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Progress of dynamic failure of 3-D textile structural composites have not been sufficiently studied. This work is aimed to investigate the progressive failure of 3-D braided, biaxial warp-knitted and angle-interlock woven composites by high-speed imaging system during impact loadings. Real-time images are listed frame by frame and located in stress-strain curves. There is a sharp decrease stage and a steady decrease stage in stress under catastrophic failures. These two stages reveal different damage morphologies in progressive failures. For the out-of-plane impact compression, if there is no catastrophic failure, composites get limited rebound because of structural recovery of their reinforcements. If catastrophic failure occurs, composite structures would be split. For the in-plane impact compression, the 3-D braided, biaxial warp-knitted and angle-interlock woven structures protect themselves from being thoroughly split under explosive cracks/shear/delamination failures. [ABSTRACT FROM AUTHOR]

This paper presents a thermal-mechanical coupled constitutive model to calculate the stress and temperature distribution of 3D braided composite under impact compressions in high temperature environment. The temperature effect and strain rate effect are involved in the coupled model. A temperature-rise equation in adiabatic state is derived to calculate the temperature rise during the impact compression. A user-defined subroutine was written for numerically simulating the impact damage with finite element method (FEM). The sensitivity of mesh size on the results was analyzed. The results reveal the temperature rise and the coupling stress of the 3D braided composite under different impact compression conditions, i.e., temperatures and compressive loadings. [ABSTRACT FROM AUTHOR]

Auxetic composites are non-conventional materials with negative Poisson’s ratio (NPR). They have received great attention in recent years due to their particular properties and high application potential in different areas. In this study, a novel kind of auxetic composite was proposed and fabricated via an injecting and foaming process by using multilayer orthogonal auxetic structure as reinforcement and polyurethane foam as matrix. The NPR effect and mechanical behavior of the composite under quasi-static compression were investigated and compared with those of the pure polyurethane foam and non-auxetic composite. The results obtained show that the auxetic composite fabricated has an obvious NPR effect and behaves more like a damping material with a large range of deformation strain. The study has provided a simple way to design and fabricate auxetic composite materials by using suitable arrangement of reinforcement materials in a multilayer orthogonal structure. [ABSTRACT FROM AUTHOR]

• Effect of current direction on electro-thermal damage of CFRP composites was studied. • Electric current induced electro-thermal damage while without crack defect. • A new electro-thermal damage mode of interfacial degradation was proposed. Electro-thermal damage mechanisms on direct current are important for the reliability design of carbon fiber reinforced composites in an electric environment. Here we studied the effect of direct current direction on the electro-thermal damage of carbon fiber/epoxy plain woven laminates. The current was applied on the composite along longitudinal/through-thickness directions. We used an infrared camera to record temperature distribution from Joule heat on the composite surface. The surface temperature distribution under the through-thickness current was more nonuniform than that under the longitudinal current. We conducted three-point bending and micro-CT tests to reveal the effect of direct current treatment on mechanical behavior. We found that the through-thickness current reduced the composite flexural performance, while the longitudinal current did not. The through-thickness current induced the electro-thermal damage in the composites but without crack defect. Interfacial degradation is a new electro-thermal damage mode. [ABSTRACT FROM AUTHOR]

This paper reports the high-strain rate properties of 3-D braided basalt/epoxy composite materials at 26 °C, −50 °C, −100 °C and −140 °C with strain-rate range from 1300 s −1 to 2100 s −1 by experimental study. A simple and effective cryogenic device was applied to the SHPB system to create the low-temperature field of the samples. It was found that the compression modulus, peak stress, failure strain and specific energy absorption of the 3-D braided basalt/epoxy composite materials had different sensitivity to temperatures and strain rates. In the out-of-plane impact, there were two failure modes, namely, compression-failure mode and shear-failure mode. Fracture of fiber tows was irregular with abundant pull-out of fiber and much finely-divided fragmentation of resin among fibers at room temperature. In cryogenic field, the fracture of fiber tows was neat and tidy with few pull-out of fiber and few finely-divided fragmentation of resin. However, in the in-plane impact, there was only compression failure mode. And there was no fracture of fiber tows and no big difference among samples tested under different gas pressures. Because of the function of squeezing and buckling, split-off separation of the composite could be blocked by the tangled fiber tows. As a whole, the reinforcement could still keep its structural integrity. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) braided shape memory polymer composites (SMPCs), combining braided structure with stimuli-responsive shape memory polymers, have broad potential for intelligent material design. We fabricated the 3D braided SMPCs with different braiding angles (15°, 25°, 35°) using a pre-impregnation method. The dynamic thermomechanical behaviors, three-point bending properties, recovery force, and shape memory behaviors were characterized. The full-field strain and temperature evolution during recovery have been recorded with 3D digital image correlation (DIC) technique and infrared camera. We found that the storage modulus, flexural modulus, and recovery force increase with the braiding angle decreased. The samples with the smaller braiding angle recover faster than that of the samples with bigger braiding angle. The shape recovery of the samples with 15° braiding angle occurred before being heated to the glass transition temperature. It is expected that the 3D braided SMPCs could be applied to smart structural design. [Display omitted] - An electro-activated 3D braided thermoplastic shape memory composite was prepared. - Full-field strain and temperature evolution during recovery were obtained. - Shape recovery force was measured using self-designed test setup. [ABSTRACT FROM AUTHOR]

