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• 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]

The effect of thermo-oxidative aging on mechanical properties is important to designing carbon fiber-reinforced composites serviced in long-term atmospheric environments. Here, we report the progressive bending damage behaviors of carbon fiber/epoxy 3D angle-interlock woven composites (3DAWCs) after thermo-oxidative aging. Three-point bending tests were conducted to characterize bending damage behaviors after different aging days. The electrical resistance change of 3DAWCs was also simultaneously measured with the two-probe method during three-point bending tests. Combining side image and digital image correlation (DIC) technology, we found that the bending strength and modulus deteriorated rapidly during thermo-oxidative aging. The strain distribution and progressive bending damage modes also changed significantly, i.e., a symmetrical strain distribution for the unaged specimens, while the existing interface cracks of the aged specimen changed this symmetry. The electrical resistance method (ERM) effectively identified the early-stage damages, and the first derivative of the rate of resistance change (FDC) revealed differences in the progressive damage modes of aged and unaged specimens. [ABSTRACT FROM AUTHOR]

Fracture toughness behaviors of 3D angle-interlock woven composites were characterized with Mode I double cantilever beam test and finite element analysis (FEA). Load–displacement curves, strain energy release rates and fracture morphologies were obtained from tests and compared with FEA. We found that the 3D woven fabric structure increases strain energy release rates. The pullout and breakages of the yarns through thickness direction are the main mechanisms for the higher fracture toughness than laminates. The tradeoff between higher fracture toughness and lower in-plane stiffness should be considered for designing the 3D woven composites. [ABSTRACT FROM AUTHOR]

Low-velocity penetration damage behaviors of Kevlar woven fabrics impregnated with shear thickening fluid (STF) were investigated. Cone-shaped tup (CST) and hemispheric tup (HST) were employed to penetrate fabric/STF composites with the velocities of 1.5 m/s and 3.0 m/s under drop-weight tests. The fabric impregnated with 3:1 diluted volume ratio has the highest energy absorption and the lowest deformation. The peak load and energy absorption under HST penetration at 3.0 m/s are 2.0 kN and 36.7 J, which are higher than the CST penetration. Energy absorption increment under HST penetration at 3.0 m/s is 61.76% while 117.88% for CST penetration. [ABSTRACT FROM AUTHOR]

The compressive behaviors of three-dimensional braided composites with different cross sections and lengths along braided direction under high strain rates were reported from numerical simulations and experimental tests. The microstructure models with and without defects were established. The microstructure model with random distributed defects was to investigate the influence of sample length and random defects on the compressive properties. The microstructure model without defects is to reveal the effect of the cross section area on the compressive behavior. We found from finite element analysis that volume fractions of interior, surface, and corner unit cells vary with the cross section area. The strength and modulus were sensitive to the volume fractions of the unit cells and defects in the braided composites. The effect of the sample length on the compressive behaviors was not as significant as the cross section area and defects. The testing validated the finite element analysis results well. [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]

The objective of this work is to investigate yarn defects and specimen size on the impact compressive properties of 3-D angle interlock woven composites (AIWCs). The size effects on impact compressive properties were tested along in plane and out of plane directions. A new finite element model, with inherent defects in the geometrical model of yarns, was established to simulate impact compressive properties of the 3-D AIWCs. The model was further used to analyze size effects on impact compressive properties of 3-D AIWCs. We found the size effect on the 3-D AIWCs was not apparent both in experimental and numerical results; however, the random defects in yarns had a great effect on the compressive properties of 3-D AIWCs along different directions. The yarns effects will weaken the compressive stiffness and strength significantly. [ABSTRACT FROM AUTHOR]

This paper reports the bending fatigue behavior of three-dimensional five-directional braided T-shaped composite from finite element analyses and experimental characterizations. The braided composite microstructure was divided into five types of unit cell models, that is, interior cell, surface cell, corner cell, interior cell in joint region, and corner cell in joint region. A user-defined material subroutine was developed to characterize the unit cells properties, damage accumulation, and failure criterion of the T-beam under different stress levels. The stiffness degradation curves and bending displacement curves were obtained from the finite element analysis to show the three stages of fatigue developments, that is, matrix cracks, interface debonding, and fiber breaking. The stress and strain concentration areas were found in the middle of the flange and the web of the T-beam composites. The high strength reinforced fibers are recommended to add in the middle of the flange and the web for improving the bending fatigue resistance. And also, we hope the mixed unit-cell model could be extended to the other braided composite structures under quasi-static or cyclic loadings. [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]

