Compressed Bi-crystal micropillars showing a sigmoidal deformation state – A computational study

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2017-07, Vol.700, p.168-174
• Main Authors: Toth, F., Kirchlechner, C., Fischer, F.D., Dehm, G., Rammerstorfer, F.G.
• Format: Article
• Language: English
• Subjects: Axial stress; Buckling; Compression tests; Computer simulation; Crystals; Deformation; Deformation effects; Deformation mechanisms; Finite element method; Hardening; Micromechanics; Pillar compression; Postbuckling; Single crystals; Stress-strain curves; Stress-strain relationships
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2017.05.098

It is the aim of this paper to show the mechanisms behind the experimental observations of rather smooth sigmoidal deformations in bi-crystal micropillar tests (in contrast to single crystal micro-compression tests) and to point out that the appearance of such deformation modes are a further reason for being careful when interpreting the force-axial displacement behavior in terms of stress-strain curves. Instabilities, i.e., buckling and subsequent post-buckling deformations, inhomogeneous strain fields and substantial deformations of the base as well as pronounced free surface effects are considered. The influences of imperfections and of friction as well as a possible clearance in the guidance of the loading device are taken into account, too. From these studies, the experimenter may get information how and with which limitations material parameters can be obtained from such compression tests in combination with simulations. •Buckling of a bi-crystal micropillar in a sigmoidal buckling mode.•Different deformation mechanisms of bi-crystal compared to single-crystal micropillars.•Understanding the loss of stiffness due to sigmodal post-buckling.•Inhomogenous stress and strain fields as well as inhomogeneous material states.•Caution if force axial displacement diagrams are interpreted in terms of stress strain curves!