Investigation of Dynamic Processes in Energetic Materials by Ultrafast Transmission Electron Microscopy at the Nanoscale
Abstract
Investigation of Dynamic Processes in Energetic Materials by Ultrafast Transmission Electron Microscopy at the Nanoscale. Fundamental understanding and prediction capability of energy localization and evolution in reactive materials are limited by the lack of understanding of the details of the processes occurring at different time and length scales. Energetic materials typically contain two or more phases/components. Under impact, mechanical energy will be localized due to the formation of stress-concentration sites such as localized contact points, friction, void collapse, and deformation bands inside the heterogeneous materials. Energy localization leads to localized temperature rise, and eventually the formation of hot spots that lead to ignition. While this general concept has been widely accepted, the desired predictive capabilities for the hot-spot formation and ignition have not been developed primarily due to the lack of quantitative experimental measurements. For example, it is likely that the hot-spot mechanism changes with loading (type, amount, etc.), rate and nature of the stress-concentration sites. Currently it is not certain exactly how the mechanism changes as conditions and materials are changed, and there is inadequate data to validate models. Despite impressive recent advances in experiments and simulations, several fundamental scientific questions remain open at all the relevant scales. For example, while hotspots are known to play a central role in shock-initiation of these materials, only indirect information about them exists; the relative importance of various microstructural features in generating critical hot-spots is not known. Recent simulations showed that the size and thermodynamic conditions of hotspots are not sufficient to determine their criticality, indicating that non-statistical processes and mechanochemistry play an important role; these predictions challenge prevailing theories and have not been confirmed or denied experimentally. Conventional experiments to date lacked the required combined spatial and temporal resolution to observe hot-spot dynamics and models lacked the fidelity or ability to reach the appropriate scales to answer these questions. This proposed research focuses on this need and will develop fundamental understandings of the hot-spot dynamics through utilization of state-of-the-art Ultrafast Transmission Electron Microscopy (UTEM) system at the PI’s laboratory at Purdue University. A successful project will result in: (i) a more fundamental understanding of chemistry and physical processes at extreme conditions, and provide definite answers to the most pressing open science questions in the field, and (ii) development of novel ultrafast instrumentation and techniques to probe dynamic processes in energetic composites to advance the molecular, crystal and microstructural level research on materials in general. The focus will be on a series of materials of increasing complexity to isolate the various physics involved, starting with crystalline HMX, then moving to HMX-polymer composites of varying microstructure and formulations including metallic nanoparticles to increase the energy content. These materials will be subject to a variety of loading including shock, thermal, and combinations thereof.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 23, 2016
- Source ID
- N000141612504
Entities
People
- Volkan Ortalan
Organizations
- Office of Naval Research
- United States Navy
- University of Virginia