Relation between thermal shock crack and stress intensity factor, and behavior of stretched zone width

Purposes in this study are to estimate validity of linear fracture mechanics for thermal shock cracking and to clarify the behavior of stretched zone width in thermal shock. Thermal shock tests were carried out with carbon steel (S53C). Thermal shock was given by jet water on the fatigue precracked surface. The following results were obtained; 1) At a given temperature, thermal shock crack length can be correlated with the maximum value of stress intensity factor which was caused by unsteady thermal stress(maximum stress intensity factor). 2) Stretched zone width is proportional to the temperature of crack tip at the time when stress intensity factor becomes maximum. Stretched zone width decreases, as the increase rate of stress intensity factor rises. The above was also confirmed by results on a different size test specimen. (author)