NONLINEAR ACOUSTIC TECHNIQUE FOR MONITORING POROSITY IN ADDITIVELY MANUFACTURED PARTS

Ultrasonic wave based techniques are widely used for damage detection, and for quantitative and qualitative characterization of materials. In this study, ultrasonic waves are used for probing the response of additively manufactured 316L stainless steel samples as their porosity changes. The additively manufactured stainless steel specimens were fabricated using a laser powder bed fusion (LPBF) metal 3D printer. Four different levels of porosity were obtained by suitably controlling the LPBF process parameters. For generating ultrasonic waves, lead zirconate titanate (PZT) transducers were used. The signals were generated and propagated through the specimens in a transmission mode setup. Both linear and nonlinear analyses were used during the signal processing of the recorded signals for damage characterization. Linear ultrasonic parameters such as the time-of-flight (related to wave velocity) and signal amplitude (related to wave attenuation) were recorded. The nonlinear ultrasonic parameter, Sideband Peak Count - Index (SPC-I), was obtained by a newly developed nonlinear analysis technique called the SPC-I technique. Results obtained for the specimens were analyzed and compared for both linear and nonlinear ultrasonic analyses. Finally, the effectiveness of the SPC-I technique in monitoring porosity levels in additively manufactured specimens is discussed.