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Karel Matous



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Numerical and experimental analysis of the Young's modulus of cold compacted powder materials


A. Salvadori1,2, S. Lee1, A. Gillman1,2, K. Matous1,2, C. Shuck1,3, A. Mukasyan1,3, M.T. Beason1,4,
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.

Download the paper here


2017 Notre  Dame  and Dr. Karel Matous