to the distinction in the compound structure of the submersion mediums.
... The faces of the specimens were polished with 600-grit sandpaper to ensure parallel loading edges. To avoid uncertainties related to size effects, the specimens in all the tests are of the same geometry 8,15 . ...
This paper discusses the experimental study on the response of multi directional satin weave E-glass/epoxy composite laminates subjected to quasi-static and high strain rate compression loading along in-plane direction. Composite laminates were fabricated from satin weave glass fabric reinforced epoxy matrix pre-impregnated tapes which were manually laid up into laminates with stacking sequence of [45/-45/0/90] The low strain rate tests were conducted with an INSTRON™ testing machine, and the high strain rate tests done using a pulse shaper modified compression Split Hopkinson Pressure Bar (SHPB) apparatus. Compressive strength, modulus and strain at peak stress are evaluated experimentally at different strain rates. The results show that compressive strength, modulus and strain at peak stress are rate sensitive and enhanced at high strain rate compared with those at quasi-static loading. Under high strain rate loading, compressive strength and modulus increase as the strain rate increases. Optical and microscopic graphs on the specimens are carefully examined to determine operative failure modes. With the studied strain rate regimes, the failure modes are observed to change from splitting followed by fiber kink buckling to predominantly delamination and shear fracture as the strain rate increases from quasi-static to high strain rate.
... Therefore, it is required to characterize the dynamic behavior of composite materials. To date, the in-plane compressive [1][2][3][4][5][6][7][8][9][10][11][12], tensile [13][14][15][16][17][18] and interlaminar shear [19][20][21][22][23][24] properties of composite materials under dynamic loading have been determined with the conventional [25] or modified split Hopkinson pressure bar (SHPB). Nevertheless, except for Refs. ...
The ultimate tensile strength of carbon/epoxy laminated composites in the through-thickness direction at deformation rates up to nearly 1 m/s is determined using the split Hopkinson bar. Two carbon/epoxy laminated composites (i.e., unidirectional and cross-ply) with almost the same thickness are tested at room temperature. Waisted cylindrical specimens are machined such that the direction of the tension loading is perpendicular to the fiber direction of the laminates. The effects of deformation rate and reinforcement geometry on the ultimate tensile strength are examined. It is shown that the ultimate tensile strength increases significantly with increasing deformation rate. The ultimate tensile strength of the unidirectional carbon/epoxy laminated composite is slightly higher than that of the cross-ply one at low and high rates of deformation.
... Frey et al. 3 documented large amount of data for compressive high strain rate response of various composite material systems. Kumar et al. 4 and El-Habak 5 have studied the behaviour of glass/epoxy composites subjected to high compressive strain rates and noted the failure modes. Walter et al. 6 and Li et al. 7 studied the damage modes in 3D glass fibre epoxy woven and 3-Dimensional Multi-Axial Warp Knitting (3D MWK) composites under high rate of impact loadings, respectively. ...
In this paper, high strain rate compression properties of aramid and ultrahigh molecular weight polyethylene composites in the out-of-plane direction are tested at room temperature on a Split Hopkinson Pressure Bar apparatus. Tests were conducted on composites reinforced with woven or Uni-Directional (UD) fabrics made from aramid or ultrahigh molecular weight polyethylene as well as on composites reinforced with hybrid reinforcement. The strain rate is varied in the tests by changing the projectile shooting pressure. Four different pressures 2, 4, 6 and 8 bar were selected to change the strain rate. Stress-strain and energy absorption behaviour of eight type of samples were noted. Hybrid samples showed better performance in the energy absorption compared with other samples.
... The Split Hopkinson Pressure Bar (SHPB), first introduced by Kolsky [15] is the most widely used technique for direct determination of high strain rate mechanical properties in the range of 200-10,000 s −1 . Since then, a number of researchers have carried out variety of high strain rate testings on different types of composite materials [16][17][18][19][20][21][22][23][24][25][26]. ...
... The stress-strain curves of the composite laminates showed that the material is strongly sensitive to fiber orientation and loading direction. El-Habak (2001) studied the mechanical behavior of 2D-woven glass fiber reinforced composites at strain rates ranging from 100 to 1000 s À1 . He studied the effect of sizing of the fiber and two different resin systems: epoxy and vinylester. ...
The in-plane compressive behavior of two- and three-dimensional woven composite was investigated at high strain rates. The Split Hopkinson Pressure Bar is employed to test the high strain rate dynamic mechanical properties of E-glass vinylester composite material. For three-dimensional woven composite, two configurations were tested: compression responses along the stitched direction and orthogonal to the stitched direction. Dynamic compression properties for two- and three-dimensional are determined and compared. Experimental results show that the strain rate has a significant effect on the two- and three-dimensional woven composite response. It is observed that the three-dimensional woven composite has higher compression strength and dynamic modulus than the two-dimensional composite at high strain rate. For this study, a high-speed camera was used to determine the damage kinetics under dynamic load. The two-dimensional woven composite is mainly damaged in a mode of matrix cracks and severe delamination, while the mode for three-dimensional woven composite is mainly cracking of matrix and delamination for in-plane along to the stitched direction and shear banding failure for in-plane orthogonal to the stitched direction.
... Frey et al. 3 documented large amount of data for compressive high strain rate response of various composite material systems. Kumar et al. 4 and El-Habak 5 have studied the behaviour of glass/epoxy composites subjected to high compressive strain rates and noted the failure modes. Walter et al. 6 and Li et al. 7 studied the damage modes in 3D glass fibre epoxy woven and 3-Dimensional Multi-Axial Warp Knitting (3D MWK) composites under high rate of impact loadings, respectively. ...
... Therefore, it is required to characterize the dynamic behavior of composite materials. To date, the in-plane compressive [1][2][3][4][5][6][7][8][9][10][11][12], tensile [13][14][15][16][17][18] and interlaminar shear [19][20][21][22][23][24] properties of composite materials under dynamic loading have been determined with the conventional [25] or modified split Hopkinson pressure bar (SHPB). Nevertheless, except for Refs. ...
