Simulating Initial and Progressive Failure of Open-Hole Composite Laminates under Tension

A finite element (FE) model is developed for the progressive failure analysis of fiber reinforced polymer laminates. The failure criterion for fiber and matrix failure is implemented in the FE code Abaqus using user-defined material subroutine UMAT. The gradual degradation of the material properties is controlled by the individual fracture energies of fiber and matrix. The failure and damage in composite laminates containing a central hole subjected to uniaxial tension are simulated. The numerical results show that the damage model can be used to accurately predicte the progressive failure behaviour both qualitatively and quantitatively.     

Modelling of fatigue damage progression and life of CFRP laminates

A progressive fatigue damage model has been developed for predicting damage accumulation and life of carbon fibre‐reinforced plastics (CFRP) laminates with arbitrary geometry and stacking sequence subjected to constant amplitude cyclic loading. The model comprises the components of stress analysis, fatigue failure analysis and fatigue material property degradation. Stress analysis of the composite laminate was performed by creating a three‐dimensional finite element model in the ANSYS FE code. Fatigue failure analysis was performed by using a set of Hashin‐type failure criteria and the Ye‐delamination criterion. Two types of material property degradations on the basis of element stiffness and strength were applied: a sudden degradation because of sudden failure detected by the fatigue failure criteria and a gradual degradation because of the nature of cyclic loading, which is driven by the increased number of cycles. The gradual degradation of the composite material was modelled by using functions relating the residual stiffness and residual strength of the laminate to the number of cycles. All model components have been programmed in the ANSYS FE code in order to create a user‐friendly macro‐routine. The model has been applied in two different quasi‐isotropic CFRP laminates subjected to tension–compression (T–C) fatigue and the predictions of fatigue life and damage accumulation as a function of the number of cycles were compared with experimental data available in the literature. A very good agreement was obtained.     

复合材料层合板低速冲击的接触力和能量响应仿真

以连续介质损伤力学（CDM）为基础,提出了一个有效的数值分析模型来模拟碳纤维增强复合材料（CFRP）层合板低速冲击的接触力响应和能量响应。该模型考虑了不同的失效模式,引入了不可逆的损伤变量和新的刚度折减方式以考虑损伤造成的刚度变化,定义了耗散能的计算方式以考虑损伤造成的能量变化。通过在Abaqus/Explicit平台上编写VUMAT子程序具体实现模型,数值仿真与试验结果吻合较好,验证了该模型的有效性。此外,还综合考虑了Hashin准则与LaRC04准则各自的优缺点,用Hashin和LaRC04相混合得到的准则对低速冲击进行了模拟。结果表明：在冲击外载作用下当CFRP层合板中存在较多基体压缩失效时,采用混合的失效准则模拟得到的接触力响应和能量响应结果更接近试验结果,而使用纯Hashin准则得到的预测结果偏保守。     

Damage Model and Progressive Failure Analyses for Filament Wound Composite Laminates

Recent improvements in manufacturing processes and materials properties associated with excellent mechanical characteristics and low weight have made composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite failure phenomenon is very complex. Several failure criteria and theories have been developed to describe the damage process and how it evolves, but the solution of the problem is still open. Moreover, modern filament winding techniques have been used to produce a wide variety of structural shapes not only cylindrical parts, but also “flat” laminates. Therefore, this work presents the development of a damage model and its application to simulate the progressive failure of flat composite laminates made using a filament winding process. The damage model was implemented as a UMAT (User Material Subroutine), in ABAQUS^TM Finite Element (FE) framework. Progressive failure analyses were carried out using FE simulation in order to simulate the failure of flat filament wound composite structures under different loading conditions. In addition, experimental tests were performed in order to identify parameters related to the material model, as well as to evaluate both the potential and the limitations of the model. The difference between numerical and the average experimental results in a four point bending set-up is only 1.6 % at maximum load amplitude. Another important issue is that the model parameters are not so complicated to be identified. This characteristic makes this model very attractive to be applied in an industrial environment.     

Low-velocity impact and residual tensile strength analysis to carbon fiber composite laminates

In this paper, low-velocity impact characteristics and residual tensile strength of carbon fiber composite laminates are investigated by experimentally and numerically. Low-velocity impact tests and residual tensile strength tests are performed using an instrumented drop-weight machine (Instron 9250HV) and static test machine (Instron 5569), respectively. The finite element (FE) software, ABAQUS/Explicit is employed to simulate low-velocity impact characteristics and predict residual tensile strength of carbon fiber composites laminates. These numerical investigations create a user-defined material subroutine (VUMAT) to enhance the damage simulation which includes Hashin and Yeh failure criteria. The impact contact force and the tensile strength are accurately estimated using the present method. Two different tensile damage modes after different impact energies are observed. The degradation of residual tensile strengths can be divided to three stages for different impact energies, and amplitudes of degradation are affected by stacking sequences.     

