Mesoscale simulations of melt production in porous metals under shock compression

Mesoscale simulations of a LiF impactor colliding with a PMMA capsule containing aluminum powder (ρ00 = 1.5 g/cc) have been performed to investigate shock-induced melting in porous metals. Impact velocities of 1-2.5 km/s are chosen to coincide with in situ X-ray diffraction experiments, which provide direct evidence of shock-induced melting in aluminum powders. Mesoscale simulations show shock heating within the powder is highly nonuniform and melting remains incomplete over hundreds of nanoseconds behind the shock front despite equilibrium pressure-temperature states from continuum simulations lying above the experimental melt line. Such incomplete melting behavior is consistent with X-ray diffraction data obtained in experiment. For an impact velocity of ∼1 km/s, mesoscale simulations predict re- solidification behind the shock front as high-temperature regions are cooled below the melt line. Reducing the grain size of the powder by a factor of two leads to a reduction in the time required to reach complete melt such that total melting of the powder may be observed experimentally for an impact velocity of 2.42 km/s.