Finite element simulations have been carried out for two key areas: indentation of ion-implanted materials and of creeping materials. Ion Implantation is a common technique for improving the surface properties of tribological materials, but characterization of implanted materials is made difficult by the fact that the properties vary with depth from the surface. Finite element simulations of implanted surfaces have been compared to nanohardness tests to show the relationship between property changes (particularly the yield stress) and hardness distributions.
These simulations [2] were carried out using the finite element code NIKE2D. The effect of the implantation is modeled by varying the yield strength of the specimen with depth from the surface. The yield stress distribution was assumed to match that of the implanted nitrogen ion concentration, which was found to be fairly linear. The results indicate that the yield stress at the surface of the model was 10 times that of the bulk yield stress. This is the first attempt at (indirectly) measuring the yield strength of ion-implanted Ti-6Al-4V alloys.
Numerous studies have used indentation tests to measure the time-dependent properties of both homogeneous materials and of thin films. There are some models for these tests in the literature, but they have not been severely tested at this point. We have used a commercial finite element code (MARC) to study both fixed-displacement and fixed-load, time-dependent indentation tests. Simulations for homogeneous molybdenum samples have yielded excellent results (as compared with experimental results) and have helped to verify and refine some of the critical assumptions of existing creep indentation models. Further work is needed to study the indentation of thin films.