Impact fragmentation of aluminum reactive materials

Abstract

We report the fragmentation of brittle, granular aluminum spheres following high velocity impact (0.5-2.0 km/s) on thin steel plates. These spheres, machined from isostatically pressed aluminum powder, represent a prototypical metallic reactive material. The fragments generated by the impacts are collected in a soft-catch apparatus and analyzed down to a length scale of 44 lm. With increasing velocity, there is a transition from an exponential Poisson-process fragment distribution with a characteristic length scale to a power-law behavior indicative of scale-invariance. A normalized power-law distribution with a finite size cutoff is introduced and used to analyze the number and mass distributions of the recovered fragments. At high impact velocities, the power-law behavior dominates the distribution and the power-law exponent is identical to the universal value for brittle fragmentation discussed in recent works. The length scale at which the power-law behavior decays is consistent with the idea that the length of side microbranches or damage zones from primary cracks is governing this cutoff. The transition in fragment distribution at high strain-rates also implies a significant increase in small fragments that can rapidly combust in an ambient atmosphere.

Lab-scale ash production by abrasion and collision experiments of porous volcanic samples

“…A similar result was described by Dufek and Manga (2008) who propelled single pumice clasts on to each other but they observed a non-linear increase in ash production rate at higher impact velocities; our results are only systematic with a correlation coefficient of 0.798. Dependency of ash production rate on available energies is described in various other studies: Salman et al (2002) and Hooper (2012), who work with metals, both find higher fragmentation rates with increasing impact velocities (that control E frac ). Cagnoli and Manga (2004) conducted abrasion experiments with pumice samples by using a rotating disc.…”

“…Collision experiments are also carried out in material sciences and show similar results to volcanic experiments: Salman et al (2002) described a relation between decreasing fragmentation rate and decreasing impact velocity, angle and particle size of spherical aluminum oxide particles projected against a target. Also Hooper (2012) produced fragments by collision down to a size of 44 μm by projecting brittle, cold pressed aluminum reactive materials on thin steel plates. An increase in impact velocity increased the resulting number of fine particles.…”

Dynamic fragmentation of Al-W granular rings with different mesostructures

“…Metal based reactive materials subjected to high strain, high strain rate plastic deformation and fragmentation are able to provide a significant release of chemical energy by intermetallic reactions 1-3 and/or oxidation 4 . Shear instability and localization of plastic deformation generate intense heat, fragmentation of particles and initiating reactions within shear bands, which can then propagate into the bulk of the surrounding material [5][6][7][8] . Bulk heating of reactive materials due to plastic deformation can also be conducive to their subsequent combustion.…”

Formation and Penetration of Jets by Shaped Charges with Reactive Material Liners

“…Reactive material is a class of solid energetic materials with an adequate amount of strength and sufficient insensitivity . Generally, they are formed by means of uniformly mixing active metal powders, alloy powders or intermetallic compounds with a polymer matrix (typically polytetrafluoroethylene) and consolidated via a pressing process.…”