Determination of the size of the fatigue prefracture zone by the method of phase-shifting interferometry

Abstract

We consider a new method for determining the size of the fatigue prefracture zone (a new structural-mechanical parameter d* of constructional materials) by the method of phase-shifting interferometry, based on the results of a comparative analysis of the surface profile of metallic specimens in the neighborhood of a constructional stress concentrator prior to and after a certain quantity of loading cycles. To obtain interferograms in laser light, we applied a Twyman–Green interferometer. Using these results, we determined the 3-D distribution of plastic strains near the concentrator vertex, which enabled us to establish that d* = 256–268 μm for low-carbon 08kp steel at a load ratio R = 0.1. The obtained value of this parameter is in good agreement with data obtained by other methods.