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Ultrasonic Measurement of Stress Using a Rotating EMAT



A V. Clark, C S. Hehman, Thao D. Nguyen


The acoustic birefringence method is primarilly used to measure differences of principal stresses in regions where principal stresses coincide with material symmetry axes. To determine the differences of principal stresses also requires knowledge of the unstressed birefringence at the measurement locations. Consequently variability in texture can introduce errors in stress determination. In contrast the ultrasonic measurement of shear stress is independent of texture. The shear stress causes a rotation φ of the pure-mode polarization directions of the SH-waves used in our experiments. We constructed a motorized EMAT and used it to measure phase as the EMAT is rotated. We developed an algorithm to determine φ and the birefringence B. We measured the shear stress along parallel scanlines in a residual stress specimen with known stress state. We calculated the shear stress gradient and used it in the stress-equilibrium equation to determine the normal stress acting along the scanline direction. The other plane stress component was determined from an acoustoelastic relation between B and the difference of normal stresses. Good agreement was obtained with data based on strain gages.
Journal of Nondestructive Evaluation


acoustoelasticity, EMAT, stress


Clark, A. , Hehman, C. and Nguyen, T. (2008), Ultrasonic Measurement of Stress Using a Rotating EMAT, Journal of Nondestructive Evaluation (Accessed May 18, 2024)


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Created October 16, 2008