Modeling High Strain Rate Plasticity in BCC Lead

High-energy lasers enable determination of metal strength at very high pressures. Here we consider the strength (flow stress) of lead in the high-pressure body-centered cubic (bcc) phase at a peak pressure of about 400 GPa. Two previous models of Pb strength were built from the low-pressure face-centered cubic (fcc) phase. Plasticity in bcc and fcc crystals can be very different. Experiments conducted at the National Ignition Facility have used ramp compression to drive Rayleigh-Taylor instability and measured the ripple growth to infer strength in the bcc phase of lead and lead alloy. We describe an Improved Steinberg-Guinan model for bcc lead strength using ab initio calculations of the shear modulus at pressure that agrees well with those experiments. We also report the results of large-scale molecular dynamics simulations on the rate dependence of the flow stress in lead at these high strain rates. The alloying, which increases strength 4x at ambient conditions, has no measurable effect at high-pressure.