A numerical study on the impact resistance of composite shells using an energy based failure model

This paper presents a numerical study on the impact resistance of composite shells laminates using an energy based failure model. The damage model formulation is based on a methodology that combines stress based, continuum damage mechanics (CDM) and fracture mechanics approaches within a unified procedure by using a smeared cracking formulation. The damage model has been implemented as a user-defined material model in ABAQUS FE code within shell elements. Experimental results obtained from previous works were used to validate the damage model. Finite element models were developed in order to investigate the pressure and curvature effects on the impact response of laminated composite shells.     

剪切载荷作用下复合材料挖补修理层合板试验及有限元分析

为了确定剪切载荷作用下含非穿透损伤复合材料挖补修理层合板的破坏模式和抗剪切能力,进行了复合材料挖补修理层合板的剪切试验,并与未损伤复合材料层合板进行对比。试验结果表明,复合材料挖补修理后的层合板具有较高的强度恢复率,且不影响层合板的后屈曲承载能力。同时,建立了剪切载荷作用下复合材料挖补修理层合板的有限元分析（FEA）模型,复合材料母板和补片采用了三维Hashin准则来判定材料失效,母板层与层之间采用零厚度界面单元以有效模拟剪切载荷作用下复合材料母板上、下子板之间的分层。该模型得到的破坏模式与试验结果基本相符。由于挖补修理的设计与工艺复杂性,理论模拟的破坏载荷与试验结果虽不能完全吻合,但其最大15%左右的差异能够满足修理设计的需要。以上结果说明,该模型对剪切载荷作用下复合材料挖补修理层合板的破坏模式和破坏载荷能够进行工程适用的预测。     

复合材料层板开孔拉伸损伤分析

针对纤维增强复合材料层板开孔拉伸, 将复合材料层板的失效分为层内失效和层间失效, 建立了复合材料层板开孔拉伸损伤分析模型。该模型基于逐渐损伤分析, 对不同复合材料开孔层板进行了失效预测, 并与文献试验结果进行了对比, 破坏强度和失效模式均与文献试验结果非常吻合。结果表明本文中所建立的层板开孔拉伸损伤分析模型能够模拟含孔层合板拉伸过程中的损伤起始、 损伤扩展和最终破坏模式, 并最终预测含孔层合板拉伸失效模式和破坏强度。      

复合材料层合板剪切稳定性试验及强度预测

对无损伤及含冲击损伤的复合材料层合板进行了剪切稳定性试验,基于数字图像相关方法 (Digital image correlation,DIC)对层合板屈曲后屈曲行为进行了实时测量。试验结果表明：引入冲击损伤后,复合材料层合板剪切屈曲波形、屈曲载荷无明显变化,失效模式转变,承载能力下降了9.69%。随后,基于断裂面失效理论,建立了考虑剪切非线性效应的复合材料渐进损伤失效模型,并对复合材料层合板剪切失效过程进行了模拟。模型采用软化夹杂法将冲击损伤等效简化,直接将损伤区的几何边界信息写入材料模型中,不需要对冲击损伤区进行切割,从而保证了整体网格质量。与试验结果对比发现：模型考虑剪切非线性对屈曲载荷预测无明显影响,对后屈曲承载能力的预测精度影响较大,不考虑剪切非线性效应时的误差可达20%以上;软化夹杂法可以有效地模拟冲击损伤,预测的含冲击损伤的复合材料层合板的屈曲载荷、破坏载荷误差分别为-3.17%、-1.27%。     

复合材料层板开孔压缩损伤分析

针对纤维增强复合材料层板开孔压缩, 将复合材料层板的失效分为层内失效和层间失效, 建立了复合材料层板开孔压缩损伤分析模型。该模型基于逐渐损伤分析, 对不同复合材料开孔层板进行了失效预测, 并与文献中试验结果进行了对比, 破坏强度和失效模式均与文献试验结果非常吻合。结果表明, 本文中所建立的层板开孔压缩损伤分析模型能够模拟含孔层合板压缩过程中的损伤起始、损伤扩展和最终破坏, 并最终预测含孔层合板压缩失效模式和破坏强度。     

