Influence of Dissipated Plastic Energies on Indented Load-Depth Curve for Materials with a Yield Strength Gradient

摘要

The present paper investigates the indentation of materials with a linear yield strength gradient by spherical indenters. These materials were discretized to several homogeneous layers. The indentation load-depth curve depends on the plastic energies dissipated in each layer made of plastically graded materials. A new mixture model is presented and allows the exact influence of the plastic energies on the load-depth curve (F-8) obtained from the instrumented indentation test to be determined. On the other hand, the model results show how the response of plastically graded materials can be obtained from the answer of homogenous materials to indentation; The properties of homogenous materials are the same as those of each thin layer in plastically graded layers, and the dissipated plastic energies dissipated in each thin layer. The use of finite element simulations of spherical indentation for materials with a yield strength gradient provide the plastic energies dissipated in plastically graded layers and in the substrate, as well as the indentation load-depth response. The proposed model was tested by using mechanical properties of nitrided steels. The comparison between the results obtained by the proposed model and those obtained numerically from known materials, confirms that the indentation curve F-8 can be reconstructed from the plastic energies in the indented zones.