Berlin 2008 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 29: Mechanical Properties I

MM 29.2: Talk

Wednesday, February 27, 2008, 14:15–14:30, H 0111

Micropillars compression test — •Nousha Kheradmand, Afrooz Barnoush, and Horst Vehoff — Saarland University Bldg. D22 P.O. Box 151150, Postcode D-66041, Saarbruecken, Germany

In order to investigate the size effect compression test of single crystal micropillars was performed. Micropillars with different crystallographic orientations were fabricated by focused ion beam and the compression test was performed in a nanoindenter utilizing a flat punch tip. As a new approach in order to observe the micropillars in their intermediate deformation conditions, the compression test was performed stepwise. Between each step the micropillars were imaged in a scanning electron microscope. The engineering stress-strain curves of the micropillars show a clear size effect on mechanical properties of the samples. The small samples show a linear elastic-perfectly plastic deformation followed by incremental strain bursts, while the larger samples show a continuously flow curve. This difference could be described by a so called source truncation strengthening model which occurs in samples with small diameter. According to this model a Frank-Read source line during the growth reaches the free surface before it is able to be multiplicated. This leaves two single-arm dislocations which are pinned from one end inside the sample and from the other end on the free surface. These dislocations introduce to the samples new yield stresses.