Computational Physics GroupKarel Matous |
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Numerical and experimental analysis of the Young's modulus of cold compacted powder materials
I.E. Gunduz1,4, S.F. Son1,4 1Center for Shock Wave-processing of Advanced Reactive Materials, 2Department of Aerospace and Mechanical Engineering, 3Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN, 46556, USA. 4School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, USA. Abstract
We present co-designed experimental, theoretical, and
numerical investigations aiming at estimating the
value of the Young's modulus for cold compacted powder
materials. The concept of image-based modeling is used
to reconstruct the morphology of the powder structure
with high fidelity. Analyses on aluminum powder
pellets provide significant understanding of the
microstructural mechanisms that preside the increase
of the elastic properties with compaction. The role of
the stress percolation path and its evolution during
material densification is highlighted.
Conclusions
In this paper, the
Young's modulus of cold compacted metal powders has been
estimated via computational simulations, using
image-based morphological reconstructions of the
microstructure and high performance computing.
Computational simulations have been compared with
co-designed experimental investigations for the
quasi-static Young's modulus. The dynamic Young's
modulus was measured, also. Proposed numerical
procedures are general and provided insightful
comparisons with the Young's modulus of alumina cold
compacted powder compounds.
Penetrating conclusions on the micro-mechanics of cold compaction processes have been drawn. As already envisaged on an experimental basis, the load response of moderately compressed powders is dominated by its particulate nature and inter-particle forces, while the load response of heavily compressed material is similar to that of a porous solid. Numerical analysis has shown that, especially at low volume fractions, the two mechanisms of powder compaction (rearrangment and deformation) interact strongly, and a unique value of Young's modulus can hardly be established as a function of the volume fraction only, because it depends on the history of deformation and of the stress percolation path. The importance of the inter-particle morphology and the surface area of such a network has been highlighted and quantified via a novel scaling law. Evidence of anisotropy at low volume fractions, as well as significant scatter in experimental investigations, also confirm this conclusion. In the current implementation, local tensile states are utterly transmitted by joints, inducing a local cohesion with no magnitude limitation. Moreover, it was not possible to estimate the dynamic Young's modulus numerically without tracking the contact regions between the particles. Further developments may numerically resolve the contact between particles, imposing pure unilateral constraints. Acknowledgment We gratefully acknowledge A. Justice
for his help in experimental investigations. This work
was supported by the Department of Energy, National
Nuclear Security Administration, under the award number
DE-NA0002377 as part of the Predictive Science Academic
Alliance Program II. M. T. Beason was also supported by
the Department of Defense (DoD) through the National
Defense Science & Engineering Graduate Fellowship
(NDSEG) Program. We also acknowledge computational
resources from the 2016 ASCR Leadership Computing
Challenge (ALCC). Finally. we acknowledge the reviewers
for useful comments that improved this paper. © 2017 Notre
Dame and Dr. Karel Matous
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