STRESS INTENSITIES IN ELASTIC-PLASTIC PLANE-STRESS FIELDS BY CAUSTICS

The experimental method of reflected caustics was extended in this paper for the study of the strength of the plastic singularity and the respective plastic stress intensity factor at the tip of a mode-I crack in an elastic-strain hardening material. The elastic-plastic field around the crack tip was defined by means of the singular plastic solutions of Hutchinson, Rice and Rosengren (HRR-asymptotic field) which gives satisfactory results for small scale yielding types of deformation. The initial curve, generating the caustic by reflection from the front face of the deformed specimen lying well within the plastic zone, was accurately determined by considering the contribution of the elastic and plastic components of stresses and strains within the plastic zone. Results with experiments executed on steel specimens single-edge notched with various values of the hardening exponent n coincided with the form and shape of the theoretically derived caustics thus confirming the validity of the developed theory. The values of the plastic stress intensity factor thus derived corroborated the already existing results from previous experiments.