The effect of strain rate up to approximately ε̇ = 102/s on the tensile stress–strain properties of unidirectional and cross-ply carbon/epoxy laminated composites in the through-thickness direction is investigated. Waisted cylindrical specimens machined out of the laminated composites in the through-thickness direction are used in both static and dynamic tests. The dynamic tensile stress–strain curves up to fracture are determined using the split Hopkinson bar (SHB). The low and intermediate strain-rate tensile stress–strain relations up to fracture are measured on an Instron 5500R testing machine. It is demonstrated that the ultimate tensile strength and absorbed energy up to fracture increase significantly, while the fracture strain decreases slightly with increasing strain rate. Macro- and micro-scopic examinations reveal a marked difference in the fracture surfaces between the static and dynamic tension specimens.
... Khan et al. examined thick S2-glass woven laminates at various loading orientations, and determined that the failure stresses and strains in the ply lay-up direction were higher than those in the plane of the lamina [22]. El-Habak found a small rate sensitivity of woven fiberglass composites under impact loading [23]; whereas Weeks and Sun examined off-axis AS4/PEEK over a wide range of strain rates and determined the point where the composite exhibited nonlinear and strain rate dependent behavior [8]. Powers et al. examined Cycom 5920/1583 uniaxial E-glass cloth with rubber toughened epoxy composites at strain rates from 60 to 1150 s −1 and determined that the ultimate strength did not significantly vary with strain rate, but the yield strength increased by a factor of 3.6 from low to high strain rates as the material transitioned from ductile to brittle behavior [24]. ...
Woven composites can offer mechanical improvements over more traditional engineering materials, yet understanding the complex interplay between the fiber-matrix architecture during loading remains a challenge. This paper investigates the evolution of shear failure behavior during the compression of high performance fiberglass composites with varying resin binders at both quasi-static and dynamic strain rates. All samples are comprised of commercially available woven glass cloth with approximately 56 % fiber volume fraction. Laminates with thermosetting resin binders of silicone, melamine, and epoxy were examined. High-speed imaging reveals that failure occurs within a localized shear band region through multiple fiber-weave matrix interface failure with a characteristic macroscopic angle. The shear evolution was spatially mapped using grayscale histograms of the light intensity in the shear regions, and the resulting characteristic angles were measured and analyzed in the context of a Mohr-Coulomb failure criterion. Optical microscopy and high-speed imaging of the shear formation shows initiation appears due to local instabilities from kinking and microbuckling, influenced by the stacking and interlacing regions of tows.
... Composite materials are increasingly being used as a substitute for metallic materials in many technological application like aeronautics, aerospace, marine, armor, automotive and civil engineering applications [1,2,3]. Many of these applications, the structure are subjected to high impact loading. ...
A series of Split Hopkinson Pressure Bar tests on 2D and 3D woven composites were presented in order to obtain a reliable comparison between the two types of composites, and the effect of the z-yarns along the 3rd direction. These tests were done along different configurations: in-plane and out-of-plan compression test. For the 3D woven composite, two different configurations in the plane were studied: compression responses along to the stitched direction (SD), and orthogonal to the stitched direction (OSD). It was found that 3D woven composite exhibit an increase in strength for both: in-plane and out-of-plane tests.
... The stressestrain curves of the composite laminates showed that the material is strongly sensitive to fiber orientation and loading direction. El-Habak [11] studied the mechanical behavior of woven glass fiber reinforced composites at failure strain rates ranging from 100 to 1000 s À1 . He studied the effect of sizing of the fiber, and two different resin systems: epoxy and vinylester. ...
... The stress-strain curves of the composite laminates showed that the material is strongly sensitive to fiber orientation and loading direction. El-Habak [11] studied the mechanical behavior of woven glass fiber reinforced composites at failure strain rates ranging from 100 to 1000 s -1 . He studied the effect of sizing of the fiber, and two different resin systems: epoxy and vinylester. ...
Split Hopkinson Pressure Bar (SHPB) is one of the most important and recognized apparatus used for characterizing the dynamic behavior of materials. In the first part, the results from a series of SHPB tests on the woven composites are presented in this paper. These tests were done in two configurations: in-plane and out-of-plane compression test. It is observed that the failure strength varies with the different loading directions. The results indicate that the stress–strain curves, maximum compressive stresses and strains evolve as strain rate changes. In the second part of this study, numerical models without damage are developed to investigate the validity of assumptions of compression Split-Hopkinson Pressure Bar technique. Abaqus software was used for the numerical simulation. The results obtained by numerical investigation (finite elements) of SHPB are compared with the in-plane and out-of-plan compression test of a woven composite. A good correlation was noted between the experimental and numerical results which allows validate the numerical approach used.
... The faces of the specimens were polished with 600-grit sandpaper to ensure parallel loading edges. To avoid uncertainties related to size effects, the specimens in all the tests are of the same geometry [21,22]. ...
The objective of this article is to investigate the compressive behaviors of [45/-45/0/90]ns satin weave E-7781 glass/Eepoxy composite laminate under different loading strain rates along the in-plane direction. The low strain rate tests were conducted with an INSTRON testing machine, and the high strain rate tests were conducted using a pulse shaper modified compression Split Hopkinson Pressure Bar (SHPB) apparatus. Failure strength and strain at peak stress were evaluated experimentally at different strain rates. The results showed that failure strength and strain at peak stress were rate sensitive. A few strain rate dependent constitutive models were referred to describe the dynamic mechanical behaviors of woven composites with various stacking sequence, and the constants in the equations could be confirmed from experiment data. Optical and microscopic graphs on the specimens were carefully examined to determine operative failure modes. Within the studied strain rate regimes, the failure mode was observed to change from splitting followed by fiber kink banding to predominantly delamination and shear fracture as the strain rate increases from quasi-static to high strain rates.
... The ultimate stress increases and the point at which complete separation takes place are delayed. El-Habak [8] therefore shows a change in the failure mode at increasing strain rates. Srikanth et al. [9] present a study of modeling the high strain rate response of the unidirectional S2Glass/8553-40 polymeric composite material system. ...
The sensitivity of glass fiber reinforced polymer is studied by testing a single laminate configuration under quasi-static compression. The compressive material properties are determined by testing the laminate systems with different orientations. Samples, of cubic geometry, are tested in-plane and out-of-plane direction for static and dynamic compression. The tests show a strong material sensitivity to the loading direction and the fiber direction. Damage investigations have revealed that the failure events differ and depend on composite sequence lay-up and loadings.
