Measurement of Stress in Steels Using Magnetically Induced Velocity Changes for Ultrasonic Waves
Because of the magnetoeiastic interaction in a ferromagnetic material, the velocity of ultrasonic waves in the material changes upon application of an external magnetic field to the material. Mechanical stresses influence the magnitude of this velocity change as well as the way the velocity change varies as a function of the applied magnetic field. This stress dependence of the magnetically induced velocity change can be used to nonde-structively determine applied and residual stresses in ferromagnetic structural steels. In this method, shear or longitudinal waves are used to determine internal stresses while surface waves are used to determine surface stresses. This paper briefly reviews the underlying physics involved in the magnetically induced velocity change phenomenon, and describes an instrumentation system used to measure such velocity changes along with examples of its stress dependence. Measurement results of residual welding stresses and surface stresses determined by using the above described method are presented as well as the capabilities and limitations of the method.
KeywordsResidual Stress Surface Wave Ultrasonic Wave Domain Magnetization Velocity Change
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