Dynamic Piezoresistivity Calibration for Eddy Current Nondestructive Residual Stress Measurements |
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Authors: | Feng?Yu Email author" target="_blank">Peter?B?NagyEmail author |
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Affiliation: | (1) Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati, Cincinnati, Ohio, 45221-0070 |
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Abstract: | It has been recently demonstrated M. P. Blodgett and P. B. Nagy, J. Nondestruct. Eval. 23, 107 (2004)] that eddy current conductivity measurements can be exploited for near-surface residual stress assessment in
surface-treated nickel-base superalloy components. To quantitatively assess the prevailing residual stress from eddy current
conductivity measurements, the piezoresistivity coefficients of the material must be first determined using known external
applied stresses. These calibration measurements are usually conducted on a reference specimen of the same material using
cyclic uniaxial loads between 0.1 and 10Hz, which is fast enough to produce adiabatic conditions. Therefore, the question
arises whether dynamic calibration measurements can be used or not for accurately assessing the sensitivity of the eddy current
method for static residual stress. It is demonstrated in this paper that such dynamic calibration measurements should be corrected
for the thermoelastic effect, which is always positive, i.e., it increases the conductivity in tension, when the material
cools down, and reduces it in compression, when the material heats up. For low-conductivity titanium and nickel-base engine
alloys the thermoelastic corrections are relatively modest at ≈5–10%, but for high-conductivity aluminum alloys the difference
between the adiabatic and isothermal properties could be as high as 50%. |
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Keywords: | Eddy current shot peening residual stress |
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