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Compression of Nanoporous Au Nanopillars

We study the compression deformation characteristics of nanoporous Au nanopillars with different nanopillar and ligament diameters using Molecular Dynamics (MD) simulations. Nanoporous nanopillars were carved from single crystal 3D bicontinuous Au structures generated from the algorithm proposed by Soyarslan [1]. Atomic nanoporous structures with metastable morphologies were obtained at the end of the relaxation process with the average zero state of stress. The relaxed structures were compressed uniaxially at a constant strain rate while the peripheral surfaces were free. Distinct deformation stages such as elastic, elastic-plastic, plastic plateau and rapid hardening were observed from the true stress-strain curves. The classical Gibson-Ashby model was modified to predict the ligament size-dependent elastic modulus by incorporating parameters representing the morphological and topological features [2]. A unique post-processing technique, namely skeletonization was adopted to represent the topological features in terms of the average number of load-bearing ligaments. The size-effect from the model is in agreement with the results from MD simulations, signifying the predominant mode of deformation of ligaments is compression. Further, the need for ensemble averaging over different topologies is emphasized. The yielded ligaments were identified during the deformation process, with the aid of Common Neighbour Analysis (CNA) and skeletonization. Hardening of nanopillar is observed to increase until the plastic plateau, despite a proportionate number of ligaments have yielded plastically. The plastic plateau region is initiated when the stacking fault area generation rate is maximum and it is terminated by a substantial increase in stress when the structure densifies. The densification is due to the coalescence of ligaments and closure of voids, which eventually leads to a polycrystalline bulk Au structure.

Dr. Santhosh Mathesan
Technion - Israel Institute of Technology
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