Indentation in Crystal Plasticity - Finite Element Simulation and Comparison with Experiments
Pyramidal indentation into an (001) oriented fcc single crystal, experiment (left) and crystal plastictiy finite element simulation for azimuthal orientation angles (angle between <100> direction and pyramid's diagonal) of 0°/22.5°/45° (from top to bottom).
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Abstract
Pyramidal microindentation into the (001) surface of an fcc single crystal has shown indent shapes which strongly depend on the azimuthal orientation of the pyramid, see the left column of the adjacent figure. This observation is experimentally elucidated by means of high resolution electron back-scatter diffraction (EBSD) technique along with digital image processing creating a digital surface model. The main findings are that pile-up formation is invariantly maximum in <110> directions (4 hillocks emerge) thus being independent of the azimuthal orientation of the pyramid. For different orientations of the indenter the material pile-up is locally accommodated to the indenter faces leading to a convex, a concave or a mixed curved contact rim at the faces of the indenter. The right column in the figure shows, that crystal plasticity finite element simulations are in good agreement with the observed surface deformation pattern. The influence of stress concentration onto the anisotropic pile-up is negligible. This is corroborated on the relative invariance of pile-up for different indenter orientations (an anisotropy in loading). The driving mechanism behind the observed phenomena is plastic glide in (111) <110> slip systems.
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