Strength size effect and post-peak softening in textile composites analyzed by cohesive zone and crack band models

In contrast to metals, the failure behavior of textile composites is quasibrittle, which entails salient structural behaviors such as the strength size effect and post peak softening. This paper presents a detailed account of numerical analysis of these aspects in woven textile composites undergoing translaminar tensile fracturing. Two of the most established fracture modeling techniques viz. the cohesive zone model (CZM) and the crack band model (CBM) are evaluated in this regard. The predictions from both techniques are compared to each other as well as to available test data on various woven composites. With a linear softening law CZM and CBM are seen to yield virtually identical results. A linear softening law is seen to be adequate to predict the strength size effect but it is not always able to accurately capture the full post-peak softening. Adapting a bilinear softening law, formulated via the R-curve approach, is seen to improve the post-peak softening predictions. Subsequently, it is shown that various numerical and physical parameters, such as the finite element type, manner of time integration (implicit vs explicit), mesh size, fracture energy, the crack band width, mass scaling, and stress state assumption could have a significant effect on the accuracy of the results, if set sub-optimally. Accordingly, recommendations for optimal settings are made.