Residual Stress Measurements in Front of a Crack Tip with High Spatial Resolution by Using Barkhausen Microscopy

Abstract

Upon loading a cracked specimen or a component, a plastic zone emerges in front of the crack tip. If an unloading takes place before the crack growth, residual stresses of first and higher order build up which influence the subsequent crack growth upon reloading. Of practical importance is the so-called WP (warm-prestress) effect which includes the possibility of increasing the brittle-fracture resistance of a pressure vessel by pre-straining. The detection of the local residual stress state in the plastically deformed zone at the crack tip by using high-resolution methods is thus an important prerequisite for the understanding of the fracture processes with broader aim of improving the damage tolerance of structural materials. Whereas there have been several reports on the application of X-ray measurement techniques,1–4 up to now only limited experience is available concerning the using of micromagnetic effects for the determination of local residual stress states in crack tip region. It is the aim of this paper to verify the methodical basis for the determination of residual stress states in crack tip region.