三维编织复合材料弹道侵彻准细观层次有限元计算

三维编织复合材料相比于层合复合材料有较高的层间剪切强度和断裂韧性,因而具有更高的冲击损伤容限。用钢芯弹对三维编织复合材料作弹道贯穿测试,得到弹体的入射速度和剩余速度,并考察侵彻破坏模式。目前对三维编织复合材料弹道侵彻性能计算主要建立在连续介质假设上,从真实细观结构计算三维编织复合材料弹道冲击性能尚有一定难度,用三维结构复合材料的纤维倾斜模型在准细观结构层次上分解三维编织复合材料,就其中的一块倾斜单向板作弹道侵彻有限元计算,由弹体动能损失得到贯穿整个复合材料靶体后弹体的剩余速度。有限元计算及与弹道测试结果的比较证明在准细观层次上计算三维编织复合材料弹道冲击性能的有效性。      

Finite element modeling of impact, damage evolution and penetration of thick-section composites

Impact, damage evolution and penetration of thick-section composites are investigated using explicit finite element (FE) analysis. A full 3D FE model of impact on thick-section composites is developed. The analysis includes initiation and progressive damage of the composite during impact and penetration over a wide range of impact velocities, i.e., from 50 m/s to 1000 m/s. Low velocity impact damage is modeled using a set of computational parameters determined through parametric simulation of quasi-static punch shear experiments. At intermediate and high impact velocities, complete penetration of the composite plate is predicted with higher residual velocities than experiments. This observation revealed that the penetration-erosion phenomenology is a function of post-damage material softening parameters, strain rate dependent parameters and erosion strain parameters. With the correct choice of these parameters, the finite element model accurately correlates with ballistic impact experiments. The validated FE model is then used to generate the time history of projectile velocity, displacement and penetration resistance force. Based on the experimental and computational results, the impact and penetration process is divided into two phases, i.e., short time Phase I - shock compression, and long time Phase II - penetration. Detailed damage and penetration mechanisms during these phases are presented.     

Dynamic penetration of graphite/epoxy laminates impacted by a blunt-ended projectile

The dynamic penetration of graphite/epoxy laminates as a result of impact by a blunt-ended projectile is investigated in the present study. The ballistic limit is determined by a series of high-velocity impact tests. A dynamic finite element analysis is performed to simulate the penetration process in composite laminates. A previously developed static penetration model is incorporated into the analysis to predict the ballistic limit. The ballistic characteristics are represented by the relationship between the striking and residual velocities of the projectile. Good agreement between experimental data and computational results implies that the ballistic limit of graphite/epoxy laminates can be predicted by the present analysis without performing dynamic impact tests.     

Effect of Frictions on the Ballistic Performance of a 3D Warp Interlock Fabric: Numerical Analysis

3D interlock woven fabrics are promising materials to replace the 2D structures in the field of ballistic protection. The structural complexity of this material caused many difficulties in numerical modeling. This paper presents a new tool that permits to generate a geometry model of any woven fabric, then, mesh this model in shell or solid elements, and apply the mechanical properties of yarns to them. The tool shows many advantages over existing software. It is very handy in use with an organization of the functions in menu and using a graphic interface. It can describe correctly the geometry of all textile woven fabrics. With this tool, the orientation of the local axes of finite elements following the yarn direction facilitates defining the yarn mechanical properties in a numerical model. This tool can be largely applied because it is compatible with popular finite element codes such as Abaqus, Ansys, Radioss etc. Thanks to this tool, a finite element model was carried out to describe a ballistic impact on a 3D warp interlock Kevlar KM2? fabric. This work focuses on studying the effect of friction onto the ballistic impact behavior of this textile interlock structure. Results showed that the friction among yarns affects considerably on the impact behavior of this fabric. The effect of the friction between projectile and yarn is less important. The friction plays an important role in keeping the fabric structural stability during the impact event. This phenomenon explained why the projectile is easier to penetrate this 3D warp interlock fabric in the no-friction case. This result also indicates that the ballistic performance of the interlock woven fabrics can be improved by using fibers with great friction coefficients.     

A simplified microstructure model of bi-axial warp-knitted composite for ballistic impact simulation

The ballistic impact damage of a bi-axial warp-knitted (BWK) composite was simulated based on a simplified microstructure model. The microstructure was simplified by transferring the BWK composite into an equivalent laminate. Residual velocities of conically cylindrical steel projectiles (Type 56 in China Military Standard) and impact damage of the BWK composite were calculated with finite element method (FEM) and compared with those in experimental. Good agreements between FEM and experimental were found. The agreements verify the availability of the simplified model for the ballistic performance prediction of the BWK composite. We expect such an effort could be extended to the design of the BWK composites in field of aircrafts, high speed vehicles and ballistic protections.     

