Mixed mode fatigue crack growth criteria

The behaviour of fatigue crack propagation of rectangular aluminum alloy plates, each consisting of an inclined semi-elliptical crack, subjected to axial loading was investigated both experimentally and theoretically. The inclined angle of the crack with respect to the axis of loading varied between 0° and 90°. In the present investigation, the growth of the fatigue crack was monitored using the AC potential drop technique, and a series of modification factors, which allow accurate sizing of such defects, is recommended. The Von Mises yield criterion was applied to define the core region, instead of assuming a core region with a constant distance r from the crack tip. The two commonly employed fracture criteria, i.e. the maximum tensile stress and the minimum strain energy density criteria, were modified by adopting Von Mises elasto–plastic boundary. The results obtained using these improved criteria were compared with those obtained using the commonly employed mixed mode fracture criteria and the experimental results. The threshold condition for non-growth of the initial crack was established based on the experimental data.