The threat of micro-meteoroid and orbital debris (MMOD) collisions with spacecraft and satellites has been increasing with the increasing worldwide use of low earth orbit. Providing low-areal-density shielding for the mitigation of these high velocity impacts is essential for ensuring successful and cost effective missions. Here, we report results obtained from hypervelocity impact testing on bulk metallic glass (BMG) matrix composites. Their carbide-like hardness, low melting temperatures, ultra-high strength-to-weight ratio and the ability to be processed like polymers are material attributes ideally suited for spacecraft shielding, particularly as an outer wall bumper shield.

Long-exposure image of a hypervelocity impact between an aluminum projectile traveling at 3 km/s and a three-layer bulk metallic glass composite foam. Owing to their unique combination of high hardness, low density, and low melting temperatures, metallic glasses appear to be optimal materials for orbital debris shields for spacecraft and satellites in low-earth-orbit. In this article, Davidson et. al. perform the first evaluation of these non-crystalline materials under hypervelocity impacts. Further details can be found by D. C. Hofmann et al. on page 27.

The mechanical behavior of single crystalline aluminum nano-pillars under uniaxial compression differs from bulk Al in that the former is characterized by a smoother transition from elasticity to plasticity. We propose an extension of the phenomenological model of dislocation starvation originally proposed in [Greer and Nix, Phys. Rev. B 73 (2006) 245410] additionally accounting for dislocation nucleation. The calibrated and validated continuum model successfully captures the intrinsic mechanisms leading to the transition from dislocation starvation to dislocation nucleation in fcc nano-pillars. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The mechanical behavior of bicrystalline aluminum nano-pillars under uniaxial compression reveals size effects, a stochastic stress–strain signature, and strain hardening. Pillar diameters range from 400nm to 2μm and contain a single, non-sigma high angle grain boundary oriented parallel to the pillar axes. Our results indicate that these bicrystalline pillars are characterized by intermittent strain bursts and exhibit an identical size effect to their single crystalline counterparts. Further, we find that the presence of this particular grain boundary generally decreases the degree of work hardening relative to the single crystalline samples. These findings, along with transmission electron microscopy analysis, show that nano-pillar plasticity in the presence of a grain boundary is also characterized by dislocation avalanches, likely resulting from dislocation nucleation-controlled mechanisms, and that at these small length scales this grain boundary may serve as a dislocation sink rather than a dislocation source.