Modeling of Coupled Electromagnetic-Thermo-Mechanical Laser Interactions and Microstructural Behavior of Energetic Aggregates.

摘要

The coupled electromagnetic-thermo-mechanical response of RDX (cyclotrimethylene trinitramine)-polymer energetic aggregates under laser irradiation and high strain rate loads has been investigated to identify laser-induced hot spot formation and failure mechanisms at different physical scales. A computational approach was developed to investigate the coupled phenomena of high frequency electromagnetic (EM) wave propagation, laser heat absorption, thermal conduction, and inelastic dynamic thermomechanical deformation in heterogeneous energetic materials. The approach couples Maxwell's equations with a dislocation density-based crystal plasticity formulation with a nonlinear finite-element approach to predict and understand thermo-mechanical response due to the interrelated effects of dielectric heating, adiabatic heating, thermal decomposition, and heat conduction. The effects of heterogeneous microstructural characteristics, such as void distribution and spacing, grain morphologies and orientations, crystal-binder interactions, and dislocation densities were analyzed to determine their influence on hot spot formation and EM and mechanical energy localization. The effects of beam intensity, incident wavelength, material electromagnetic absorption coefficient, and the heterogeneous microstructure on spatial and temporal behavior and mechanisms of laser-induced hot spot formation were characterized and related to the thermo-mechanical response. Different mechanisms for hot spot initiation under dynamic laser and pressure loads were identified, which are a function of shear strain localization and laser heat absorption. The predictions indicate that hot spot formation was accelerated by higher absorption coefficients and by localized plastic deformations that occurred in areas of significant laser heating.