Fig. 4.

Example data from a single typical intermediate rate compression experiment at the fastest rate (nominally 10 s⁻¹ or equivalently 250 mm/s). (a) Time-history of mean axial Lagrangian strain (E₂₂), with example images selected at zero compression and maximum compression. The red dashed box indicates the region of interest used for DIC. (b) Example 2D-DIC displacement fields (u₁, top, and u₂, bottom) on the specimen surface at approximately 15 % mean axial strain. Note that u₁ is nominally symmetric about the vertical centerline and the u₂ component is maximum at the bottom edge and minimum at the top edge, since the uniaxial compression is applied between a fixed top platen and moving bottom platen (in contrast to the quasi-static case). (c) Analogously to (b), the 2D-DIC displacement fields (u₁, top, and u₂, bottom) on the specimen surface at approximately 60 % mean axial strain, showing a less even and noisier gradient in u₂, which is may be related to the non-monotonicity of the stress-strain curve at this rate and strain level and increased uncertainty associated with the high-speed imaging configuration. (d) The axial engineering stress and mean transverse Lagrangian strain plotted against the mean axial Lagrangian strain for one example. Standard uncertainty on stress is circa ±1.1 kPa.