An empirical methodlogy to estimate a local yield stress in work-hardened surface layers |
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Authors: | J P Nobre A M Dias M Kornmeier |
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Institution: | (1) Mechanical Engineering Department, University of Coimbra, P-3030 Coimbra, Portugal;(2) European Patent Office, Munich, Germany |
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Abstract: | A methodology is proposed for estimating the local yield stress in work-hardened surface layers. It is based on the concept
of in-depth normalized variation of hardness and x-ray diffraction peak width, both of which measure the strain-hardening
attained by the materials' surface-treated layers due to, for example, shot-peening. Its principle is directly founded on
the classical hardness theory. To study the evolution of those values with plastic deformation, specimens of five steels with
different mechanical properties were subjected to interrupted tensile tests. The tests were performed at successive increments
of plastic strain, until fracture occurred. The specimens were loaded and unloaded in increments of about 2% true strain.
After each plastic strain increment, hardness and diffraction peak width were measured. It was observed that the variations
of diffraction peak width and hardness are related to the material's strain-hardening, and their normalized variations can
be considered proportional to the normalized variation of the material's yield stress. Thus, where the yield stress of the
bulk material, its hardness or a characteristic diffraction peak width value, and their relative variations along the hardened
layers, are known, an empirical expression could be used to estimate the local yield stress as a function of the treated depth. |
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Keywords: | Mechanical behavior shot-peening yield strength strain-hardening micro-hardness x-ray diffraction |
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