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  • Study of indentation in linear viscoelastic solids using axisymmetric indenters of arbitrary profiles
    Author:   | Date:2006-04-10   | Click Rate:    | 【Close
    Instrumented indentation is playing an increasing role in the study of small-scale mechanical behavior of “soft” matters, such as polymers, composites, biomaterials, and food products. Many of these materials exhibit viscoelastic behaviors, especially at elevated temperatures. Modeling of indentation into viscoelastic solids thus forms the basis for analyzing indentation experiments in these materials. Using analytical and numerical modeling, professor Y.T. Cheng and C.M. Cheng examined the relationship between the initial unloading slope, contact depth, and the instantaneous relaxation modulus for indentation in linear viscoelastic solids by a rigid indenter with an arbitrary axisymmetric smooth profile. In particular, they studied the effects of “hold-at-peak-load” and “hold-at-maximum-displacement” on initial unloading slops and contact depths. These derivations show that with increasing unloading rate, unloading slope converges to a limiting case. Thus, fast unloading is essential in determining the instantaneous modulus from the unloading slope. And presently, very little attention is paid in literatures to the unloading rate when viscoelastic properties are measured using instrumented micro- and nano- indentation techniques. This lack of attention is believed to be the main cause for the reported disagreement in expression of unloading slope. Finally based on the expression of unloading slope, the instantaneous modulus can be obtained by fast jumps during either loading or unloading for indentation in linear viscoelastic solids using axisymmetric indenters of arbitrary profiles. These results provide a sound basis for using the relationship for determining properties of viscoelastic solids using indentation techniques. The papers have been published in Applied Physics Letters, 87(11),2005, J. Mater. Res. 20(11), 2005, and Materials Science and Engineering R 44, 91-149,2004.
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