Microstructural Simulation of Nano- and Microindenter Tests

Research project P 13908 Microstructural Simulation of Nano- and Microindenter Tests Reinhard Pippan 11.10.1999 Hardness is the resistance of a material against the indentation of the probe and the accompanying extension of the plastic zone into the test material. It is defined as the load divided by the contact area between indenter and test material. In case of nano- and micro hardness the load is monitored continuously as a function of the indentation depth. Microstructural features of materials that have an influence on the dislocation motion and on the plastic behaviour of materials also determine the shape of measured hardness curves. This could be used, on the other hand, to characterise the effect of microstructural features on hardness and plastic deformation provided the relation of hardness and involved micro processes is known. The aim of the project is to gain such information. This should be done by a simulation of the processes during the indentation of the probe. The simulation technique is a microstructural method where plasticity is described as growth of shear bands. Here the evolution of the dislocation density in predefined shear planes is computed. Microstructural features, like grain boundaries, second phase particles, laminate structures, thin films at the surface, etc, enter explicitly the simulation. We expect to answer the following 4 fundamental questions: 1) When (at which indentation depths) do the various microstructural features become effective? 2) Is it possible by interpreting load/indentation depth curves to figure out which microstructural features took part at the plastic deformation and to which extent? 3) What can be learned about the effect of microstructural features by hardness measurements? Is it, for instance, possible to figure out an averaged Hall-Petch coefficient? 4) At which indentation depths do the various microstructual effects smear-out to a macroscopic material behaviour. (When is a macroscopic simulation based on Finite Elements reasonable?). The result of the project should be an understanding of the physical processes during the indentation in order to be able to better interpret measured hardness curves and to figure out the microstructural information provided by the depth sensitive hardness tests. This is not possible by other methods.