Nonlinear ultrasound (NLU) is used to quantify differences in microstructure due to the formation of dislocations and chemical segregation in embrittled austenitic steels. Recent studies have demonstrated that NLU is sensitive to nano- and microscale changes in microstructure due to a variety of damage mechanisms such as thermal, sensitization and fatigue damage.&nbsp;The physical effect being monitored by NLU is the generation of higher harmonic frequencies in an initially monochromatic ultrasonic wave.&nbsp; The degree of nonlinearity is quantified with the acoustic nonlinearity parameter, β which is an absolute, measurable material constant.&nbsp;One critical issue with using a single β parameter to track complicated microstructure changes is the lack of selectivity to specific features. A multi-physics approach has the potential to overcome this lack of selectivity. We are comparing these NLU results with thermoelastic NNDE measurements.&nbsp;&nbsp;This research examines&nbsp;a side-by-side comparison of the results of these two measurements techniques that use different physics (acoustic and electrical), on exactly the same set of cold rolled specimens; this multi-physics approach is the best way to separate the influence of competing microstructural parameters (such as dislocations and precipitates) by using truly unrelated, independent measurements.&nbsp;This research&nbsp;uses an NLU measurement setup at Georgia Tech that combines contact and non-contact sensors for generation and detection of β. This research uses both Rayleigh surface waves and through thickness longitudinal waves to measure the differences in the β parameter for each of the five different cold work states (0%, 20%, 40%, 60% and 80%) in all four material types (SS-304, SS-316, SS-A286 and SS-348).&nbsp;These NLU results show similar trends for both austenitic stainless steels (304 and 347) due to&nbsp; strong martensitic phase formation.This is different from the behavior of the 316 and&nbsp; A286 which may have little or no martensitic phase formation.

Characterization of Fracture Properties of Embrittled Austenitic Stainless Steels Using Nonlinear Ultrasound

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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