This paper reports the influence of temperature and braided angle on compressive behaviors of 3D braided carbon fiber–epoxy composites. The compressive behaviors of the 3D braided with three braided angles (26°, 35° and 48°) were tested at various temperatures (−100℃, −50℃, 0℃, 20℃). The compressive damage morphologies were observed with SEM photographs. It was observed that the temperature and the braided angle have significant effect on the longitudinal compressive behaviors of 3D braided composites. The overall effect of braided angle on the 3D braided composites was greater than the temperature. The influence of the braided angle on the compressive behaviors is from the yarn orientation angle, while the influence of the temperature is from the temperature-dependent behaviors of the epoxy resin. Under low temperatures, the 3D braided composite behaved as brittle material and the compressive damage was easier than that of room temperature. The changes of yarn trajectory also led to generate the damage zone, especially in the edge and surface regions of the 3D braided composites. [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]

This article focuses on the quasistatic axial compression behavior and the consequent energy absorption of three different types of carbon/epoxy braided composite tubes. The focus is to evaluate the effect of sample length and braiding angle on the energy absorption and failure mechanism of the braided composite tubes. All tubes were manufactured with carbon fiber through four-step 1 x 1 braiding process and epoxy resin. Quasistatic axial compression tests were carried out to comprehend the failure mechanism and the corresponding compressive load-displacement characteristics of each braided composite tube. The quasistatic compression test parameters such as the compression peak load and the energy absorption of all these composite tubes were compared. It was found that as the length of the sample increased, the peak load reduced and the energy absorption of the braided tubes at 458 braiding angle was considerably higher than that of other braiding angles of 258 and 358. The failure modes included matrix crack along the braiding angle, fiber breakage, bulging and debonding between yarns. [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 purpose of the current study was to evaluate the use of near infrared spectroscopy to predict the physical traits of yak ( Bos grunniens ) meat. Near infrared spectra data of M. longissimus thoracis from 162 yaks were collected, as well as physical traits data. Prediction models of physical traits using near infrared spectroscopy were established through partial least squares regression (PLSR) combined with mathematical pretreatments such as orthogonal signal corrections (OSC) and detrending corrections (DT). The coefficients of determination of calibration ( R C 2 ) of prediction models were higher than 0.6 except WBSF. The ratio performance deviation for a* and b* values and their derived values SI and HA exceeded 2.0, which are suitable for screening. Through modeling separately for steers and heifers, we found that prediction ability for cooking loss would be increased but for b* would be decreased. Conclusively, near infrared spectroscopy is useful for predicting physical traits of yak meat and could be a potential tool for monitoring beef quality of the yak. [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]

Highlights: [•] Fatigue behavior of 3D orthogonal woven composites (3DOWC) is studied at microstructure level. [•] Fatigue damage and degradation were revealed with numerical analyses. [•] The influences of the microstructure on the fatigue behaviors have been analyzed. [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]

This article reports the trapezoid tearing behaviors of uncoated and coated woven fabrics in experimental and finite element analyses approaches. In experimental, trapezoid tearing behaviors of uncoated and coated woven fabrics were tested to obtain tearing load–displacement curves and tearing failure developments. The tearing strength and damage morphologies of the two kinds of fabrics were compared to find the tearing damage differences between uncoated and coated woven fabrics during the trapezoid tearing process. In finite element analysis, microstructure geometrical models of both the uncoated and coated woven fabrics were constructed to calculate the stress distribution and tearing failure propagation. There are good agreements between the finite element analysis results and those in experimental. Moreover, the influence of the coating on the trapezoid tearing properties was discussed. The tearing failure differences of the uncoated woven fabric and the base fabric in the coated woven fabric was also compared for finding the tearing failure mechanisms of the coated fabric. Such an investigation can be extended to the design of the coated woven fabric with high tearing strength. [ABSTRACT FROM AUTHOR]

