Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session I01: Resolved MesoscaleFocus Recordings Available
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Chair: Judith Brown, Sandia National Laboratories Room: Anaheim Marriott Platinum 5 |
Tuesday, July 12, 2022 9:15AM - 9:45AM |
I01.00001: Implications of reaction chemistry models for multiscale predictions of shock sensitivity of eneregtic materials Invited Speaker: Uday Kumar The sensitivity of energetic materials depends on molecular and microstructure. The former determines material properties, some of which are fairly well established for widely used energetic species, such as HMX, RDX, TATB etc. However, one primary driver of sensitivity remains quite unsettled, viz. reaction chemistry models for the decomposition and combustion. Traditionally, sensitivity (in Pop-plots/James curves) of these energetic materials have been characterized experimentally or through global, semi-empirical reactive burn models that have not demanded accurate reaction chemistry models. With the recent advances in multi-scale, first-principles models to develop predictive, microsructure-aware energy deposition models, it is now imperative to settle reaction chemistry models for individual energetic molecular species. In this presentation, we will show how uncertainties in reaction chemistry models for popular species such as HMX can significantly influence structure-property-performance predictions for HMX-based heterogeneous EMs. Uncertainties in reaction chemistry models are quantitatively linked to the uncertainties in macro-scale SDT predictions. The physics of hotspots underlying these uncertainties are eluciated. Finally, some insights and guidelines are offered regarding the characteristics of "acceptable" reaction chemistry models from the viewpoint of making reliable SDT predictions. |
Tuesday, July 12, 2022 9:45AM - 10:00AM |
I01.00002: Influence of Shock Pressure on Hot Spot Formation in a Model Plastic-Bonded Explosive Belinda P Johnson, Xuan Zhou, Dana D Dlott Hot spot behavior influences the sensitivity and shock-to-detonation transition of plastic-bonded explosives (PBX). Yet, experimental observation of hot spots has been precluded by detection techniques which can resolve the multiple time and length scales at which they exist (fs-µs, nm-µm). We developed a model PBX consisting of a single crystal of the high explosive HMX (cyclotetramethylene-tetranitramine) embedded in a transparent polyurethane binder which allowed us to directly observe hot spots at the time and length scales they exist. In this work, we investigated the influence of shock pressures on hot spot behavior by 1) visually tracking hot spots with micron-resolved high-speed gated imaging, and 2) tracking hot spot temperatures with nanosecond-resolved optical pyrometry. We shocked ~100 HMX single crystals at pressures ranging from 12-26 GPa. Two distinct shock pressure thresholds were observed. At 15 GPa some crystals began producing slow growing, discrete hot spots, while over 23 GPa the hot spot density was sufficient to result in massive deflagration. Additionally, initial estimates for the velocity of the flame front across an HMX crystal were calculated from the high speed images taken at median pressures. |
Tuesday, July 12, 2022 10:00AM - 10:15AM |
I01.00003: The Effects of Microstructure on Detonation Wave Spreading in Nanoparticle TATB Ryan R Wixom One of the most critical performance characteristics of the explosive triaminotrinitrobenzene (TATB), is detonation wave spreading. This phenomenon is also often referred to as “corner turning,” and describes how well a detonation wave can spread laterally into unreacted material that isn’t directly in the path of the normal wave. In non-ideal explosives, like TATB, detonation waves tend to travel forward at a higher rate than they spread to the side, which can leave unconsumed explosive material in certain configurations such as transfer from one explosive charge into another of larger diameter. There are several well established tests for characterizing this undesirable behavior, but they provide only an empirical understanding. I will present on a new small scale experiment we developed for testing detonation wave spreading, and make comparisons between commercially available TATB and nanoparticle TATB. We have characterized the microstructure of both materials at three densities, and used those microstructures in mesoscale simulations that give insight into the underlying mechanisms. Nanoparticle TATB behaves like an ideal explosive at lower densities, spreading nearly as fast as the normal propagation. At high density it doesn’t appear to spread at all, “tunneling” through the material. This unusual behavior can be explained by analyzing the distribution of temperatures resulting in mesoscale simulations of the different microstructures. These results suggest a path for designing a formulation with improved detonation spreading performance. |
Tuesday, July 12, 2022 10:15AM - 10:30AM |
I01.00004: From A Single Grain to Microstructure: An Experimental View of How Explosive Grains Interact Under Shock Compression Lawrence Salvati, Dana D Dlott, Siva Kumar Valluri Experimental observations of hot spot initiation and propagation in explosives have proven a challenging goal. We have developed an experiment where a small piece of polymer bonded explosive is shocked with a laser-launched flyer plate and probe the response with nanosecond video and time-resolved emission spectroscopy. This shows us the spatial dependence and temperature of thermal emission, providing insight on how microstructure affects shock initiation. Due to the high throughput of the tabletop shock compression experiments, large quantities of many different materials can be tested. In this study, we will discuss HMX in a polymer binder. By precisely controlling the particle size distribution as well as the particle loading in binder, we begin to understand in detail how the hot spots on individual particles react and spread to the bulk material. We observe a transition between isolated explosive particles, being either single or polycrystalline, up to a limit of HMX-loading where it can be viewed as a traditional plastic-bonded explosive. This method provides greater detail about how microstructure of plastic-bonded explosives changes the performance. |
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