SUBJECT: Ph.D. Proposal Presentation
BY: David Hardin
TIME: Friday, April 18, 2014, 2:30 p.m.
PLACE: MRDC Building, 4211
TITLE: Geometric and Thermomechanical Influences on the Ignition Sensitivity of Polymer-Bonded Explosives (PBXs) to Impact Loading
COMMITTEE: Dr. Min Zhou, Chair (ME)
Dr. Julian Rimoli (AE)
Dr. C. Michael Lindsay (Air Force Research Laboratory)
Dr. Naresh Thadhani (MSE)
Dr. Rick Neu (ME)


The process of formulating a new energetic composite is a long, expensive process that is heavily reliant on years of experience and extensive experimental testing. One issue standing in the path of a more streamlined process is a fundamental lack of understanding of how formulations respond to mechanical insult such as heating, dragging, or dropping. The proposed research centers on developing a reliable understanding of the thermal and mechanical response mechanisms due to impact loading that directly lead to initiation in polymer-bonded explosives (PBX). The primary focus is on quantifying and characterizing the spatial and temporal distribution of energy localization sites termed “hotspots”. The methodology proposed here combines a deterministic analysis of the thermal and mechanical response to impact loading of PBXs with a statistical treatment of the critical results. The deterministic analysis will be performed using the cohesive finite element method (CFEM) which embeds potential fracture surfaces along all element boundaries of a finite element mesh and allows for the consideration of large deformation, thermo-mechanical coupling, semi-arbitrary crack initiation and growth, friction along crack faces, and plastic heating. In the CFEM analysis, the HMX phase of the PBX microstructures will be modeled using an elastic-viscoplastic constitutive model and a thermo-viscoelastic relation will be used for the polymeric binder. The second step will be a statistical treatment of the hotspots generated during the CFEM calculations. This treatment will be used to quantify the variability in specimen response due to distinct, statistically similar PBX microstructures. Finally, the material response will be framed in terms of essential macroscopic quantities as a function of controllable microstructural attributes of the original sample. These microstructure – performance maps will help provide a guide for the design specifications of future energetic composites.