Mixed-mode fracture in a quasi-brittle material: R-curve and fracture criterion – Application to wood

Mixed-Mode Bending tests are performed on spruce specimens for several mixed mode ratios and are completed by pure mode I (DCB) and pure mode II (ENF) fracture tests. For each test, the mixed mode resistance to crack growth and those relative to its mode I and mode II components are estimated. The separation of the fracture modes is estimated from an analytical formulation and verified from the invariant MθMθ-integral method. A mixed mode fracture criterion applicable to the overall R-curve (i.e., rising part and plateau regime) is then proposed and allows describing the mixed mode resistance with a reasonable accuracy.