三维编织复合材料渐进损伤的非线性数值分析

基于考虑纤维束相互挤压的八边形纤维束截面单胞模型，引入周期性位移边界条件，采用 细观非线性有限元方法，建立了三维四向编织复合材料的渐进损伤拉伸强度模型. 该模型考 虑了增强体纤维束纵向非线性剪切应力-应变关系，采用Hashin型损伤失效准则定义了纤维 束的典型损伤类型，并根据纤维束和纯基体相应损伤类型所造成的材料性能退化，模拟了不 同编织角试件各类损伤产生、扩展及材料最终破坏的整个过程. 模型数值结果与实验数据吻 合较好，证明了该模型的合理有效性. 探讨了组分材料剪切非线性、损伤对材料宏观非线性 本构行为的影响，结果表明：随着编织角增大，纤维束剪切非线性效应和累积损伤对材料非 线性力学行为的影响明显增强.

NONLINEAR NUMERICAL ANALYSIS OF PROGRESSIVE DAMAGE OF 3D BRAIDED COMPOSITES

A tensile strength model to predict the damage initiation and propagation of 3D braided composites is proposed based on the representative volume element and using the nonlinear finite element method. The geometrical unit-cell model taking account of the mutual contact and jamming of yarns is applied in the FEM model coupled with the periodical displacement boundary conditions. Particularly, the nonlinear shear stress-strain behaviors of the yarns are considered in the model and Hashin-type failure criteria are adopted to identify the occurring of damage events of the yarns. Based on the degradation scheme of elastic mechanical properties, the simulation of the whole process of damage initiation, propagation and catastrophic failure of the structure is carried out in detail. To verify the numerical model, two typical specimens with different braiding angles are selected in the simulations. The calculated values by the model well agree with the measured values. Numerical results show the effectiveness of the model. The effects of the shear nonlinearity of the yarn and damage accumulation on the nonlinear mechanical behavior of 3D braided composites are discussed. It is concluded that the nonlinear mechanical behaviors of the composites are affected remarkably by the shear nonlinearity of yarns and accumulation of damages when the braiding angle of the composites is increased.