The Dynamic Response of Polymers Interrogated by 3rd Generation X-ray Light Sources

Abstract

Cellular silicones reinforced with silica filler and prepared using additive manufacturing (AM) have been used widely for vibrational damping and shockwave mitigation. The two most commonly printed cellular silicone structures-simple cubic (SC) and face-centered tetragonal (FCT)-display distinctly different static and dynamic mechanical responses. In this work, the relationship of filler size and composition with mechanical response is investigated using polydimethylsiloxane-based silicones filled with aluminum oxide (alumina, Al 2 O 3), graphite, or titanium dioxide (titania, TiO 2). SC and FCT structures of porous, periodic silicone pads were printed using new DIW resin formulations containing up to 25 wt.% of functional filler. All AM pads were characterized using chemical, thermal (TGA, DSC), and mechanical techniques (DMA, compression). Dynamic compression experiments coupled with time-resolved X-ray imaging were performed to obtain insights into the role of filler interactions in the in situ evolution of shockwave coupling in these functional, periodic, and porous polymers. Understanding the kinetics of phase transition and decomposition during extreme condition events is not a trivial undertaking. Capturing these processes require: 1) diagnostics that probe on the timescales and at energies capable of interacting with the dynamically evolving products, penetrating the opaqueness of the changing system; and 2) detectors sensitive enough to observe these events. Synchrotrons provide access to keV X-ray beams capable of penetrating the opaqueness of the dynamic event with a wavelength adept at interacting with the evolved or compressed crystal structures. At the Dynamic Compression Sector at the Advanced Photon Source, gas guns produce planar shocks at a myriad of projectile velocities while capturing in situ X-ray diffraction of the evolving material under dynamic compression. Specifically, we shocked high density polyethylene to 7.45 GPa observing compression and orientation of the polymer chains.