... Although the mechanical properties of most composite materials illustrate strain rate dependency at dynamic loading, there is no consensus about their degree of sensitivity, which changes markedly depending on the composite type. The influence of high strain rate compressive forces on different kinds of fibre reinforced composite has been investigated [6][7][8]. On the other hand, various researchers have performed impact tensile tests on different kinds of carbon/epoxy and glass/epoxy composites at quasi-static and various high strain rates [9][10][11][12][13][14][15][16]. Laminate composite materials have also been widely examined due to their crucial role in structural applications. ...
Unidirectional normal modulus CFRP (CF130) and Araldite 420 and MBrace saturant adhesives are now commonly used to strengthen steel and concrete structures. However, there is a lack of understanding regarding their mechanical properties under dynamic tensile loads. This paper focuses on the experimental determination of the tensile mechanical properties of such materials at quasi-static and intermediate strain rates. A drop-mass rig and an impact Instron testing machine were utilised to conduct impact tests of CFRP and epoxy. It was found that the tensile properties of CFRP and the two adhesives are strain rate-dependent, even though their general trends and percentages of enhancement differ. Considerable changes in the failure patterns of CFRP and both adhesives are observed. Empirical equations in terms of strain rates are proposed to estimate the tensile properties of CFRP and both adhesives at any strain rate within the range considered.
... All the mentioned properties are met by advanced polymer composites. The above properties are strongly dependent on the factors such as the matrix and fibre material and their volume fractions, the fibre orientation, the applied stress levels and strain rates, as well as the loading conditions and the nature of fibre polymer interface [4,5]. Interface is said to be the heart of the composite. ...
The aim of the present study is to investigate the interlaminar fracture behavior of glass-reinforced polyester composites at liquid nitrogen temperature. Short beam shear (SBS) test, which generally promotes failure by interlaminar shear, was performed to assess interfacial bond strength between fiber and matrix. The mechanical assessment is extended to evaluate and compare the loading rate sensitivity of cryogenically conditioned and untreated glass/polyester composites at 2, 50, 100, 200, and 500 mm/min crosshead speeds. Microstructural changes after cryogenic treatment of glass/polyester composites were explained by scanning electron microscope (SEM). The behavior of these composites at cryogenic temperature may be attributed to stress relaxation, polyester curing shrinkage, large amount of residual stresses, cryogenic contraction of the matrix, greater misfit strains, and matrix crackings.
... It was demonstrated that in agreement with corresponding theoretical findings of Schuler (1970) the free-surface velocity profiles of materials with strain-rate dependence are characterized by a rapid initial rise time and gradual convergence to the peak velocity afterwards. Habak (1991) studied the behavior of glass-fiber-reinforced composites by application of split Hopkinson pressure bars, and found that the overall response of the composite depends on the resin type and the fiber volume fraction. The relevancy of the constituents' properties to the composite overall response also depends on the reinforcement spatial arrangement. ...
In recent years there has been an increased demand for advanced materials that can sustain rapid dynamic loadings. To this end, we simulate the transient response of composites with nonuniform arrangements of their microstructures. First, a constitutive model that reproduces experimentally measured response of a glass-fiber composites is identified and adjusted. This involves a Mie–Grüneisen equation of state for the dilatational response together with a Voigt model for the isochoric behavior which is modified to include damage effects from void nucleation and growth. Then, with the aid of this constitutive model, a sequence of simulations of composites with nonuniform distributions of the reinforcement are executed. We find that composites with increasing volume fraction of the reinforcement along the impact direction tend to attenuate the intensity of the propagating waves. This attenuation delays the initiation of failure mechanisms to higher impact velocities and improves the composite’s sturdiness.
... The failure stresses under impact loading conditions were found to be considerably higher when compared to those obtained under quasi-static loading conditions. In recent years the dynamic response of glass–fiber reinforced composites has been investigated utilizing the Split Hopkinson Pressure Bars (SHPBs) under relatively simple states of stress, e.g., uniaxial compression, uniaxial tension, and pure shear (Elhabak, 1991; Agbossou et al., 1995; Tay et al., 1995; Barré et al., 1996; Sierakowski, 1997; Gama et al., 2001a,b; Song et al., 2002; Vural and Ravichandran, 2004). In these studies the failure and ultimate strength of the GRP composites were found to increase with increasing strain rates. ...
In the present paper results of a series of plate impact experiments designed to study spall strength in glass–fiber reinforced polymer composites (GRP) are presented. Two GRP architectures are investigated—S2 glass woven roving in Cycom 4102 polyester resin matrix and a balanced 5-harness satin weave E-glass in a Ciba epoxy (LY564) matrix. The GRP specimens were shock loaded using an 82.5mm bore single-stage gas-gun. A velocity interferometer was used to measure the particle velocity profile at the rear (free) surface of the target plate. The spall strength of the GRP was obtained as a function of the normal component of the impact stress and the applied shear-strain by subjecting the GRP specimens to normal shock compression and combined shock compression and shear loading, respectively. The spall strengths of the two GRP composites were observed to decrease with increasing levels of normal shock compression. Moreover, superposition of shear-strain on the normal shock compression was found to be highly detrimental to the spall strength. The E-glass reinforced GRP composite was found to have a much higher level of spall strength under both normal shock compression and combined compression and shear loading when compared to the S2-glass GRP composite. The maximum spall strength of the E-glass GRP composite was found to be 119.5MPa, while the maximum spall strength for the S2 glass GRP composite was only 53.7MPa. These relatively low spall strength levels of the S2-glass and the E-glass fiber reinforced composites have important implications to the design and development of GRP-based light-weight integral armor.
The escalating use of fiber-reinforced composites (FRCs) in aerospace, defense, automotive, and renewable energy industries underscores the need for a comprehensive understanding of their impact resistance and damage tolerance. This review meticulously examines low-velocity impact (LVI) on FRCs, covering impact mechanics, velocity classification, energy absorption, fiber architecture, and hybridization. Emphasizing the critical importance of damage assessment, the study analyzes intricate failure mechanisms and damages induced by LVI, addressing their potential impact on composite structural attributes. The paper critically reviews parameters influencing impact resistance and damage mechanics, evaluating performance through instrumented drop-weight impact testing. Additionally, the review explores nondestructive testing methods crucial for ensuring the reliability of composite structures. The aerospace sector and other applications requiring enhanced dynamic loading characteristics stand to benefit from a deeper understanding of composite behavior under transient impact loading. Specifically focusing on woven textile-reinforced composites, which offer specific material properties and a cost-effective manufacturing route. However, their susceptibility to out-of-plane impact loading leads to various failures, including delamination and spalling, limiting their applicability in advanced scenarios where structural integrity is paramount. It discusses advanced technology like 3D weaving as reliable methods to enhance impact resistance, damage tolerance, and delamination resistance. Notably, 3D woven composites demonstrate superior through-thickness fracture toughness, eliminating delamination as a failure mode. The findings offer valuable insights for designing structures with enhanced compression after impact and through-thickness tension characteristics. Overall, this review consolidates key advancements, challenges, and future prospects in the realm of woven composite materials and their behavior under impact loading, providing a valuable resource for academics and industry professionals alike.