Damage evolution and energy absorption of E-glass/polypropylene laminates subjected to ballistic impact

High-velocity transverse impact of laminated fiber reinforced composites is of interest in military, marine and structural applications. The overall objective of this work was to investigate the behavior of laminated thermoplastic composites of varying thicknesses under high-velocity impact from an experimental and modeling viewpoint. In order to analyze this problem, a series of ballistic impact tests have been performed on plain weave E-glass/polypropylene (E-glass/PP) composites of different thicknesses using 0.30 and 0.50 caliber right-cylinder shaped projectiles. A gas gun with a sabot stripper mechanism was employed to impact the panels. In order to analyze the perforation mechanisms, ballistic limit and damage evaluation, an explicit three-dimensional finite element code LS-DYNA was used. Material model 162, a progressive failure model based on modified Hashin’s criteria, has been assigned to analyze failure of the laminate. The projectile was modeled using Material model 3 (MAT_PLASTIC_KINEMATIC). The laminates and the projectile were meshed using brick elements with single integration points. The impact velocity ranged from 187 to 332 m s⁻¹. Good agreement between the numerical and experimental results was attained in terms of predicting ballistic limit, delamination and energy absorption of E-glass/PP laminate.     

A combined experimental and numerical approach to study ballistic impact response of S2-glass fiber/toughened epoxy composite beams

A combined experimental and 3D dynamic nonlinear finite element (FE) approach was adopted to study damage in composite beams subject to ballistic impact using a high-speed gas gun. The time-histories of dynamic strains induced during impact were recorded using strain gages mounted on the front of the composite beam specimen. During ballistic impact tests, the impact velocity was also measured. The commercially available 3D dynamic nonlinear FE code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model, was then used to simulate the experimental results. In addition, LS-DYNA with the Chang–Chang linear-orthotropic damage model was also used for comparison. Good agreement between experimental and FE results was found from the comparisons of dynamic strain and damage patterns. Once the proposed nonlinear-orthotropic damage model was verified by experimental results, further FE simulations were conducted to predict the ballistic limit velocity (V₅₀) using either the number of damaged layer approach or a numerically established relation between the projectile impact velocity versus residual velocity or energy similar to the classical Lambert–Jonas equation for metals.     

Finite Element Analysis of Thermo-Mechanical Properties of 3D Braided Composites

This paper presents a modified finite element model (FEM) to investigate the thermo-mechanical properties of three-dimensional (3D) braided composite. The effective coefficients of thermal expansion (CTE) and the meso-scale mechanical response of 3D braided composites are predicted. The effects of the braiding angle and fiber volume fraction on the effective CTE are evaluated. The results are compared to the experimental data available in the literature to demonstrate the accuracy and reliability of the present method. The tensile stress distributions of the representative volume element (RVE) are also outlined. It is found that the stress of the braiding yarn has a significant increase with temperature rise; on the other hand, the temperature change has an insignificant effect on the stress of the matrix. In addition, a rapid decrease in the tensile strength of 3D braided composites is observed with the increase in temperature. It is revealed that the thermal conditions have a significant effect on the strength of 3D braided composites. The present method provides an effective tool to predict the stresses of 3D braided composites under thermo-mechanical loading.     

Finite Element Analysis of Mechanical Properties of 3D Four-directional Rectangular Braided Composites—Part 2: Validation of the 3D Finite Element Model

In the first part of the work, we have established a new parameterized three-dimensional (3D) finite element model (FEM) which precisely simulated the spatial configuration of the braiding yarns and considered the cross-section deformation as well as the surface contact relationship between the yarns. This paper presents a prediction of the effective elastic properties and the meso-scale mechanical response of 3D braided composites to verify the validation of the FEM. The effects of the braiding parameters on the mechanical properties are investigated in detail. By analyzing the deformation and stress nephogram of the model, a reasonable overall stress field is provided and the results well support the strength prediction. The results indicate it is convenient to predict all the elastic constants of 3D braided composites with different parameters simultaneously using the FEM. Moreover, the FEM can successfully predict the meso-scale mechanical response of 3D braided composites containing periodical structures.     

