Effects of 'sinking in' and 'piling up' on estimating the contact area under load in indentation

The phenomena of the `piling up' and `sinking-in' of surface pro les in conical indentation in elastic-plastic solids with work hardening are studied using dimensional and nite-element analysis. The degree of sinking in and piling up is shown to depend on the ratio of the initial yield strength Y to Young' s modulus E and on the work-hardening exponent n. The widely used procedure proposed by Oliver and Pharr for estimating contact depth is then evaluated systematically. By comparing the contact depth obtained directly from nite-element calculations with that obtained from the initial unloading slope using the Oliver Pharr procedure, the applicability of the procedure is discussed.

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