The acousto-elastic effect was studied experimentally by analyzing the Fourier spectrum of ultrasonic waves. Uni-axial tensile stress was applied to several specimens made from rolled plates of aluminum, copper and steel, and ultrasonic transverse pulses were sent into these specimens with a PZT transducer, which was also used to detect reflected pulses. Since an incident transverse pulse was resolved into two constituents due to the slight orthotropy of a rolled plate and the application of stress, certain frequency components disappeared in the spectrum of a reflected resultant pulse. This frequency, called the zero-point frequency here, was measured with an analog-type spectrum analyzer, and its variation with the stress was examined.
In the specimens with the loading direction parallel or perpendicular to the rolling direction, the experimental results showed that the reciprocal of the zero-point frequency varied linearly with the stress, and the acousto-elastic constant of each plate was determined from the slope of this linear variation. In the aluminum specimen whose loading direction was inclined by 45° against the rolling direction, it was shown that the polarization direction of transverse pulses rotated with the stress. These results agreed well with the acousto-elastic law for a slightly orthotropic material. It is concluded that the method of spectrum analysis is much suited for the measurement of acoustoelastic effect.
