Spherical indentation of elastic–plastic solids

Abstract
The finite–element method is used to perform an accurate numerical study of the normal indentation of an elastic–plastic half–space by a rigid sphere. The effects of elasticity and strain–hardening rate of the half–space are explored, and the role of friction is assessed by analysing the limiting cases of frictionless contact and sticking friction. Indentation maps are constructed with axes of contact radiusa (normalized by the indenter radiusR and the yield strain of the half–space. Competing regimes of deformation mode are determined and are plotted on the indentation map: (i) elastic Hertzian contact; (ii) elastic–plastic deformation; (iii) plastic similarity regime; (iv) finite–deformation elastic contact; and (v) finite–deformation plastic contact. The locations of the boundaries between deformation regimes change only slightly with the degree of strain–hardening rate and of interfacial friction. It is found that the domain of validity of the rigid–strain–hardening similarity solution is rather restricted: it is relevant only for solids with a yield strain of less than 2 x 10−4 anda/R < 0.16. Friction between the indenter and the substrate strongly affects the strain field beneath the indenter, and has a significant effect on the contact size as a function of indent depth. The effect of pre–stress within the half–space is also explored; it is found that the indentation response is hardly affected, except for the case of the elastic–plastic indentation regime.

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