Beyond classical fracture mechanics: A micromechanics-informed non-local fracture onset criterion for mixed-mode loading of orthotropic materials

Non-local micromechanics-informed mixed-mode fracture onset criteria are proposed for isotropic and orthotropic materials. First, a general framework for a non-local mixed-mode fracture criterion is developed based on a non-local stress condition. Subsequently, a novel micromechanics-based damage parameter is introduced to capture micromechanical interactions ahead of the crack tip within a characteristic length of the fracture process zone (FPZ) for isotropic materials. This parameter is then extended to account for orthotropic materials. The fracture limit curve (FLC) of the proposed orthotropic criterion is compared to established classical fracture criteria and experimental data for Eastern red spruce and Scots pine, both considered as orthotropic materials. The impact of microcrack density on the proposed damage parameter and material fracture limit curve is studied, and a prediction band is presented that captures the interplay between FPZ influence and LEFM conservative criteria, offering a more accurate prediction. Furthermore, a valuable methodology for estimating critical material microcrack density based on experimental data and fracture limit curves is provided.