Size Effects in Micro-Cantilever Bending
Ed Tarleton (University of Oxford), Daniel Balint (Imperial College London), Jicheng Gong (University of Oxford), Angus Wilkinson (University of Oxford)
Discrete Dislocation Plasticity
Tue 4:20 - 5:40
RI Hall 108
Focused ion beam milling allows small scale single crystal cantilevers to be produced with cross-sectional dimensions on the order of microns which are then tested using a nanoindenter allowing both elastic and plastic material properties to be measured. EBSD allows these cantilevers to be milled from any desired crystal orientation. Micro-cantilever bending experiments suggest that sufficiently smaller cantilevers are stronger, and the observation is believed to be related to the effect of the neutral axis on the evolution of the dislocation structure. A planar model of discrete dislocation plasticity was used to simulate end-loaded cantilevers to interpret the behaviour observed in the experiments. The model allowed correlation of the simulated dislocation structure to the experimental load displacement curve and GND density obtained from EBSD. There are similarities between the predictions of this model and those of earlier discrete dislocation plasticity models of pure bending. However, there are notable differences, including a strong source density dependence of the size effect that cannot be explained by GND arguments, and the effect of the cantilever stress distribution on the locations of the soft pile-ups. The planar model is sufficient for identifying the roles of zero resolved shear stress isolines, rather than the neutral axis, and source spacing in the observed size effect, and is particularly appropriate for comparisons to experiments conducted on crystals orientated for plane strain deformation. The effect of sample dimensions and dislocation source density are investigated and compared to small scale mechanical tests conducted on Titanium and Zirconium.