Bohong Gu

Investigations of puncture behaviors of woven fabrics from finite element analyses and experimental tests

This paper reports the puncture behaviors of woven fabrics from experimental and finite element analyses (FEAs) approaches. In the experimental approach, the puncture behaviors of three kinds of woven fabrics, plain woven, 2/2 twill woven, and 2/1 twill, were tested under quasi-static conditions and the puncture load-displacement curves of the fabrics were obtained. The puncture damage morphologies were also observed. In FEA simulation, the puncture damage evolutions were calculated at the microstructure level and compared with those in experimental approach. Good agreements between the experimental and FEA approaches were found. From the FEA results, it was found that the puncture damage includes three stages: fabric tension, weft and warp yarn slippage, and yarn breakage and pullout. It was also found that there are almost no differences when the puncture acts at the interweaving point or between interweaving point for the three kinds of woven fabric. It is expected that such an investigation could provide guidance to the design of technical woven fabrics, such as geotextiles, tufted carpet the background layer, and flexible pipeline tubes, which often suffer from the puncture damages.

Transverse impact behaviors of four-step 3-D rectangular braided composites from unit-cell approach

Transverse impact behaviors of 3-D carbon/epoxy braided composite are reported in experimental and finite element analysis (FEA) approaches. In the experimental approach, the quasi-static penetration and transverse impact behaviors were tested to obtain load–displacement curves and fracture morphologies of the braided composite. In FEA, a unit cell model was established to derive the constitutive equation and failure criteria. Based on the model, a user-defined material subroutine (VUMAT) was written and connected with commercial FEA code ABAQUS/Explicit to calculate the impact damage. Good agreements between the experimental and FEA results prove the validity of the unit cell model and the subroutine VUMAT.

A refined quasi-microstructure model for finite element analysis of three-dimensional braided composites under ballistic penetration

The nondelamination characteristics of three-dimensional (3-D) braided composites under ballistic impact makes them possess considerable potential in ballistic protection applications. However, there are only a few references concerning the calculation of ballistic properties of these composites, and all are based on the continuum assumption of composite materials. In this paper, a refined quasi-microstructure model constructed with crossed inclined laminae of the same braided yarn with the same diameter and fiber volume fraction as in the 3-D braided composite at the actual microstructure level is established to analyze the ballistic penetration of 3-D braided composites target by a rigid projectile. The calculated results of the finite element analysis (FEA) are conservative to estimate the penetration resistance of the composite. From the acceleration-time history of the projectile and the damage morphology of the 3-D braided composite in FEA, it is indicated that the refined quasi-microstructure model can approximately simulate the real ballistic impact damage of these composites. The original ideas of this refined quasi-microstructure model are the scheme of decomposing the 3-D braided composite with the inclined lamina at its actual microstructure level and the adoption of constitutive equations of the reinforced fibers at a high strain rate. This model can also be extended to calculate the ballistic penetration of other 3-D textile preform-reinforced composites by rigid projectiles.

A Numerical Simulation on Ballistic Penetration Damage of 3D Orthogonal Woven Fabric at Microstructure Level

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.

Frequency Analysis of Stress Waves in Testing 3-D Angle-interlock Woven Composite at High Strain Rates:

This article presents Fourier transform and wavelet packet analysis of stress waves in a split Hopkinson pressure bar apparatus where the compressive behaviors of 3-D angle-interlock woven composite were tested at strain rate of 800/s, 1600/s and 2100/s. The stress waves in incident and transmission bar are transformed into frequency domain to analyze the impact energy spectrum under different lengths and impact velocities of the strike bar. It was found that the energy-frequency distribution is irrelevant to impact velocity and will be left-shifted when the length of the striker bar (i.e., width of incident stress wave) increases. The impact energy is mainly concentrated on the low-frequency region. The wavelet packet analysis of the incident and transmission stress waves shows that the transform coefficients decrease from the low-frequency region to the high-frequency region. Furthermore, the coefficients in the high-frequency region only occur at the ascending and descending part of stress waves. Based on the time-frequency analysis results, a unique start point of the stress wave can be determined for the stress-time and strain-time history calculation. This method can improve the calculation precision of stress—strain curves of the 3-D woven composite under different strain rate compression. The calculating results indicate that the stress—strain curves of the 3-D angle-interlock woven composites are sensitive to strain rate. The compressive modulus, maximum compressive stress linearly increases with strain rate. The failure strain decreases when the strain rate increases. This start point determination method can also be extended to high strain rate tests (including compression, tension, etc.) of other materials with split Hopkinson bar apparatus.

Dynamic Response of 3D Biaxial Spacer Weft-knitted Composite under Transverse Impact

The transverse impact of 3D biaxial spacer weft-knitted reinforced fabric composite is performed with a split Hopkinson pressure bar. The load versus displacement history of the composite under different impact velocities is obtained. The failure load and failure deformation both increase with the increasing of impact velocity. The energy absorption of the composite also increases with the increasing of impact velocity. The failure mode of the composite is compression failure in the front side and tension failure in the distal side. The matrix crack, fiber pullout and form interface debonding form the main failure mode for transverse impact loading. The composite has no delamination either for quasi-static loading or for transverse impact loading.

