Non-destructive surface characterization of carburized steel using Rayleigh waves

Abstract

The research described in this thesis involves the use of surface acoustic waves to interrogate materials with property gradients, such as carburized steel, for depth of the surface treatment. A 3.5 MHz wedge transducer was used to generate Rayleigh waves which were detected with a fiber optic based interferometer. Experimental dispersion data, phase velocity as a function of frequency, was calculated from the recorded displacement-time waveforms. The phase velocity was lower in the carburized case of the material which has a greater carbon content and hardness value. Dispersion was observed by plotting phase velocity versus wavelength/residual case depth ratio. A linear fit was applied to the data with wavelength/residual case depth less than 2, and using this fit, it would be possible to non-destructively estimate case depth.