This article presents the quantitative characterization of cumulative fatigue damage behavior for the three-dimensional angle-interlock woven composite undergoing three-point bending cyclic loading. The S–N curve was obtained to demonstrate the fatigue life of the three-dimensional angle-interlock woven composite under different stress levels. The increment of cycles for each 5% interval of stress level was reported to show the difference of fatigue resistance performances of the three-dimensional angle-interlock woven composite among the high, middle, and low intervals of stress level. In addition, the Cumulative Fatigue Damage versus Number of Cycles (D–N) curve and the Deflection Index versus Number of Cycles (F–N) curve were deduced to characterize the three-stage cumulative fatigue damage. Furthermore, the damage morphologies of the three-dimensional angle-interlock woven composite after fatigue tests were photographed to compare with those in quasi-static test. The cracks initiation and propagation in the three-dimensional angle-interlock woven composite during the process of cyclic loading were summarized to find the mechanisms of fatigue damage development. [ABSTRACT FROM PUBLISHER]

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]

This paper reports experimental results of the transverse impact behaviors of four-step three-dimension carbon/epoxy rectangular braided composite. We employed Split Hopkinson Pressure Bar apparatus to test the transverse impact behaviors. The impact load-displacement curves and impact damages of the braided composite were recorded to analyze the energy absorptions and the impact damage mechanisms. The quasi-static indentation tests and drop-weight impact tests were also performed to compare with those in transverse impact tests. It was found that the failure area and energy absorption is increased as the increase of impact velocity and the failure area is in a saw tooth shape owing to the breakage of the braided fiber tows. [ABSTRACT FROM AUTHOR]

The impact tensile behaviors of co-woven-knitted (CWK) composites were tested with split Hopkinson tension bar apparatus along 0°, 45°, and 90° directions under the strain rates from 1589 to 2586 s−1 and compared with that in quasi-static strain rate of 0.001 s−1. The impact tension damage mechanisms were analyzed in frequency domain with the Hibert–Huang transform (HHT) method. Specifically, the stress time histories curves of the CWK composite were transformed to find the frequency distributions for the different tension failure modes. It was found that thefailure mode of fiber breakages, fiber pull-out, resin cracks, and resin shear failurewere located at a specific frequency band. And also, the different failure modes under high strain rate loading are all located at the high frequency range. With such kind of HHT analyses, the damage mechanisms could be explored more precisely when combined with the observation results of the fractographs of the CWK composite under various strain rates. [ABSTRACT FROM PUBLISHER]

The ballistic impact damages of 3D orthogonal woven fabric (3DOWF) penetrated under a conically cylindrical rigid projectile were investigated from experimental tests and finite element simulations. A microstructure model of the 3DOWF was established and imported into finite element geometrical preprocessor. In the microstructure model, the architecture of the 3DOWF has the same spatial configurations with that of the real 3DOWF, including the spatial distributions and cross-sections of warp, weft yarns, and Z-yarns. Mechanical parameters of the yarns were obtained from high-strain rate tests which near to the impact loading condition in ballistic tests. The impact damage evolutions of the 3DOWF were simulated with the commercial finite element code ABAQUS/Explicit. From the comparisons of damage morphologies and residual velocities of the projectile after perforation between experimental and finite element simulation, it was found that the simulation can reflect the impact damage precisely. Furthermore, the stress wave propagation and damage mechanisms can be revealed from the microstructure model. Insights gained from this study will prove extremely useful in further material and architectural studies that will ultimately lead to optimization of the 3DOWF structure. [ABSTRACT FROM PUBLISHER]

This paper reports ballistic impact properties of a biaxial multilayer warp knitted basalt/vinyl ester composite from experimental and finite element analysis approach. In experimental, the ballistic perforation tests were conducted to obtain the energy absorption and impact damage of the composite plate penetrated under cylindro-ogive steel projectile (Type 56 in China Military Standard). In finite element analysis approach, a unit-cell model of the biaxial multilayer warp knitted composite has been developed based on the microstructure of the biaxial multilayer warp knitted composite. Critical damage area failure criterion was combined in the unit-cell model to determine the composite damage. A user-defined subroutine vectorized user defined material law was written to define the composite constitutive equation and failure criterion under impact. Incorporated with commercial finite element software package ABAQUS/Explicit, impact damage and energy absorption of the composite plate were calculated. Numerical predictions are compared with the experimental observations in terms of impact damage and energy absorption. We hope such an effort could be extended to the ballistic protection design of knitted composite. [ABSTRACT FROM AUTHOR]

