Experimental study of effects of prior overload on fracture toughness of A533B steel

Abstract This paper presents the results of an extensive study carried out to examine the effects of prior overloading over the entire fracture transition regime for 50-mm thick A533B steel. The main variables examined are temperature, crack orientation with respect to the rolling direction, level of prior overload, the initial crack length, and the statistical variation of prior overload effects. It is found that the effect of prior overload on fracture toughness at lower temperatures is dependent on orientation, so that in the L-T orientation for short and medium cracks (0·2 and 0·5 a/W) there is a benefit throughout the transition regime of 50-mm thick A533B steel. In the T-L orientation no benefit is obtained for temperatures greater than the initiation of tearing temperatures. Above these temperatures the prior overload sequence lowers the fracture toughness. For L-T orientation long cracks ( a / W = 0·7) it is found for temperatures lower than −140°C that prior overload apparently increases the toughness. At higher temperatures there is a loss of toughness even though failure is cleavage dominated up to −80°C. On the lower shelf at −170°C in the L-T orientation the fracture toughness variability after preloading is found (based on a sample of 14 specimens) to exhibit a bimodal distribution. This distribution is similar to that exhibited by non-preloaded material.