Abstract: There are huge potential applications of 3-D braided composite in aerospace engineering because of the non-delamination feature of the composite under impact loading. This paper presents the analysis of energy absorption features of 3-D braided composite under compression with different strain rates. The 3-D 4-step rectangular braided composite coupons were tested on a material tester MTS 810.23 and a split Hopkinson pressure bar (SHPB) apparatus to obtain out-of-plane and in-plane compression stress vs. strain curves at quasi-static and high strain rate state. The failure modes and energy absorption features of the 3-D braided composite under different strain rates were analyzed both in time domain and frequency domain. The energy absorbed by the 3-D braided composite increases with the strain rate. From fast Fourier transform (FFT) analysis of compression stress vs. time histories, the power of energy absorption of the 3-D braided composite increases with strain rate and mostly concentrate on the high frequency region. While for quasi-static compression, the power distributes in very narrow frequency region and also is less than that in high strain rates. This feature corresponds to the different damage and energy absorption mechanisms of the 3-D braided composite under quasi-static and high strain rate compression. [Copyright &y& Elsevier]

Abstract: The compressive properties of 3-D angle-interlock E-glass/vinyl ester woven composites at quasi-static and high strain rate loadings have been investigated to evaluate the compressive failure mode at different strain rates. The through-thickness compressive properties at high strain rates from 800 to 2700s−1 were tested using the split Hopkinson pressure bar (SHPB) technique. The compressive properties at quasi-static strain rate were also tested and compared with those at high strain rates. The results indicate that the stress– strain curves are rate sensitive and compressive stiffness, maximum compressive stress and corresponding compressive strain are also sensitive to the strain rate. The compressive stiffness, maximum compressive stress, of the 3-D woven fabric composites linearly increased with the strain rate. The compressive failure of the composite specimen tends to be in shear failure mode and it is completely broken at high strain rates while only compressive deformation could be observed in quasi-static loading. [Copyright &y& Elsevier]

The ballistic perforation test results of 4-step 3-dimensional (3D) braided Twaron®/epoxy composites, which were subjected to impact by conically cylindrical steel projectile, are presented. The residual velocities of projectile perforated composites target at various strike velocities were measured and also compared with that from finite element calculation. ‘Fiber inclination model’ for 3D textile composites was adopted to decompose the 3D braided composite at quasi-microstructure level for the geometrical modeling in preprocessor of FEM. The material modeling was also based on this simplified model. The finite element code of Ls-Dyna was used to simulate the impact interaction between projectile and inclined lamina. The residual velocity of projectile perforating the entire 3D braided composite can be calculated from the sum of kinetic energy loss of the projectile that obtained from FEM. From the simulation of ballistic penetration process and comparison between numerical results and experimental results, it proves that the analysis scheme of quasi-microstructure level in this paper is valid and reasonable. The simplified method in this paper could be extended to model other kinds of 3D textile composites under ballistic impact. [Copyright &y& Elsevier]

Prediction of the uniaxial tensile curve and tensile strength of 3-dimensioanl braided preforms is the first step in predicting the uniaxial tensile strength of 3-dimensional braided composite. This paper presents an analytical model to predict the uniaxial tensile strength and uniaxial tensile curve within the whole tensile strain range. First, the equations of spatial configuration of trace yarn in each yarn group were obtained from the coordinates of center point of the trace yarn cross-section in preform and the microstructure of 3-dimensional braided preform was described in mathematical way. Based on the mathematical description of trace yarn and microstructure of preforms, the uniaxial tensile strain relations between 3-dimensional braided preform and braiding yarn at small and large strain were established. Then, from the energy conservation law that the sum of strain energy of all braiding yarns equals to the work of external force applied to the preform, the uniaxial tensile load at every uniaxial tensile strain points of braiding yarn can be calculated and then the whole uniaxial tensile curve of 3-dimensional braided preform can be obtained (also for uniaxial tensile strength). The maximum strain failure criterion is used in calculations. From experimental verification, the method proposed in this paper predicting the uniaxial tensile load and tensile strain simultaneously from the uniaxial tensile curve of braiding yarn is valid and simple in application. [Copyright &y& Elsevier]

This paper presents an analytical model to calculate decrease of kinetic energy and residual velocity of projectile penetrating targets composed of multi-layered planar plain-woven fabrics. Based on the energy conservation law, the absorbed kinetic energy of projectile equals to kinetic energy and strain energy of planar fabric in impact-deformed region if deformation of projectile and heat generated by interaction between projectile and target are neglected. Then the decrease of kinetic energy and residual velocity of projectile after the projectile perforating multi-layered planar fabric targets could be calculated. Owing to fibers in fabric are under a high strain rate state when fabric targets being perforated by a high velocity projectile, the mechanical properties of the two kinds of fibers, Twaron® and Kuralon®, respectively, at strain rate from 1.0×10−2 to 1.5×103 s−1, are used to calculate the residual velocity of projectile. It is shown that the mechanical properties of fibers at high strain rate should be adopted in modeling rate-sensitivity materials. Prediction of the residual velocities and energy absorbed by the multi-layered planar fabrics show good agreement with experimental data. Compared with other models on the same subject, the perforating time in this model can be estimated from the time during which certain strain at a given strain rate is generated. This method of time estimation is feasible in pure theoretical modeling when the perforation time cannot be obtained from experiments or related empirical equations. [Copyright &y& Elsevier]

