SHEAR LOCALIZATION IN A SPHERE-IMPACTED ARMOR-GRADE BORON CARBIDE

摘要

Three armor-grade boron carbide cylinders were previously impacted with cemented carbide spheres at velocities 103 m/s, 209 m/s, and 312 m/s, respectively. These cylinders were subsequently sectioned and metallographically prepared to reveal subsurface damage as a function of impact velocity. Each cylinder exhibited severe cracking including radial, shallow lateral, ring, and Hertzian cone cracks. The shallow lateral cracks extended to the upper surface, allowing spallation of material surrounding the impact site. No Mescall zone (i.e. comminuted region) was observed immediately beneath the impact site. At the impact site, an intact truncated cone was observed for an impact velocity of 103 m/s, while at the higher impact velocities, erosion of the cone was observed. Examination of these eroded cones revealed intense cracking. Furthermore, at the highest impact velocity of 312 m/s, narrow bands, which appear consistent with shear localization, were observed. Characterization of the sub-surface damage and shear localization "bands" by field-emission scanning electron microscopy is presented. Preliminary micro-Raman spectroscopy of the shear localization "bands" is also included.