Finite Element Simulations of Harmonic Structured Materials in Two Dimensions

Sammanfattning: Most of today’s materials show either high strength with low ductility, or relatively low strength combined with high ductility. It is strongly desired in the industry to obtain materials whose mechanical properties can display a combination of high strength and elongation. That is why the new concept of harmonic structure has been introduced recently. This structure consists of strong ultrafine grains in a uniform continuous pattern surrounding the islands of softer coarse grain. The aim for the work presented in this dissertation was to develop a finite element model in two dimensions for harmonic structured materials to facilitate future work in this novel field. The model of harmonic structure in this work was intentionally simplified to reflect most critical structural characteristics. Subsequently, three different mesh densities were implemented. After successful validation against existing experimental data valuable results were obtained. In consistency with experimental data obtained by other research groups, both total elongation and yield strength were extended thanks to the “harmonic” microstructure topology. The results were also found to be strongly dependent on mesh types. The finer the mesh, the lower amount of deformation was possible to apply to the model. The early model failure resulted from severe element distortion in some local areas. Important results were the uniformly distributed macro- stresses and strains along the entire model along with local shear stresses on the core/shell interface. The latter is considered to be the reason of initial cracking in the same areas reported in other publications on harmonic structured materials. It was also shown that harmonic structured material outperforms that with a randomly distributed bimodal structure.