Mapping deformation in small-scale testing

A method is demonstrated for mapping the displacements in small-scale test samples using digital image correlation. The deformation associated with crystallographic slip and with the lattice rotation has been determined in a copper micropillar oriented for single slip, in areas as small as 0.16 × 0.16 μm2. It is shown that gradients of slip accompanied the curvature of the lattice at the ends of the pillar, allowing the lattice to rotate. The spacing of slip bands was also seen to decrease in these regions. The observed deformation was associated with gradients of compressive stress across the section of the pillar given by the superimposition of bending moments, caused by the constraint at both ends of the pillar. The curvature of the lattice observed at the base of the pillar was found to be the same as that at the end of a protruding slip step, although the deformation gradients were different. This provides experimental evidence of the non-unique relationship between lattice curvature and deformation gradients.

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