• The study focused on interlaminar fracture in 3DBC under LVI. • Explored the connection between the crack path and the braided structure. • Compare the impact effects of different braiding angles and loading energies. • An FEA for Mode-I fracture reveals the damage mechanism in 3DBC. • A 45° braided angle of 3DBC is optimal to resist LVI damage in applications. Mode-I low-velocity impact fracture very often happens during the lifetime service of fiber-reinforced composites. Three-dimensional braided carbon fiber/epoxy composites (3DBC) have higher fracture toughness than laminate, while the Mode-I fracture is also an important behavior. Here we report the Mode-I fracture of 3DBC under low-velocity impact. A single cleavage triangle (SCT) specimen was prepared for the Mode-I impact test. A high-speed camera was used to capture images of the fracture initiation and growth. The inner damages were observed using X-ray microcomputed tomography (Micro-CT). The fracture behaviors were also compared among three braided angles and three impact energies. We found that the crack propagation follows the path of the crimped yarn. The propagation direction changes upon reaching interweaved points. The energy absorption at rupture increases as the braiding angle. A finite element analysis (FEA) model was developed to analyze the internal crack propagation behaviors and failure mechanisms. The fracture mechanisms of 3DBC have been compared between the tests and the FEA results. It was found the braided angle of 45°has a higher impact fracture toughness than the can 10°, 20° and 30° samples. [ABSTRACT FROM AUTHOR]

Dynamic compressive damages of 3D woven composites in low temperature environments are crucial for the design of engineering structures in cryogenic applications. This study presents the compressive damage behaviors of 3D angle-interlock woven composites under low-temperatures. We developed a homogeneous model incorporating the strain rate effect and thermo-mechanical coupled constitutive relation to numerically analyze compressive damages at low temperatures. Dynamic compression tests were conducted on split Hopkinson pressure bar (SHPB) apparatus with strain rates ranging from 300 to 1500/s at temperatures of 20 °C, −40 °C, and −80 °C, respectively. We found that the compressive stiffness and strength are more temperature-sensitive along the out-of-plane direction, while they exhibit greater sensitivity to strain rate along the in-plane direction. The failure mode is characterized by shear failure along the out-of-plane and warp directions, and delamination along the weft direction. The test results and finite element analyses (FEA) show that the 3D woven composites exhibit brittleness at low temperatures and experience more severe compressive damages compared to those at room temperatures. Importantly, we observed accumulations of inelastic heat in the compressive damage zone, indicating that the compressive damages are also converted into thermal energies under low temperatures. [ABSTRACT FROM AUTHOR]

• The electrical conductivities and temperature distributions along different current directions have been studied. • The electrical and thermal behaviors was simulated with finite element analysis (FEA) model. • The influence of woven architectures and contacts on electrical and thermal behaviors was analyzed. Electrical conductivities and temperature generations are related closely for carbon fiber composites under electric fields. Here we reported the current conductivity and electro-thermal behavior of carbon fiber reinforced 3D orthogonal woven structure composites (3DOWCs) along different current directions. The influence of woven architectures and contacts on electrical and thermal behaviors was analyzed with finite element analysis (FEA) model. We found that the conductivity was the highest along warp direction and the lowest along Z-binder direction. The conductivity increased with the increase of in-plane angles. The overall conductivity of Z-binder direction was affected by weft/Z-binder yarn interface. In-plane angle directions, the warp/weft interfacial conductivity affected overall conductivities, which had the largest temperature contribution. The maximum current density and temperature of warp yarns decreased with the increase of in-plane angles. The proportion of weft yarns in current density and temperature rise increased with the increase of in-plane angles. [ABSTRACT FROM AUTHOR]

• Influence of braided angle and atmospheric aging on torsion behaviour was studied. • Strain and damages were observed with 3D-DIC and Micro-CT. • Stress distribution and damage propagations were visually displayed. The torsional behaviors of 3-D braided composite tubes are influenced by braided structure and environmental conditions. This paper reports the properties of aged and unaged 3-D braided carbon fiber/epoxy resin composite tubes with braided angle of 30°, 45° and 55°. The proposed multi-scale model aims to analyze the coupling effects of thermo-oxidative aging and braided structure, while supporting experimental measurements. Results show that the 45° specimens exhibit the highest torsional performances. Thermo-oxidative aging degrades failure torque, shear stress, strain and modulus of composite tubes. This effect weakens as the braided angle increases due to the tighter braided structure. The damage pattern extending along the braided angle is unaffected by aging, but earlier damage onset and more microcracks can be induced after aging. Designing tubes with larger braided angles helps maintain torsional performances under thermo-oxidative environment. [ABSTRACT FROM AUTHOR]

Abstract Matrix shrinkage induced in thermo-oxidative ageing process of composites may lead to interfacial damage and thus significantly affect their mechanical properties. This work aims to characterize the oxidation-induced matrix shrinkage in three-dimensional (3-D) braided composite. Specimens were exposed at hot air (180 °C) for 4, 8, and 16 days respectively. Interferometric microscope was employed to determine the matrix shrinkage in composite surface under different ageing conditions. The resulting interfacial damage was observed by optical microscopic examination. Based on the experimental results, we propose a two-step numerical methodology to investigate the effect of thermo-oxidative ageing on compressive properties of braided composite. The established finite element model can effectively capture the deformed and degraded configuration of the aged material. Further simulation results reveal that the shrinkage-induced interfacial damage leads to a lower stress distribution in the exposed ends of braiding yarns. The ultimate deterioration in compressive properties of braided composite is attributed to both resin degradation and yarn-matrix interfacial damage. [ABSTRACT FROM AUTHOR]

