Steven F. Son

Professor of Mechanical Engineering

Telephone: (765) 494-0539
More about Steven F. Son


Graduate Students

Aaron Afriat
School: Mechanical Engineering
Expected Graduation: May, 2021
Project/Thesis: Additive Manufacturing of Functional Energetic Materials using Vibration Assisted Printing

Julie Bach
School: Mechanical Engineering
Expected Graduation: May, 2021
Project/Thesis: Study on modifying the pressure time history of additively-manufactured gun propellant using infill parameters

Michael Baier
Christian Blum-Sorensen
School: Mechanical Engineering
Expected Graduation: August, 2021
Project/Thesis: Hot Spots & and explosives initiation, finding the right spark

Alex Brown
School: Mechanical Engineering
Expected Graduation: 2022
Co-advisor: Dr. Terrence Meyer
Project/Thesis Title: Laser Diagnostics for Species and Temperature in Explosive Fireballs

Alex Casey

Wesley Chapman
School: Mechanical Engineering
Expected Graduation: May, 2022
Project/Thesis: Additive manufacturing of energetic sensors

Kate Clements
School: Mechanical Engineering
Expected Graduation: May, 2020
Project/Thesis: An Experimental Study of Factors Affecting Hypergolic Ignition of Ammonia Borane

Diane Collard
School: Mechanical Engineering
Expected Graduation: 2021
Project/Thesis: Additively manufactured reactive components in composite propellant
Co-Advisor: Terry Meyer

Nick Cummock
School: Mechanical Engineering
Expected Graduation: May, 2021
Project/Thesis: The change of impact and shock sensitivity due to thermal damage and phase transition in HMX systems

Josh Dean
School: Mechanical Engineering
Expected Graduation: May, 2020.
Project/Thesis: The Kinetics of Thermal Decomposition and Hot-Stage Microscopy of Selected Energetic Cocrystals

Spencer Fehlberg
School: Mechanical Engineering
Expected Graduation: May, 2020
Project/Thesis: Decomposition of Ammonium Perchlorate Encapsulated Nanoscale and Micron-scale Catalyst Particles

Mateo Gomez
School: Mechanical Engineering
Expected Graduation: 2021
Project/Thesis: Advanced diagnostics in detonations and multiphase environments
Co-Advisor: Terry Meyer

Thomas Hafner
School: Mechanical Engineering
Expected Graduation: May, 2024
Project/Thesis: The Use of External Stimuli to Alter the Burning Characteristics of Multifunctional Energetic Materials

Josh Ludwigsen
School: Mechanical Engineering
Expected Graduation: 2023
Project/Thesis: Application of pulse burst laser diagnostics for measurement of high speed reacting flows
Co-Advisor: Terry Meyer

Monique McClain
School: Aeronautics and Astronautics
Expected Graduation: June, 2020
Project/Thesis: Additive manufacturing of viscous materials: development and characterization of 3D printed energetic and composite structures

Derek Messer
School: Aeronautics and Astronautics
Expected Graduation: May, 2023
Project/Thesis: Manipulating Sensitivity of Energetic Materials with Piezoelectric Properties

Brandon Montano
School: Mechanical Engineering
Expected Graduation date: May, 2021
Project/Thesis: Characterization of vibration assisted printer for the additive manufacturing of energetic materials

Gabriel Montoya

Patrick B. Moore
School: Mechanical Engineering
Expected Graduation: May, 2021
Project/Thesis: Thermographic Nanophosphors
Co-Advisor: Terry Meyer

Caitlin O'Grady

Michael Powell
School: Mechanical Engineering
Expected Graduation: May, 2020
Project/Thesis: Ultrafast Broadband Midinfrared Absorption Spectroscopy On Shocked Energetic Materials

Morgan Ruesch
School: Aeronautics and Astronautics
Expected Graduation: May, 2021
Project/Thesis: Characterization of the flame structure of composite solid rocket propellants using laser diagnostics
Co-Advisor: Chris Goldenstein

Ryan J. Tancin
School: Aeronautics and Astronautics
Expected Graduation: 2021
Project/Thesis: Ultrafast laser-absorption spectroscopy in the mid-infrared for spatiotemporally resolved measurements of gas properties

