INVESTIGATION OF CRACK PROPAGATION PROCESS BY MEASUREMENTS OF LOCAL DEFORMATION RESPONSE: Ⅱ. RESIDUAL STRESS FIELD

摘要

The principal questions in relation to determining the fracture mechanics parameters for cracks in a residual stress field are analyzed using a modified version of the crack compliance method. It is shown that this approach can be effectively used for non-symmetrical cracks, which appear near a welded seam. Detailed metrological verification of the process used to generate initial experimental data is presented. The procedure is based on comparing corresponding values measured by reflection hologram interferometry and electronic speckle interferometry. Special attention is paid to the measurements of the in-plane displacement components near the area of local material removal. Both residual stress determination and determination of the stress intensity factor (SIF) and T-stress values for a small crack length increment are considered for the same residual stress field. For this purpose, a scheme for a combined interferometer is developed and realized. This optical system is capable of simultaneous measurement of the local deformation response by two different interference techniques on opposite faces of a thin plate. The practical implementation of the developed technique is illustrated by constructing dependencies of the SIF and T-stress values from a crack length, which is located in the vicinity of the joint made by electronic beam welding.