Mixed-mode fracture assessment of wooden structures with cracks initiated along and across the fibers considering non-singular T-stress term

A new criterion for investigating the failure of wooden structures using maximum shear stress (MSS) under mixed mode I/II was presented for two conditions in which the crack is oriented along and across the fibers. The impact of non-singular stress terms in Williams series expansion (T-stress) is also included. This criterion is presented by considering the reinforcing effects of fibers in which the orthotropic material is assumed as an isotropic material that is reinforced with the fibers. The proposed failure criterion includes a damage coefficient that establishes an effective relationship between the fracture toughness of isotropic and orthotropic materials. The assumption is that at the onset of fracture, from the microscopic point of view, the crack makes a small kink in a direction where the shear stress has the critical value at a critical distance based on the MSS criterion. Then, the crack will propagate along the fibers after colliding with them. The results are verified by using available experimental data of different wood species. It was shown that with the proposed criteria both the crack growth path and the moment of crack growth are well predicted.