含紧固穿透分层复合材料层板的疲劳扩展

对含预置穿透分层复合材料层板开展压缩强度和压缩疲劳试验,获得结构的极限载荷,并研究层板的分层扩展特性。基于ABAQUS软件建立含穿透分层复合材料层板有限元模型,通过VCCT计算能量释放率,采用B-K准则来模拟层间分层的扩展。引入VUMAT子程序,采用改进的Hashin准则判断单元损伤;基于累积损伤理论和剩余强度理论,弱化材料性能,对含穿透分层和含紧固穿透分层复合材料层板的疲劳力学行为进行分析,讨论了紧固件等参数对层板分层扩展的影响。     

含分层损伤缝合复合材料层板的剩余压缩强度

基于渐进损伤方法,研究了含单脱层缝合复合材料层板在压缩载荷下的剩余强度。通过商用软件ABAQUS建立了含单脱层缝合复合材料层板剩余压缩强度计算模型,考虑了子层屈曲和分层扩展对剩余强度的影响。通过UMAT子程序实现了层板失效、层间失效和缝线失效的模拟。通过嵌入式杆单元结构模拟了缝线桥联作用及失效。采用Hashin准则及刚度折减法对纤维拉压、基体拉压失效进行了模拟。通过渐进损伤分析,揭示了缝合情况下含单脱层复合材料层板的失效机理,讨论了缝合参数对剩余压缩强度的影响。所预测的破坏模式和剩余强度结果与实验能较好地吻合。分析表明缝合可以明显提高含分层损伤复合材料层板的子层屈曲载荷,抑制分层扩展,并提高层板的剩余压缩强度。     

纤维增强复合材料层板高速冲击损伤数值模拟

推导了复合材料应变率相关三维本构关系, 并将其用于复合材料层板高速冲击损伤的数值模拟。该模型在复合材料层间引入界面单元模拟层间分层, 结合三维Hashin失效准则进行单层板面内损伤识别, 引入材料刚度退化, 采用非线性有限元方法, 研究了复合材料层板高速冲击的破坏过程及层板的损伤特性。数值分析结果表明, 剩余速度预报结果与实验结果吻合较好, 层板的主要损伤形式是层间分层、 基体微裂纹和纤维断裂, 减小弹体直径、 增大铺层角度和层板厚度能够有效降低层板损伤面积。      

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。     

含脱粘损伤的复合材料加筋板压缩破坏渐进损伤数值分析

本文提出了基于连续损伤力学的复合材料层合加筋壁板渐进损伤分析模型。该模型采用界面单元模拟筋条和壁板之间的连接界面,连接界面和复合材料层板分别采用Quads准则和Hashin准则作为失效判据,基于内嵌连续损伤状态变量的材料刚度退化方案,采用非线性有限元方法,研究了复合材料加筋壁板在压缩载荷下的破坏过程,分析了结构相应失效模式的细观失效机理。数值分析结果与实验数据吻合较好,证明该方法的合理性和有效性,并详细探讨了界面单元关键参数和层板铺设角度对加筋壁板结构力学响应的影响规律,得到了一些富有价值的结论。     

复合材料层板静压入破坏机制

建立一个有效的计算模型, 以分析复合材料层板在静压入过程中发生分层、 纤维断裂的现象。该计算模型基于有限元程序的三维逐渐损伤理论对层板的静压入全过程进行模拟, 对逐层逐个单元的损伤进行判断, 可以模拟任意角度、 铺层厚度的层板在递增载荷下的逐渐损伤破坏过程。对炭纤维增强环氧树脂基复合材料层板在静压入过程中发生的分层和纤维断裂现象进行预测,并与实验结果进行比较; 对炭纤维增强双马来酰亚胺树脂基复合材料层板在静压入过程中的分层损伤和最终破坏接触力的大小进行预测,并与低速冲击下的结果进行比较。数值仿真与实验结果吻合较好, 表明静压入分析方法是复合材料层板在低速冲击下产生损伤的可替换分析方法。      

面内损伤对埋藏分层影响的三维有限元分析

运用大型有限元软件ANSYS,基于复合材料层合板损伤理论,建立了含面内损伤和埋藏分层的复合材料层板三维有限元模型.分析了面内损伤对复合材料层板分层的影响.采用三维Hashin准则预测复合材料损伤,分层区损伤采用多种损伤模型,损伤发生后,认为材料仍连续,并修改损伤单元对应的材料参数.通过虚拟裂纹闭合技术（VCCT）计算分...     

