Failure analysis of composite laminates under large deflection

This paper presents the results of the application of a procedure, developed by Reddy & Reddy [ Composites Science and Technology 1992, 44, 227–255], for the evaluation of the first ply-failure load in multilayered composite plates. The procedure, which is based on the use of the finite element method (FEM) and which is suitable for the analysis of generally loaded plates, uses the non-linear von Karman formulation and, therefore, allows comparison of the failure loads in both the linear and the geometrically non-linear behaviour. Nevertheless, the use of the Newton-Raphson technique in searching the non-linear equilibrium points restricts its application to the case of plates without limit-point behaviour. The displacement model adopted in the FEM formulation is the traditional firstorder Reissner-Mindlin plate model that takes the shear deformation effect into consideration. Concerning the failure criteria, the analysis is based on a tensor polynomial criterion to which all other polynomial and independent criteria are brought back as particular cases. The study refers to the failure analysis of thin and thick plates under a uniformly distributed transverse load. Furthermore, a comparison of the failure criteria when the shear stresses are evaluated by means of the constitutive equations and by means of the local equilibrium equations is carried out. Finally, adopting a very simple degradation model of the mechanical properties to account for the stiffness decrease consequent to the failure, the qualitative behaviour of plates after the first non-catastrophic failure is also presented.     

低速冲击下复合材料层板压缩许用值

为评估航空结构中常用的T300级和T800级2种碳纤维/环氧树脂复合材料层压板的冲击后压缩许用值,对2种材料体系下具有不同厚度及铺层的层板进行了低速冲击和冲击后压缩试验;讨论了冲击能量、凹坑深度、损伤面积及冲击后剩余压缩强度等之间的关系,以及厚度、铺层、表面防护等因素对其造成的影响;重点关注了2种材料体系下各组层板的目视勉强可见冲击损伤(BVID)形成条件以及含BVID层板的剩余强度.结果表明:厚度及铺层对层板的凹坑深度-冲击能量关系影响较大,而对冲击后压缩强度-凹坑深度及冲击后压缩破坏应变-凹坑深度关系影响较小,且在相同铺层比例下,BVID对应的冲击能量随厚度近似呈线性增长.X850层板的损伤阻抗性能明显优于CCF300/5228层板的,但二者损伤容限性能相当.加铜网、涂漆等表面处理显著提高了层板的损伤阻抗,但对损伤容限性能影响不大;在损伤不超过BVID时,所有CCF300/5228试件的压缩破坏应变均大于4 000 με,而X850材料体系下压缩破坏应变均在3 000 με之上.     

冲击载荷下(纤维/聚合物)-金属层合板的大挠度动力响应

对冲击载荷下固支（纤维/聚合物）-金属层合方板和圆板的大挠度动力响应进行了理论研究。基于理想刚塑性假定和塑性极限屈服条件,建立了质量块体和爆炸冲击载荷下（纤维/聚合物）-金属层合板大挠度动力响应的理论模型,给出了固支（纤维/聚合物）-金属层合方板和圆板考虑弯曲和拉伸相互作用的大挠度响应解析解,进一步忽略弯曲的影响,得到了其动力响应的膜力解。研究结果表明,理论预测与已有实验结果吻合较好,该理论模型可以有效地预测质量块体和爆炸冲击载荷下（纤维/聚合物）-金属层合板的最大挠度。      

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.     

Analytical prediction of large mass impact damage in composite laminates

Analytical models are suggested for prediction of impact damage initiation and growth during quasi-static response caused by large mass impactors. Comparisons with experiments are presented for different layups, geometries and boundary conditions. The critical load for delamination growth is found almost insensitive to geometry and boundary conditions. The critical energy for delamination growth is separated in bending, shear and indentation contributions. Further growth depends on the number of delaminations developing, and is in thin laminates limited by the early occurrence of penetration. Observed delamination sizes are compared with a suggested upper bound and predictions based on the observed number of delaminations.     