Graphical Abstract
The split Hopkinson pressure bars (SHPB) system is the most commonly employed machine to study the dynamic characteristics of different materials under high strain rates. In this research, a numerical investigation is carried out to study different bar shapes such as square, hexagonal, and triangular cross-sections and to compare them with the standard cylindrical bars. The 3D finite element model developed for circular cross-sectional shapes was first validated with the experimental results and then compared with the other proposed shapes. In most scientific research, cylindrical cross-section bars with a square cross-section specimen are traditionally used as they have several advantages, such as in situ imaging of the side surfaces of the specimen during stress wave propagation. Moreover, the flat surfaces of the proposed shapes counter the problem of debonding strain gauges, especially at high impact pressures. Comparison of the results showed an excellent confirmation of the sample dynamic behaviour and different geometric shapes of the bar geometries, which validates the choice of the appropriate system.
From past two-three decades there has been a gradual shift from monolithic to composite materials in order to meet the increasing demand for lighter, high performance, environment friendly, corrosion and wear resistant materials. Composite materials are majorly used in massive production like boats, automotive and air craft Industry etc. in order to improve hardness and impact strength. The manufacturing of hybrid composite laminates is difficult to handle by traditional methods and gives size restrictions, wetting, poor surface finish, more number of moulding required for manufacturing. The Hand lay-up chosen as the fabrication technique when product needs smooth finish slight variations in thickness and number of moldings required is less. The moulding made from materials like plastics, wood, clay, plaster or plywood depending on the availability. Hand lay-up technique has been adopted to manufacture the hybrid composite laminated plate (sawdust with 1%, 2% and 3% variation) and impact strength and hardness is to be calculated.
As a high-demand material, polymer matrix composites are being used in many advanced industrial applications. Due to ecological issues in the past decade, some attention has been paid to the use of natural fibers. However, using only natural fibers is not desirable for advanced applications. Therefore, hybridization of natural and synthetic fibers appears to be a good solution for the next generation of polymeric composite structures. Composite structures are normally made for various harsh operational conditions, and studies on loading rate and strain-dependency are essential in the design stage of the structures. This review aimed to highlight the different materials' content of hybrid composites in the literature, while addressing the different methods of material characterization for various ranges of strain rates. In addition, this work covers the testing methods, possible failure, and damage mechanisms of hybrid and synthetic FRP composites. Some studies about different numerical models and analytical methods that are applicable for composite structures under different strain rates are described.
Fiber-reinforced polymer-based composites may experience various strain rates under different dynamic loads. As the mechanical behavior of these composites varies with strain rate, their response will be dependent on the strain rate. This paper presents a comprehensive review on glass fibers and composites reinforced with these fibers, as the most practical polymer-based composite, under dynamic loading. First, the properties of long glass fibers under different strain rates will be reviewed in detail. In the following, experimental studies on the effects of strain rate on various types of glass fiber-reinforced polymer-based composites will be categorized and presented. The behavior of thermoset polymers will be also addressed under different strain rates. Finally, various analytical and numerical macromechanical and micromechanical models will be comprehensively described for this type of composites.
Glass fiber reinforced polymer composites were prepared by different manufacturing technology and are extensively used for various applications. In recent times more research is carried out on glass fiber reinforced composites owing to their excellent mechanical properties. This study deals with the analysis of glass fiber reinforced polymer composites manufactured by different types of glasses, Matrix materials prepared using different production technologies. Glass fibers possesses good properties such as high strength, flexibility, stiffness, durability etc. With an increase in the content of glass fiber volume the properties of GFRP composites were improved. The mechanical & thermal attributes of various polymer composites reinforced by glass fiber when subjected to mechanical loading have been studied and reported.
The conventional woven fabrics (plain, twill, satin, etc.) have yarn undulations, that may lead to the fibre breakage and loss of mechanical strength. This problem was resolved using unidirectional woven structures having straight yarns, but they provide strength in one direction only. A possible solution is the use of biaxial fabric having yarns at ±45 ° as reinforcement, but its fabrication cost is too high. The current study focussed on the development of a composite material using conventional fabrics having comparable properties with biaxial fabric composites. Three different reinforcements (plain, twill and unidirectional) were prepared using glass fibre. For composite fabrication, plies were cut, stacked at ±45° and infused with unsaturated polyester resin to produce a composite equivalent to the biaxial composite. Similarly, the stitched composites were also fabricated by stitching the similar stack (using chain stitch class 101) before impregnating with resin. Laminated composites from biaxial fabric (both stitched and unstitched) were also produced for comparison. All these composites were characterised for tensile and impact properties. The tensile strength of stitched unidirectional composites was higher as compared to the other woven and biaxial structures. Similarly, the impact strength was also higher for stitched unidirectional composite. Hence, the ±45° stacked unidirectional composite may be used as a potential replacement of biaxial composite.
In this study, the influence of hybridization on the compression response of thermoplastic matrix-based composites under high strain rate loading was investigated. The intra-ply and inter-ply hybrid composites were manufactured with Kevlar/Basalt yarns as the reinforcements with Polypropylene as a matrix. Cylindrical composite specimens were laser cut from the flat compression moulded laminates. The composite specimens were loaded under high strain rate using split-Hopkinson pressure bar setup at strain rates ranging from 2815/s to 5481/s. The study revealed differences in the rate-dependent growth of peak stress, peak strain and toughness with the strain rate. Intra-ply hybrid composites with alternate weaving of Kevlar and basalt yarns exhibited highest peak stress as compared to the Inter-ply hybrid composites (alternate layers of Kevlar and basalt fabrics) and another intra-ply composite containing Kevlar in the warp and basalt in the weft direction. Whereas in inter-ply hybrid composite, with Kevlar as the loading face attained higher stress, while composite with Basalt as the loading face attained higher strain. SEM micrographs revealed that Kevlar on the loading face can bear the impact with lesser delamination as compared to the Basalt on the loading face. Damage studies revealed that Kevlar fiber surface loading results in higher stress as compared to basalt (brittle) surface loading with lower overall damage.
