Simulation of nanomechanical Tests Using Discrete Dislocation Dynamics

The ongoing miniaturization in many technical fields (e.g. micro-electronic systems, medical devices, etc.) requires smaller and smaller mechanical systems and components. For a successful use of such miniaturized devices their mechanical properties have to be known in this small dimensions. A simple transfer of their "macroscopic" properties is not useful in the case of many materials because size-effects can alter them. Due to new manufacturing processes (e.g. focused ion beam technique) an extensive investigation of the mechanical properties in the micrometer regime could be performed in the last years. These miniaturized compression and bending samples made of common metals and alloys showed a pronounced size-effect in the size regime from 10 m down to 500 nm. For example, copper showed an increase of the flow stress up to almost 1 GPa for the smallest samples. The physical mechanisms, which are responsible for the observed size-effect, are not completely understood up to now. There are different, partly competing, models in the literature. Experimental methods can measure the extent of the size-effect and can examine the principle underlying mechanisms, however, they cannot capture all parameters (e.g. dislocation source density, etc.), which govern the mechanical response. Thus, numerical simulations are an ideal completion to study the complex interaction of the different parameters and mechanisms, which is important to get a full understanding of the mechanical properties in small dimensions. In this project, 3D discrete dislocation dynamic simulations should be performed on miniaturized samples. For the chosen size regime from 100 nm to approx. 10 m, which can also be captured by experimental methods, this simulation method is a good tool to acquire the necessary information on mechanical properties in small dimensions. At the beginning, simulations on simple compression test samples (pillars) with sizes from 100 nm up to 20 m will be performed using simple boundary conditions. In a subsequent step, more complex boundary conditions will be used, like hard surface layers, which are introduced by many manufacturing methods, and are compared to experimental results. Furthermore, the influence of different material parameters, like dislocation source density, etc., on the mechanical response in small dimensions will be studied. Finally, the influence of more complex dislocation-dislocation interactions (e.g. cross-slip, etc.) will be studied. The aim of the project is to identify the basic dislocation mechanisms, which are controlling the mechanical properties in small dimensions and to verify these assumptions with specific experiments. The team of Professor Gumbsch at the University of Karlsruhe delivers an superior scientific environment for the proposed project and experience an excellent international reputation.