Acceleration of Crack Growth Under Intermittent Overloading at Elevated Temperature

Abstract

Ahtract-Acceleration of crack growth by intermittent overloading was investigated at 650°C by using specimens of different thickness made of Type 304 stainless steel. When the hold time of overload was very short (-20 s), the crack growth rate was significantly accelerated (20-50 times) and the fracture surface morphology showed extremely ductile transgranular fracture by glide plane decohesion or microvoid coalescence, suggesting significant recovery of the material. In the thinner plate specimens, the crack growth rate under intermittent overloading was correlated well with the modified J-integral, i.e. f (C*) and agreed with the growth rate of static creep cracks in a f versus da/dt diagram. In the thicker plate specimens, however, this is not the case and the growth rate was about 20% of that in the thinner plate specimens in the f diagram. Transgranular fatigue type crack growth appeared in the low growth rate region.