Publications by John Chalker

Understanding the damage of polymer matrix composites by integrating chemical, morphological and mechanical properties

Proceedings of the American Society for Composites - 30th Technical Conference, ACS 2015 (2015)

D Nepal, A Ecker, S Barr, J Moller, J Chalker, B Rooths, E Mungall, G Kedziora, R Berry, T Breitzman

Copyright © 2015 by DEStech Publications, Inc. and American Society for Composites. All rights reserved. Detailed physical and mechanical characterization of the matrix as well as the interphases of polymer matrix composites can lead to a more complete understanding of failure mechanisms in polymer matrix composite (PMC). This study illustrates mechanical damage of polymers in both the bulk, as well as around the interphase region through integrated computation & experimentation approach. We have developed a quantum mechanics-molecular dynamics framework, which has enabled the prediction of bond scission under load, creation of intermittent free radicals, and exploration of the potential energy surface for possible secondary reactions immediately following bond scission. In parallel, we have conducted experiments with epoxy systems with varying molecular weight and cross-linker density at different load conditions to benchmark the simulation findings of the chemical species present on fracture surfaces of the polymer. In order to evaluate experimentally molecular level effects of mechanical load in epoxy-systems, detail characterizations were conducted combing spectroscopy (X-ray photoelectron spectroscopy, FT-Infrared spectroscopy), microscopy (HRTEM, AFM-IR, SEM), X-ray diffraction (SAXS) and mechanical testing (3-point bending). Similarly, the nanoscopic nature of interphases of PMCs in terms of topography, chemical mapping/bonding, fractography, and modulus are also studied in order to find a bridge between nanoscopic, microscopic and macroscopic mechanical properties.

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