褶皱缺陷影响L型层合板失效行为:实验和数值研究

通过实验和数值分析相结合的方法开展了褶皱缺陷对L型复合材料层合板承载能力和失效过程影响的研究。实验方面，通过“横条法”人为引入褶皱缺陷，制备了含两种缺陷大小的L型层合板，研究了其在弯曲载荷作用下的承载能力和损伤扩展形式，并与无缺陷L型层合板进行对比分析。数值分析方面，基于3D Hashin失效准则的渐进损伤失效模型, 研究其失效过程中应力分布特征和失效模式，探求褶皱缺陷对L型层合板失效行为的影响机制。实验结果表明，褶皱缺陷会显著降低曲梁的承载能力，并使分层损伤演化的空间扩展特征从无褶皱试样的逐层扩展转变为褶皱区域的聚集式扩展。数值预测与实验现象吻合，并共同表明褶皱处横向应力和面法线应力的集中是导致结构提前失效的主导因素，且褶皱区域的应力集中改变了损伤过程中应力逐层重分配的趋势，导致含褶皱试样呈现出聚集式扩展的破坏特征。该工作可扩展应用于含褶皱缺陷L型层合板的安全性能评估及损伤容限设计。 

Impact of wrinkle defects on failure behavior of L-shaped laminates: Experimental and numerical study

The mechanical responses and failure evolution process of L-shaped composite laminates with effect of wrinkle defects were investigated using experimental and numerical methods. In experimental study, L-shaped laminates containing different magnitudes of wrinkle defects were prepared with the aid of ‘transverse-strip’ method. The loading capability and damage propagation of L-shaped samples containing wrinkle defects were investigated within bending test and compared with ones of the intact samples. In numerical study, a progressive damage failure model was created based on 3D Hashin failure criterion. Afterwards, the numerical model was applied to predict the evaluation of stresses distribution and failure mode during failure process. The mechanism of wrinkle impact on the failure behavior of L-shaped laminates was explored further. Test result shows that wrinkle defects significantly reduce the loading capacity of L-shaped laminates and the spatial extension characteristic of delamination damage evolution is changed from the layer-by-layer extension to the aggregation extension of wrinkle area. The numerical predictions consist with the experimental observations. It is revealed that concentrations of transverse stress and out-of-plane stress at wrinkle area are the dominant factors response for the premature failure. In addition, the stress concentrations in wrinkle area destroy the tendency of layer-by-layer damage, leading to the wrinkled samples to exhibit agglomerated extended failure characteristics. The above-mentioned researches can provide a strategy to assess the structural integrity of L-shaped laminates containing wrinkle defects and determine their design of damage tolerance.