Experimental and numerical investigations on the consolidation in single and polycrystals under cyclic loading (Bauschinger effect)

  Deformed micro bending beam of a nickel-based single crystal in the scanning electron microscope Deformed micro bending beam of a nickel-based single crystal in the scanning electron microscope

The material behavior under cyclic load is of high practical relevance, especially in mechanical engineering. The service life of metallic components is often limited by the fatigue characteristics of the materials used. Cyclic loading can cause irreversible plastic deformations, which will lead to strain localization, crack formation and finally to fracture of the components. In order to precisely predict and improve the service life of cyclic loaded components, a thorough understanding of the underlying material-mechanical phenomena is essential. The so-called Bauschinger effect, which determines the hardening of the material under cyclic loading and thus significantly influences the material behavior, is of central importance in this context.

Although many aspects of the cyclic plasticity mechanisms are well known and have been implemented in models, a reliable, quantitative description of the material behavior on a micromechanical scale is missing. For the qualitative and quantitative analysis of the Bauschinger effect, different approaches are combined in this project. First, the cyclic material behavior is analyzed by microbending tests on single crystals of a nickel-based alloy. The bended beams with an edge length of a few micrometers have the advantage that individual glide systems, defined crystal orientations and the effects of grain boundaries can be precisely evaluated. The resulting data form the basis of a single crystal plasticity model, which allows the simulative analysis of the Bauschinger effect.

The investigations on single crystals will be transferred to polycrystalline materials in the second part of the project. Cyclic indentation tests as well as tensile-compression tests serve to quantify the macroscopically observable Bauschinger effect and bridge the gap between microstructural investigations and practical applications. The results of various experimental and theoretical investigations provide insights into the relationships between the crystal plastic phenomena and the macroscopically observable Bauschinger effect, thus making an important contribution to the explanation of predictive mechanism-based fatigue life models.