Dynamic behavior of boron carbide

Abstract

Boron carbide displays a rich response to dynamic compression that is not well understood. To address poorly understood aspects of behavior, including dynamic strength and the possibility of phase transformations, a series of plate impact experiments was performed that also included reshock and release configurations. Hugoniot data were obtained from the elastic limit (15–18 GPa) to 70 GPa and were found to agree reasonably well with the somewhat limited data in the literature. Using the Hugoniot data, as well as the reshock and release data, the possibility of the existence of one or more phase transitions was examined. There is tantalizing evidence, but at this time no phase transition can be conclusively demonstrated. However, the experimental data are consistent with a phase transition at a shock stress of about 40 GPa, though the volume change associated with it would have to be small. The reshock and release experiments also provide estimates of the shear stress and strength in the shocked state as well as a dynamic mean stress curve for the material. The material supports only a small shear stress in the shocked (Hugoniot) state, but it can support a much larger shear stress when loaded or unloaded from the shocked state. This strength in the shocked state is initially lower than the strength at the elastic limit but increases with pressure to about the same level. Also, the dynamic mean–stress curve estimated from reshock and release differs significantly from the hydrostate constructed from low-pressure data. Finally, a spatially resolved interferometer was used to directly measure spatial variations in particle velocity during the shock event. These spatially resolved measurements are consistent with previous work and suggest a nonuniform failure mode occurring in the material.

Atomic structure of amorphous shear bands in boron carbide

“…Therefore, B 4 C has been an important structural ceramic for the applications where both high strength and lightweight are required 6,7 . However, unlike other high performance ceramics, B 4 C displays an anomalous reduction in shear strength under pressures [8][9][10][11] . High-resolution electron microscopy of shock-loaded fragments revealed that the formation of nano-scale amorphous shear bands is responsible for the dramatic loss of shear strength at high pressures 12 .…”

Plasticity and Spall in High Density Polycrystals: Modeling and Simulation

“…Such information should provide increased understanding of experimentallyobtained results from plate impact tests [6,7].…”

“…The theory is implemented in a dynamic Lagrangian finite element (FE) code [5], and 2D FE meshes are constructed of the initial microstructures of a KE rod sectioned either transversely or parallel to the rod axis (i.e., the extrusion direction). Simulations of high rate impact, wave propagation, and spall are conducted, reminiscent of conditions present in plate impact experiments [6,7]. We show how statistical data acquired from simulations depict effects of the microstructure and model parameters.…”

Quantum and classical molecular dynamics simulation of boron carbide behavior under pressure

“…After that it drops and shear strength could be obtained by the value of shear component. The calculated values are compared with the data, obtained from the release and reshock experiments [18]. These data correspond to the damaged state of the boron carbide, which is realized after the propagation of the first shock wave.…”