记及压应力的内聚力单元及其厚度对复合材料分层损伤预测的影响

THE INFLUENCES OF COHESIVE ELEMENT COMPRESSIVE STRESS AND ITS THICKNESS ON DELAMINATION PREDICTION OF COMPOSITE

内聚力单元可以同时预测分层的起始和扩展,但单元尺寸对计算结果影响较大,而且无法模拟压应力导致的界面失效。首先,建立不同内聚力单元计算厚度的双悬臂梁模型、端边加载模型和冲击动力学模型,模拟分层损伤演化过程,研究内聚力单元厚度对载荷-位移曲线和界面损伤面积的影响;然后,通过子程序自定义内聚力单元的本构关系,考虑压缩应力引起的复合材料层间界面失效;最后,分析考虑压应力引起的界面层失效对复合材料冲击响应的影响。计算结果表明:内聚力单元厚度对界面层的损伤面积影响明显;相同的载荷条件下,内聚力单元厚度越大,界面损伤面积越小;考虑压缩应力引起的界面层失效,界面损伤面积较大且界面失效包含压缩和剪切两种失效模式。

To model the delamination initiation and propagation of the composite laminates,the cohesive element is often used. But,unfortunately,the numerical result may depend on element size,and it can't model the interface failure caused by large compressive stress. Firstly,three models with different thickness of the cohesive element, i.e. the double cantilever beam model,the end-loaded split model and the dynamic impact model,are established to simulate the delamination evolution of the composite. The influences of the cohesive element thickness on the load-displacement curve and interface damage area are studied. Then,the constitutive relation of cohesive element is defined by the subroutine to consider the interface failure caused by compressive stress,and the impact of interface failure caused by compressive stress during impact response of composites is analyzed. The results show that the thickness of cohesive element has a significant influence on the interface damage area. Under conditions of the same loading,the damage area of the interface becomes smaller as the cohesive element thickness becomes larger. With the consideration of the interface layer failure caused by compressive stress,the interface damage area would be larger and the interface modes contains compression failure and shear failure.