Engineering topics
Publications and source records attributed to Yost, William T..
The effects of material structure on the nonlinearity parameters are reviewed. Problems discussed include definition of nonlinearity parameters, square-law nonlinearity and collinear beam-mixing, structure dependence of the nonlinearity parameters, negative nonlinearity parameters, and implications for materials characterization.
The paper reviews nonlinear bulk compressional wave acoustic measurement systems and the applications of measurements from such systems to engineering materials. Preliminary measurements indicate that it is possible to determine percent second phase precipitates in aluminum alloys, while other measurements show promise in the determination of properties related to the fatigue states of metals. It is also shown that harmonic generation can be used for the study of crack opening loads in compact tension specimens, which in turn gives useful information about the fatigue properties of various engineering materials.
An ultrasonic apparatus determines crack opening load by placing a transmit transducer on one side of the crack and a receive transducer on the opposite side of the crack. An acoustic signal passing through a region of the crack is mechanically rectified to produce a second harmonic of an input signal. A harmonic output signal of the receive transducer is converted into an electrical signal and the peak harmonic amplitude is determined while increasing a tension load on the specimen. The peak harmonic amplitude indicates crack opening load.
A mathematical model was developed for the liquid-membrane coupling response of the submersible electrostatic acoustic transducer (ESAT) described by Cantrell et al. (1979). The model accounts for the ESAT's rolloff response and predicts the essential features of the ESAT frequency response. Model predictions were found to agree well with measurements taken over the frequency range from 1 to 11 MHz.
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The controversy surrounding the magnitude of the radiation-induced static strain accompanying acoustic wave propagation in solids is resolved by a consideration of the associated Boussinesq radiation stress. Experimental verification of the results is presented for waves propagating along the pure mode directions of crystalline silicon.
Ultrasonic radio frequency tone-bursts are launched into a sample of material tested. The amplitude of the tone-bursts and the slope of the resulting static displacement pulses are measured. These measurements are used to calculate the nonlinearities of the materials.
It is shown that the radiation-induced static strains associated with acoustic waves propagating in solids are obtained directly from the virial theorem for an elastic continuum and that the radiation stresses result from combining the virial theorem with the Boltzmann-Ehrenfest principle of adiabatic invariance. The experimental confirmation of critical theoretical predictions in solids is reported. The implications of the results for the fundamental thermal properties of crystals are addressed.