Finite Element Analysis of Mechanical Properties of 3D Four-Directional Rectangular Braided Composites Part 1: Microgeometry and 3D Finite Element Model

Based on the microstructure of three-dimensional (3D) four-directional rectangular braided composites, a new parameterized 3D finite element model (FEM) is established. This model precisely simulates the spatial configuration of the braiding yarns and considers the cross-section deformation as well as the surface contact due to the mutual squeezing in the braiding process. Moreover, it is oriented in the same reference frame as the composites, which coincides with the actual configuration of 3D braided composites and facilitates the analysis of mechanical properties. In addition, the model investigates the relationships among the structural parameters, particularly the braiding angle and the interior braiding angle, which were not taken into account in the previous models. Based on the parameterized FEM, the structural geometry of the composites is analyzed and some conclusions are drawn herein. Good agreement has been obtained between the calculated and measured values of the geometric characteristics of braided composite samples.     

Meso-Scale Finite Element Simulations of 3D Braided Textile Composites: Effects of Force Loading Modes

Meso-scale finite element method (FEM) is considered as the most effective and economical numerical method to investigate the mechanical behavior of braided textile composites. Applying the periodic boundary conditions on the unit-cell model is a critical step for yielding accurate mechanical response. However, the force loading mode has not been employed in the available meso-scale finite element analysis (FEA) works. In the present work, a meso-scale FEA is conducted to predict the mechanical properties and simulate the progressive damage of 3D braided composites under external loadings. For the same unit-cell model with displacement and force loading modes, the stress distribution, predicted stiffness and strength properties and damage evolution process subjected to typical loading conditions are then analyzed and compared. The obtained numerical results show that the predicted elastic properties are exactly the same, and the strength and damage evolution process are very close under these two loading modes, which validates the feasibility and effectiveness of the force loading mode. This comparison study provides a suitable reference for selecting the loading modes in the unit-cell based mechanical behavior analysis of other textile composites.     

三维四向编织复合材料宏观有限元模型冲击损伤仿真及试验验证

三维编织复合材料作为整体编织材料,能够克服层合复合材料层间强度低、易分层的缺陷,相对于金属材料,还具有质量轻、高比刚、高比强度以及良好的抗冲击性能、较高的损伤容限,在汽车、高铁、航海、航空及航天领域中具有广泛应用前景。使用空气炮发射系统开展了钢珠以约210 m/s速度冲击三维四向编织复合材料平板的不同位置试验,基于宏观观察和细观观测,分析了三维编织复合材料在受到钢珠高速冲击下的破坏模式和破坏机制。此外,本文建立了三维四向编织复合材料宏观连续介质损伤（CDM）有限元模型,其中模型计算剩余速度和试验测得剩余速度误差在5%以内,试验和数值模拟的破坏形貌也高度一致,验证了所建立的宏观CDM有限元模型的有效性。     

Multi-Scale Modeling of an Integrated 3D Braided Composite with Applications to Helicopter Arm

A study is conducted with the aim of developing multi-scale analytical method for designing the composite helicopter arm with three-dimensional (3D) five-directional braided structure. Based on the analysis of 3D braided microstructure, the multi-scale finite element modeling is developed. Finite element analysis on the load capacity of 3D five-directional braided composites helicopter arm is carried out using the software ABAQUS/Standard. The influences of the braiding angle and loading condition on the stress and strain distribution of the helicopter arm are simulated. The results show that the proposed multi-scale method is capable of accurately predicting the mechanical properties of 3D braided composites, validated by the comparison the stress-strain curves of meso-scale RVCs. Furthermore, it is found that the braiding angle is an important factor affecting the mechanical properties of 3D five-directional braided composite helicopter arm. Based on the optimized structure parameters, the nearly net-shaped composite helicopter arm is fabricated using a novel resin transfer mould (RTM) process.     

Low-Velocity Impact Response and Finite Element Analysis of Four-Step 3-D Braided Composites

The low-velocity impact characters of 3-D braided carbon/epoxy composites were investigated from experimental and finite element simulation approaches. The quasi-static tests were carried out at a constant velocity of 2 mm/min on MTS 810.23 material tester system to obtain the indentation load–displacement curves and indentation damages. The low-velocity tests were conducted at the velocities from 1 m/s to 6 m/s (corresponding to the impact energy from 3.22 J to 116 J) on Instron Dynatup 9250 impact tester. The peak force, energy for peak force, time to peak force, and total energy absorption were obtained to determine the impact responses of 3-D braided composites. A unit cell model was established according to the microstructure of 3-D braided composites to derive the constitutive equation. Based on the model, a user-defined material subroutine (VUMAT) has been compiled by FORTRAN and connected with commercial finite element code ABAQUS/Explicit to calculate the impact damage. The unit cell model successfully predicted the impact response of 3-D braided composites. Furthermore, the stress wave propagation and failure mechanisms have been revealed from the finite element simulation results and ultimate damage morphologies of specimens.     

