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    Author(s): Don S. Stone; Joseph E. Jakes; Jonathan Puthoff; Abdelmageed A. Elmustafa
    Date: 2010
    Source: Journal of materials research. Vol. 24, no. 4 (Apr. 2010): pages 611-621.
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (598.34 KB)

    Description

    Finite element analysis is used to simulate cone indentation creep in materials across a wide range of hardness, strain rate sensitivity, and work-hardening exponent. Modeling reveals that the commonly held assumption of the hardness strain rate sensitivity (mΗ) equaling the flow stress strain rate sensitivity (mσ) is violated except in low hardness/modulus materials. Another commonly held assumption is that for self-similar indenters the indent area increases in proportion to the (depth)2 during creep. This assumption is also violated. Both violations are readily explained by noting that the proportionality “constants” relating (i) hardness to flow stress and (ii) area to (depth)2 are, in reality, functions of hardness/modulus ratio, which changes during creep. Experiments on silicon, fused silica, bulk metallic glass, and poly methyl methacrylate verify the breakdown of the area-(depth)2 relation, consistent with the theory. A method is provided for estimating area from depth during creep.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    Stone, Don S.; Jakes, Joseph E.; Puthoff, Jonathan; Elmustafa, Abdelmageed A. 2010. Analysis of indentation creep. Journal of Materials Research. 24(4): 611-621.

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    Keywords

    Materials, creep, hardness, deformations, nanostructured materials, measurement, nanotechnology, strains, stresses, mechanical properties, elasiticity, modulus of elasticity, metallic glasses, finite element method, testing, silicon, silica, polymethyl methacrylate, nanoindentation, flow stress strain rate sensitivity, hardness strain rate sensitivity, surface properties

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