Finite element modelling of fatigue crack growth of surface cracked plates: Part II: Crack shape change

Abstract

Investigations into the shape change of surface fatigue cracks are made by using the multiple degree of freedom model described in Part I. Three combinations of tension and bending loads are considered, i.e. DOB = 0 (pure tension), 0.5 and 1 (pure bending). Analyses of the shape of propagating crack fronts show that the semi-elliptical profile is approximately maintained during crack growth for all loading cases. Generally, the trend of aspect ratio changes predicted agrees with that from the Newman and Raju method for all three loading cases. However, for pure tension, as the crack closely approaches the plate back surface, a slight rise of aspect ratio was calculated, an effect which is absent in the predictions using the Newman and Raju method. The free boundary correction produces a slight effect on aspect ratio variations but seems to have extremely little influence on fatigue crack growth curves. The present predictions are in good agreement with limited experimental results on surface crack shape changes found in the literature.