Buckling and Vibration of Composite Laminate with Multiple Delaminations

本文从理论和实验两方面研究了含多个脱层复合材料层合板在压缩载荷作用下的屈曲和振动问题。首先，对含单个脱层复合材料层合板的屈曲行为进行了理论和实验研究。研究了分层长度和分层深度对屈曲载荷的影响，发现分层后层合板所承受的载荷仍在增加。当脱层区域较薄部分的载荷保持不变时，较厚部分的载荷在屈曲后增加。基于脱层尖端的势能释放率，研究了脱层屈曲变形导致脱层扩展的可能性。其次，对含多个脱层的复合材料层合板的屈曲行为进行了理论和实验研究。屈曲载荷被发现是由多个脱层降低。与单层脱层的情况类似，即使在分叉之后，层合板所承受的载荷也会增加。由于多个分层尖端处的势能释放率较高，分层易于扩展。通过有限元分析和实验验证了所得到的屈曲解析解的正确性。最后，研究了含多个脱层复合材料层合板的振动问题。通过对无面内载荷的层合板的研究，阐明了脱层长度和深度对固有频率的影响。分析了层合板在面内载荷作用下的固有频率，结果表明，由于面内压缩，层合板的固有频率急剧下降。对含多处脱层复合材料层合板的振动分析结果有助于复合材料层合板脱层缺陷检测方法的发展。

Buckling and vibration of composite laminates with multiple delaminations subjected to compressive loading were studied theoretically and experimentally.First, the theoretical and experimental investigations of the buckling behavior of composite laminates with single delamination were performed. The effects of the delamination length and depth on the buckling load were clarified, It was found that the load carried by the laminate increases even after the bifurcation. While the load in the thinner part of the delaminated region remains constant, the load in the thicker part increases after the buckling. The possibility of the growth of delamination due to the buckling deformations was investigated based on the potential energy release rate at the delamination tips.Next, the theoretical and experimental studies of the buckling behavior of composite laminates with multiple delaminations were conducted. The buckling load was found to be lowered by the multiple delaminations. Like for the case of single delamination, the load carried by the laminate increases even after the bifurcation. The delamination growth is prone to occur due to the higher potential energy release rate at the multiple delamination tips. The analytical solutions obtained for the buckling behavior were verified by the finite element solutions and the experimental observations.Finally, the vibration of the composite laminates with multiple delaminations was studied. By investigating the laminate without inplane loading, the effects of the delamination length and depth on the natural frequencies were clarified. And the analysis of the laminate subjected to inplane loading showed that the natural frequency decreases drastically due to the inplane compression. The results of the vibration analysis of laminates with multiple delaminations contribute to the development of the method to detect the delaminations in composite laminates.