带或不带脱层的复合材料层板强度的预报

PROBABILISTIC PREDICTION OF LAMINATES WITH OR WITHOUT DELAMINATION

首先用实验直接测定或从文献中引用单向纤维增强层板的强度的Weibull分布参数α和β。用经典层板理论分析层板中的面内应力;邻层的裂纹引起的应力集中用剪滞法计算;层间应力用简化的平衡方程来确定,层板中单层的当地强度由于邻层的约束作用而提高,假定单层的承载能力直到其裂纹密度饱和时才耗尽;用增强软X光照相技术来监测裂纹密度的发展并测定相应的约束系数,建立最普遍的统计强度准则,结合作用应力的计算和统计强度预报,确定不同层板中各单层的破坏顺序和最终损伤状态。根据最终损伤状态来确定层板的统计强度,并用试验验证。

The laminate with different construction, i.e.with laminae laying up with different orientations, will have different failure sequence and different final damage state from which the strength can be predicted.The failure sequence of laminae in a laminate can be determined by a stress analysis integrated with an apropriate strength criterion.The stress analysis will be extremely complicated due to the randomness and rich variety of damage modes.In this paper, the free edge delamination will net be taken into consideration, since it will not give well-defined failure sequence. For the case of clear-cut failure sequence, the in-plane stresses were found with the classical laminate theory. Only one matrix crack was taken to calculate the stress concentration factor with the shear lag method. Interla-minar stresses were calculated with simplified equilibrium epuations.The constraint effect from adjacent laminae was characterized by m=σs/σm, where σs, is the stress level corresponding to the state of crack density saturation in the lamina in question, while σm is the average strength of separate single lamina.Special computational program was developed to determine the failure seguence and final damage state and the statistical strength of 1 aminates was predicted. The experimental results justified the prediction of laminates both with and without pre-made through-width delamination. However, the laminates with free edge delamination have strengths much lower than predicted. This is because the free edge delamination, enables the matrix cracks to join each other and finally to form a continuous macroscopic crack separating the specimen into two qarts, before any of the laminae fails completely.