Elastic and Plastic Strain Effects on Eddy Current Response of Carbon Steel

Author:  Yuichi Motoyama, Yoshiyasu Makino, Nobukazu Kondo, Hideaki Kaga, Toshimitsu Okane
Source:  ICSP-13
Doc ID:  2017059
Year of Publication:  2017
Introduction: Shot peening causes plastic deformation in a peened surface and induced a compressive residual stress. The compressive residual stress of the surface can increase a fatigue life of components. Therefore, monitoring the residual stress and/or plastic strain distribution in a peened layer of the component is important to guarantee its fatigue life. However, the induced residual stress is typically difficult to measure or predict. Presently, X-ray diffraction (XRD) is the widely used method that is able to measure the residual stress of the peened components. However, it is difficult for XRD to measure the residual stress distribution in the peened layer without a destructive method. The eddy current (EC) testing has the potential to measure the residual stress and plastic strain distribution induced by the shot peening because the electrical conductivity of metals is affected by both stress and plastic strain. Consequently, effects of stress and plastic strain on the EC response must be revealed for establishing EC testing to determine the residual stress and plastic strain distribution of the peened components.[1] Morozov et al.[1] conducted the EC measurements and revealed the dependence of the electrical conductivity on stress for aluminum alloys to establish a cheap indicator of the state of residual stress in metals and alloys. However, they did not investigate on steel materials. Dahia et al.[2] developed a methodology for the modelling of stress detection using the EC technique. They applied the method to the Iron-Cobalt alloy and concluded that the uniaxial tensile stress could be detected. However, their investigation was only within the elastic region.

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