In this study, a new experimental approach in which the deformation, the damage kinetic, and the temperature are measured simultaneously during a high strain rate on adhesively bonded composite joints. Especially, our goal is to quantify the amount heat dissipation during impact and to identify the mechanisms that induce this dissipation. Out of plane dynamic compression tests were conducted on assembled specimens over a range of strain rate from 372 s⁻¹ to 1030 s⁻¹ using the Split hopkinson Pressure Bars technique. The specimen surface temperatures were monitored using an infrared camera. The increase in the strain rate has a dramatic effect on the stress–strain behavior producing a significant heat dissipation in the material. The infrared monitoring provides the spatial distribution of temperature that increase near the adhesive/adherent interfaces of the specimen. The observed temperature increase profiles clearly show that the stress concentration appears in the adhesive area and provide valuable information regarding the damage mechanisms and their role in the heat dissipation during dynamic loading conditions. The dependence of these results on strain rate indicates that there exists a correlation between the thermo-mechanical behavior and the strain rate effect, which might be useful when developping damage models taking into account the energy balance for adhesively bonded joints under impact loading conditions.
The effect of the strain rate on the mechanical behavior and the damage of adhesively bonded joints is one of the most important factors to consider in designing them. Vast research has been carried out on the dynamic behaviour of adhesives at different strain rates; however, the investigation about the dynamic behaviour of the adhesively bonded joints is limited. In this paper, the main objective is to study and assess the effect of the strain rate on the out-of-plane mechanical behaviour of adhesively bonded joints under dynamic compression using Hopkinson bars. These joints are studied using glass/vinylester composite materials which are commonly used in naval applications. The experimantal results have shown a strong material sensitivity to strain rates. Moreover, damage investigations have revealed that the failure mainly occurred in the adhesive/adherent interface because of the brittle nature of the polymeric adhesive. Results have shown good agreement with the dependency of the dynamic parameters on strain rates.
This study examines the behaviour of adhesively-bonded composite joints under dynamic compression tests. The purpose of this work is to use the split Hopkinson pressure bar (SHPB) for the dynamic characterization of adhesively bonded joints subjected to in-plane compression loading and in particular, the effect of strain rate on the mechanical behaviour and the damage kinetics. These joints are studied using glass/vinylester composite materials which are frequently used in naval applications Compression tests are performed at different strain rates using SHPB and high speed camera has been used to follow the damage progression. The experimental results have shown that the dynamic properties change with respect to the change in strain rate. Fibre buckling and delamination are the main damage criterias seen in the specimens under in-plane compressive tests. Therefore, this study not only allows us to understand the dynamic response of the adhesively bonded joints under dynamic compression but also enables us to establish damage models based on strain rate effect, for structure design purposes.
In the present work, dynamic compression response of polypropylene (PP) composites reinforced with Kevlar/Basalt fabrics was investigated. Two homogeneous fabrics with Kevlar (K3D) and Basalt (B3D) yarns and one hybrid (H3D) fabric with a combination of Kevlar/Basalt yarns were produced. The architecture of the fabrics was three-dimensional angle-interlock (3D-A). Three different composite laminates were manufactured using vacuum-assisted compression molding technique. The high strain rate compression loading was applied using a Split-Hopkinson Pressure Bar (SHPB) set-up at a strain rate regime of 3633–5235/s. The results indicated that the dynamic compression properties of thermoplastic 3D-A composites are strain rate sensitive. In all the composites, the peak stress, toughness and modulus were increased with strain rate. However, the strain at peak stress of Basalt reinforced composites (B3D, H3D) decreased approximately by 25%, while for K3D specimens it increased by approximately 15%. K3D composites had a higher strain rate as compared to the B3D and H3D composites. The dynamic properties of K3D except strain at peak stress were lower than the B3D composite, however, hybridization increased these properties. The failure mechanisms of 3D-A composites were characterized through macroscopic and scanning electron microscopy (SEM).
Here we report the results of compressive split Hopkinson pressure bar experiments (SHPB) conducted on unidirectional glass fibre reinforced polymer (GFRP) in the strain rate regime 5 × 10²–1.3 × 10³ s⁻¹. The maximum compressive strength of GFRP was found to increase by as much as 55% with increase in strain rate. However, the corresponding relative strain to failure response was measured to increase only marginally with increase in strain rates. Based on the experimental results and photomicrographs obtained from FE-SEM based post mortem examinations, the failure phenomena are suggested to be associated with increase in absorption of energy from low to high strain rates. Attempts have been made to explain these observations in terms of changes in deformation mechanisms primarily as a function of strain rates.
dynamic behavior of composites
The objective of this work is the presentation of the research in the Institute in the fields of dynamic properties of composite materials and their development for civil and military applications. These properties are related to the nature of the high strain rate phenomena. Mainly, the shock wave transmission in heterogeneous composite materials. The effects of failure mechanisms induced by shock-waves at ballistic impact on composites are analyzed. Also, the strain-rates effects on the composite energy absorption process are discussed. It is concluded that damages energy absorb capacity changed with the failure mechanism. It is also related to the nature of the regime, sonic or supersonic and also is rate dependent. A computational code is developed in order to investigate the shock-waves in the composite material. Some results of the high impact characteristics of the ultra high molecular weight polypropylene laminate composites are presented. The development of geopolymeric materials are also discussed and the characterization of microstructure and fracture behavior are outlined. Two main efforts are devoted to investigate alternative ballistic materials. One research is the development of organic polymer in laminates and the other research is the development of inorganic polymers (geopolymers) for particulate and laminate composites.
To understand the quasi-static and dynamic compressive mechanical properties of a kind of glass-fiber polymer composites embedded with ZnO whiskers, several quasi-static and dynamic compression experiments in the normal and in-plane direction were conducted, by means of universal test machines and Hopkinson bars technology respectively. SEM images of fracture of specimen were achieved in each direction. The experimental results showed that the materials had obvious non-linear constitutive relation and strain rate strengthening effect. Specimens had various failure modes, which failed as shear fracture in the normal direction and as de-lamination and splitting failures, respectively.