一种改进的内聚力损伤模型在复合材料层合板低速冲击损伤模拟中的应用

针对传统内聚力损伤模型(CZM)无法考虑层内裂纹对界面分层影响的缺点,提出了一种改进的适用于复合材料层合板低速冲击损伤模拟的CZM。通过对界面单元内聚力本构模型中的损伤起始准则进行修正,考虑了界面层相邻铺层内基体、纤维的损伤状态及应力分布对层间强度和分层扩展的影响。基于ABAQUS用户子程序VUMAT,结合本文模型及层合板失效判据,建立了模拟复合材料层合板在低速冲击作用下的渐进损伤过程的有限元模型,计算了不同铺层角度和材料属性的层合板在低速冲击作用下的损伤状态。通过数值模拟与试验结果的对比,验证了本文方法的精度及合理性。     

Macroscale assessment of low-velocity impact on hybrid composite laminates

Composites are usually brittle materials and have low impact properties. Structural dimensions, stacking sequence, ply materials, ply thicknesses and ply angles are standard variables that influence composite‘s performance against impact loads. Stacking sequence in hybrid laminates affects the failure and impact resistance. Failure mechanisms at the low-velocity impact of a rigid object in hybrid laminates are complex, and the subsurface damage in a composite laminate cannot be detected directly. However, various simulation platforms make it easy to see the impact damage between the plies of laminate. This paper numerically investigated the effect of stack sequence and hybridization of two fiber types against low-velocity impact. The current study adopted four-layer composite laminates of carbon and glass fiber layers with a stacking plan [C/C/C/C], [C/G/C/G] and [G/C/G/C], having lay-up angles as [0°/45°/−45°/90°]. Keeping the impactor mass and the incident velocity constant, the laminates were subjected to low-velocity impact. The damage contours for a failure mode were recorded and compared at the ply level. The numerical study resulted in impact imitations showing comparisons of the damage contours using Hashin failure criteria. Hybrid laminates display better performance in absorbing impact energies; however, hybrid laminates experienced more subsurface damage due to more impact energy absorption.     

Modelling damage evolution in composite laminates subjected to low velocity impact

In this paper, the impact damage of composite laminates in the form of intra- and inter-laminar cracking was modelled using stress-based criteria for damage initiation, and fracture mechanics techniques to capture its evolution. The nonlinear shear behaviour of the composite was described by the Soutis shear stress–strain semi-empirical formula. The finite element (FE) method was employed to simulate the behaviour of the composite under low velocity impact. Interface cohesive elements were inserted between plies with appropriate mixed-mode damage laws to model delamination. The damage model was implemented in the FE code (Abaqus/Explicit) by a user-defined material subroutine (VUMAT). Numerical results in general gave a good agreement when compared to experimentally obtained curves of impact force and absorbed energy versus time. The various damage mechanisms introduced during the impact event were observed by non-destructive technique (NDT) X-ray radiography and were successfully captured numerically by the proposed damage evolution model.     

基于实体-壳耦合模型的复合材料层压板冲击损伤阻抗优化

为优化复合材料层压板的冲击损伤阻抗, 提出了基于实体-壳耦合模型的优化方法。模型以实体单元模拟冲击点区域, 以壳单元模拟周围区域, 采用耦合约束连接实体与壳, 引用渐进损伤材料本构, 提出了冲击下与纤维方向种数相关的损伤变量, 优化过程利用遗传算法。通过算例对冲击阻抗的优化方法进行了验证, 并对复合材料盒段壁板进行了铺层优化。结果表明: 基于实体-壳耦合模型的遗传优化方法, 计算效率高, 收敛速度快, 提高了层压板的抗冲击性能。     

基于超弹性特性的SMA复合材料层合板低速冲击损伤数值模拟方法

基于ABAQUS有限元软件结合VC++6.0程序设计,建立了含不同铺层角度、不同排列密度形状记忆合金(SMA)纤维的复合材料层合板有限元模型。将基于Brinson本构模型的SMA分段线性超弹性模型以及判断复合材料层内失效的三维HASHIN失效准则编译至ABAQUS/VUMAT子程序,使用界面单元模拟复合材料层间区域,建立了SMA复合材料层合板的低速冲击损伤及冲击后剩余强度数值模拟方法。对比了不含SMA纤维层合板、含SMA纤维层合板、含普通金属丝层合板在不同冲击能量下的损伤响应。进一步分析了SMA纤维体积分数和直径变化对冲击响应的影响。冲击后剩余压缩强度模拟结果表明:冲击能量为16J时,含体积分数25%、直径0.5mm的SMA纤维层合板的冲击后剩余压缩强度相比不含SMA纤维层合板提高5.78%、相比含普通金属丝层合板提高4.69%。随着SMA纤维体积分数提高,层合板的抗低速冲击能力增强,当体积分数一定时,较细的(0.3mm)SMA纤维比粗的(0.6mm)SMA纤维对层合板的抗低速冲击能力增强效果更好。     

