Behavior of Composite Laminates with Defects under Thermal Load

纤维增强复合材料层合板容易发生分层，因为增强纤维未沿层间方向放置。在设计成抵抗热负荷的层压结构的情况下，分层的存在可能阻碍厚度方向上的导热性，这可能导致局部热集中。因此，可能发生不可预测的热变形或相关的表观强度降低。本文针对含脱层层板在热载荷作用下的行为进行了研究，首先在理论推导的基础上，假设材料各向同性，进行了后屈曲分析。利用初始压缩屈曲变形分析了热机械复合载荷作用下层合板的后屈曲行为。基于层合板各向异性的配方也进行了更精确的分析。计算了相关的能量释放率，以评估分层扩展的可能性。由热载荷和机械载荷的组合引起的变形通常大于没有热载荷的变形。计算的能量释放率在热载荷作用下呈现出复杂的变化趋势。还进行了实验。然而，由于热源中的疑似缺陷，结果并不一致。

Fiber reinforced composite laminates are susceptible to delaminations as the reinforcing fibers are not placed in the interlaminar directions. In case of laminate structures designed to resist the thermal loads, the existence of delaminations can obstruct the thermal conductivity in the thickness direction, which may result in the local thermal concentration. As a consequence, unpredicted thermal deformation or associated decrease in apparent strength may take place. Present research is aimed to investigate the behavior of laminates with delaminations subjected to the thermal loads.Post-bucking analyzes are first performed assuming the isotropy of the material, based on the theoretical derivation. The initial compression bucking deformation is used to analyze the post-bucking behavior of the laminate under combined thermal and mechanical loads. More precise analysis based on the formulation with laminate anisotropy is also conducted. Associated energy release rates are calculated to evaluate the possibility of delamination propagation. The deformations induced by the combined thermal and mechanical loads are, in general, larger than those without thermal loads. The calculated energy release rates show the complicated tendency under the presence of the thermal loads. Experiments are also conducted. However the results were not consistent due to the suspected defects in the heat source.