Within the EUCLID project, ‘Survivability, Durability and Performance of Naval Composite Structures’, one task is to develop improved fibre composite joints for naval ship superstructures. In many practical situations, the structures are subjected to loading at very high strain rates like slamming, impact, underwater explosions or blast effect. Material and structural response vary significantly under such loading as compared to static loading. In this paper, the results from a series of Split Hopkinson Pressure Bar tests on the woven composites are presented. These tests were done in two configurations: in-plane and out-of-plan compression test. It is observed that the failure strength varies with the different loading directions. The results indicate that the stress–strain curves, maximum engineering stresses and strains evolve as strain rate changes. The woven composites have higher values of engineering stress and dynamic stiffness for in-plane than for out-of-plane compression at the same strain rate; however, the in-plane strain at maximum stress is higher than that of out-of-plane compression. During the experiments, a high speed camera was used to determine the damage mechanisms. The specimens are mainly damaged in a crushing and shear failure mode under out-of-plane loading, as for in-plane test, the failure was dominated by fibre buckling and delamination.
This paper discusses the experimental study on the response of multi directional satin weave E-glass/epoxy
composite laminates subjected to quasi-static and high strain rate compression loading along in-plane direction.
Composite laminates were fabricated from satin weave glass fabric reinforced epoxy matrix pre-impregnated
tapes which were manually laid up into laminates with stacking sequence of [45/-45/0/90]13s. The low strain
rate tests were conducted with an INSTRONTM testing machine, and the high strain rate tests done using a
pulse shaper modified compression Split Hopkinson Pressure Bar (SHPB) apparatus. Compressive strength,
modulus and strain at peak stress are evaluated experimentally at different strain rates. The results show that
Compressive strength, modulus and strain at peak stress are rate sensitive and enhanced at high strain rate
compared with those at quasi-static loading. Under high strain rate loading, Compressive strength and
modulus increase as the strain rate increases. Optical and microscopic graphs on the specimens are carefully
examined to determine operative failure modes. With the studied strain rate regimes, the failure modes are
observed to change from splitting followed by fiber kink buckling to predominantly delamination and shear
fracture as the strain rate increases from quasi-static to high strain rate.
IntroductionAnalytical AnalysisPlate-Impact Experiments on GRPsTarget AssemblyExperimental Results and DiscussionSummaryReferences
Fiber-reinforced polymer (FRP) composites are increasingly becoming suitable and durable materials in the repair and replacement of traditional metallic materials. The built-in promise of performance assurance and retention of structural integrity in harsh and hostile environments of these materials certainly offers an alternative and attractive avenue for a wider range application to explore its potential to the zenith. The toughest challenge faced by material scientists is to assess and ascertain its behavioral log in a range of loading rates. The heterogeneity and responses of multiple distinct phases to varying loading conditions are most often complex and far away from comprehensive conclusion. Furthermore, composites with common structural polymer matrices quite often absorb moisture during service period. Then, FRPs become a much more complex system to comprehend its sensitivity to experimental variation. The present article emphasizes the need for understanding this perpetual problem of FRPs which might pose a threat to its prospects.
Fiber reinforced composites are widely used instead of traditional materials in various technological applications. Therefore, by considering the extensive applications of these materials, a proper knowledge of their impact behavior (from low- to high-velocity) as well as their static behavior is necessary. In order to study the effects of strain rates on the behavior of these materials, special testing machines are needed. Most of the research efforts in this field are focused on application of real loading and gripping boundary conditions on the testing specimens. In this paper, a detailed review of different types of impact testing techniques and the strain rate dependence of mechanical and strength properties of polymer composite materials are presented. In this respect, an attempt is made to present and summarize the methods of impact tests and the strain rate effects on the tensile, compressive, shear and bending properties of the fiber-reinforced polymer composite materials. Moreover, a classification of the state-of-the-art of the testing techniques to characterize composite material properties in a wide range of strain rates are also given.
Methods for dynamic characterization of composite materials were extended and applied to the study of strain rate effects under transverse compression as well as shear. Falling weight impact and Split Hopkinson Pressure Bar systems were developed for dynamic characterization of composite materials in compression and shear at strain rates up to 1800 sO. Strain rates below 10 s5l were generated using a servohydraulic testing machine. Strain rates between 10 sol and 300 sol were generated using the drop tower apparatus. Strain rates above 500 s-l were generated using the Split Hopkinson Pressure Bar.
Seventy-two and forty-eight ply unidirectional carbon/epoxy laminates (IM6G/3501-6) loaded in the transverse direction were characterized. Off-axis (15°, 300, 450 and 600) compression tests of the same unidirectional material were also conducted to obtain the in-plane shear stress-strain behavior. Strain rates over a wide range, from 10 ⁻⁴ s ⁻¹ (quasi-static) up to 1800 s ⁻¹ , were recorded. The 90-degree properties, which are governed by the matrix,show an increase in modulus and strength over the static values but no significant change in ultimate strain. The stress-strain curve stiffens as the strain rate increases. This stiffening behavior is very significant in the nonlinear region for strain rates between 10 ⁻⁴ s-I and 1 s51. For strain rates above 1 s ⁻¹ , the stress-strain behavior continues this stiffening trend until it is almost linear at a strain rate of 1800 s ⁻¹ . The shear stress-strain behavior, which is also matrix-dominated, shows high nonlinearity with a plateau region at a stress level that increases significantly as the strain rate increases.
In the current investigation, the response of glass/epoxy laminated composites under high strain rate compression loading is considered using SHPB setup at different strain rates of 100 s-1 to 4000 s-1. The laminates were fabricated using 40 plies of unidirectional glass/epoxy. The samples were tested in the thickness as well as in-plan direction (figure 1). The fiber orientations of simples are 0°, 45° and 90°. Dynamic stress-strain plot was obtained for each sample and compared with the static compression test result.