Abstract: Ballistic impact damage of 3D angle-interlock woven composite (3DAWC) under a hemispherical-cylindrical steel projectile has been investigated in experimental and finite element method (FEM) based on a unit cell model. In the unit cell model, the composite was simplified into a combination of resins, weft yarns and warp yarns to define the stiffness matrix and failure evolution of the material. VUMAT (FORTRAN vectorized user-material) subroutine which based on the unit cell model has been developed and connected with commercial FEM code ABAQUS/Explicit (ver. 6.8) to calculate the ballistic impact damage and energy absorption of the composite. The experimental and FEM results of residual velocities of the projectile, and damages of the composite target were compared. Good agreement between experimental and theoretical proves the unit cell model and the VUMAT subroutine are reasonable for ballistic performance design of the 3D angle-interlock woven composite. [Copyright &y& Elsevier]

Abstract: The tensile properties of basalt filament tows were tested at quasi-static (0.001s−1) and high strain rates (up to 3000s−1) with MTS materials tester (MTS 810.23) and split Hopkinson tension bar (SHTB), respectively. Experimental results showed that the mechanical properties of the basalt filament tows were rather sensitive to strain rate. Specifically, the stiffness and failure stress of the basalt filament tows increased distinctly as the strain rate increased, while the failure strain decreased. From scanning electronic microscope (SEM) photographs of the fracture surface, it is indicated that the basalt filament tows failed in a more brittle mode and the fracture surface got more regular as the strain rate increases. The strength distributions of the basalt filament tows have been evaluated by a single Weibull distribution function. The curve predicted from the single Weibull distribution function was in good agreement with the experimental data points. [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]

The dynamic responses of T-beam structures made of 3D biaxial weft-knitted composite were tested under different impact velocities to characterize strength and energy absorptions of the T-beam with different rib heights. The transverse impact tests were carried out at a modified split Hopkinson pressure bar (SHPB) apparatus and also compared with the quasi-static test results. A user defined material subroutine named MAT/UMAT, which was based on a unit-cell model of the 3D knitted composite was developed to calculate the impact responses with a commercial FEM code ABAQUS. The load-displacement curves of the composite T-beam with different rib height under impact were calculated and compared with those from experiment. Mechanisms of the load-displacement curve fluctuations obtained from experiments are also discussed. The effect of the rib height on the load-displacement cures and energy absorptions have also been analyzed. Such an approach could also be extended to the design of other 3D knitted composite structures with different shapes under impulsive loading. [ABSTRACT FROM AUTHOR]

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]

The punch shear behavior of 3-D biaxial spacer weft knitted E-glass/ vinyl ester composite was investigated at quasi-static (0.01/s) and high strain rates ranging from 1200 to 3200/s in wale and course directions respectively. The quasistatic shear behavior was tested on a MTS 810.23 material tester and was compared with high strain rate shear behavior from a modified split Hopkinson pressure bar (SHPB) technique. The experimental results indicate that the shear stiffness, failure stress, and failure strain are rate sensitive both in wale and course directions. The shear stiffness and failure stress increase with the the increase of strain rate. The failure strains along the wale and course directions decrease with increasing strain rate. Furthermore, the shear failure becomes more severe in the course direction than in the wale direction at high strain rates. The damage mode in the wale direction at various strain rates is punch shear failure, while that of the course direction is filament tow breakage and matrix cracks. The unique features of this article are to conduct the punch shear tests at high strain rates successfully using a modified SHPB apparatus for the novel 3-D knitted composite and find the strain rate sensitivity both in shear behavior and failure mode. The results will benefit the structural design of the 3-D knitted composite owing to the higher in-plane tension stiffness and strength of the composite than any other 3-D textile structural composites. [ABSTRACT FROM AUTHOR]

The out-of-plane and in-plane compressive failure behavior of 4-step 3D braided composite materials was investigated at quasi-static and high strain rates. The out-of-plane and in-plane direction compressive tests at high strain rates from 800/s to 3,500/s were tested with the split Hopkinson pressure bar (SHPB) technique. The quasi-static compressive tests were conducted on a MTS 810.23 tester and compared with those at high strain rates. The comparisons indicate that the failure stress, failure strain and compressive stiffness both for out-of-plane and in-plane loading directions are rate sensitive. For example, the failure stress, failure strain and stiffness are 55.19 MPa, 6.70% and 1.35 GPa respectively as opposed to 145.00 MPa, 1.21% and 13.50 GPa respectively for strain rate of 2,500 s−1 under in-plane compression. The 3D braided composites have higher values of failure stress and strain for out-of-plane than for in-plane compression at the same strain rate; however, the in-plane compression stiffness is higher than that of out-of-plane compression at high strain rates. The compressive failure mode of 3D braided composites in the out-of-plane direction is mainly shear failure at various strain rates, while for the in-plane direction it is mainly cracking of matrix. [ABSTRACT FROM AUTHOR]

