The stiffness degradation of the damage model of composite laminates is shown by defining its damage variables. We give two uniform expressions that are damage independent and damage dependent and use the strain equivalent hypothesis to deduce the stiffness matrix of the three-dimensional damage so as to reduce the assumptions on damage degradation. By simulating the damage progress of a composite laminate under impact load-ing, we analyze the effects of different definitions of the damage variables on impact damage. The analysis results show that different definitions of damage variable have effects on the delamination and matrix damage but have a small effect on impact force. Therefore, we suggest that attention should be paid to the definition of the damage vari-ables.%复合材料层合板损伤模型中的刚度退化需要通过损伤变量来实现。针对通常采用的2种损伤变量定义，给出了统一表达式。此外，损伤刚度矩阵是损伤变量的函数，基于应变等效假设推导了三维损伤刚度矩阵，从而避免了对损伤刚度矩阵的人为假定。最后，通过复合材料层合板在冲击载荷作用下的数值模拟，讨论了损伤变量的2种定义对数值结果的影响，表明损伤变量的不同定义对分层和基体损伤分布存在一定的影响，对冲击载荷的影响不大。建议在复合材料损伤模拟中，应予关注损伤变量。
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