Specimen Size Effects on the Compressive Stress?Strain Response of Equal Channel Angular Extrusion (ECAE) Tantalum

Report No. ARL-TR-8729
Authors: Daniel Casem, Daniel Magagnosc, Jonathan Ligda, Timothy Walter, and Brian Schuster
Date/Pages: June 2019; 19 pages
Abstract: Compression tests were performed on tantalum over a range of strain rates using conventional servo-hydraulic load frames and the Kolsky (split-Hopkinson pressure) bar. To obtain a large range of strain rates (0.001/s to 500k/s), different diameter Kolsky bars were required: 3.18 mm, 1.59 mm, 794 μ m, and 305 μ m. These different bars were used to test different sample geometries: nominally 1.6-, 0.8-, and 0.4-mm cubes, and small cylinders with 60- μ m diameter and 30- μ m height. It was found that the four different sample sizes led to drastically different measured strengths, even for samples tested at the same strain rates. The tantalum studied has a fine grain structure (~2 μ m) so this is not believed to be due to the grain size. However, the reason for the discrepancy is unknown.
Distribution: Approved for public release
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Last Update / Reviewed: June 1, 2019