Creep Rupture

Abstract

Experimental studies involving creep rupture indicate the existence of two different rupture mechanisms. In ductile or transcrystalline rupture one observes a reduction of cross-section as a result of large creep strains caused by slip inside grains. Rupture takes place by propagation of cracks from the surface to the specimen interior along slip planes. Ductile rupture is characteristic of low temperatures and significant strain rates at high stress levels and large strains. Brittle or intercrystalline rupture is the result of material weakness caused by microcracks on grain boundaries because of slips between grains. Rupture takes place if the effective surface of the cross-section is reduced to the critical value. Brittle rupture is characteristic of high temperatures and small strain rates, for low stress level and small strains. The influence of temperature and strain rate on the type of rupture is illustrated in Fig. 12.1. The continuous line refers to large, and the dotted line to small strain rates. The characteristic creep rupture curves, showing the transition from ductile to brittle rupture, are presented in Fig. 12.1b (Grant and Bucklin 1965).