Abstract This paper reports the damage mechanisms of 3-D carbon fiber/epoxy braided composite under multiple impact compressions along out-plane direction. The multiple compression tests were conducted on a split Hopkinson pressure bar (SHPB) apparatus. The compressive deformations and damages were photographed with high speed camera and compared with those from finite element analyses (FEA). We found that the initial compressive damages are fiber/resin interface damage and resin fragmentation. Then the braided preform was in a severe shear damage which accompanied with further damages of interface and resin under the followed impact compressions. The energy absorptions by the reinforcement and epoxy resin at the multiple impacts were decomposed. The braided composite has the highest energy absorption capability at the first impact. The yarn orientation in braided preform leads to non-uniform stress and strain distribution. This non-uniformity easily induced the local damage and furthermore the catastrophic failure under the multiple compressions. [ABSTRACT FROM AUTHOR]

This paper reports the influence of specimen size and inner defects on high strain rates compressive behaviors of plain woven composites. The compressive behaviors of plain woven composites along out-of-plane direction were investigated from experimental and numerical approaches. In experimental, the compressive stiffness and strength decreased as the size of plain woven composite specimens increased. In finite element analysis (FEA) model, a new microstructure model with random defect distribution was established to find the influence of inner defects and specimen size effect on the compressive behaviors under high strain rates. From the numerical results, the compressive strength, modulus and fracture strain decreased obviously with the increase of volume fraction and size of defects. We found that the good agreement existed between the testing and the FEA results. The defects size and distribution were the main factors to weaken the compressive stiffness and strength. [ABSTRACT FROM AUTHOR]

The present work constructs a meso-structure finite element model to characterize the effect of thermo-oxidative ageing on compressive behaviors of 3-D carbon fiber/epoxy braided composites. Nanoindentation tests were carried out to investigate the thermo-oxidation effect on localized property of aged resin. Based on the experimental results obtained from both macro-compression tests and nanoindentation tests, two different models referred to as ‘homogeneous model’ and ‘multilayer model’ were proposed, respectively. Both of the two models gave satisfactory predictions. We found that the post-curing stiffening and thermal degradation of matrix are the main ageing mechanisms at lower temperatures (below glass-transition temperature). At higher temperatures above the glass-transition point, interfacial damage also contributes a lot to the property degradation of the composite. The combination of matrix ageing and interfacial weakening leads to a significant reduction in compressive behaviors of the 3-D braided composite. We also found that the presence of oxidized layer has little effect on the compressive properties of aged braided composites. Simulation results have confirmed that ageing mechanism strongly depends on the ageing conditions. [ABSTRACT FROM AUTHOR]

This paper presents the impact shear fracture mechanisms of 3D braided composite observed from computed tomography (CT) and the comparisons with finite element analyses (FEA). The effects of braiding parameters on the damage modes have been analyzed from micro-CT and FEA. It revealed that there are multiple damage modes of fiber tows fracture, debonding, resin cracks and inter-yarn delaminations under impact shear loading. The failure mode mainly depends on the braiding structural parameters, which in return determines the energy absorption capacity. A meso-structure geometrical model based on braided preform structure was developed to calculate the stress distribution and to simulate the shear damage modes. The failure modes from FEA were compared with those obtained from the micro-CT. Both the micro-CT and FEA observations capture the impact shear damage morphologies and unveil the energy absorption mechanisms. [ABSTRACT FROM AUTHOR]

The transverse impact performance of three dimensional (3-D) braided composite tubes has been studied both experimentally and numerically. Three types of braided composite tubes were manufactured by changing the number of braiding layers. The transverse impact test was performed on a modified split Hopkinson pressure bar (SHPB) apparatus under three impact gas pressures. From the tests, impact load, displacement and energy absorbed all increase with the increase of gas pressure. The increase of braiding layers leads to the increase of the impact load and energy absorption, but leads to the decrease of impact displacement. The specific load normalized by the linear density of the tubes also increases with the increment of braiding layers. The results indicated that more braiding layers contributed to higher stiffness. The impact damage modes were matrix crack, fiber breakage and shear bands at the area of impact. From the finite element method (FEM), the stress distribution on the impacted tube was highlighted plus the damage progression during the transverse impact cycles. [ABSTRACT FROM AUTHOR]

This paper reports a numerical modeling on the compressive behaviors of 3-D braided carbon/epoxy composites with different braided angles under high temperatures at microstructure level. The coupling effect of temperature and braided angle on the compressive failure mechanisms and damage morphologies have been calculated with finite element method (FEM) and compared with experimental results. In the FEM model, the imperfect interfacial bonding and the fibers with waviness were introduced into the FEM model. The ductile/brittle transition temperature was investigated and the ductile failure criterion was employed in the FEM model at high temperatures. It was found that braided angle affects the compressive failure. The compressive failure changes from ductile to brittle when the braided angle changes from larger to smaller one. The high temperature has almost no influence on the damage mode but it leads to the failure modes more ductile. The thermal stress improves the longitudinal compressive properties. The higher temperature and larger braided angle lead to the ductile behaviors of the 3D braided under longitudinal compression. [ABSTRACT FROM AUTHOR]

