Christopher Miller

  • Program Year: 4
  • Academic Institution: Georgia Institute of Technology
  • Field of Study: Mechanical Engineering
  • Academic Advisor: Min Zhou
  • Practicum(s):
    Lawrence Livermore National Laboratory (2016)
    Sandia National Laboratories, New Mexico (2018)
  • Degree(s):
    B.S. Mechanical Engineering, University of Colorado Boulder, 2014

Summary of Research

My research involves simulating the response of pressed granular explosives (HMX) under shock loading. I use a cohesive finite element framework (called CODEX) to simulate the grain structure at the mesoscale level, and can closely study how hotspots evolve in the material over time due to fracture and plastic deformation. The overall goal of this research is to better understand the ignition process in high energy-density explosives, and how variations in microstructure affect it. This research is done in collaboration with the Air Force Research Laboratory (AFRL); we are trying to further develop and refine CODEX by simulating the same results as seen in experiments performed by AFRL.

Ignition in granular explosives is defined as the timeframe between a mechanical insult to the sample (simulated by a piston impact), and a self-sustained chemical reaction which leads to detonation. During this period, the grains of the material deform and inter-granular fracture leads to shear stress as grains slip past each other. Both of these mechanisms generate heat as a method to dissipate energy in the system. This localized concentration of heat leads to temperature spikes in the material, known as hotspots, which can reach criticality (starting the chemical ignition process) assuming that the temperature is high enough, or the hotspot area is large enough.

By simulating hotspot development of HMX crystals computationally, various microstructural parameters can be isolated and analyzed to understand their specific role in ignition behavior. Some variable microstructure aspects include modifying the average grain size, grain distribution, HMX volume fraction, or material cohesive properties.

While the results of this work are specifically focused on explosive materials, the potential results of this research are wide ranging. A better understanding of polycrystalline strength and structure can lead us to design new, stronger materials for use in everyday applications.

Publications

1) S. Kim, C. Miller, Y. Horie, C. Molek, E. Welle, M. Zho. "Computational prediction of probabilistic ignition threshold of pressed granular
Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under shock loading", Journal of Applied Physics 120, 115902 (2016)

2) E. Chason, J.W. Shin, C.-H. Chen, A.M. Engwall, C.M. Miller, S.J. Hearne, L.B. Freund. "Growth of patterned island arrays to identify origins of thin film stress", Journal of Applied Physics 115, 123519 (2014)

3) E. Chason, A.M. Engwall, C.M. Miller, C.-H. Chen, A. Bhandari, S.K. Soni, S.J. Hearne, L.B. Freund, B.W. Sheldon. "Stress evolution during the growth of 1-d island arrays: kinetics and length scaling", Scripta Materialia 97, pgs. 33-36 (2014)

Awards

1) Graduated Magna Cum Laude with Honor, CU Boulder (2014)
2) Deans List, CU Boulder (2010-2014)
3) President's Fellowship, Georgia Tech (2014)
4) Guy Kelley Scholarship - Engineering, CU Boulder (2012)
5) Hong Mechanical Engineering Scholarship, CU Boulder (2012)
6) DLC Research Scholarship, CU Boulder (2013)
7) Engineering RAP Award, CU Boulder (2013)