|ELECTRON BACK SCATTER DIFFRACTION
Electron back scatter diffraction patterns are used to measure the orientations of individual grains and grain boundary misorientations in polycrystals. Within the group the technique is used widely (i) to characterize overall statistics of grain size and orientation distributions, (ii) to select specific grain boundary types for subsequent micromechanical testing, and (iii) for mapping lattice curvature and strains within individual grains and semiconductor devices. (strain mapping with CrossCourt2 from BLG Productions)
We are developing new methods of testing mechanical properties at the micron scale, using a combination of focussed ion beam (FIB) machining to produce bend test specimens. A nanoindenter is then used to test the specimens. We are exploring how well elastic, plastic and fracture properties can be extracted from the measured load-displacement data. The methods are being applied to testing individual grains and grain boundaries in polycrystalline metals, and ion-irradiated surface layers.
|DISLOCATION BASED ANALYSIS OF CRACKS AND PLASTICITY
We are developing dynamic and static simulations to understand the mechanics of crack propagation in different materials and loading environments. We have used dynamic discrete dislocation simulations to study stage I (mode II) fatigue crack propagation thresholds, and brittle fracture of microcracks. Current work is using dislocation based boundary elements for a static analysis of multiply kinked and branched cracks that are often found in intergranular stress corrosion cracking.
|STRAIN LOCALIZATION AND CRACK INITIATION
A long term interest is in understanding micro-mechanisms of strain localization and crack initiation in metals and alloys during deformation - both as it limits forming processes in manufacturing and performance in service. A particular interest is in understanding material response to fatigue loading. We have conducted fundamental studies of dislocation patterning and PSB formation in Cu single crystals using electron channelling contrast imaging. More currently we have been mapping how local grain morphologies and orientations leads to patterning in the local plastic strain, dislcocation density and stresses.