Subproject 2

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Adiabatic shear band formation occurs as a deformation process in metallic materials, particularly at high deformation speeds. Shear band formation is characterised by energy dissipation during plastic deformation, a resulting local increase in temperature, a resulting local softening and ultimately an increasingly pronounced localisation of further deformation over time. An in-depth understanding of shear band formation is interesting from a materials science perspective, challenging from an experimental point of view and also particularly relevant from a technological perspective, especially in the context of high-speed shear cutting (HGSS). A central objective of subproject 2 is to investigate the influence of different initial microstructures on the formation and growth of different types of shear bands in low-alloy steels and a naturally hard aluminium alloy. Amongst other things, this involves the targeted use of stopped, highly dynamic experiments to document different stages of shear band formation and propagation and then systematically characterise the shear bands microstructurally. Figure 1 shows an example of light microscopic images of cross-sections of differently compressed compression-shear specimens. In these samples, shear bands are preferentially formed at the edge of the end faces and grow diagonally through the sample in the direction of the shear stresses superimposed by the primary compressive load.

In subproject 2, criteria for evaluating the shear tendency of the investigated materials in HGSS are developed with special consideration of strain rate sensitivity, strength and thermal conductivity. In particular, correlations between the initial microstructures and the resulting shear band properties are to be understood. In addition to the macroscopic investigation of the mechanical behaviour, the focus is also on the microstructural and micromechanical characterisation of the shear bands with an additional focus on the influence of different stress states. Figure 2 shows, for example, that microstructural investigations (especially in the scanning electron microscope, SEM, with the aid of electron back-scatter diffraction, EBSD) enable the analysis of microstructural changes during adiabatic shear band formation in steel materials. This makes it possible to recognise the highly deformed transition areas next to the actual adiabatic shear band, whose microstructure ultimately determines the properties of the functional surfaces investigated by the research group

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