复合材料加筋板低速冲击损伤的数值模拟

建立了复合材料加筋板在横向低速冲击载荷作用下的渐进损伤有限元模型。该模型考虑了复合材料加筋板受低速冲击时的纤维断裂、基体开裂及分层脱粘等五种典型的损伤形式, 在层内采用应变描述的失效判据, 结合相应的材料性能退化方案, 通过编写VUMAT用户自定义子程序以实现相应损伤类型的判断和演化。在层间以及筋条与层板间加入界面元, 模拟层间区域的情况, 结合传统的应力失效判据和断裂力学中的能量释放率准则来判断分层损伤的起始和演化规律。通过对数值模拟结果与实验数据的比较, 验证了模型的合理性和有效性。同时探讨了不同位置、不同冲击能量以及含初始损伤(脱粘)等因素对复合材料加筋板低速冲击性能的影响。     

复合材料加筋板低速冲击损伤的数值模拟

建立了复合材料加筋板在横向低速冲击载荷作用下的渐进损伤有限元模型.该模型考虑了复合材料加筋板受低速冲击时的纤维断裂、基体开裂及分层脱粘等五种典型的损伤形式,在层内采用应变描述的失效判据,结合相应的材料性能退化方案,通过编写VUMAT用户自定义子程序以实现相应损伤类型的判断和演化.在层间以及筋条与层板间加入界面元,模拟层间区域的情况,结合传统的应力失效判据和断裂力学中的能量释放率准则来判断分层损伤的起始和演化规律.通过对数值模拟结果与实验数据的比较,验证了模型的合理性和有效性.同时探讨了不同位置、不同冲击能量以及含初始损伤(脱粘)等因素对复合材料加筋板低速冲击性能的影响.     

边界条件对纤维增强复合材料层板高速冲击损伤影响的数值模拟

根据复合材料三维粘弹性本构关系,建立纤维增强复合材料层板高速冲击损伤的有限元分析模型。模型中引入界面单元模拟层间分层,结合三维Hashin失效准则进行单层板面内损伤判断。对数值结果进行分析,得到如下结论:边界四面不带应力层板的损伤面积最大,两个对面带应力层板的损伤面积次之,一面和三面带应力层板的损伤面积最小;边界应力增大而冲击速度不变时,剩余速度基本不变,损伤面积先增大后减小;冲击速度增大而边界应力不变时,剩余速度线性增大,损伤面积先增大后减小。     

Structural design of single lap joints with delaminated FRP composite adherends

This paper deals with the structural design of single lap joints (SLJs) with delaminated adherends using fracture mechanics principles. The interlaminar stresses and Strain Energy Release Rate (SERR) are considered as damage characterizing parameters used for designing the SLJ when delamination damages are pre-embedded in both the adherends at similar positions. Three dimensional geometrically non-linear finite element analyses (FEAs) of SLJ with delaminated adherends have been performed to determine the interlaminar and SERR values along the delamination fronts by simulating the simultaneous interaction delamination damages when pre-embedded at similar positions in both the adherends. SERR values are evaluated using Modified Crack Closure Technique (MCCI) which is based on energy principle. The delaminations are assumed to be of linear front, and have been considered to be embedded in both the laminated FRP composite adherends beneath the surface ply of the adhesively bonded SLJ. The delamination damages are presumed either to pre-exist or get evolved at the interlaminar locations. Such delaminations have been modelled using the sublaminate technique. The critical issues of modelling pre-embedded delamination damages are discussed in detail. The numerical results presented in this paper are based on the validated FE model compared with the available literature. Based on the present analyses, the structural design recommendations have been made for the SLJ when pre-embedded delamination damages are present in both the adherends. It is observed from the stress based design that the delamination damage when present in the bottom adherend is more detrimental for failure of SLJ compared to that for the case when it is present in the top adherend. Also, SERR based design reveals that the opening mode predominantly governs the propagation of delamination damage for all positions of the pre-embedded delaminations in both the adherends of the SLJ.     

低速冲击作用下碳纤维复合材料铺层板的损伤分析

建立了一个有效计算模型, 以分析碳纤维复合材料层合板在低速冲击作用下的层内和层间失效行为。针对铺层板的层内损伤, 在基于应变描述的Hashin 失效准则的基础上, 建立了单层板的逐渐累积损伤分析模型;针对铺层板的脱层损伤, 建立了各向同性脱层损伤模型, 通过结合传统的应力失效准则和断裂力学中的能量释放率准则定义了界面损伤演化规律, 并在潜在产生脱层的区域模拟为粘结接触, 并将脱层损伤模型作为界面的接触行为。该计算模型通过商用有限元软件ABAQUS/ Explicit 的用户子程序实现。使用该计算模型对碳纤维增强环氧树脂复合材料层合板在横向低速冲击作用下的损伤和变形行为进行预测分析。数值仿真的结果与试验结果进行了比较, 取得了满意的结果, 验证了该模型的正确性。      

z-pin增韧复合材料层合板低速冲击损伤过程研究

从z-pin增韧复合材料层合板低速冲击实验出发,考虑了复合材料层合板在受低速冲击时的分层及基体开裂等四种损伤形式,引入适当的损伤判据,对T300/3234碳纤维树脂基复合材料层合板的低速冲击损伤过程进行有限元模拟。结果表明,采用碳纤维钉z-pin增韧使得冲击后层间分层区域面积减小50%左右,有限元结果与实验数据吻合。     

Prediction of Delamination Onset and Critical Force in Carbon/Epoxy Panels Impacted by Ice Spheres

