An Optimized Geometry of Double-Cone Compression Test Samples for a Better Control of Strain Rate

Double-cone samples offer the great advantage of drastically reducing the number of required tests to correlate between processing parameters and microstructural evolution, as their characteristic geometry results in an equivalent strain gradient after compression. Their usual drawback is a relatively poor control of the equivalent strain rate (((epsilon) over bar) over dot), which varies along the radius and in time. To tackle this drawback, a parametric optimization of the geometry of these double-cone samples for compression tests was performed based on FE simulations. This optimization aims at minimizing the average equivalent strain rate standard deviation in time, among five numerical tracking points placed along the radius. The optimized geometry provides, for all cases tested, an average variation in time within a 10 pct range regarding the mean equivalent strain rate at the center of the sample. Another advantage is a homogeneous plastic strain path along the radius at the mid-height plane of the double-cone sample, as also throughout the deformation. The optimized geometry was compared with other found in literature and systematically showed improvement in terms of strain rate control, especially at the center of the sample, where the variation for the tested geometries rose up to 50 pct regarding the average strain rate value, compared to a 10 pct variation for the optimized geometry at the same conditions. (C) The Minerals, Metals & Materials Society and ASM International 2021