A Unified Framework Which Uses Multi-Scale Microstructural Information for Modeling Dynamic Failure in Brittle Materials
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Date
2014-06-13
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Johns Hopkins University
Abstract
Developing improved armor ceramic materials necessitates an understanding of the active failure mechanisms during an impact event and the interactions between these mechanisms that lead to material failure. Similarly, within planetary science, the mechanisms active within impact events provide insight into the origin, evolution, and internal structure of asteroids and other planetary bodies. While careful experiments interrogate the true physical process, real time, high resolution data in three dimensions needed for investigating the competition between dynamic deformation mechanisms is not yet available. Simulations provide a vehicle for testing our understanding of the physical processes, evaluating the effectiveness of experiments, and illuminating the competition between deformation mechanisms.
We develop a material model that includes physically based material variability, micromechanics-based damage growth, granular flow, compaction of the granular material, and a Mie-Gr\"uneisen equation of state. Using this new modeling framework, we simulate three experimental configurations including Edge On Impact, dynamic uniaxial compression, and simplified ballistic loading. Using simulations of Edge On Impact experiments in AlON, we demonstrate that the failure front observed in experiments propagates as a result of stress waves interacting with the free surfaces favoring damage growth on the interior of the tile (consistent with experimental observations). In simulations of simplified ballistic impact on boron carbide, we demonstrate that the extent of granular flow and material microcracking is linked to the slope of the granular flow surface, suggesting that materials capable of forming larger, high aspect ratio fragments may provide better resistance to penetration.
Finally, we demonstrate the versatility of the model by investigating the collisional evolution of the near Earth asteroid Eros. Using two different potential internal flaw distributions, we demonstrate that the stronger of the two flaw distributions creates a heterogeneous damage and granular flow pattern within the asteroid (which is consistent with observations). Once this network of highly damaged material develops, subsequent impacts of similar severity do not significantly alter the orientation of the failure zones.
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Keywords
micromechanics, dynamic failure, impact, ceramic materials, materials by design, Eros, porosity, granular flow