Extension of Puck failure criterion for mixed mode I/II fracture investigation of orthotropic materials with cracks along and perpendicular to the fiber direction, considering T-stress effects

The current study, which breaks new ground, investigates the behavior of cracked orthotropic composite materials under mixed-mode I/II in-plane loading, a combination of tension and shear within the purview of linear elastic fracture mechanics (LEFM). This paper examines the use of advanced failure criteria in analyzing the fracturing of cracked orthotropic materials. A single initial crack is considered in two orientations: parallel and perpendicular to the fibers. Puck criterion, recognized as a reliable method for investigating failure in laminated composite materials, is utilized for basic formulation. This study presents a generalized analytical formulation of the Puck criterion, referred to as the extended Puck (E-Puck) criterion. This formulation combines the singular stress field associated with a crack tip in orthotropic materials to investigate fractures in these materials. Moreover, considering the nonsingular stress components, the effect of the T-stress term in the mixed-mode criterion is examined. Also, an equivalent fracture toughness in mode I (\(K_{IC}^{eq}\)) has been defined as a new fracture property. To confirm the efficiency, the results obtained using the proposed criterion are presented as fracture limit curves compared to experimental data of Norway spruce and Scot pine wood species and other available mixed-mode criteria. Wood is a highly orthotropic material, meaning it has different strength characteristics depending on the direction of the fibers. The strength of wood along the fiber direction is approximately 12 times greater than its strength in the transverse direction. This significant difference in mechanical properties between the two main orientations can lead to crack propagation along the fibers. This phenomenon is considered when developing the E-puck criterion.