Nayebi - Shahid Chamran University, Engineering Faculty, Mechanical engineering Department, Ahwaz, Iran
Bartier - LARMAUR Laboratory, Université de Rennes۱, Rennes, France
Mauvoisin - LARMAUR Laboratory, Université de Rennes۱, Rennes, France

A new numerical approach to indentation problems is developed for materials with a yield strength gradient and a relationship for the indentation load – depth, F-δ, is presented. The ratios of the dissipated energy in every thin layer to all of plastic energies in indented zones allow determining the F-δ curve of these materials. The proposed model is applied to three nitrided steels. The comparison between the numerical results and those experimentally obtained from known materials, confirms the important influence of the plastic energy in the indented zone on the determination of the indentation curve F-δ.