Boron carbide is a candidate in many armor applications because it has an exceptional
specific strength (hardness approaching 30 GPa and low density of ~2.5 g/cc). In
practice, wider use of this material has been limited because it is well-known to show
a loss of shear strength at pressures exceeding 20 GPa. Here, the large-scale ballistic
response was investigated using the High voltage In-situ Diagnostic Radiography
Apparatus (HIDRA) at ARL. The penetrator-target interactions and activated damage
modes were observed using radiography, high speed imaging and velocimetry. The
small-scale impact and shock response was investigated using propagation phase
contrast imaging (PCI) and X-ray diffraction under shock loading at the Dynamic
Compression Sector (DCS, 35-ID-E) at the Advanced Photon Source. At the lowest
peak stresses investigated, experiments at both length scales show the penetrator
undergoes dwell and the target response is consistent with cone crack formation at
the impact site. At higher striking velocities there is a distinct transition to massive
fragmentation leading to the onset of penetration. Imaging and diffraction suggest
that the loss of shear strength at high pressures can be attributed to fine-scale brittle
fracture above the Hugoniot Elastic Limit (HEL). Finally, we will discuss how these
small-scale impact experiments are used for validation of meso and continuum-scale
computational models.
2021-04-07 08:00:00
