Abstract:
The shock to detonation transition (SDT) in a condensed phase heterogeneous energetic material is thought to be initiated by energy localization at defect sites such as pores, cracks and interfaces in the material. “Hotspots” at pore collapse and shear band sites ignite, grow, and coalesce to pump thermal energy into the shock, which progressively builds into a detonation. However, there are fundamental unanswered questions regarding the mechanisms by which chemical energy release at reaction fronts (propagating at deflagaration velocities – meters per second) couple with the fast-moving shock wave (kilometers/second). In this talk, through resolved high-fidelity numerical simulations in evolving microstructures of a pressed energetic material, we elucidate the mechanisms that contribute to the early stages of SDT, i.e., the regime where the shock initiates a field of hotspots that co-evolve with the amplifying shock as it transits to detonation. We show the important role played by pressure wavelets in the amplification process, identifying regimes dominated by hydrodynamics and plastic dissipation, leading thereafter to recruitment of reactive heat release and then in the final stage to the full coupling between the shock and reaction fronts driving the rapid transition toward the von Neumann spike. The calculations and results provide a clearer picture of the physico-chemical phenomena contributing to SDT and will lead to improved reactive burn models that better represent the physics of the transition zone from inert shock to reaction fronts propagating at detonation velocity.

Bio:
Udaykumar is the Allen S Henry Chair and associate dean for graduate programs, research and faculty at the University of Iowa college of engineering. His research focus is on modeling and simulation of moving boundary problems in thermomechanical systems, ranging from phase change thermal storage, biomedical applications involving cardiovascular and gastrointestinal mechanics, energetic material dynamics in propulsion and munitions, and multiphase flows. His work has been supported by grants from NSF, Whitaker Foundation Biomedical Engineering Grant, NIH, VA Research grants and various DoE and DoD labs and agencies.  He has led an AFOSR-MURI (2020-2025) and is currently PI on an ONR-MURI (2026 start). Udaykumar serves on various university-level committees, and is also an invited participant in DoD Visioning Workshops, such as the ARL Disruptive Energetics Far-Term Tech Forecasting Workshop (multiple years), a member of the organizing committee for the APS Shock Compression conference, an associate editor of Combustion and Flame: Condensed Phase, and a member of the advisory board for the Propellants, Explosives and Pyrotechnics journal.