Shock Response of Boron Carbide

Abstract

Boron carbide is of interest because of its potential application in protective systems both for personnel and structures. Therefore it is necessary to determine its mechanical response when subjected to impact loading. The present work was undertaken to determine tensile/spall strength of boron carbide under plane shock wave loading and to analyze all available shock compression data on boron carbide materials obtained from different sources. The principal conclusions are: (1) the tensile/spall strength of boron carbide when shocked between 2 and 15 GPa is 0.35 ± 0.07 GPa, (2) the existing shock compression data indicates that boron carbide tends to suffer a gradual loss of its shear strength as the magnitude of shock stress exceeds its Hugoniot Elastic Limit (HEL), i.e., 15-20 GPa, (3) the underlying reason or reasons for the inferred loss of shear strength under plane shock wave compression remains to be investigated, and (4) a general equation of state for boron carbide in its ambient phase is formulated which can adequately represent its hydrodynamic compression up to a strain of 0.25, i.e., to a maximum stress around 70 GPa.u

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 .…”

Analysis of Shock and High-Rate Data for Ceramics: Equation of State Properties and Fragmentation in the Ballistic Environment

“…where 3 2520 kg/m o ρ = is the theoretical density of boron carbide [Dandekar, 2001]. These shock velocity versus particle velocity states, shown as the solid symbols in the right hand plot in Figure (10), provide sensible shock velocity versus particle velocity Hugoniot states within the hydrodynamic equation-of-state surface (the hydrodynamic Hugoniot) for boron carbide referenced from the initial theoretical density.…”

“…In the range of 40 GPa shock pressure, containing a nice cluster of both 1900 kg/m 3 and 2400 kg/m 3 material Hugoniot points, temperatures of the lower initial density material subjected to Hugoniot shock compression are readily estimated. Based on a constant specific heat of 961.6 J/kg/K [Dandekar, 2001], an ambient average temperature rise due to shock heating is calculated to be about 2700 K. This level of temperature rise would approach the ambient melt temperature of boron carbide, which is also about 2700 K [Dandekar, 2001]. The specific heat can be expected to increase with temperature and therefore the calculated temperature rise is likely an overestimate.…”

“…It is the lowest density and the highest strength ceramic among a suite of ceramics under consideration for such applications. The necessary physical and mechanical properties of boron carbide have been studied extensively and access into much of the literature is available in the report of Dandekar [2001]. In particular, the Hugoniot and ultrasonic data integral to the development of shock wave and high-strain-rate constitutive response models are reviewed in the same report.…”

“…Strength states on the Hugoniot for near full density ceramic is an issue of current research and is pursued for boron carbide, for example, in the work of Vogler et al [2004]. Further references on the same topic are collected in the ARL report of Dandekar [2001]. The lowest three Hugoniot points for the nominal 5% porous material appear to exhibit some strength on the Hugoniot, although it is known that the test method of McQueen et al [1970] is not reliable at the lower shock amplitudes where structured shock waves are probably present.…”