Polyimide dynamically compressed to decomposition pressures: Two-wave structures captured by velocimetry and modeling

Abstract

We performed a series of six plate impact experiments on polyimide and modeled them using new reactant and products equations of state combined with an Arrhenius rate model. The first experiment was diagnosed with embedded electromagnetic velocity gauges through which we directly observed attenuation of the lead shock to an approximately constant state over a propagation distance of roughly 4 mm. Simulated gauge profiles were in excellent qualitative agreement with experiment and suggested a sluggish chemical reaction that did not proceed to completion. The remaining five experiments were conducted in a transmission geometry and diagnosed velocimetrically at the sample/window interface. All five of these yielded profiles with a sharp shock followed by a more gradual approach to maximum interface velocity that was “rounded” to varying degree. These profiles proved difficult to interpret unambiguously due to the convolution of the reactive wave upon first shock with reflection of the lead wave and reshock or release by the window. Comparison with thermochemical calculations strongly suggests that the point of maximum interface velocity corresponds to the equilibrium reshock or release locus. We discuss the implications of this point for the practice of impedance matching based on the reflected Hugoniot of reactive materials such as polymers. The reactant and thermochemical products equations of state are developmental SESAME tables 97710 and 97720, respectively.

Atomic Insight into Multilevel Microstructure Evolution and Energy Variation Mechanisms of Polyimide under Shock Compression

“…Figure displays the density and energy curves during the PI model preparation, indicating that the system tends toward equilibrium and an energy-minimum state. The final density of the PI model is approximately 1.355 g/cm 3 , which aligns with MD results ranging from 1.33 to 1.36 g/cm 3 reported in the refs ,, and is also close to the actual experimental density of PI material (ranging from 1.35 to 1.42 g/cm 3 ,, ).…”

“…The Hugoniot relations delineate the trajectory of matter’s shock-compression state, forming the foundational underpinning for modeling the EOS relevant to the studied material. ,, Figure presents the Hugoniot profiles for PI on the shock wave velocity versus particle velocity ( U s – U p ) and shock pressure versus volume ( P – V ) planes. The black symbols denote experimental data gathered from diverse published sources, ,,, while the red circles represent MD calculations. Notably, a discernible concurrence between the experimental and MD outcomes is observed within the current shock range, affirming the validity of the developed MD model for characterizing the shock responses of PI material.…”

“…It is important to emphasize that prior research has documented the disintegration of PI materials occurring when subjected to shock pressures exceeding approximately 20 GPa. ,, In this study, our focus lies within the shock pressure regime of 0–20 GPa (corresponding to shock velocities, U s , of 2.5–6.0 km/s), without considering the implications of polymer disintegration. Therefore, PCFF is implemented as a nonreactive potential and has been well validated for effectively modeling the shock behaviors of various polymers, including polyethylene, polyurethane, and polyurea. ,, …”

“…The authors probed the structure of shocked PI specimens in the range of 28−163 GPa using X-ray diffraction, noting shock-induced melting below a shock pressure of 32 GPa. Huber et al 21 subjected the PI material to decomposition pressures (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40), tracking the shock wave with embedded electromagnetic velocity gauges. They directly observed the attenuation of the leading shock wave and argued that the change in the PI Hugoniot curve originates from shockinduced chemical reactions rather than shock melting.…”