Dynamic Compressive Tests of Alumina Dumbbells Using a Spherical Joint

Abstract

The dynamic compressive strength of ceramic armor materials is difficult to obtain experimentally due to the sensitivity of fracture strength to small misalignments, end effects, and surface effects. In this work we introduce a spherical joint into a compression Kolsky bar to investigate whether the joint can alleviate bending stresses due to minor misalignment in compression tests on alumina dumbbell specimens. Tests are conducted both with and without the spherical joint, and high-speed (75,000 frames/s) three-dimensional Digital Image Correlation (3D DIC) is used to measure both the strain field on the dumbbell specimen and motion, if any, in the spherical joint. Results indicate that the spherical joint is extremely sensitive to eccentric loading and in most cases increases rather than decreases the bending stresses in the test, leading to lower apparent fracture strengths.