Notch and Temperature Effects on Crack Propagation in SS 304 Under LCF Conditions

Abstract

Crack growth behavior at room temperature and at 600°C of SS 304 plates with a central circular hole is studied using linear elastic and elastic-plastic fracture mechanics concepts. Due to large local plastic zone at the hole edge, short fatigue crack propagation is strongly affected by closure phenomena; and the extension rate of a short crack could not be adequately expressed in terms of stress intensity factor ΔK. However, the parameter ΔK would be appropriate for investigating the behavior of long cracks. Crack acceleration due to temperature increase is discussed and a strain-based normalization factor for ΔK is suggested for long cracks. The J-integral obtained from a finite element analysis is successful in establishing the propagation rate of both short and long cracks; simple power relations exist between da/dN and cyclic J-integral (ΔJf) at room temperature and at 600°C. With the modified J-integral, using the actual flow strain, the temperature effect could be incorporated in the correlation between da/dN and ΔJf.