CRACKING INSTABILITIES IN A LOW-CARBON STEEL SUSCEPTIBLE TO DYNAMIC STRAIN-AGING

Crack jumps occurring in concert with stable cracking in a low-carbon steel, used in nuclear power plants, are examined. These jumps occur i n steels susceptible to dynamic strain aging at liquid water reactor t emperatures. Through fractographic studies, a connection between the n ature of cracking and fracture morphology is attempted. Numerical simu lation of a crack growth experiment is carried out. The results of the study indicate that there may be certain conditions, such as crack-ti p constraint and triaxiality and the dominance of elastic stored energ y over plastic dissipation (in addition to the material's susceptibili ty to dynamic strain aging), which need to be met for crack jumps to o ccur. The numerical results also indicate that approximate methods, su ch as ASTM E1152 method, for estimating driving force for growing crac ks may not be viable for materials susceptible to dynamic strain aging . (C) 1998 Acta Metallurgica Inc.