Prediction models of creep crack initiation for different specimen geometry

Abstract

In this article, the prediction models of the creep crack initiation for the specimen geometry was quantified by six different types of cracked specimens [including C-ring in tension CS(T), compact tension C(T), single notch tension SEN(T), single notch bend SEN(B), middle tension M(T), and double edge notch bend tension DEN(T)]. Load-independence constraint parameter Q* was introduced to quantify the in-plane constraint. The specimen order of Q* and the creep damage accumulation rate of the different specimen geometries from high to low was C(T), CS(T), SEN(B), SEN(T), DEN(T), and M(T), which generally represented the distinctions of in-plane constraint level in these specimens. For a specific load level, C(T) and CS(T) specimens showed the highest crack damage accumulation rate or the shortest creep crack initiation time, whereas the lowest rates or the longest CCI time existed in M(T). Moreover, the relationship between the CCI times and specimen thickness and crack depths was obtained, and a series of empirical equations were fitted. Finally, the power law relation between the CCI times and constraint parameter Q* was extrapolated.