Using the Poisson’s Ratio and Acoustic Anisotropy Parameter to Assess Damage and Accumulated Plastic Strain during Fatigue Failure of Austenitic Steels

The effect of fatigue failure on the elastic characteristics of metastable austenitic steel AISI 321, Poisson’s ratio and acoustic anisotropy parameter, was studied. The elastic characteristics were calculated based on the data of ultrasonic measurements of the propagation time of longitudinal and shear elastic waves. The volume fraction of the strain-induced martensite was determined by the eddy current method. Theoretical studies have shown that the main factors influencing Poisson’s ratio are the accumulation of microdamage and changes in the phase composition. The change in the acoustic anisotropy parameter is associated with the effect of cyclic deformation on the crystallographic texture of the material matrix and the formation of oriented crystals of strain-induced martensite. Based on the analysis of experimental results, expressions have been obtained for calculating damage and relative accumulated plastic strain according to acoustic measurements, which are widely used in engineering practice to determine the fatigue life of structural materials.