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]

The uniaxial tensile behavior of multiaxial multilayer warp knitted (MMWK) E-glass/ epoxy composite materials along warp, weft, and bias directions was investigated at high strain rates to analyze the influence of strain rate on tensile properties and failure mode of the MMWK composites under tensile impact. The uniaxial tensile test at strain rates from 1100 to 2200 s-1 were conducted with the split Hopkinson tension bar (SHTB) technique. The tensile test at quasi-static state was tested on MTS 810.23 system and compared with those in high strain rates. The results indicate that the failure stress, failure strain, and tensile stiffness are rate sensitive along warp, weft, and bias directions. The failure modes of the MMWK E-glass/epoxy composites under in-plane direction loading are matrix shear failure and yarn breakage in quasi-static state while interface failure and yarn pullout in high-strain-rate loading. [ABSTRACT FROM AUTHOR]

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 mechanical properties of four-step three-dimensional braided composite at high strain rates are important in evaluating this kind of composite under dynamic and impulsive loading. The in-plane and out-of-plane compressive properties of E-glass/epoxy four-step three-dimensional braided composite at strain rates from 300 to 3500 s-1 were tested with split Hopkinson pressure bar. The compressive properties at quasi-static strain rate (10-3 s-1) were also tested and compared with those at high strain rates. From the experimental data, the stress-strain curves, compressive stiffness, and compressive deformation of the composite are rate-sensitive in in-plane and out-of-plane compressive directions. In the out-of-plane direction, the compressive deformation mode was observed to have a deformation transition from axial compression to shear as the increase of strain rate, whereas only compressive deformation was found for in-plane direction compression. The failure stress and strain under compression at various strain rates have no regular tendency as the strain rate increased from 10-3 to 3500 s-1. [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]

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 aim is to investigate the advantages of blending affordable, lightweight, and biodegradable plant fibers with carbon fibers compared to single‐fiber composites. Adding ramie fiber to carbon fiber to produce carbon‐ramie fiber (CRFRP) and ramie–carbon fiber‐reinforced composites (RCFRP), and prepare pure carbon fiber and pure ramie fiber composites (carbon fiber‐reinforced composite [CFRP], RFRP) for comparison. Then, their static and dynamic mechanical properties (stretching, bending, low speed, and high‐speed impact) are illustrated. The results show that the CRFRP and RCFRP hybrid composites exhibit excellent properties, although slightly lower than the CFRP composites, but much higher than the RFRP, and the CRFRP composites show a slightly higher performance advantage over the RCFRP composites. Compared with CFRP composites, the tensile strength, flexural strength, and high‐speed impact peak load of CRFRP composites are reduced by 24.07%, 0.12%, and 5.44%, respectively, and the RCFRP composites are reduced by 32.11%, 45.82%, and 37% respectively. The results of the low‐speed impact test also show that the two mixed composites have good fracture elongation and stiffness. Therefore, the mechanical properties of CRFRP and RCFRP composites are comparable to those of CFRP composites, which not only reduces the material cost and reduce weight of the composite but also boosts the solution of the two‐carbon problem. Highlights: Innovative combination with natural fibers and synthetic fibers to fabricate hybrid fiber‐reinforced composites.The static (tensile and flexural) and dynamic (low‐speed and high‐speed impact) mechanical properties of CRFRP, RCFRP, CFRP, and RFRP composites are measured.The mechanical properties of CRFRP and RCFRP composites are comparable to those of CFRP composites. [ABSTRACT FROM AUTHOR]

