Non-Destructive Technique of Determining Plastic Deformations Using Pulse Transmission and Acoustic Emission Transducers in 304 Stainless Steel

An empirical method of non-destructive testing of a material was developed using pulse transmission by acoustic emission transducers to determine plastic deformation of 304 stainless steel specimens. This was done by means of comparison of pulse signals detected in an undeformed section with the pulse signals detected after passing through the deformation zone in the specimens. The pulse signals provided the Rayleigh waves in which the amount of plastic deformation can be detected for each test article. The rate of plastic deformation was investigated on seven double-edge-notched (DEN) identical test specimens which were subjected to different tensile loading. The data was initially in the time domain. The experiment results showed that there is some correlation between the plastic deformation and ultrasonic attenuation properties of a given material. A least square straight line fit was made for an isolated section of each plastic deformation signal and the signals after the linear fit were removed from the time domain into frequency domain using a Fourier Transfer Function (FTF) program. This enabled better comparison of the frequencies detected as a result of plastic deformation change in all seven test specimens.