Dynamic fragmentation of Al-W granular rings with different mesostructures

Explosively driven fragmentation mechanisms of Al-W particulate composite rings were investigated. The effect of mesostructures (particulate Al and W, particulate Al and W fibers) and bonding between Al particles (processing via cold isostatic and cold isostatic+hot isostatic pressing) were determined. The kinematics of the expansion process was monitored using Photon Doppler Velocimetry measurements of the velocity of the outer surface of the rings. Numerical simulations of the expansion velocity of rings were in agreement with experimental data. Agglomerated fragments larger than sizes of initial Al particles were observed in experiments. The characteristic size of these agglomerates is most likely determined by the spacing between W inclusions. The simulations show that the dynamically expanded rings had clusters of particulates between shear bands (developing into macrocracks), which expand without significant plastic deformation, generating agglomerated fragments with sizes larger than initial Al particles, as observed in experiments. It was also demonstrated that debris has a measurable fraction of particles with sizes below the original particle sizes. The mesostructure of the fragments demonstrated that Al particles were heavily deformed within the regions having locally high strain plastic flow, which may result in fragments sizes below initial Al particle diameter. Simulations agree with experiments in that Al particles between neighboring W particles/fibers are heavily plastically deformed in comparison with Al particles away from W inclusions. Simulations also demonstrated that increasing initial porosity increases the plastic straining of Al particles between W particles/fibers. Thus, initial porosity may cause an increase in temperature of the Al fragments and cracking their surface oxide layers, therefore increasing the chance of subsequent rapid oxidation in air. Published by AIP Publishing.