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An ultrasonic shear wave technique to measure stress in metals is described. The technique utilizes a pulse-echo system operating at 7 MHz to measure changes in the time of travel of the ultrasonic shear wave to 1 part per million. Linear changes in the velocity of a shear wave occur with stress and are dependent on the higher order elastic constants of the material. The linear change in velocity with stress allows the definition of a constant called the stress acoustic constant for the material. The amount of birefringence in a specimen is measured, and after accounting for the portion caused by anisotropy of the material, the remainder gives an accurate measure of the residual stress in the material. The amount of birefringence caused by anisotropy is a constant for specimens having the same nominal mechanical and thermal treatments. Measurements using the ultrasonic technique of simulated residual stress, introduced by bending of a 6-ft (1.8-m) section of A-36 steel I-beam, yielded values in the vicinity of those measured using strain gage and O-ring techniques. Application of this technique to the measurement of other simple states of stress is suggested, along with the precautions to be observed for measuring stress.

A technique which utilizes ultrasonic rediation has been developed to measure residual stresses in metals. This technique makes it possible to detect and measure the magnitude of the principle stresses and also to obtain their direction. The velocities of ultrasonic waves in materials are measured as the time to travel a fixed path length, and the change in transit time is related to the applied stress. The linear relationship obtained allows a procedure based on this principle to be used for the measurement of residual stress using surface waves and shear waves. A method for plotting stress profiles through a material using surface waves uses varying frequencies for the ultrasonic wave. A limitation of the shear wave method is considered. The system used for this technique is called the Modified Time of Flight System.