Influence of constraint on creep stress distribution in notched bars

Abstract

Stresses and strains occuring during creep were determined for circumferentially notched round bars having several specimen notch geometries representing different degrees of constraint. The specimen geometries and the material data used in the calculations were those pertaining to a parallel experimental investigation. It was found that, for the wide notch specimens, the notch to net-section radius ratio has a greater influence on the degree of constraint than the notch depth ratio. For the thin slit specimen, the small slit tip radius to net section radius ratio caused a big difference in stress distribution from that for the wide notch specimen of the same net-to-gross radius ratio. Global and local events were distinguished by the change of notch sharpness: for the relatively wide notch, creep was mainly a global process, whereas for the sharp slit, the creep process remained in a very local region near the slit tip. Various indicators for the degree of constraint are discussed, of which the triaxiality factor I1/σ seemed to be the most useful.