An equivalent thickness conception for evaluation of corner and surface fatigue crack closure

The out-of-plane constraint-based equivalent thickness conception developed previously for corner cracks is extended here to surface-cracked plates based on systematical finite element simulations for the purpose to evaluate the plasticity-induced fatigue closure of corner and surface cracks. A semi-analytical solution for equivalent thickness of semi-elliptic surface cracks is obtained by numerical analyses of three-dimensional stress fields near the crack borders and comparing with that of ideally straight-through cracks in plates of finite thickness. The fatigue opening stresses of corner and surface cracks are evaluated based the recognized equations of straight-through cracks using the equivalent thickness conception. Comparison against available finite element and experimental results shows that the developed method can provide satisfied prediction of fatigue closure for both corner and surface cracks.

► Explicit formula for the equivalent thickness of semi-elliptic surface cracks.
► Opening stress along the border of surface fatigue crack is evaluated explicitly.
► Validation against 3D finite element results shows excellent agreement.