Quantification of the effect of specimen geometry on the fatigue crack growth response by two-parameter fracture mechanics

Discrepancies in fatigue crack growth rate and threshold values observed in different specimen geometries are analyzed and discussed. To explain the discrepancies, a phenomenological approach is suggested going out from the assumption of linear elastic fracture mechanics. To this aim, two-parameter constraint-based fracture mechanics is used and the different levels of constraint in the vicinity of the fatigue crack tip are characterized by means of the T-stress. The results of the theoretical analyses correspond to the presented experimental data. It is concluded that under small scale yielding conditions (corresponding to high cycle loading) low level of the constraint (corresponding to negative values of the T-stress) substantially increases the rate of the fatigue crack propagation. sults presented make it possible to relate the experimentally measured data obtained on the specimens with different geometries and thereby contribute to more reliable estimates of the residual fatigue life of structures.