Thermal stress concentration, induced by the mismatch of coefficients of thermal expansion (CTE), contributes significantly to fatigue and failure of composites. We demonstrated the practicality of fiber Bragg grating sensors and high-resolution digital image correlation technique for in-situ characterization of thermal strain field evolution in 3D angle-interlocked woven composites (3DAWC). Multiscale representative volume element (RVE) models were constructed for studying its steady-state and transient-state thermomechanical behaviors. We found the CTE mismatch causes stress localization at the interface and it exhibits a periodic distribution within the 3DAWC, which attributes to its 3D architecture. Stresses and strains concentrate mainly on the sharp interfaces close to the diamond-shaped yarns and the resin-rich areas, respectively. The thermal stress in the resin reaches a maximum of 22 MPa around T g , close to half of its yield stress. The macroscopic homogenized CTEs calculated from the RVE model in thickness and in warp directions are greater than those of each component. Transient analysis reveals that the non-uniform temperature field induced by heat transfer effects has little effect on maximum stress values in each component. [Display omitted] • In-situ characterization of thermal strain fields with high-resolution 2D-DIC and FBG. • Period stress/strain localization at the interface caused by CTE mismatch in 3DAWC. • 3DAWC has greater CTEs in thickness/warp directions compared to its components. • Thermal stress in resin reaches a maximum around Tg and is close to its yield stress. • Heat transfer have little effect on maximum stress of each component in composites. [ABSTRACT FROM AUTHOR]

3D braided shape memory composite (SMPC) tubes have great potential in designing smart structural components because of high inertia moment and near-net shape manufacturing. Here we developed a 3D braided carbon fiber reinforced shape memory polyurethane-based composite tube and investigated their thermal/electrical shape memory behaviors subjected to compression. The radial and axial compressive behaviors, thermally-electrically shape memory behaviors, and shape recovery forces of the SMPC tubes with different braiding angles were analyzed. The out-of-plane displacement and temperature field were obtained with 3D digital image correlation (DIC) and infrared thermography to characterize transverse compression deformation. We found that the 60° sample had the highest recovery force compared to the other braided angle samples, while the shape recovery speed was lower than small-angle samples. In the transverse compressive electro-thermal recovery test, the 30° sample reaches to glass transition temperature faster at the same voltage, and the 45° sample exhibits maximum shape recovery speed. The 3D braided SMPC tubes exhibited excellent electro-thermal shape memory behaviors and high recovery force, which were expected to extend the application of smart actuators. [Display omitted] • 3D braided SMPC tubes with thermal-electrical stimuli recovery was prepared. • Influence of braiding angle on thermal/electrical shape recovery was presented. • Out-of-plane displacement and temperature fields in shape recovery were measured. [ABSTRACT FROM AUTHOR]

This paper presents an approach to simulate the high strain-rate compression of 3-D braided basalt/epoxy composite materials under room and low temperatures. A microstructure model of 3-D braided composite was established to characterize a fully coupled thermo-mechanical response during the fast deformation. High stress state and low heat generation have been found in braided reinforcement. For out-of-plane compression, adiabatic heat concentration is along single diagonal direction at −100 °C, while a cross-shape heat concentration region is found along two crossed diagonal directions at 26 °C. There are fewer cracks among fiber tows at low temperature. Once the single diagonal shear failure occurs at low temperature, the 3-D braided reinforcement can not keep structure integrity and will be separated into two parts. For in-plane compression, the damage morphology at −100 °C is similar to that at 26 °C. Under the influence from the fiber tows, the adiabatic heating develops the zigzag-shape damage with veins and stripes along the braiding angle in composite, while the 3-D braided reinforcement still keeps its structural integrity. [ABSTRACT FROM AUTHOR]

We proposed a multi-scale structure modeling scheme to analyze the damage behaviors of three-dimensional orthogonal woven composite materials subject to quasi-static and high strain rate compressions. The multi-scale structure model includes: (1) micro/meso/macro-structure model with periodic boundary conditions for homogenizing the heterogeneous fiber/resin system into unit cells, and (2) a macroscopic rate dependent plasticity model combined with critical damage area failure theory that accounts for the compressive deformation and failure strength of the composite material. The numerical results from the multi-scale structure model provide the locations of stress propagation and the progressive failure behavior within the 3D orthogonal woven composite material. The multi-scale model and the numerical simulation results are validated using compression test results at the strain rate range from 0.001 to 2100 s −1 . The methodology we proposed could be applied to understand the microstructure damage mechanisms of 3-D textile composite materials from meso- and macro-structure levels in simpler geometrical model and easier design approaches. [ABSTRACT FROM AUTHOR]

The electrical properties of carbon fibers serve as the foundation for the multifunctional applications of carbon fiber-reinforced composite structures. In scenarios that exploit the electrical characteristics of materials, accurate estimation of electrical resistivity stands as a critical factor. This study endeavors to elucidate the electrical conduction behaviors in unidirectional composites with different fiber orientation angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) and aspect ratios, thereby deriving the volume resistivity within an arbitrary Cartesian coordinate system. Employing thermal infrared imaging technology and finite element analysis, we identified distinctive electrical conduction behaviors associated with aspect ratios in carbon fiber composite plates. Notably, a critical aspect ratio exists wherein the diagonal yarn is the only conductive path between two electrodes. Below this critical threshold, no direct conductive path exists, and current flows through the shortest distance between parallel yarns. Conversely, beyond the critical aspect ratio value, multiple yarns form conductive paths between the two electrodes. Based on the electrical conduction behavior of unidirectional composites under different angles and aspect ratios, the volume resistivity with finite boundaries was derived and examined under an arbitrary Cartesian coordinate basis. [Display omitted] • The electrical conduction behaviors of unidirectional composites with various angles and aspect ratios were investigated experimentally and numerically. • Based on the electrical conduction mechanism, we derive the volume resistivity of unidirectional composites with various angle configurations and aspect ratios. • The distinct electrical conduction behavior of each segment of the composite is closely linked to the aspect ratio. • The variations in volume resistivity of the composites under different angles and aspect ratios enunciate the crucial factors influencing the electrical properties of the composite. [ABSTRACT FROM AUTHOR]