The finite element analysis of composite laminates and shell structures subjected to low velocity impact

In this investigation, the composite laminate and shell structures subjected to low velocity impact are studied by the ANSYS/LS-DYNA finite element software. The contact force is calculated by the modified Hertz contact law in conjunction with the loading and unloading processes. In the case of composite laminate, the impact-induced damage including matrix cracking and delamination are predicted by the appropriated failure criteria and the damaged area are plotted. Two types of shell structure, cylindrical and spherical shells, are considered in this paper. The effects of various parameters, such as shell curvature, clamped or simple supported boundary conditions and impactor velocity are examined through the parametric study. Numerical results show that structures with greater stiffness, such as smaller curvature and clamped boundary condition, result to a larger contact force and a smaller deflection. The impact response of the structure is proportional to the impactor velocity.     

Reliability formulation for composite laminates subjected to first-ply failure

Methods formulated on the basis of the concept of first-ply failure and the structural reliability theory are presented for the reliability analysis of laminated composite plates. In the reliability formulation, an appropriate phenomenological failure criterion is used to establish the limit state equation of the laminated composite plates, and different numerical techniques are employed to evaluate the reliability of the plates. Experimental investigations of lamina strengths and first-ply failure loads of laminated composite plates were performed. Baseline probability distributions of lamina strength parameters constructed from the test data are used to study the reliability of the laminated plates. The accuracy of the proposed models in reliability assessment of the laminated plates are verified by the experimental results on first-ply failure load distributions.     

对称角铺设矩形复合材料叠层板受低速冲击时的应力波传及解层破坏分析

采用碰撞力分段模型和一阶剪切理论分析了给定初始速度的铁球与四边简支的复合材料叠层板中心发生碰撞的动力学行为,包括碰撞力及接触时间的变化规律、叠层板的振动响应、应力波传、表面沉陷等。并根据忽略厚度的界面模型假设及简化的Tsai Wu张量理论对复合材料叠层板的解层破坏进行了计算和分析,并给出了破坏区大小与铁球初始速度的关系。研究表明:碰撞力与铁球的初始速度成正比;复合材料叠层板中应力波传沿固定方向的相速度在各层内相同,拉伸应力波传速度沿纤维总体占优的方向大于其垂直的方向,而剪切应力波传速度则相反。即使在较低的初始碰撞速度下, 复合材料叠层板的解层破坏也很明显,并且破坏区域随初始碰撞速度的增大而不断扩展,其形状也会发生改变。      

Dynamic response testing of columnar composite structures subjected to impulsive loading

An experimental technique designed to study the dynamic response of columnar composite structures to impulsive loading has been developed. The technique uses a vibration shaker to subject a vertically mounted specimen to impulsive forces. Miniature accelerometers are used to monitor the dynamic response of the specimen. Results obtained from impulse tests with bone specimens have been presented to illustrate the testing technique.     

Failure analysis of fiber-reinforced composite laminates subjected to biaxial loads

A nonlinear constitutive model for a single lamina is proposed for the failure analysis of composite laminates. In the material model, both fiber and matrix are assumed to behave as elastic-plastic and the in-plane shear is assumed to behave nonlinearly with a variable shear parameter. The damage onset for individual lamina is detected by a mixed failure criterion, composed of the Tsai-Wu criterion and the maximum stress criterion. After damage takes place within the lamina, the fiber and in-plane shear are assumed to exhibit brittle behavior, and the matrix is assumed to exhibit degrading behavior. The proposed nonlinear constitutive model is tested against experimental data and good agreement is obtained. Then, numerical analyses are carried out to study the failure behavior of symmetric angle-ply composite laminates and symmetric cross-ply composite laminates subjected to biaxial loads. Finally, the conclusions obtained from the numerical analysis are given.     

Dynamic response analysis of geometrically non-liner structures subjected to high impact

An efficient digital computer method is presented for the determination of propagation of elastic stresses and deformations in certain geometrically non-linear structures subjected to high impact loading. The finite element matrix displacement approach utilizing curved quadrilateral shell elements in conjunction with a nodewise predictor–corrector method employing Runge–Kutta extrapolation techniques has been adopted for the present solution. The related computer program written in FORTRAN V for the UNIVAC 1108 computer has proved to be effective for the solution of a range of practical problems including rectangular and cylindrical panels. Numerical results are presented for a relevant structure, the cell container and the negative electrode of an impact-resistant battery subjected to high impact, simulating its free landing on a planetary surface.     

