Surface Buckling and Postbuckling of Composite Laminates with Delaminations

对各种机器和车辆的高性能和高效率的需求日益增长，导致了一系列先进复合材料层压板的开发和应用，因为它们具有高刚度、高强度和轻重量。因此，准确评估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。本文基于最新的拉格朗日理论，编制了有限变形有限元程序，对分层叠层的压缩响应进行了数值模拟和相关实验研究。重点研究了局部不对称对分层层合板屈曲和后屈曲行为的影响，得到了以下结论：分层层板的局部不对称性会显著降低层板的整体承载能力。例如，在这种情况下的临界平均压应力…更多的研究发现，降低了近12%。从三维和二维分析中得到的能量释放率的简单总和之间的差异似乎很小。然而，由于脱层层板的局部不对称，能量释放率沿宽度方向的分布是不均匀的，这意味着脱层可能沿着该方向不均匀生长。层压板的整体屈曲对短层脱层起主导作用。本研究发现，短分层的层合板的临界载荷（分层长度/层合板长度）<0.2，与未分层的层合板的临界载荷基本相同。实验研究中观察到由于局部不对称导致的非均匀分层扩展和扭转变形，定性地验证了数值模拟的预测。为了准确评估分层层合板的损伤和强度，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