Abstract
In many applications nondestructive testing (NDT) of the physical properties is desirable. This paper describes the use of signal processing and wave theory to experimentally determine the acoustic wave speed in sample materials. Through this, an estimate of a material's modulus of elasticity and other properties can be made. The testing was done using an acoustic emission (AE) acquisition system with two surface-mounted piezoelectric transducers in conjunction with a digital oscilloscope. A longitudinal stress wave was induced in the specimen and the wave data collected. Analysis involving FFT and nonlinear equation solving was performed on a mainframe computer. For verification, steel and aluminum specimens (for which wave speeds could be empirically determined) were used. Epoxy resin specimens were also tested. The best results from these tests yielded errors of 2.2% in the wave speed for aluminum, and 1.8% for steel. However, since the results are based on the solution of simultaneous nonlinear equations that may converge to erroneous answers, a good first guess was needed in order to get reliable results. A possible development of a better equation-solving algorithm is discussed.
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