Comparisons of static bending and fatigue damage between 3D angle-interlock and 3D orthogonal woven composites

This paper presents the comparisons of quasi-static three-point bending and fatigue damage behaviors between the three-dimensional angle-interlock woven composite and the three-dimensional orthogonal woven composite. The stress–deflection curves and failure modes were recorded to compare both composites’ mechanical properties under quasi-static bending loading condition. The S-N curves were obtained to demonstrate the comparison of fatigue life under various stress levels between three-dimensional angle-interlock woven composite and three-dimensional orthogonal woven composite. In addition, the damage indexes versus number of cycles (D-N) curves were given to characterize the three-stage cumulative fatigue damage evolution of both types of textile structural composites. Furthermore, the ultimate damage morphologies were compared to deduce the structural effects of the composites under three-point bending cyclic loading condition.

Micro/meso-scale damage analysis of three-dimensional orthogonal woven composites based on sub-repeating unit cells

The mechanical responses including damage mechanisms for surface and interior parts of three-dimensional orthogonal woven composite have been analyzed by the multi-scale finite element method. Based on fabric architecture and fiber volume fraction in the three-dimensional orthogonal woven composite, the meso-scale repeating unit cells model and micro-scale repeating unit cell model are established. The periodic boundary conditions are applied to the micro-repeating unit cell and meso-repeating unit cell models. Appropriate failure criteria and a post-damage constitutive model are used to simulate the failures of fiber/fiber-bundles and resin in the micro/meso-scale repeating unit cells. A new elastic material model with damage propagation is defined with the user-defined material subroutine in commercial finite element software package ABAQUS/Standard. Mechanical behaviors including initiation and propagation of damage in micro/meso repeating unit cells under different loadings have been simulated with the user-defined material subroutine and the ABAQUS/Standard. The simulation results are compared with the experimental observations and they are in good agreement.

Impact Damage of 3D Cellular Woven Composite from Unit-cell Level Analysis

The high ratio of strength/area density of 3D cellular woven composite (3DCWC) leads the widely potential application of the composite in aircraft, vehicle, and sports facilities. The objectives of this investigation are to characterize the microstructures, impact responses, and failure modes of the 3DCWC under transverse impact. The 3D woven fabrics and composites were manufactured based on 3D angle-interlock woven fabric with cellular structures. The impact responses and energy absorption of the 3DCWC were tested with a modified split Hopkinson bar apparatus. A unit-cell model of the composite was established from the microstructure features, i.e., same fiber volume fraction and mechanical behaviors. A user subroutine VUMAT (FORTRAN Vectorized User-Material) was developed and connected with a commercial available finite element method (FEM) software package Abaqus/Explicit for calculating the impact responses of the composite. This subroutine describes the elasto-plastic constitutive equations of the unit-cell, maximum stress failure criteria, and critical damage area failure criteria. It was found that there is a good agreement of the impact load-displacement, failure modes between FEM calculation and experimental. This proves the validity of the unit-cell model, failure criteria and user-defined subroutine VUMAT. The user-defined subroutine VUMAT can also be extended to characterize the impact responses of the 3DCWC engineering structures.The high ratio of strength/area density of 3D cellular woven composite (3DCWC) leads the widely potential application of the composite in aircraft, vehicle, and sports facilities. The objectives of this investigation are to characterize the microstructures, impact responses, and failure modes of the 3DCWC under transverse impact. The 3D woven fabrics and composites were manufactured based on 3D angle-interlock woven fabric with cellular structures. The impact responses and energy absorption of the 3DCWC were tested with a modified split Hopkinson bar apparatus. A unit-cell model of the composite was established from the microstructure features, i.e., same fiber volume fraction and mechanical behaviors. A user subroutine VUMAT (FORTRAN Vectorized User-Material) was developed and connected with a commercial available finite element method (FEM) software package Abaqus/Explicit for calculating the impact responses of the composite. This subroutine describes the elasto-plastic constitutive equations of the un...

A microstructure model for finite-element simulation of 3D rectangular braided composite under ballistic penetration

The non-delamination feature of 3D braided composites under transverse impact leads to their potential application in the field of ballistic impact protection. One of the effective ways to investigate the ballistic impact damage of the 3D braided composite is to simulate the penetration process by numerical method, such as finite element method. However the numerical simulations of ballistic impact damage are seldom conducted based on the microstructure level. This paper presents a microstructure model for simulating ballistic impact damage of 4-step 3D braided rectangular composite penetrated by a rigid steel projectile. The microstructure model is based on the same yarn spatial configuration with that of the braided composite and also on the assumptions of the braided yarns appear straight inside the braided preform, bending and then change to other directions only at the surface. The ballistic perforation of the braided composite specimen by a cylindrical-conically steel projectile has been simulated with finite element method. The comparisons between FEA and experimental results show the validity of the microstructure model, especially for the penetration resistance and impact damage of the composite. Compared with the other continuum models of the braided composite, the microstructure model can simulate impact damage more precisely. The velocity history and acceleration history of projectile, and impact damage development of the composite in FEM simulation indicate the different damage and energy absorption mechanisms of the braided composite compared with those of laminated composite.