MMS Seminar - Pradeep Guduru, Brown University - Dynamic Strength of Energetic Material Simulants: Experiments and Modeling

2:00–3:00 pm

Abstract

While the mechanical behavior of energetic materials and their simulants has been widely studied under normal impact, their shearing response under large pressures and shear strain-rates has not been well studied. Such measurements are crucial to inform constitutive models that aim to predict hot-spot formation and ignition behavior of energetic materials subject to multi-axial loading. In this study, dynamic strength of hydroxyl terminated polybutadiene - HTPB (an elastomeric binder), monolithic sucrose (an energetic material simulant) and their composites, under normal stresses of 3-10 GPa and shear strain rates of the order of 105-106 s-1 is studied. While the shearing resistance of HTPB remains constant under large shear strains, the shear strength of sucrose and the composites show a dramatic fall. The loss of shear strength of sucrose is attributed to the formation of shear localization. The shearing resistance of HTPB is shown to be highly pressure-sensitive whereas that of sucrose shows relatively small sensitivity to pressure. Moreover, at normal stresses of 9-10 GPa, the shear strength of HTPB becomes similar to that of sucrose and beyond these normal stresses, a transition in the localization and failure modes of the composite is expected. A viscoelastic model with pressure-dependent shear wave speeds and shearing resistance is used to describe the experimentally observed dynamic response of HTPB. A thermodynamically consistent constitutive model is presented to model the thermoelastic, thermo-viscoplastic response of sucrose. A complete Mie-Gruneisen equation of state is presented to model the volumetric behavior while the deviatoric response is captured through the Johnson-Cook Model. The material model captures experimental observations and predicts localization in the form of adiabatic shear bands, which explains the sharp drop in shearing resistance of sucrose observed in the experiments. The talk will also present an experimental effort at studying the dynamics of shock loaded pore collapse under plane strain conditions by combining high speed X-ray phase contrast imaging with digital image correlation.   

Apr 13