Finite-element analysis of deformation during indentation and scratch tests on elastic-perfectly plastic materials

We have studied the distribution of plastic strain around normal indentation and scratches in elastic-perfectly plastic materials. A three-dimensional finite-element analysis of a cone scratching and indenting elastic-perfectly plastic materials is presented. The indenter is the axisymmetric equivalent cone of the Berkovich indenter, with semiapical angle theta = 70.3. The plastic behaviour of the material is modelled with the yield stress To. No strain hardening and no sensitivity to the strain rate occur. The elasticity of the material is modelled with Young's modulus E, which varies from 2.79 to 2793 GPa. In fact, the behaviour of the scratched or indented material depends on the parameter X = (E/sigma(0)) cot theta, called the rheological factor (X = 1..... 1000). For small rheological factors, the deformation is mainly elastic; for high rheological factors. the deformation is essentially plastic, and in this case the behaviour of the material is close to the behaviour of a metal. The contact between the indenter and the mesh is frictionless. We have defined a mean representative strain in indentation and scratch tests, This value is independent of the scratch length and the penetration depth. It has been shown that the mean representative strain increases with X, and that it is larger in scratch tests than in indentation tests.