Associate Professor of Mechanical Engineering
School: Mechanical Engineering
Expected Graduation: 2020
Project/Thesis: Damage evolution and temperature rise in polymer bonded explosives under impact and vibrations
Camilo A. Duarte
School: Mechanical Engineering
Expected Graduation: 2021
Project/Thesis: Continuum modeling of fracture and plastic deformation in HMX single crystals under shock compression
The effect of the particle surface and binder properties on the response of polymer bonded explosives at low impact velocities
Dandekar, Akshay ; Roberts, Zane A ; Paulson, Shane ; Chen, Weinong ; Son, Steven F ; Koslowski, Marisol
Computational Materials Science, August 2019, Vol.166, pp.170-178
Polymer bonded explosives are designed to initiate under controlled conditions. However, accidental ignition leading to a deflagration, and even detonation, may occur during manufacturing, handling and transport. Understanding how ignition depends on microstructural features, such as cracks and voids in the particles, and on the adhesive and mechanical properties of the binder through predictive numerical simulations and modeling will help to improve safety. Finite element simulations and experiments of a single high energetic material particle embedded in polymer binders are performed to investigate the effect of the material properties of the binder and the particle surface properties, on damage and temperature at an impact velocity of 10 m/s. Particles with low and high quality surface properties, and two different binders are analyzed. The simulations with the lower stiffness binder do not show a significant increase in temperature after impact. A polymer with higher stiffness induces more particle damage under impact contributing to a larger temperature rise. Furthermore, high quality surface and higher adhesion strength induces larger stresses and increase the temperature rise.
The effect of crystal anisotropy and plastic response on the dynamic fracture of energetic materials
Grilli, Nicolò ; Koslowski, Marisol
Journal of Applied Physics, 21 Oct. 2019, Vol.126(15)
The thermomechanical behavior of solids includes dissipative processes such as plastic deformation and fracture. The relative importance of these processes on the response of energetic materials has been a subject of study for many decades due to their significance on ignition and reaction. However, a constitutive model to simulate the anisotropy of the crack patterns and the effect of plastic deformation due to slip in energetic materials is not yet available. Finite strain thermomechanical constitutive equations that couple crystal plasticity, an equation of state, and an anisotropic phase field damage model are presented. The model is implemented in a multiphysics finite element solver and used to simulate recent experiments on β -HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) by Zaug et al . The simulations reproduce qualitatively the crack pattern and the crystal orientation dependence of the observed damage. Specifically, more damage is observed when the crystal is impacted in the ( 010 ) direction, while more plastic deformation is observed when the load is applied in the ( 110 ) direction. The present model represents a step forward to understand the interplay between plasticity and fracture in shocked β -HMX single crystals. It can be used to gain insights into temperature increase and hot-spot formation under shock.
Duarte, Camilo A. ; Hamed, Ahmed ; Drake, Jonathan D. ; Sorensen, Christian J. ; Son, Steven F. ; Chen, Weynong W. ; Koslowski, Marisol
Propellants, Explosives, Pyrotechnics, February 2020, Vol.45(2), pp.243-253
Heat generation in the vicinity of a void during shock compression plays a key role in the initiation of energetic materials. The shock response of a single ‐HMX crystal with a single void is studied with simulations that include plasticity and heat transport. The numerical results are validated with an experiment in which a 500 m void is machined in an HMX single crystal and impacted. Experiments and simulations of the dynamical evolution of the morphology of the void during the collapse and the rate of the area are in very good agreement for weak shocks.