复合材料层板低速冲击后剩余压缩强度

对两种材料体系和铺层的复合材料层合板进行低速冲击后压缩强度试验 , 以研究低速冲击后层合板的压缩破坏机理。讨论了表面凹坑深度、 背面基体裂纹长度、 损伤面积以及剩余压缩强度与冲击能量的关系。在试验研究的基础上 , 建立了复合材料低速冲击后剩余强度估算的一种椭圆形弹性核模型。该模型将冲击损伤等效为一刚度折减的椭圆形弹性核 , 采用含任意椭圆核各向异性板杂交应力有限元分析含损伤层合板的应力应变状态 ,并应用点应力判据预测层板的压缩(或压、 剪)剩余强度。理论分析与试验结果对比表明 , 该模型简单有效。      

Finite element model for compression after impact behaviour of stitched composites

A finite element (FE) model using coupling continuum shell elements and cohesive elements is proposed to simulate the compression after impact (CAI) behaviour and predict the CAI strength of stitched composites. Continuum shell elements with Hashin failure criterion exhibit the composite laminate damage behaviour; whilst cohesive elements using traction-separation law characterise the laminate interfaces. Impact-induced delamination is explicitly modelled by reducing material properties of damaged cohesive elements. Computational results have demonstrated the trend of increasing CAI strength with decreasing impact-induced delamination area. Spring elements are introduced into the model to represent through-thickness stitch thread in the composite laminates. Results in this study validate experimental finding that CAI strength is improved when stitching is incorporated into the composite structure. The proposed FE model reveals good CAI strength predictions and indicates good agreement with experimental results, making it a valuable tool for CAI strength prediction of stitched composites.     

变刚度复合材料开孔板拉伸行为数值模拟及试验验证

纤维曲线铺放是提高复合材料构件力学性能的有效方法之一。本文针对复合材料开孔板铺放轨迹进行了研究,利用B样条曲线插值拟合获取了开孔板最大主应力铺放轨迹,并通过离散网格法建立了变刚度开孔板模型,通过引入Tsai-Wu损伤失效判据以及常刚度退化准则,进行了拉伸失效数值模拟及损伤失效分析,并分别铺放了两组常刚度和变刚度开孔板试验样件,进行了拉伸对比试验。结果表明：数值模拟与实验数据吻合较好,变刚度开孔板相比常刚度开孔板,拉伸强度提升了26.92%,且两者损伤失效演化过程显著不同。     

Damage growth analysis of low velocity impacted composite panels

Low velocity impact loading in aircraft composite panels is a matter of concern in modern aircraft and can be caused either by maintenance accidents with tools or by in-flight impacts with debris. The consequences of impact loading in composite panels are matrix cracking, inter laminar failure and, eventually, fiber breakage for higher impact energies. Even when no visible impact damage is observed on the surface at the point of impact, matrix cracking and inter laminar failure can occur, and the carrying load of the composite laminates is considerably reduced. The greatest reduction in loading is observed in compression due to laminae buckling in the delaminated areas.

The objective of this study is to determine the limit loading capacity and the damage growth mechanisms of impacted composite laminates when subjected to compression after impact loading. For this purpose a series of impact and compression after impact tests were carried out on composite laminates made of carbon fiber reinforced epoxy resin matrix. Four stacking sequences representative of four different elastic behaviours were used. Results show that the compressive, after impact, failure stress is influenced by the stacking sequence but a relatively independent strain to failure is observed.     

形状记忆合金-玻璃纤维/环氧树脂复合材料在振动边界条件下的低速冲击数值模拟

采用有限元方法（FEM）研究了振动边界条件对形状记忆合金（SMA）-玻璃纤维/环氧树脂复合材料的抗低速冲击性能的影响。在数值模拟过程中,将改进的三维Hashin失效准则和Brinson模型分别应用于玻璃纤维/环氧树脂复合材料层合板和SMA,以表征其本构关系。首先通过与固定边界条件下的SMA-玻璃纤维/环氧树脂复合材料板低速冲击实验进行比较,验证了数值模拟过程中所用模型及材料参数的准确性。其次,在模拟过程中,应用了包含不同振幅的一系列振动边界条件,对其进行模拟,揭示了振动边界条件对其抗低速冲击性能的影响。数值模拟结果表明,在大振幅条件下,无SMA复合材料的抗冲击性能比小振幅条件下弱;在相同振动边界条件下,SMA-玻璃纤维/环氧树脂复合材料与无SMA复合材料相比,其抗低速冲击性能提高。