Fabric‐reinforced shape memory polymer composites are lightweight, strong, formable, controllable, and suitable for various engineering and innovative applications. This study aims to fabricate and characterize electrothermal dual drive shape memory polymer composite fabrics (SMPCFs) of different densities with three‐dimensional (3D) angle‐interlock structures. The tensile properties, electrothermal properties, recovery forces (both tensile and bending), and shape recovery properties of SMPCFs were evaluated. The SMPCFs exhibited a tensile elongation of over 20% at the transition temperature. SMPCFs can reach transition temperatures when loaded with 2 V. The recovery forces are up to 225 N in tensile recovery force and 3.6 N in bending recovery force. In the shape recovery test, the recovery ratio exceeded 97%. Finally, the demonstration of recovery properties can stimulate the possibilities of SMPCFs in innovation and applications. Highlights: Core‐shell structured composite filaments were prepared.3D angle‐interlock composite fabrics: high strength, electrothermal drive.Tensile recovery force of composite fabrics can be up to 225 N.Elongation at transition temperatures was up to 20%. [ABSTRACT FROM AUTHOR]

The thermo-oxidative aging behavior of carbon/matrix composite material reinforced with 3D angle-interlock woven perform (3DAWC) was investigated experimentally and numerically. The aim is to explore the damage mechanism of thermo-oxidative aging through micro-CT 3-D reconstruction. We found that the interface between adjacent orthogonal yarns is favorable sites for crack onset. Cracks extend horizontally from four free outer surfaces to the interior of the sample. The propagation of the crack is continuously hindered by the undulating warp tows. Crack volume and maximum crack depth are positively correlated with aging day. Realistic finite element models of 3DAWC are constructed according to CT slices to detect the influence of yarn architecture on the sensitivity to damage mechanism. The results show that diamond-shaped weft is the stress concentration areas caused by a temperature drop and the shrinkage of the nearby resin region is more serious. The finite element model can predict the most likely location of the crack initiation. [ABSTRACT FROM AUTHOR]

• Revealing Mode I fracture toughness of 3-D woven composite under low-velocity impact. • To characterize crack initiation and propagation with high speed camera and FEA. • Crack path begins in resin, moves along the crimped path of warp or weft yarns. We report Mode-I low-velocity impact fracture behaviors of 3-D angle interlock woven carbon fiber/epoxy composites. The wedge-loaded compact tension (WLCT) specimen was used to test Mode-I fracture behaviors. The crack initiation and propagation were photographed with a high-speed camera. We found that the crack initiated from resin-rich zone and then propagated along yarn / resin interface. The crack propagation direction changed along the crimped yarn orientations. A finite element analysis (FEA) model was established to simulate internal crack propagation behaviors. The FEA results indicated that the crack propagation path depends on the weaving architecture of the 3-D woven composites. [ABSTRACT FROM AUTHOR]

Axial electromechanical properties after transverse compression of carbon nanotube (CNT) fibers were studied for their potential application in constructing lightweight structures. The structure-property relationship under two different compression modes was revealed due to their unique mechanical and electrical properties. Change of disentanglements and slippage between CNTs or CNT bundles during transverse compression significantly altered the axial tensile performance. The axial tensile strength of aerogel-spun and dry-spun CNT fibers increased by 20.6 % and 11.9 % under individually compressed at 60 MPa and 90 MPa, respectively. The tensile moduli of both fibers increased by 0.05 GPa. Followed by reduction of tensile performance as compressive strain level increased. The corresponding electrical resistance of both deformed CNT fibers increased more rapidly than that of the uncompressed fibers. In the cyclic compression mode, the axial tensile strength and modulus decreased by 40% and 45.7% for the aerogel-spun CNT fibers and by 17% and 14.2% for dry-spun CNT fibers owing to permanent damage accumulation. Scanning electron microscope examinations showed that tensile failure mode after compression transitioned from slippage into a new mode based on the fracture of CNT bundles. The failure mechanisms were finally investigated by a theoretical model. Unlabelled Image • Effect of transverse compression on tensile properties of carbon nanotube fibers were studied through experimental and theoretical methods. • Axial tensile performance of carbon nanotube fibers exhibited nonlinearly trend as compressive level increased. • Dry-spun carbon nanotube fibers show better electromechanical properties and is more suitable for ballistic and cut protection applications. [ABSTRACT FROM AUTHOR]

