Investigation of pile-up during a rigid ball sliding on coated surface based on elastic–plastic analysis

• Pile-up phenomenon was investigated in sliding indentation using finite element simulations.
• Nano-indentation and sliding indentation experimental tests were carried out and employed to verify the results of FEM.
• Friction affects pile-up in a manner that depends on strain hardening exponent, n.
• The dependencies of pile-up to E/σy and penetration depth h/R can be conveniently described by the single parameter (E/σy) (2hc/ac).

A three-dimensional finite element model (FEM) is used to study the development of pile-up and contact situation during nano-indentation and sliding indentation of elastic–plastic coated solids. The FEM results were verified by nano-indentation and sliding indentation tests which were carried out on TiN specimens. Then, the influence of elastic–plastic deformation, penetration depth, contact friction and strain hardening on pile-up was investigated for a wide range of materials with different elastic modulus, yield stresses, strain-hardening exponents and friction coefficients. The results indicated that the pile-up/sink-in geometry depends on the relative amounts of elastic and plastic deformation characterized by (E/σy), in a way that pile-up grows by increasing (E/σy). At small non-dimensional penetration depth (h/R), the deformation is only elastic, then by increasing the load, the plastic zone grows and spreads upward and the sink-in diminishes. It was found that friction severely enhances pile-up only in small amounts of strain hardening exponent. In addition, the influence of a unified parameter on pile-up was utilized to investigate some parameters simultaneously for various strain hardenings which depicted that increasing strain hardening exponent leads to smaller pile-up. The finite element results may be used as a first estimate of the pile-up/sink-in behavior if the material parameters are known.