ON THE EFFECTS OF LOADING CONDITIONS AND GEOMETRY ON TIME-DEPENDENT SINGULAR CRACK-TIP FIELDS

The amplitudes C(t) of non-steady singular crack tip fields in power l aw creeping solids are investigated under pure mode I loading and comb ined mode I and II loading conditions. Approximations to both transien t and steady state values of the C(t)-integral for three different spe cimen geometries and for an intersection geometry representative of a typical power plant component configuration are compared with results obtained from detailed finite element analyses. The effect of crack de pth, geometry, creep exponent, and primary (mechanical) loading on the accuracy of C(t) estimates is determined. Finite element solutions fo r the intersection geometry are used to study the extent of mode mixit y under creep conditions in the resulting combined mode I and II crack tip fields, These solutions showed that, within the crack tip region where creep strains dominate, the opening stresses appear more singula r than the Hutchinson-Rice-Rosengren (HRR)-type fields, r(-1/(n+1)), w hile the in-plane shear stress component and the equivalent stress are slightly less singular. The solutions also revealed that mode I domin ance increases primarily during a very short period immediately after the load is applied, while small scale creep conditions prevail, and d oes not significantly change thereafter. HRR-type plane strain approxi mations based on known solutions for mixed mode elastic-plastic cracks under a moderate degree of mode mixity accurately predict axisymmetri c finite element solutions.