Polymer matrix composite structures are exposed to a variety of impact threats including hail ice. Internal delamination damage created by these impacts can exist in a form that is visually undetectable. This paper establishes an analysis methodology for predicting the onset of delamination damage in toughened carbon/epoxy composite laminates when impacted by high velocity ice spheres (hailstones). Experiments and analytical work focused on ice sphere impact onto composite panels have determined the failure threshold energy as a function of varying ice diameter and panel thickness, and have established the ability to predict the onset of delamination using cohesive elements in explicit dynamic finite element analysis. A critical force associated with damage onset was found to be independent of the ice diameter and thus can be expressed as a function of basic panel-describing parameters, namely bending rigidity and interlaminar fracture energy. Critical force can be used as a failure criterion in simpler models (e.g., shell elements) when predicting the onset of delamination by high speed spherical ice impact.     

Prediction of low velocity impact damage in carbon–epoxy laminates

It is well known that composite laminates are easily damaged by low velocity impact. This event causes internal delaminations that can drastically reduce the compressive strength of laminates. In this study, numerical and experimental analyses for predicting the damage in carbon–epoxy laminates, subjected to low velocity impact, were performed. Two different laminates (0₄,90₄)_s and (0₂,±45₂,90₂)_s were tested using a drop weight testing machine. Damage characterisation was carried out using X-rays radiography and the deply technique. The developed numerical model is based on a special shell finite element that guarantees interlaminar shear stresses continuity between different oriented layers, which was considered fundamental to predict delaminations. In order to predict the occurrence of matrix failure and the delaminated areas, a new failure criterion based on experimental observations and on other developed criteria, is included. A good agreement between experimental and numerical analysis for shape and orientation of delaminations was obtained. For delaminated areas, reasonable agreement was obtained.     

高温环境下碳纤维增强树脂复合材料的层间力学性能老化行为与失效预测

为了研究碳纤维增强树脂(CFRP)复合材料层间力学性能在高温环境中的老化失效行为,设计了CFRP复合材料层间拉伸和层间剪切实验,在高温(80℃)环境中进行0(未老化)、 120 h、 240 h、 360 h、 480 h、 600 h和720 h的老化测试,分析CFRP层间失效强度和失效形式随老化时间的变化规律,得到随高温老化的二次应力准则响应面。建立CFRP复合材料层间力学性能预测模型,得到不同老化衰减系数下的退化模型,并通过CFRP复合材料层间仿真模型进行了验证。结果表明:随着高温老化时间的增加,层间拉伸和层间剪切强度总体上都发生了一定程度的退化,层间拉伸时更容易发生碳纤维丝剥离,层间剪切发生局部的树脂剥离,纤维之间的分层更加明显,高温老化使树脂与纤维丝的界面结合力显著下降。通过CFRP复合材料层间力学性能随高温老化的二次应力准则,计算不同老化时间后的内聚力模型参数,预测CFRP复合材料在高温老化条件下的层间强度,发现仿真与实验误差小于10%,说明了CFRP复合材料层间失效预测模型的准确性。     

Failure analysis of multiple delaminated composite plates due to bending and impact

The present work aims at the first ply failure analysis of laminated composite plates with arbitrarily located multiple delaminations subjected to transverse static load as well as impact. The theoretical formulation is based on a simple multiple delamination model. Conventional first order shear deformation is assumed using eight-noded isoparametric quadratic elements to develop the finite element analysis procedure. Composite plates are assumed to contain both single and multiple delaminations. For the case of impact, Newmark time integration algorithm is employed for solving the time dependent multiple equations of the plate and the impactor. Tsai-Wu failure criterion is used to check for failure of the laminate for both the cases. To investigate the first ply failure, parametric studies are made for different cases by varying the size and number of delaminations as well as the stacking sequences and boundary conditions.     

Interaction between matrix cracking and edge delamination in composite laminates

Matrix cracking and edge delamination are two main damage modes in continuous-fibre composite laminates. They are often investigated separately, and so the interaction between two damage modes has not yet been revealed. In this paper, a simple parallel-spring model is introduced to model the longitudinal stiffness reduction due to matrix cracking and edge delamination together. The energy release rate of edge delamination eliminating the matrix crack effect and the energy release rate of matrix cracking in the presence of edge delamination are then obtained. Experimental materials include carbon- and glass-fibre-reinforced bismaleimide composite laminates under static tension. The growth of matrix cracks and edge delaminations was recorded by means of NDT techniques. Results show that matrix cracks may initiate before or after edge lamination. This depends on the laminate layup, and especially on the thickness of the 90° plies. Edge delamination may also induce matrix cracking. Matrix cracking has a significant effect on the stiffness reduction in GRP laminates. The present model can predict the stiffness reduction in a laminate containing both matrix cracks and edge delaminations. The mixed-mode delamination fracture toughness obtained from the present model shows up to 50% differences compared with O'Brien's model for GRP laminates. However, matrix cracking has a small effect on the mixed-mode interlaminar fracture toughness of the CFRP laminates.