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Indentation curve in viscoplastic alloys: mathematical model, fitting program and its application in room temperature creep of Al Sn alloys

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Document pages: 9 pages

Abstract: Hardness is an important design parameter, but in rate dependent materials, its value depends on the indentation speed and residence time during measurement. The dimensional analysis of indentation test provides a strict description of the load displacement curve of elastic-plastic materials; Viscoplastic materials can also be treated by ignoring the plastic part of deformation, which is inaccurate for most engineering alloys. This work proposes a method to construct the model indentation curve, which considers the concurrent viscous and plastic strains, as well as the correction of tip roundness, load frame flexibility and the first contact point. This paper introduces a method to calculate the parameters of single model curve by fitting multiple experimental curvesating the numerical solutions of the differential equation describing viscoplastic behaviour. The procedure is applied to Vickers indentation in brass and steel calibration blocks and to a SAE783 Al-Sn alloy for journal bearings, where creep at room temperature is observed. The soundness of the approach is demonstrated by the large reduction of statistical uncertainty on the parameters describing the indentation curves. A rate-independent hardness will be found and a brief comment is provided on the comparison between creep analysis by indentation and uniaxial tension.

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