Viscoelastic behavior of the matrix affects the thermomechanical response of polymer composites. This study investigated the structural effects of the time-dependent thermal expansion response of 3D orthogonal woven composite (3DOWC) by combining experiments and finite element modeling (FEM), incorporating the viscoelasticity of its constituents. The deformation characteristics at three orthogonal cross-sections, in the presence of structure-related strain fields at various temperatures, were investigated using digital image correlation method. Findings reveal heterogeneity and localization of the thermal strain, characterized by periodic stripes with alternating high strain regions on the resin and low strain regions on the yarn. This localization intensifies at higher temperatures, but diminishes with increased distance from the interface. Furthermore, the composites exhibit time-dependent thermal expansion behavior derived from the time-independent thermal expansion of its constituents, which cannot be captured in classic elastic material model. FEM reveals that thermal stresses are concentrated at the interfaces between constituents with significant differences in their coefficients of thermal expansion (CTE), particularly at the interface between the resins and axial yarns. The maximum thermal stress occurs in the binder yarns over the considered temperature range due to their low volume content, which should be considered in practical applications. • Time-dependent thermo-viscoelastic constitutive behavior in CTEs. • Characterization of local thermal strain fields with high-resolution 2D-DIC. • Structure-related of heterogeneous stress/strain localization in 3DAWC. • Implementation of anisotropic viscoelasticity with user subroutine. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study aimed at the compressive properties of three-dimensional (3D) braided composites subjected to quasi-static and high strain rate loadings using finite element method from fiber/matrix scale to composite scale. It focuses on a computationally efficient multi-scale methodology for prediction of the effective elastic properties and the failure strength of 3D braided composites. First, finite element models with strain rate sensitive elasto-plastic constitutive relationship and ductile and shear failure criterion were established to investigate the mechanical properties and failure mechanism. Second, the failure mechanism in micro-scale fiber/matrix was investigated. The mechanical properties of the interior unit cell, surface unit cell and corner unit cell were predicted and compared, which shows that the surface and corner region of braided preform play an important role during both quasi-static and high strain rate loading. The results obtained from the whole structure heterogeneous composite model and the homogeneous composite model were also analyzed and compared. Finally, the numerical results were verified by the experimental data and the results are encouraging. This method can provide an important guidance for evaluating the mechanical properties and selecting structural parameters for braided composites. [ABSTRACT FROM AUTHOR]

Proper prediction of material microstructure from known processing conditions and constituent material properties is a critical step to determine the bulk properties of the composite. This paper reports a meso-structure model of multi-axial multi-layer warp-knitted (MMWK) composites from an elastic–plastic material model considering the strain rate effect for the components of the MMWK composite. The representative unit cell (RUC) of fiber tow is created to obtain the elastic–plastic parameters of the fiber tow. The 3D meso-structure model of the MMWK composite is based on an idealized geometrical model according to the preform structure of the MMWK fabric. The model is used to investigate the effect of the volume fraction of the knitting yarn on the dynamic in-plane compressive properties. The results show that the fiber tow failure at large extent is mainly caused by the micro cracking of the matrix, and the effects of the knitting yarn on the mechanical properties of MMWK composite are very limited. Particularly, MMWK composites could be considered as laminates when the volume fraction of the knitting yarn is low, such as below 1.5%. Experiments were also conducted to validate the results from the simplified meso-structure model of the MMWK composite. The material is found to be strain rate sensitive, and the experimental and predicted results agree well with respect to the compressive strength and modulus of the composite. This confirms that the meso-structure MMWK composite model proposed is capable of capturing the essential features for the response of the composite under different strain rate conditions at the meso-level. [ABSTRACT FROM AUTHOR]

The impact behavior of warp-knitted spacer fabrics (WKSFs) impregnated with shear thickening fluid (STF) under low-velocity impact loadings have been investigated from experimental and finite element analyses (FEA) approaches. From the experimental approach, the impact load–displacement curves have been obtained. It was observed that the WKSF impregnated with the STF composite material (the WKSF/STF composite) shows a higher stiffness and lower peak force than those of the WKSF under the same impact loadings. In FEA approach, the geometrical models of the WKSF and the WKSF/STF composite material were established based on the WKSF fabric architectures. The dynamic responses including the impact load–displacement curves and impact deformation of the samples were predicted based on finite element analyses at the microstructure level. It was found that the STF and the coupling effect between the STF fluid and fiber tows are the key factors which influence the cushioning behaviors of the composite. The energy absorption mechanisms include the buckling of the spacer finer tows and the thickening effect of the STF under impact loading. The WKSF/STF composite could be expected as a damping or energy-absorptive materials under impact loading. [ABSTRACT FROM AUTHOR]

