Ultrasonic Measurement of Stress Using a Rotating EMAT

Published

October 16, 2008

Author(s)

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

Abstract

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.

Citation

Journal of Nondestructive Evaluation

Pub Type

Journals

Keywords

acoustoelasticity, EMAT, stress

Citation

Clark, A. , Hehman, C. and Nguyen, T. (2008), Ultrasonic Measurement of Stress Using a Rotating EMAT, Journal of Nondestructive Evaluation (Accessed May 11, 2025)