Morphological changes in polyethylene subjected to shock waves
Rafael Rodrigues Dias5, Laura Caetano Escobar Silva2, Matheus da Silva Domingos1, Iaci Miranda Pereira1, Frank Bagusat3, Martin Sauer3, Tomás S. Plivelic4, Bluma Guenther Soares5
[1] Brazilian Technological Center, Materials Lab, Rio de Janeiro, Brazil; [2] Centro Nacional de Pesquisa em Energia e Materiais (CNPEM), São Paulo, Brazil, [3] Fraunhofer Institute of High Speed Dynamcs, Freiburg, Germany; [4] MAX IV Laboratory, Lund University, Lund, Sweden; [5] LIMNC, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
Thermoplastic polymers have gained prominence in individual ballistic armor owing to their advantageous properties. Its lightweight and flexible nature, along with its high impact resistance, makes it a feasible option as an alternative to metals and ceramics. They are mainly employed as fibers (para-aramid fibers and polyethylene) or matrices (epoxy, phenolic, polyethylene, polyurethane) in ballistic composites1.
A ballistic impact creates a shock wave front on the bullet/armor interface travelling through the material2. The propagation of a shock wave front in a solid medium is characterized by an abrupt discontinuity in the thermodynamic properties of the material, notably pressure, internal energy and specific volume3. The balance of mass, momentum and energy that governs this phenomenon can be mathematically treated by the Hankine-Hugoniot equations. For polymeric materials, the application of high pressures at high strain rates (106 - 108 s-1), with increase of temperatures above the melting temperature, leads to significant morphological changes.
In this communication, high density polyethylene (HDPE) samples were subjected to shock wave compression tests (flyer plate) of different values. The estimated thermodynamic responses were calculated and compared with existent values in the literature4,5 , obtaining consistent results.
Synchrotron Scanning SAXS/WAXS measurements were performed on the different samples in the Normal (ND) and Transversal direction (TD) to the shock wave. The results allow the morphological characterization of the system at the atomic and nanometric scale.
Keyword: polyethylene, shock wave, morphology, SAXS, WAXS
References
(1) Kulkarni, S. G., et al. "Ballistic Helmets: Their Design, Materials, and Performance Against Traumatic Brain Injury." Composite Structures 101 (2013) 313–331, doi:10.48550/arXiv.1206.354.
(2) Lassig, T. et al. "Investigations on the Spall and Delamination Behavior of UHMWPE Composites." Composite Structures 182 (2017) 590–597, doi:10.1016/j.compscitech.2017.09.013.
(3) Lassig, T. et al. "Analysis of the shock response of UHMWPE composites using the inverse planar plate impact test and the shock reverberation technique.", International Journal of Impact Engineering, 86 (2015) 240-248 doi:https://doi.org/10.1016/j.ijimpeng.2015.05.003.
(4) Carter, W.J., Marsh, S.P. “Hugoniot Equation of States of Polymes”. Los Alamos National Laboratory. Report, 1995
(5) Millet, J.F.C, Bourne, N.K. “The shock induced equation of state of three simple polymer”. J. Phys. D: Appl. Phys. 37 (2004) 2901–2907. doi:10.1088/0022-3727/37/20/018