Electrothermally actuated and mechanical properties are important for multifunctional application of fabric-reinforced shape memory polymer composites (SMPCs). Here we presented a new method to prepare the fabric-reinforced shape memory polymer thermoplastic composite molded with plain composite fabric. The composite fabric was weaved with continuous carbon fiber/shape memory polyurethane (CCF/SMPU) core–shell structure yarn. The effects of microstructure, layer number and carbon fiber (CF) content on flexural property, thermo-mechanical, shape recovery behaviors of SMPCs were studied. The flexural load and storage modulus were improved due to the introduction of carbon fiber. The shape recovery ratio of SMPCs could reach 99.3% under thermal and electrical stimulation. Some demonstrations of the SMPCs showed excellent electro-thermal recovery and higher deformability. The yarn and fabric structure are expected to have good potential in smart structure design. [ABSTRACT FROM AUTHOR]

3-D braided composites are a promising material for manufacturing tubular structures. However, a thorough understanding of their damage mechanisms under torsion is required to maximize their potential applications. The present work constructed a multiscale equivalent model, integrating mesoscopic and homogeneous structures to reveal torsional behavior of 3-D braided carbon fiber/epoxy resin composite tubes. The cumulative failure process, spatial stress distribution and interface damage were calculated to illustrate stress transfer and damage initiation and propagation. It is found that stress varies on the surface and internally within the representative unit cell (RUC). The yarns experience both axial tension parallel to the direction of torsion and axial compression perpendicular to the direction of torsion. The stress difference between them leads to damage initiation and propagation. Interfacial cracking as main damage mode hinders the stress transfer between resin and fiber bundles. The results show that the braided yarn path, axial stress dispersion in two directions and localization of damage effectively impede the torsional damage propagation. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of braided structure on shape memory behaviors of 3D braided composites is critical to design the responses of the composite under external fields. Here we report the effect of axial yarn on shape memory behaviors of three-dimensional five-directional (3D5d) braided shape memory polymer composites (SMPCs) under bending. It was found that the axial yarns will improve bending stiffness and electro-thermal behaviors significantly. The thermomechanical deformation and shape memory effect of SMPCs are influenced by the braiding structural parameters. Specifically, the 3D5d SMPCs exhibits a 53.6% increase in bending recovery force and a faster shape recovery speed than those of 3D four-directional SMPCs. We found from finite element analyses (FEA) that the axial yarns positions influence the inner stress distribution and shape memory behaviors of SMPCs. The axial yarns distributed on both sides of SMPC influence the shape memory behaviors more than those of the middle layer. [ABSTRACT FROM AUTHOR]

Highlights: [•] To decompose 3-D woven composite into micro repeat unit cells (RUCs) and meso-RUCs. [•] Using finite element method to calculate 3-point bending based on multi-scale RUCs. [•] Bending failures compared between numerical and theoretical are in good agreement. [ABSTRACT FROM AUTHOR]

Highlights: [•] To decompose 3D woven composite into micro repeat unit cells (RUCs) and meso-RUCs. [•] Using finite element method to calculate tension damage based on multi-scale RUCs. [•] Stress distribution and crack propagation have been revealed from RUCs model. [Copyright &y& Elsevier]

Abstract: This paper reports the ballistic impact damage of three-dimensional angle-interlock woven composite (3DAWC) under a hemispherical rigid projectile penetration on the basis of high strain rate constitutive equations of fiber tows and multi-scale geometrical model of the 3DAWC. The constitutive equations of the Twaron® fiber tows (poly paraphenylene terepthalamide, PPTA) under high strain rates have been established to characterize the mechanical behaviors under impact loading. The Twaron® fiber tows were assumed as transversely isotropic viscoelastic material to derive the constitutive equations. The maximum strain failure criterion was adopted for defining the failure of the PPTA fiber tows. A user-defined subroutine UMAT (FORTRAN user-material subroutine) was written for combining both the constitutive equations and the failure criterion in numerical calculation. Based on a micro-scale geometrical model of the 3DAWC, the UMAT for the PPTA fiber tows was combined with a commercial available finite element method (FEM) software package LS-DYNA to calculate the ballistic impact damage when the 3DAWC panel penetrated under a hemispherical–cylindrical steel projectile. It was found that the FEM simulation agrees well with the experimental results. The impact damage morphologies and damage propagations, the energy absorptions and the stress distributions in the 3DAWC panel were presented to elucidate the ballistic penetration damage mechanisms for optimizing the ballistic protection capacity of the 3-D woven composite material. [Copyright &y& Elsevier]

Abstract: This paper reports the three-point bending fatigue behavior of 3-D carbon/epoxy braided composite in experimental and finite element analyses (FEAs) approaches. In the experimental approach, the stiffness degradation and maximum deflection curves were obtained to illustrate the relationship between applied stress levels and number of cycles to failure. In FEA approach, a user-defined material subroutine UMAT which characterizes the stiffness matrix and fatigue damage evolution of the 3-D braided composite was developed. It was incorporated with a finite element code ABAQUS/Standard to calculate the stiffness degradation and maximum deflection of the 3-D braided composite during each loading cycle. From the comparisons between experimental and FEA results, good agreements prove the validity of the unit cell model and the subroutine UMAT. [Copyright &y& Elsevier]

