Surface Buckling and Postbuckling of Composite Laminates with Delaminations

各种机械和车辆对高性能和高效率的需求日益增长，导致了高刚度、高强度和轻质的先进复合材料层合板的一系列开发和应用。因此，准确评价复合材料层合板在不同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，并对分层层合板的压缩响应进行了数值模拟和实验研究。重点研究了局部不对称对层合板屈曲和后屈曲行为的影响，得到了以下结论：1.局部不对称会显著降低层合板的整体承载能力。例如，在这个r…的情况下，临界平均压应力更多的研究发现减少了近12%。2.从三维和二维分析得到的能量释放率的简单和似乎差别很小。然而，由于分层层合板的局部不对称性，能量释放率沿宽度方向的分布是不均匀的，这意味着分层可能不会沿该方向均匀地增长。3.对于短分层，层合板的整体屈曲占主导地位。研究发现，短脱层层合板的临界载荷(脱层长度/层合板长度)和lt；0.2与非脱层层合板的临界载荷基本相同。4.实验研究中观察到了局部不对称引起的非均匀脱层扩展和扭转变形，定性地验证了数值模拟的预测。较少

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