First Principles Calculation of Stress Induced Amorphization in Armor Ceramics

Report No. ARL-MR-0779
Authors: D. E. Taylor, T. W. Wright, and J. W. McCauley
Date/Pages: May 2011; 24 pages
Abstract: Recent experimental work within the U.S. Army Research Laboratory has identified the formation of nanoscale-sized intragranular amorphous bands leading to a marked reduction in ballistic performance of boron carbide (B4C). This pressure-induced amorphization has been examined through application of the Born stability criterion that imposes restrictions on the relative magnitudes of the elastic constants of a stable crystal. The analysis has been conducted for B4C as a function of structural polytype using ab initio solid-state density functional methods and the results of the pressure evolution of the B4C elastic constants are reported. It is shown that the C-C-C polytype, a minority phase in the B4C lattice, fails at a pressure of ≈20 gigapascals less than the other polytypes tested in this survey, indicating that it may serve as one of the initial points of failure upon impact.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2011