三维编织复合材料损伤容限性能试验

为研究三维编织复合材料的损伤容限性能,首先,利用同种纤维、基体和工艺分别制作了4种三维编织复合材料和1种层合复合材料;然后,进行了相同复合材料在不同冲击能量下的及不同复合材料在相同冲击能量下的低速冲击试验和冲击后压缩试验;最后,进行了冲击后的C扫描损伤检测,并对比了冲击后凹坑深度、损伤面积和损伤宽度。结果显示:层合复合材料的损伤形貌主要呈椭圆状,且分层损伤严重,而三维编织复合材料的损伤形貌主要呈十字状,三维编织复合材料的整体性较好;层合复合材料和三维编织复合材料冲击能量的拐点均出现在30 J附近;三维编织复合材料的剩余压缩强度较高,其损伤容限性能优于层合复合材料。所得结论可为三维编织复合材料的工程应用提供指导。      

Transverse impact damage and energy absorption of 3-D multi-structured knitted composite

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.     

三维四向编织复合材料力学性能的有限元分析

在已有研究的基础上,提出了一个新的三维编织复合材料单元胞体模型,该模型正确地反映了纤维束的交织方式,十分接近三维编织复合材料的真实结构,可用于三维四向编织复合材料有效模量的有限元数值预报,并合理确定复合材料内部全场应力分布。采用有限元软件对该模型进行了力学分析,得到了相关等效弹性性能参数。结果表明:有限元计算得到的三维编织复合材料的等效弹性性能与实验结果和理论预测值都吻合较好,从而验证了该模型的有效性。此外,基于新的单元胞体模型还确定了三维四向编织复合材料的应力场,为进一步的强度计算奠定了基础。      

Ti/Al3Ti金属间化合物基层状复合材料抗侵彻性能数值模拟

采用LS-DYNA非线性有限元软件对Ti/Al₃Ti金属间化合物基层状（MIL）复合材料靶板的弹道侵彻过程进行了数值模拟。考察了等厚度下Ti体积分数、层数和材料梯度分布对复合材料抗侵彻性能的影响。结果表明,Ti体积分数约为20%时,靶板的抗侵彻性能最好。随着层数的增加,复合材料靶板的抗侵彻性能逐渐增强;但超过25层后,靶板的抗侵彻性能逐渐趋于稳定。不同铺层结构功能梯度板的抗侵彻性能相差较大,正向铺层梯度板的抗侵彻性能明显优于等厚均质复合材料靶板。     

A new analytical model to simulate impact onto ceramic/composite armors

A very simple one-dimensional and fully analytical model of ballistic impact against ceramic/composite armors is presented in this paper. The analytical model has been checked both with ballistic tests and numerical simulations giving predictions in good agreement with them. The model allows the calculation of residual velocity, residual mass, and the projectile velocity and the deflection or the strain histories of the backup material. These variables are important in describing the phenomenological process of penetration. Described are modifications to previous work of impact into ceramics combined with a new composites model. The development of this composite model is based on studies of the impact in yarns, fabrics and finally composites.     

Thickness influence on ballistic impact behaviors of GLARE 5 fiber-metal laminated beams: Experimental and numerical studies

This paper presents experimental and numerical investigations on ballistic impact behaviors of GLARE 5 fiber-metal laminated (FML) beams of various thicknesses. A high-speed camera was used to measure impact and residual/rebound velocities and also to assess damage evolution in the FMLs. The incident projectile impact velocity versus the residual velocity (V_I–V_R) was plotted and numerically fitted according to the classical Lambert–Jonas equation for the determination of ballistic limit velocity, V₅₀. The results showed that the V₅₀ varied in a parabolic trend with respect to the metal volume fraction (MVF) and specimen thickness. The interfacial debonding as well as bending and stretching in aluminum layers played the significant roles in dissipating the impact energy in the GLARE 5 FML beams. The 3D finite element (FE) code, LS-DYNA, was used to model and validate the experimentally obtained results. Good agreement between experimental and numerical results was achieved. It was found that for a given specimen configuration, by increasing the projectile incident velocity up to its V₅₀, the maximum contact force increased. By further increasing the projectile velocity above its V₅₀, the maximum contact force was relatively invariant with respect to an increase in the projectile incident velocity.