Study of the Influence of the substrate on penetration depth by the flat cylindrical indenter

The indentation process of a soft thin film on a harder substrate by the flat cylindrical indenter has been simulated by means of the finite element method (FEM). The emphasis was put on the critical indentation depth with the influence of the yield strength ratio of the soft film to the harder substrate and the size of the indenter. The results show that the influence of the hard substrate on the indentation depth can be negligible at a small indentation depth, but this influence can not be negligible after the indentation depth arrives at a critical value. Further studies show that there exists an approximate linear relationship between the yield strength ratio of the soft film to the harder substrate and the critical indentation depth, and the linear relationship is not varied with the size of the indenter. And the critical indentation depth increases with the yield strength ratio of the soft film to the harder substrate when the other conditions are same. Analyses also reveal that on relationship between the critical indentation depth and the enhanced material pile-up around the flat cylindrical indenter.