Revisiting facet nucleation under mixed mode I + III loading with T-stress and mode-dependent fracture properties

We study the problem of crack front segmentation into facets under mixed mode I + III loading. Discrete facet network nucleation is determined based on the match asymptotic expansion approach of the coupled criterion considering both the influence of T-stress (parallel to the initial crack front) and mode-dependent fracture properties. We show that considering exclusively either T-stress or mode dependent properties, facet nucleation may be more favorable than straight crack propagation but in conditions that are incompatible with experimental observations. It is only by coupling mode-dependent fracture properties with T-stress that we are able to determine configurations compatible with experimental observations for which facet nucleation is more likely to occur than straight crack propagation. These configurations depend on the T-stress magnitude and critical shear energy release rate. We thus highlight that crack front segmentation into facets is material and loading dependent phenomenon that is not related to a sole mode mixity threshold but also to T-stress magnitude and shear critical energy release rate.