© Max-Planck-Institut für Eisenforschung GmbH

Micron sized cantilevers and the Bauschinger effect

The mechanical response of miniaturized material systems strongly depends on the sample size. Macroscopically well documented material properties like the yield stress or the hardening rate are changing when the smallest sample dimension reaches the micrometer range.

Image montage of Laue reflections recorded on a micron sized Copper bending beam. The elongated peaks indicate massive storage of geometrically necessary dislocations.

Due to the strong localization of slip – often occurring in only one slip system promoted by the activation of a single dislocation source at these length scales – other yet not fully investigated effects occur. For instance, the Bauschinger effect, being a strong reduction of the yield stress upon load sign reversion, does not appear in single crystalline macro samples. Aim of the underlying project was the quantification of reversible plasticity in micron sized bending beams, which further provides deep insights into the dislocation-dislocation interplay, strain-gradient dependent hardening behavior, cross slip probabilities, the role of long range stress fields on the Bauschinger effect. Additionally, comparison of experimental results with crystal plasticity based finite element calculations as performed in the Microstructure Physics and Alloy Design (MA) Department fostered understanding when continuums approaches are still valid.

Besides the in-house cooperation with the MA department this project benefited from our close cooperations with the Universität des Saarlandes (Prof. Motz), the Austrian Academy of Sciences (Prof. Pippan) and the European Synchrotron Radiation Facility ESRF (Dr. Micha).

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