The deterioration of resin and interface in composites deteriorate during high-temperature service, would impact both the thermal stability and overall performance significantly. This paper focused on the experimental characterization of multi-scale damage and resin shrinkage within composites induced by thermo-oxidative aging using Micro-CT, SEM and Confocal Interferometric Microscopy (CIM), and exploring the coupling mechanism between them. The results show that damage distribution and propagation are affected by the hierarchical structure of 3-D angle-interlock fabric. Macro-CIM shows that maximum resin shrinkage depth depends on the resin width and aging time. Resin shrinkage profile evolution demonstrated the accelerating effect of resin crack on shrinkage. Micro-CIM shows that macro yarn cracks form through the accumulation of micro resin cracks in resin-rich areas and fiber/resin interface debonding. The formation of fiber/resin interface crack is tied to the resin shrinkage state, only occurring when the surrounding resin shrinkage slope exceeds a specific threshold value. [Display omitted] • Micro and macroscopic damages propagation in 3D woven composites have been shown. • Thermo-oxidative aging induced multi-scale damages was analyzed. • Multi-scale and multi-component shrinkage during aging were visualized. • Trigger mechanisms of interface debonding were presented. [ABSTRACT FROM AUTHOR]

• Anisotropic electrical conductivities of 3-D carbon/epoxy angle-interlock woven composites were investigated. • Electrical conductivities were measured and modeled at microscopic scale with finite element analysis and 3-D resistor network model. • Electric current density distribution depends on woven structures along different directions. Carbon fiber composites have widely been used in aircrafts and high speed vehicles. Electrical conductivity of the carbon fiber composites is critical to electrical safety for the aircrafts and vehicles under high voltage applications. Here we report microstructural modeling on electrical conductivities of three-dimensional (3-D) carbon/epoxy angle-interlock woven composites along on-axis and off-axis directions. A 3-D resistor network model and finite element analysis (FEA) model based on fabric microstructure have been developed to reveal the electric conductivities along different directions. We have found that the conductivity of the woven structure exhibits full anisotropy. The difference of electrical conductivity between in-plane and through-thickness direction decreased due to the existence of through-the-thickness carbon fibers. The electrical conductivity through-thickness direction increases with warp directional length. With increasing off-axis directional length, the conductivity perpendicular to the off-axis direction increases, while the conductivity parallel to the off-axis direction remains basically unchanged. Electric potential distribution and electrical current density are highly related with fabric structure and current directions. Owing to the dependence of mechanical properties are also related with fabric structure and directions, it is expected that both the electrical and mechanical properties of the 3-D woven carbon/epoxy composites could be optimized simultaneously from the composite microstructure designs. [ABSTRACT FROM AUTHOR]

• Effect of hybrid ratios on ballistic penetrations were revealed via FEA and tests. • Ballistic impact damages of hybrid laminates have been shown for optimization. • Hybrid schemes have been recommended for high ballistic energy absorptions. Fiber hybrid is a promising strategy for improving ballistic penetration behaviors of fiber-reinforced laminated composites. Ballistic impact performance of hybrid fiber laminates against projectiles depends on various parameters not only with respect to the material properties, fiber types, yarn properties, fabric structures of the constituent plies but also with the hybrid configuration, material combinations and stacking sequences. It has a substantial growth demand to obtains the optimal hybrid design of the fiber hybrid composites, for maximizing the potential of the constituent materials and improving the overall anti-impact performance of the hybrid composites. However, the effect of the hybridization ratios on ballistic penetration behaviors of the hybrid composites is still infant. Here we report the hybridization ratios on ballistic impact damage of carbon/Kevlar/UHMWPE (ultra-high molecular weight polyethylene) hybrid laminates through ballistic impact experiments and three-point bending tests. The fiber hybrid laminates with different hybrid ratios had been fabricated and studied under the impact of FSP (fragment simulating projectiles). The effect of the hybridization ratios on the flexural behaviors, ballistic curves, energy absorptions and damage modes were investigated. The FEA (finite element analysis) was carried out from meso- to macro- scale model. We found that the flexural behaviors are related to the material properties and mechanical balance among different material components in the hybrid systems. The damage modes for various hybrid ratios have a typical impact damage mode like matrix cracking, fiber breakage and delamination. A rational accuracy in residual velocities and damage modes can be obtained between ballistic experiments and FEA results. The hybrid ratios would affect the stress wave propagation in the composites with a gradual attenuation development and lead to different failure mechanisms. This study is expected to reveal a fundamental failure mechanism for the fiber hybrid composites incorporated with three different fiber combinations in different hybrid ratios under ballistic impact. The results can provide important theoretical basis and experimental reference for designing and developing hard multiphase anti-impact composite structures. [Display omitted] [ABSTRACT FROM AUTHOR]