Abstract: Knitted composites have higher failure deformation and energy absorption capacity under impact than other textile structural composites because of the yarn loop structures in knitted performs. Here we report the transverse impact behavior of a new kind of 3-D multi-structured knitted composite both in experimental and finite element simulation. The knitted composite is composed of two knitted fabrics: biaxial warp knitted fabric and interlock knitted fabric. The transverse impact behaviors of the 3-D knitted composite were tested with a modified split Hopkinson pressure bar (SHPB) apparatus. The load–displacement curves and damage morphologies were obtained to analyze the energy absorptions and impact damage mechanisms of the composite under different impact velocities. A unit-cell model based on the microstructure of the 3-D knitted composite was established to determine the composite deformation and damage when the composite impacted by a hemisphere-ended steel rod. Incorporated with the unit-cell model, a elasto-plastic constitute equation of the 3-D knitted composite and the critical damage area (CDA) failure theory of composites have been implemented as a vectorized user defined material law (VUMAT) for ABAQUS/Explicit. The load–displacement curves, impact deformations and damages obtained from FEM are compared with those in experimental. The good agreements of the comparisons prove the validity of the unit-cell model and user-defined subroutine VUMAT. This manifests the applicability of the VUMAT to characterization and design of the 3-D multi-structured knitted composite structures under other impulsive loading conditions. [Copyright &y& Elsevier]

Abstract: This paper presents ballistic impact damages of 3-D orthogonal woven composite in finite element analysis (FEA) and experimental. A unit-cell model of the 3-D woven composite was developed to define the material behavior and failure evolution. A user-defined subroutine VUAMT was compiled and connected with commercial available FEA code ABAQUS/Explicit to calculate the ballistic penetration. Ballistic impact tests were conducted to investigate impact damage of 3-D kevlar/glass hybrid woven composite. Residual velocities of conically-cylindrical steel projectiles (Type 56 in China Military Standard) and impact damage of the composite targets after ballistic perforation were compared both in theoretical and experimental. The reasonable agreements between FEA results and experimental results prove the validity of the unit-cell model in ballistic limit prediction of the 3-D woven composite. We believe such an effort could be extended to bulletproof armor design with the 3-D woven composite. [Copyright &y& Elsevier]

Abstract: The compressive properties of multi-axial multi-layer E-glass/epoxy warp knitted (MMWK) composites at quasi-static and high strain rates loadings have been investigated to evaluate the compressive failure mode at different strain rates. The through-the-thickness compressive properties at high strain rates from 600/s to 2100/s were tested using the split Hopkinson pressure bar (SHPB) technique. The compressive properties at quasi-static strain rate were also tested and compared with those in high strain rates. The results indicate that the stress strain curves are rate sensitive, and compressive stiffness, maximum compressive stress and corresponding compressive strain are also sensitive to the strain rate. The compressive stiffness, maximum compressive stress of the multi-axial multi-layer warp knitted composites is linearly increased with the strain rate. The compressive failure of the composite specimen tends to be in shear failure mode and becomes debris at high strain rate while only compressive deformation could be observed in quasi-static loading. [Copyright &y& Elsevier]

Revealing electric potential distributions in carbon fiber reinforced polymer composites (CFRPs) is important in structural health monitoring (SHM). Here we report effects of current injection modes, probing depth and preform structure on the electric potential distributions in carbon fiber/epoxy plain-woven (PW) laminates. We have conducted a series of electric distribution measurements and established a linear anisotropic conductivity model to show the electric potential distribution. It was found that fiber tow waviness and bridging region in the PW laminates lead to the decrease of electric conductivities along in-plane direction, and the increase along thickness direction. Two pairs of electrodes with vertical current flow paths lead to a positive superposition effect, while a negative superposition effect from opposite current flow paths. The electric current along thickness direction decreases because of high inter-laminar contact resistance. [ABSTRACT FROM AUTHOR]

• A 3D angle interlock woven fabric under ballistic penetration was investigated. • Full-size mesoscale yarn-level 3D angle interlock woven fabric model based on membrane elements was established. • Numerical simulation was validated based on experimental data. • Using microstructure model and dynamic parameters shows a better prediction of the fabric impact behavior. 3D woven fabric has great potential applications in body armor due to its good mouldability. This paper reports the ballistic mechanism of 3DAWF under the Full Metal Jacket (FMJ) projectile impact. Numerical simulation of 3DAWF under ballistic impact employing strain rate effect material models was established to capture the yarns' behaviors under high-speed impact loadings. Membrane elements construct a full-size mesoscale model based on real 3DAWF structure to improve computational efficiencies. The ballistic impact tests of 3DAWF subjected to the FMJ projectile were carried out to validate and evaluate the finite element analysis (FEA) model. From the results of the tests and theoretical model, it was found that the FEA model exhibits a relatively good correlation with tests on residual velocities, deformation, and damages. This work revealed the impact damage evolution, energy absorption mechanism, and the stress wave distribution in the 3DAWF, and the findings are instructive for the design of 3DAWF for ballistic protection. [ABSTRACT FROM AUTHOR]

A microstructure model based on fully thermo-mechanical coupling behavior of 3-D braided composites has been proposed for characterizing multiple transverse impact damage. The interfacial contact and cohesive debonding, as well as ductile and shear damage, incorporate with thermo-mechanical coupling constitutive equations have been employed in the model. It was shown that the adiabatic temperature rise and interfacial damage are concentrated on the impact surface with local plastic deformation. The heat energy generated in impact interaction caused local temperature rise, which further leads to thermal expansion of epoxy resin. The thermal expansion produced from the increased compression between the epoxy resin and braided preform will cause the extra internal stress and local deformation. A coupled thermal-stress closed loop will be formed during transverse impact. Compared with braided preforms with and without axial yarns, we found that the axial yarns improve heat energy absorption and impact damage tolerances, while impede impact damage growth. [ABSTRACT FROM AUTHOR]