Material and structural response vary significantly under impact loading conditions as compared to static loading. The strain rate sensitivity of glass fiber reinforced polymer (GFRP) is studied by testing a single laminate configuration at strain rates of 200 s-1 to 2000 s-1. The compressive material properties are determined by testing the laminate systems with different orientations at low to high strain rates. The laminates were fabricated from 40 layers of cross-ply glass fiber/epoxy matrix. Samples were tested in-plane direction for seven fiber orientations, 0°, ±20°, ±30°, ±45°, ±60°, ±70° and 90°. High-speed photography was used in association with optical techniques to check the damage scenarios. Preliminary compressive stress–strain vs. strain rates data obtained show that the dynamic material strength increases with increasing strain rates. Macrostructural and microstructural investigation have revealed that the sequence of damage events differs and depends on composite sequence lay-up. The tests show a strong material sensitivity to the dynamic loading. The failure and damage mechanisms are implicitly related to the rise in temperature during static and dynamic compression.
Quasi-static and dynamic mechanical properties of glass-fiber reinforced polymer composites embedded with and without tetraneedle-shaped ZnO whiskers (T-ZnOw) in two loading directions are investigated by a split Hopkinson pressure bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by a high-speed camera and a scanning electron microscope. Strain rate effects on the mechanical behavior are discussed and the corresponding models are derived by fitting the experimental data. The experimental results show that the composites with T-ZnOw under dynamic loading have multiple failure modes and better mechanical properties. Finally, the strengthening and toughening mechanisms of T-ZnOw are analyzed. It is shown that T-ZnOw can improve mechanical properties of the composites, and can make the composites have some new features. The present results provide a reliable basis for advanced composite design and manufacture, and have broad applications in the field of aerospace.
The strain rate sensitivity of glass fiber-reinforced polymer is studied by testing a single laminate configuration at strain rates of 200—2000 s-1. The compressive material properties are determined by testing the laminate systems with different orientations from low to high strain rates. Samples of cubic geometry are tested in in-plane direction for seven fiber orientations, 08, ±208, ±308, ±458, ±608, ±708, and 908. Preliminary compressive stress—strain vs. strain rates data obtained show that the dynamic material strength increases with increasing strain rates. The tests show a strong material sensitivity to dynamic loading and fiber direction. For in-plane tests, there is a transitional strain rate and a transitional fiber orientation in the trends, reflecting the dependencies on strain rate and fiber orientation observed in experiments. Damage investigations have revealed that the failure events differ and depend on composite sequence lay-ups.
A pulse-shaped split Hopkinson pressure bar (SHPB) was employed to determine the dynamic compressive mechanical responses and failure behaviors of a S-2 glass/SC15 composite along two perpendicular directions under valid dynamic testing conditions. The loading pulses in SHPB experiments were precisely controlled to ensure that the composite specimen deforms at a nearly constant strain rate under dynamically equilibrated stress during dynamic compression. Quasi-static experiments were conducted with an MTS and an Instron to study material rate sensitivity over a wider range. The compressive stress–strain behaviors along both directions were found to be strain-rate sensitive, but with different strain-rate sensitivities. A compressive constitutive model with strain-rate and damage effects was modified to accurately describe both quasi-static and dynamic compressive stress–strain behaviors of the composite material along the two perpendicular directions.
Charpy impact properties of mixed glass fibre/carbon fibre composites have been measured as a function of composition on notched and un-notched rod samples. The notched impact energy varies in a simple mixture-rule manner with proportions of grp and cfrp, despite the fact that the mode of failure changes with composition. The flexural modulus also varies linearly with volume fraction of the two components, but the observed drop in fracture energy with increasing cfrp content cannot be simply explained in terms of a change in stored elastic energy at failure.
For a 50: 50 carbon-fibre/glass-fibre sandwich structure the impact energy is increased by a factor of 2·5 to 5 depending on the resin system, compared with that of an all carbon-fibre composite of the same percentage volume loading. The enhanced impact energy of sandwich beams together with their non-catastrophic failure in flexure, relative cheapness compared with beams made entirely of carbon fibres and resins, and excellent flexural strength and stiffness make them appear very attractive for use in structures subject to bending stresses only.
A study was made of the wetting behavior of epoxy resins on glass filaments and its relation to the fabrication and the properties of filament wound glass-resin composites. The experiments were designed to determine how wetting is affected by the surface finish on the glass, the molecular structure of the epoxy liquid, and the presence in the liquid of a curing agent. Wetting behavior on freshly drawn E-glass fibers was compared with the wetting of commercial HTS-finished E-glass filaments and of glass fibers coated with hydrolyzed silane finishing agents. It was found that the HTS and the silane finished glass were poorly wet by all the epoxy liquids regardless of the chemical structure of the liquid or the presence of amine. The dynamic advancing contact angle formed against a fiber as it moves into the liquid was generally about 10 to 20 degrees higher than the static, equilibrium advancing angle. The HTS and silane finished glass fibers were covered with a visible coating of the sizing material. The coating materials were only partially soluble in the epoxy liquids. Observations of filament winding on pilot plant equipment, as well as the examination of segments of impregnated glass roving taken from the machine, revealed that air bubbles amounting to a significant portion of the total volume were entrapped in the glass-resin composite. For optimum impregnation it is necessary that the resin wet the glass fiber at a zero contact angle and mechanical means must be provided in the winding operation of minimize air entrainment and to release air bubbles from the roving.
Two unidirectional carbon fibre reinforced plastic composites have been used to study the experimental variables when specimens under tensile stress were subjected to impact. Two of these variables were the width and thickness of the specimens; here the results were consistent in that increasing either parameter led to an increase in the critical stress for complete fracture at a given impact energy. Other variables connected with the impacting wedge were the wedge bkuntness, its width relative to the specimen, and the angle of impact. Here the results were complex and, for instance, the order of toughness given by three different wedge profiles depended not only on the wedge bluntness, but also on the material being impacted. It has also been shown that repeated impact with a blunt wedge when the specimen was under subcritical stress could lead to fracture, although before failure the specimen showed little sign of damage.Scanning electron microscopy and cine photography have been used to study cracking during the impact of stressed specimens. Where there is no delamination tensile cracking is a simple process, but when delamination does happen it is suggested that it must be the first stage in the cracking process, occurring before tensile cracking.
