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 .