UC San Diego

The fragmentation and constitutive response of tailored aluminum-based compacts is examined under dynamic conditions. Mesostructured Al compacts having interfaces between the powders (with sizes of 40, 100, and 400 μm) with controlled strengths were produced by swaging. Nickel-aluminum compacts were also produced and studied because the Ni-Al system is an optimum model system to investigate exothermic reactions initiated by dynamic events, such as ballistic impact.

In order to obtain a fundamental quantitative understanding of the process the fragmentation of pre-compacted powders is essential for the modeling of the energetics and kinetics of exothermic reactions. Thus, in this work the Mott theory was extended by incorporating fracture toughness. The fracture toughness and yield stress are used to calculate fragment sizes in a variety of particle sizes and geometries which are compared with experimental results.

The fragmentation generated in the explosively-driven rings expanded at a velocity of approximately 100 m/s was captured by high-speed photography. The fragment size distributions obtained varied widely and correlated with the interfacial strength of the compacts as well as with powder size. Finite element simulations were also conducted to help better understand the influence of material properties on fragmentation. Experimental results and finite element simulations both confirm that the modified Mott theory, which incorporates fracture toughness, can successfully calculate fragment size.