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This study develops a new method to measure internal stress in materials. By using critically refracted longitudinal wave transducers with frequency of 1 and 5 MHz and relevant critically refracted longitudinal ultrasonic technique, we investigated how stress influence ultrasonic propagation time and critically refracted longitudinal wave propagating velocity along different directions in pre-stretched 7075 aluminium alloy plate. The experimental results from this study indicate that when specimen is axially tensioned and the angle between the direction of stress and the propagation orientation of critically refracted longitudinal wave increases, stress has decreasing effect on critically refracted longitudinal wave velocity. Besides, the velocity of longitudinal wave propagating perpendicular to axial hardly changes in stressed state and this demonstrates that the velocity of critically refracted longitudinal wave propagating perpendicular to the direction of stress has no relation with the applied stress. Therefore, critically refracted longitudinal ultrasonic technique has high potential to measure the stress component along one direction in the stressed material. This study presents a non-destructive method that can be used for measuring and evaluating internal stress of the material of interest.
Jin et al. (Wed,) studied this question.