Assessment of crack tip plastic zone size and shape and its influence on crack tip shielding

Abstract

<jats:title>Abstract</jats:title><jats:p>This paper presents a novel methodology for the experimental quantification of the crack tip plastic zone during fatigue crack growth. It is based on the application of yielding criteria to estimate the area and shape of the crack tip plastic zone using both the von Mises and Tresca yield criteria. The technique employs strain maps calculated from displacement fields obtained by digital image correlation. Stress maps were subsequently found by applying these yield criteria. Fatigue cracks were grown in compact tension specimens made from commercially pure titanium at <jats:italic>R</jats:italic> ratios of 0.1 and 0.6, and the ability was explored of three different analytical elastic crack tip displacement models [Westergaard, Williams and Christopher–James–Patterson (CJP)], to predict shape and size of the crack tip plastic zone. This analysis indicated that the CJP model provided the most accurate prediction of the experimentally obtained plastic zone size and shape.</jats:p>