2D and 3D Analyses of Cracks Via DIC

Abstract

Several digital image correlation and extraction techniques exist for measuring stress intensity factors and locating crack tips during propagation experiments. Some of these techniques are based upon the analysis of local displacements in the vicinity of the crack tip and their decomposition onto a set of mechanically relevant fields, e.g. Williams' series. Such methods are often employed using 2D displacement fields from digital image correlation. This paper proposes to use 3D displacement fields from a stereocorrelation algorithm in order to observe the change of mode I, II and III stress intensity factors during a uniaxial loading of a thin titanium CCT specimen. Under loading, and particularly at the end of crack propagation, this specimen proves to be a 3D case of study. This experiment aims at evaluating the capacities of such techniques when using 3D displacements fields. It is shown that 3D fields lead to very similar stress intensity factors as 2D fields. The crack tip determination method is also applicable and allows the propagation law to be determined when out-of-plane effects are accounted for.