On the evaluation of stress intensity factor from displacement field affected by 3D corner singularity

Three-dimensional effects near crack front were subject of many analytical, numerical and experimental studies over the past 50 years. These studies were facilitated by obvious discrepancies between experimental evidences and predictions of two-dimensional theories of elasticity, which singular solutions currently form through a framework of contemporary Fracture Mechanics. In particular, the classical plane solutions of the theory of elasticity fail to describe the displacement, stress and strain fields in the close vicinity of the crack tip. Subsequently, the existing experimental techniques for determining stress intensity factor fully rely on the measurements taken outside the region affected by the three-dimensional effects, and, in particular, by 3D corner (vertex) singularity. In the present paper, we attempt for the first time to develop and validate an experimental procedure for accurate evaluation of mode I stress intensity factor from surface measurements of the transverse (out-of-plane) displacements over the area encapsulating the crack tip with a radius less than five per cent of the plate thickness. The proposed procedure can have several advantages in comparison with the existing experimental techniques. These are discussed in the paper