Surface Buckling and Postbuckling of Composite Laminates with Delaminations

随着各种机械和车辆对高性能和高效率的要求不断提高，先进复合材料层合板因其高刚度、高强度和轻质等特点而得到了一系列的发展和应用。因此，准确评价复合材料层合板在各种载荷条件下的力学行为和强度特性变得至关重要。本文基于修正的拉格朗日理论，编制了有限变形有限元程序，对含分层损伤层合板的压缩响应进行了数值模拟和实验研究。重点研究了局部非对称性对含脱层层板屈曲和后屈曲行为的影响，得到以下结论：1.含脱层层板的局部非对称性会显著降低其整体承载能力。例如，在这种情况下，临界平均压应力为： 关于我们 由三维和二维分析得到的能量释放率的简单总和之间的差异似乎很小。但是，由于脱层的局部不对称性，能量释放率沿宽度方向沿着是不均匀的，这意味着脱层可能不会沿该方向沿着均匀扩展。研究发现，短脱层层的临界载荷，（脱层长度/层长）<0.2，与未脱层的层合板的脱层长度基本相同。4.在实验研究中观察到了由于局部不对称性引起的非均匀脱层扩展和扭曲变形。这从定性上验证了数值模拟的预测，但要准确地评估脱层层板的损伤和强度，还需要进一步的数值和实验研究。少

Increasing demands for high performance and efficiency of various machines and vehicles lead to a series of developments and applications of advanced composite laminates due to their high stiffness, high strength and light weight. Conseuquently, the accurate evaluation of the mechanical behaviors and strength characteristics of composite laminates under various loading conditions becomes crucial. In this research, a finite deformation FEM program is developed based on the updated Lagrangian theory and numerical simulations and associated experiments are conducted to investigate the compressive response of delaminated laminated. Special attention is put on the effects of local asymmetry on the buckling and postbuckling behavior of delaminated laminates and following conclusions are obtained.1.The local asymmetry of delaminated laminates may significantly reduce the global load carrying capacity of the laminate. For instance, the critical averaged compressive stress in the case of this r … More esearch is found to be reduced by nearly 12%.2.The difference between the simple sums of energy release rates obtained from the three and two dimensional analyzes seems to be small. However, the distributions of energy release rates are non-homogeneous along the width direction due to the local asymmetry of the delaminated laminate, which implies that the delamination may not grow homogeneously along this direction.3.The global bucking of the laminate is dominant for short delaminations. in this research, it is found that the critical load of the laminate with short delamination, (delamination length/laminate langth)<0.2, is almost the same with that of a laminate without delamination.4.Nonhomogeneous delamination propagation and twist deformation due to the local asymmetry have been observed in the experimental research, which verifies the prediction of the numerical simulation qualitatively.Further nemerical and experimental researches are still needed to accurately evaluate the damage and strength of delaminated laminates. Less