Crack onset and propagation stability from a circular hole under biaxial loading

The brittle crack initiation from a circular hole in an infinite slab subjected to remote biaxial loading is investigated by means of the coupled finite fracture mechanics criterion, focussing on the behaviour of the average energy release rate. The work then analyzes the stability/instability of crack growth, following the terminology put forward by Wei ss graeber et al. (Eng Fract Mech 168:93-104, 2016). Depending on the loading biaxiality and on the ratio between the crack advance and the hole radius, the crack propagation could reveal to be either unstable (positive geometries), or stable (negative geometries). Furthermore, it is shown that stable paths could follow unstable paths and vice-versa, leading to locally positive/globally negative or locally negative/globally positive configurations, which are discussed in detail case by case.