Impact fragmentation of a brittle metal compact

The article of record as published may be found at https://doi.org/10.1063/1.5026711The fragmentation behavior of a metal powder compact which is ductile in compression but brittle in tension is studied via impact experiments and analytical models. Consolidated metal compacts were prepared via cold-isostatic pressing of <10 lm zinc powder at 380 MPa followed by moderate annealing at 365 C. The resulting zinc material is ductile and strain-hardening in high-rate uniaxial compression like a traditional metal, but is elastic-brittle in tension with a fracture toughness com- parable to a ceramic. Cylindrical samples were launched up to 800 m/s in a gas gun into thin alumi- num perforation targets, subjecting the projectile to a complex multiaxial and time-dependent stress state that leads to catastrophic fracture. A soft-catch mechanism using low-density artificial snow was developed to recover the impact debris, and collected fragments were analyzed to deter- mine their size distribution down to 30 lm. Though brittle fracture occurs along original particle boundaries, no power-law fragmentation behavior was observed as is seen in other low-toughness materials. An analytical theory is developed to predict the characteristic fragment size accounting for both the sharp onset of fragmentation and the effect of increasing impact velocity.Office of Naval ResearchThe authors acknowledge support from the Office of Naval Research Grant No. N0001417WX0088