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 profiles in conical indentation in elastic-plastic solids with work hardening a re studied using dimensional and finite-element analysis. The degree o f sinking in and piling up is shown to depend on the ratio of the init ial yield strength Y to Young's modulus E and on the work-hardening ex ponent n. The widely used procedure proposed by Oliver and Pharr for e stimating contact depth is then evaluated systematically. By comparing the contact depth obtained directly from finite-element calculations with that obtained from the initial unloading slope using the Oliver-P harr procedure, the applicability of the procedure is discussed.