Plasticity, fatigue and fracture are the most established research areas of ESI, which have brought the institute a high recognition in the last two decades. Our research is devoted on one hand to fundamental unsolved questions, such as the proper description of the behavior of cracks in inhomogeneous materials, or the scale effects of strength, ductility, and fracture resistance. On the other hand, we investigate the deformation-, fatigue-, and fracture properties of existing or new materials as a function of their micro- and nanostructure, for example nanocrystalline metals that are produced by high-pressure torsion (HPT).
Due to the ongoing miniaturizations in many areas of modern technologies (micro-electronics, medical devices, etc.) the mechanical properties in the micro- and nanometer regime are becoming more and more important. “Size effects” influence these properties and prohibit the usage of macroscopic values. Furthermore, unusual mechanical responses are often experienced at these small scales. Hence, miniaturized testing methods have to be developed to reliably measure mechanical properties in small dimensions and to identify the underlying physical mechanisms causing the size dependence.
Real materials are from perfection. As a consequence, most material properties depend on the microstructure. The hierarchical structure of a material, usually referred to as microstructure, spans over several orders of magnitude starting from the atomic dimensions and extending across the µm level to the macroscopic dimensions of the material component or device. Microstructural quantities, which need to be understood to establish microstructure-property relationships, include grain size, phase, chemical composition, interfaces, dislocations, and point defects.
Heavy plastic deformation, now usually called severe plastic deformation at relatively low temperatures are now one of the main research topics in the material science community. It permits a large scale production of materials or composites with crystallite sizes between few nanometers and few 100 nm. They have extraordinarily high strength, some of them excellent ductility and offer tunable physical properties.
Materials fulfil in technological applications structural and/or functional properties, however, in all cases the structural integrity determines the performance and life time of devices and their components (see Deformation, Fatigue and Fracture). Structural materials studied at the Erich Schmid Institute include steel, alloys and composite materials. New insights into structural integrity are obtained by understanding local material inhomogeneities. Nature teaches new lessons in that field. Biological materials such as dentin and enamel in teeth as well as silica-protein structures in the deep sea sponge Euplectella demonstrate nature’s capability to synthesize fracture tolerant and resistant materials.