Carefully controlled experimental techniques were used to study the effect of variations in bulk E glass surfaces on bound life and wetting. Bond life (stability of the bound in the presence of moisture) was determined visually as the time required for hot water to remove an epoxy resin coating from the glass surface. Wetting was determined by the captive bubble technique. Both properties were significantly affected by variations of the glass surface. The bound life studies emphasized the importance of the coupling agent in promoting bound stability in a hot water environment. The only example of the glass surface not treated with a coupling agent that had a satisfactory bound life was the alkali-deficient glass surface prepared by acid leaching. The surprisingly poor bound lives of the degassed and freshly cleaved (high energy) glass surfaces indicated that the wet strength retention of laminates would be poor when prepared by instantaneously applying epoxy resin without a coupling agent to the glass fibers directly as the fibers are formed. Cleanliness and surface and surface roughness were the only two variables found that promoted wetting. This discrepancy with respect to cleanliness indicated that wetting was not the controlling factor for bond life.
The qualitative dependence of the mechanical behavior of some materials on strain rate is now well known. But the quantitative relation between stress, strain and strain rate has been established for only a few materials and for only a limited range. This relation, the so-called constitutive equation, must be known before plasticity or plastic-wave-propagation theory can be used to predict the stress or strain distribution in parts subjected to impact stresses above the yield strength.
In this paper, a brief review of some of the experimental techniques for measuring the stress, strain, strain-rate relationship is given, and some of the difficulties and shortcomings pointed out. Ordinary creep or tensile tests can be used at plastic-strain rates from 10−8 to about 10−1/sec. Special quasi-static tests, in which the stress- and strain-measuring devices as well as the specimen geometry and support have been optimized, are capable of giving accurate results to strain rates of about 102/sec. At higher strain rates, it is shown that wave-propagation effects must be included in the design and analysis of the experiments. Special testing machines for measuring stress, strain and strain-rate relationships in compression, tension and shear at strain rates up to 105/sec are described, and some of the results presented. With this type of testing machine, the analysis of the data requires certain assumptions whose validity depends upon proper design of the equipment. A critical evaluation of the accuracy of these types of tests is presented.
The compression behaviour of a series of polyester resins of various compositions and in different states of cure has been investigated. Their mechanical characteristics having been established, the same range of resins was then used as a matrix material for a series of composites reinforced with carbon, glass and aromatic polyamide fibres. The composites were unidirectionally reinforced, having been manufactured by pultrusion, and were compression tested in the fibre direction after a series of experiments to assess the validity of a simple testing procedure. Rule of Mixtures behaviour occurred in glass-polyester composites up to limiting volume fractions (V
f) of 0.31 for strength and 0.46 for elastic modulus, the compression modulus being equal to the tensile modulus, and the apparent fibre strength being in the range 1.3 to 1.6 GPa at this limiting V
f. At a V
f of 0.31 the strengths of reinforced polyesters were proportional to the matrix yield strength,
my, and their moduli were an inverse exponential function of
my. For the same matrix yield strength a composite with an epoxy resin matrix was stronger than polyester based composites. At V
f=0.30, Kevlar fibre composites behaved as though their compression modulus and strength were much smaller than their tensile modulus and strength, while carbon fibre composites were only slightly less stiff and weaker in compression than in tension. The compression strengths of the polyester resins were found to be proportional to their elastic moduli.
A brief review is given of techniques which have been employed in attempts to determine the mechanical properties of composite materials under tensile impact loading. The difficulties encountered in the design of a satisfactory tensile impact testing machine for composite materials are discussed and a new method, using a modified version of the standard tensile split Hopkinson's pressure bar (SHPB), is described. Dynamic stress-strain curves for unidirectionally-reinforced carbon/epoxy composite, in which failure occurs in less than 30 sec at a mean strain rate of about 400 sec–1, are presented and their validity is established. An extension of the technique to allow the testing of wovenroving reinforced glass/epoxy composites is described and dynamic stress-strain curves obtained for which the times to failure approach 100 sec and the average strain rate is of the order of 1000 sec–. Comparative stress-strain curves at low and intermediate rates of strain are obtained and the effect of strain rate, over about 7 orders of magnitude, on the tensile modulus, and strength, fracture strain and energy absorbed in fracturing is determined. The limitations of the technique are discussed.
Carbon fibre, Kevlar 49 fibre and carbon fibre/Kevlar 49 fibre hybrid reinforced epoxy laminates, comprising 0°, 90° and 45° layers, were subjected to dropweight and ball gun impact at incident energies up to 18 J. Residual tensile, flexual and shear strengths were measured after impact. It was shown that a hybrid composite can have significantly better overall impact properties than laminates reinforced with only one type of fibre. Tests on unidirectional laminates showed that the static mechanical properties of hybrid composites were not as good as all-carbon fibre reinforced composites; for multidirectional laminates the difference was less.
The dynamic stress-strain behaviour of unidirectional glass-epoxy composite has been studied at an average strain rate of 265 s−1 for fibre orientations of 0°, 10°, 30°, 45°, 60° and 90° with respect to loading axis, using the Kolsky pressure bars technique. GFRP (glass fibre reinforced plastic) is found to be strain rate sensitive for all fibre orientations. Compared to quasi-static, the dynamic ultimate strength increases almost 100% for 0°, 80% for 10° fibre orientations and about 45% for all other orientations. Failure occurs predominantly by tensile splitting in 0° specimens and by shear for all other orientations preserving the fibre direction in each case.
A unified set of composite micromechanics equations of simple form is summarized and described. This unified set includes composite micromechanics equations for predicting: (1) ply in-plane uniaxial strengths; (2) through-the-thickness strength (interlaminar and flexural); (3) in-plane fracture toughness; (4) in-plane impact resistance; and (5) through-the-thickness (interlaminar and flexural) impact resistance. Equations are also included for predicting the hygrothermal effects on strength, fracture toughness and impact resistance. Several numerical examples are worked out to illustrate the ease of use of the various composite micromechanics equations.
The effect of surface
- P E Throekmorton
- M F Brown
Throekmorton, P.E. and Brown, M.F. 'The effect of surface
Application of fibrous composites to aerospace and commercial structures
- Zweben
Fracture behaviour and residual strength of carbon fibre composites subjected to impact loading
- Dorey
The effect of surface tension and strength of glass fiber reinforced plastics
- Throckmorton
Dynamic compressive strength and failure of steel reinforced epoxy composites
- Sierakowski
Behaviour of woven graphite epoxy at very high strain rates
- Werner
Mechanical behaviour of GFRP composites under impact compressive load
- El-Habak
‘Instabilite’ plastique de geometrie
- Dannawi