Applying Fracture Mechanics to Cracked Components Subjected to Unloading

Abstract

The J-integral is widely used as a fracture parameter for elastic-plastic materials. The J-integral describes the intensity of the stress field close to the crack tip in a power-law hardening material under a set of well-known restrictions. This study investigates what happens when one of these restrictions is broken, namely the requirement for no unloading to occur. In this work, a centre-cracked plate is subjected to a single cycle of load in which unloading occurs. A remote tensile stress is applied, then released, then applied again up to and beyond its initial magnitude. The J-integral at each step of the analysis is calculated using finite element analysis. Its validity as a fracture parameter at each step is discussed with the aid of results from a strip yield analysis of the same problem. The relevance of the results in the context of structural integrity assessment is discussed.

In-situ measurements of stress during thermal shock in clad pressure vessel steel using synchrotron X-ray diffraction

“…The steady state measurements carried out before thermal shock on the crack-free specimen at room temperature should be comparable to residual stress measurements made on the original clad plate in previous work [5]. Figure 5b compares the stresses measured in a crack-free specimen by X-ray diffraction (XRD) in this work with those measured in the original clad plate by deep hole drilling (DHD) in previous work [34]. Briefly, DHD operates on a similar bases as centre hole drilling in which by removing the material, the residual stress is relived in stages and by measuring the relaxation strain during the process, the residual stress is backcalculated.…”