A comparative study on low-velocity impact response of fabric composite laminates

Impact behaviors at low velocity of composite laminates reinforced with fabrics of different architectures are investigated. Unidirectional prepreg, 2D woven and 3D orthogonal fabrics, all formed of Ultrahigh Molecular Weight Polyethylene (UHMWPE) filaments, were selected as reinforcements to form composite laminates using hot pressing technology. Low velocity impact tests were conducted using a drop-weight impact equipment at the energy level of 35 J. A three-coordinate measuring device was employed to determine the volume of plastic deformation and surface dent diameter. The results show that the composite laminates of single-ply 3D orthogonal woven fabric exhibit better energy absorbed capacity and impact damage resistance as compared to those of unidirectional and 2D plain-woven fabric.     

Multi-site impact response of S2-glass/epoxy composite laminates

High velocity transverse impact to laminated fiber reinforced composites is of interest in marine, military and civilian applications. Most studies in literature have addressed single point isolated impact events; while this work draws distinction in that we consider multi-site sequential and simultaneous impacts to composite structures. The overall objectives of this work were to investigate the response of laminated composites subjected to high velocity, multi-site impacts from a modeling and experimental viewpoint. Energy absorption, new surface creation, and failure mechanisms from sequential and simultaneous multi-site high velocity impacts are compared to assess additive and cumulative effects of these scenarios. Finite element modeling (LS-DYNA 3D) was used to gain insight into failure modes, energy absorption, and damage prediction. The modeling results correlated well with experimental data obtained from three layer laminates of vacuum assisted resin transfer molding (VARTM) processed S2-glass/SC-15 epoxy. The impact damage has been characterized using optical nondestructive evaluation (NDE) techniques. Specimens subjected to sequential impact exhibited average of 10% greater energy absorption and 18% increase in damage than specimens impacted simultaneously.     

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。     

移动式复合载荷作用下自紧身管的动态冲击响应研究

为研究某大口径自紧身管在火药燃气压力和弹带动态载荷复合冲击下的动力学响应演化历程,先提出三维残余应力场生成方法并利用脚本建模方式完成身管网格划分,而后计及挤进中诸能量形式及其相对比变化,通过联合多个用户子程序重新定义次要功系数及摩擦力模型并建立弹炮耦合非线性模型与内弹道方程组的关联通信,实现了上述载荷随火药燃烧而动态加载的过程,研究表明:基于该加载方式获得的数值结果能够比较准确地反映发射中身管真实响应,残余应力对身管应力场模式及演化有明显影响,两种复合载荷分布范围存在差异,弹带对身管动态作用力不可忽略。     

Post-buckling behaviour of thermoplastic matrix composite laminates subjected to pure shear

The present study focuses on the determination of the buckling load and post-buckling behaviour of simply supported laminated composite rectangular panels loaded in shear. The nonlinear structural response is studied with a non-linear finite element approach. In order to determine the accuracy of the procedure, several tests have been performed comparing the finite element solutions for isotropic and laminated composite rectangular panels with existing ones, adopting different sequences of lamination and different length to width ratios. The analysis then considers the behaviour of laminates produced with innovative thermoplastic matrix composites developed in the frame of a national research program.     

缝合复合材料层板低速冲击及冲击后压缩实验研究

通过对缝合复合材料层板进行低速冲击和冲击后压缩实验, 研究了不同类型的缝合复合材料层板的冲击损伤特性及冲击后压缩的剩余强度。实验研究表明: 基体损伤和分层是缝合层板与未缝合层板低速冲击的主要损伤模式, 缝合层板具有更好的抗冲击性能, 更高的冲击后压缩强度。缝合密度越大的层板其抗冲击性能越好, 冲击后压缩强度越高。缝合方向为0°的缝合层板较缝合方向为90°的缝合层板具有更好的抗冲击性能和更高的冲击后压缩强度。增加0°方向铺层, 减少45°、-45°方向铺层, 可以提高缝合层板的抗冲击性能和冲击后压缩强度。