Failure zone homogenization at mode II and mixed mode loading including gradient-extended damage and interface debonding at finite strains

Homogenization based on Hills approach is widely used in many scale breaching applications such as the analysis of repeating unit cells (RUCs). However, it was shown that Hills approach is not applicable at the presence of localization phenomena, since in the standard averaging sense the representativeness of the considered micro-scale volume is lost. The failure zone averaging method was shown to overcome these drawbacks and yield converging results even in the softening region. In this paper the failure zone homogenization approach is applied to shear and mixed mode loading of long fiber reinforced plastics. For an accurate description of material failure within the epoxy matrix, a scalar damage model at large strains with gradient enhancement - for mesh size independent results - is used. After a mesh and size convergence study, a statistical analysis of different RUC sizes with random micro structures is performed. Further, the influence of crack closure effects as well as different loading conditions such as simple shear and mixed mode loading are analyzed. It is shown that the implementation of crack closure and application of simple shear lead to different stress-stretch responses. Additionally, crack closure can lead to a different orientation of the failure zone. Finally, an analysis of RUCs with cohesive zone elements for fiber-matrix debonding are shown. Here, lower stresses but higher strains until final failure are observed as well as generally higher dissipation compared to RUCs with perfect interfaces.

Automated summary

In this paper, the failure zone homogenization approach is applied to shear and mixed mode loading of long fiber reinforced plastics. A scalar damage model with gradient enhancement is used to accurately describe material failure within the epoxy matrix. Statistical analysis of different RUC sizes with random micro structures is performed, and the influence of crack closure effects and different loading conditions is analyzed.