Session: 21-01: Poster Session

Paper Number: 98131

98131 - In Situ Nonlinear Longitudinal Wave Technique to Correlate β to the Tensile Plastic Deformation of Stainless Steel 316l 

Nonlinear Ultrasound (NLU) allows us to detect damage accumulation in the very early stage because of its sensitivity to dislocation parameters, dislocation substructures, microstructural features, and internal stress. Although internal stress affects the acoustic nonlinearity parameter (β), which quantifies the nonlinearity in materials, its effect has not been fully studied due to experimental challenges and the interdependence of dislocation parameters beyond the elastic regime. In situ β measurements, made while a load is applied, have potential to deconvolve the stress-dependent and the stress-independent β terms. This research presents a NLU measurement method to track the effect of applied load on β using longitudinal waves, by measuring β in situ as the tensile load increases. Multiple paths of incremental tensile load were applied to a stainless steel 316L sample, up to a total strain of 6.0%, under stress controlled loading. During each path, ultrasonic in situ measurements were made at several intervals as the stress increased up to and above the yield stress. These longitudinal wave experimental results characterize the dependence of β on applied stress in both the elastic and plastic regimes in stainless steel 316L. The in situ measurements allow us to isolate the effect of internal stress, which has not been possible during ex situ measurements. Because of this, the nonlinear longitudinal wave measurement method developed in this research may offer a better understanding of how β evolves under tensile loading in the elastic and plastic regimes.

Presenting Author: Hyelim Do University of Illinois, Urbana-Champaign