MIXED-MODE FATIGUE-CRACK PROPAGATION OF PENNY-SHAPED CRACKS

A three-dimensional penny-shaped crack under combined tensile and shea r loadings is analyzed. The assumptions of Dugdale are applied to esti mate the effects of plasticity around the edge of the crack. The solut ion for mode I tensile loading is well established within the context of the Dugdale assumptions, and for the case of shear loading, approxi mate results are derived for the yield ring width and crack sliding di splacements, with the assumptions similar in form to the mode I case. By superposing the results of the tensile and shear loading, the solut ions for a penny-shaped Dugdale crack under mixed mode static loading and modified for the analysis of fatigue crack growth. Based on the mi xed mode Dugdale model and the accumulated plastic displacement criter ion for crack growth, a fatigue crack growth equation with four-power effective stress intensity factor dependence is developed for a penny- shaped crack under conditions of mixed mode loading and small-scale yi elding.