Uniaxial stress in-situ measurement using EMAT shear and longitudinal waves: Transducer design and experiments

Abstract

As a typical stressed state, uniaxial stress widely exists in the components, such as bolt stress, which requires to be tested in-situ regularly. In this article, the uniaxial stress in-situ measurement using the electromagnetic acoustic transducer (EMAT) shear and longitudinal waves is proposed. To improve the EMATs efficiency and meet the measurement resolution constraints based on Lorentz mechanism, the EMAT parameters are optimized through numerical analysis, including the coil size, the permanent magnet size and the distance between magnet and coil. The relationship between the propagation velocity and the stress is analyzed, and a joint model of shear and longitudinal waves for measuring the uniaxial stress is established. Finally, the pre-tightened 7075 aluminum alloy bolt is employed to verify the validity of the designed shear wave EMAT and longitudinal wave EMAT.