電磁超音波共鳴法による金属薄板の音弾性応力測定

概要

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Ultrasonic resonance frequency is measured using noncontacting electromagnetic acoustic transducers (EMATs) for acoustoelastic stress determination. An EMAT consists of a permanent magnet and a coil, which is dynamically driven by high-power rf bursts. It generates bulk waves through Lorentz forces arising from the static magnetic field and the induced eddy current, and detects them with the inversed process. The low efficiency of EMATs is well compensated by bringing the object into resonance. Longitudinal and shear resonance frequencies up to 20 MHz are determined by sweeping the operating frequency and processing the reverberation signals with a superheterodyne receiver linked to a computer. Slight frequency shift with stress application is available with the improved sensitivity on the order of l0^6 fractional changes. The main features of the measurement system are demonstrated in an experiment utillizing the uniaxial and plane stress field in 1. 2-mm-thick steel and aluminum sheets.
一般社団法人日本機械学会の論文
1994-01-25