Strains and stress-concentration factors in plates under out-of-phase biaxial cyclic loads

Abstract

An elastic theoretical analysis for the strains in an infinite plate and the stress-concentration factors for small elliptical holes in an infinite plate, under sinusoidally varying alternating out-of-phase biaxial loads, is presented. The experiments were performed to substantiate a theoretical analysis for circular and elliptical holes by means of a specially designed and built ‘biaxial cyclic stress machine’. For biaxial alternating stresses, the stress-concentration factor is defined as the ratio of the amplitude of the maximum alternating stress around the geometrical discontinuity to the larger of the amplitudes of the two principal alternating stresses which would occur at the same point if the geometrical discontinuity were not present. Both values are considered over a stress cycle. The results of the theoretical analysis are presented in the form of curves which show the effect of phase differences between stresses and strains upon stress ratio and cyclic stress-concentration factors. The test results of the experiments are also summarized in the form of the curves. Since the experiments were performed on a finite plate compared to an infinite plate considered for theoretical analysis, the experimental curves do not coincide with the theoretical curves. But in general the experimental curves follow the same trends as the theoretical curves. Fatigue implications of out-of-phase biaxial cyclic loads are discussed.