Kyle Uhlenhake
School: Mechanical Engineering
Expected Graduation: May 2023
Project/Thesis: Flash Ignition of Energetic Materials

Eric Westphal
School: Aeronautics and Astronautics
Expected Graduation: Fall 2021
Project/Thesis: High-frequency surface and near-surface temperature measurements of burning composite propellants via phosphor thermometry

Jason Wickham
School: Chemical Engineering
Expected Graduation: December, 2020
Project/Thesis: Effects of Interfacial and Mechanical Properties of Compounded Explosives on Their Sensitivity
Co-Advisor: Steve Beaudoin


Recent Publications

The Effects of Confinement on the Fracturing Performance of Printed Nanothermites

Westphal, Eric R. ; Murray, Allison K. ; Mcconnell, Miranda P. ; Fleck, Trevor J. ; Chiu, George T. ‐C. ; Rhoads, Jeffrey F. ; Gunduz, I. Emre ; Son, Steven F.
Propellants, Explosives, Pyrotechnics, January 2019, Vol.44(1), pp.47-54


Nanothermites have shown the potential to controllably fracture substrates in applications such as electromechanical systems security. In prior work, both equivalence ratio and material formulation have been varied to tailor fracturing performance. In this paper, material confinement was utilized to further tailor the fracturing performance of aluminum bismuth (III) oxide (Al/BiO) and aluminum copper (II) oxide (Al/CuO) nanothermites. These nanothermites were selectively deposited onto representative substrates through inkjet printing. Al/BiO nanothermites were prepared over a range of equivalence ratios and showed a range of resulting fragmentation, with a maximum near the equivalence ratio of ϕ=2. Burning rate measurements correlated with the trends seen in these experiments. All of the previous attempts at fragmenting a substrate using unconfined Al/CuO were unsuccessful. The prepared Al/CuO nanothermites at stoichiometric conditions resulted in fractured silicon substrates when confined. These results demonstrate the ability of confinement to further tailor the fracturing performance of nanothermites.


Characterization of the Hypergolic Ignition Delay of Ammonia Borane

Baier, Michael J ; Ramachandran, P Veeraraghavan ; Son, Steven F
Journal of Propulsion and Power, Jan/Feb 2019, Vol.35(1), p.182


Hypergolic hybrid motors have the potential to improve the safety, reliability, and versatility of rocket systems. They may also serve as a viable replacement for highly toxic liquid fuels (for example, hydrazine, monomethyl hydrazine, etcetera) conventionally used in hypergolic systems. Ammonia borane (AB)-based fuels are relatively nontoxic hydrogen-dense solids that have good theoretical performance. AB has also been found to be highly hypergolic with white fuming nitric acid (WFNA), potentially enabling it to replace existing toxic hypergolic fuels. In this work, hypergolic ignition delay tests were performed on AB synthesized with a novel water-promoted scalable process to characterize its performance as a hypergolic fuel. Typical ignition delays with WFNA were found here to be approximately 2–10 ms. Ignition delay tests performed with AB powder sieved into different particle size ranges indicated a particle size dependency for the ignition delay, with the finer AB particles (D<45  μm) igniting after shorter delays. AB was successfully incorporated into Sylgard®-184, which is a silicone elastomer binder, and ignition delay tests were performed on high solids loading (80%) Sylgard-184-AB pellets. Mean ignition delays for the Sylgard-184-AB fuel pellets tested were less than 50 ms, which may make the formulation viable for use in hypergolic hybrid motors.


Detonation Velocity Measurement of a Hydrogen Peroxide Solvate of CL‐20

Vuppuluri, Vasant S. ; Bennion, Jonathan C. ; Wiscons, Ren A. ; Gunduz, I. Emre ; Matzger, Adam J. ; Son, Steven F.
Propellants, Explosives, Pyrotechnics, March 2019, Vol.44(3), pp.313-318


Synthesis and development of new energetic molecules is a resource‐intensive process, yielding materials with relatively unpredictable performance properties. Cocrystallization and crystalline solvate formation have been explored as possible routes towards developing new energetic materials that reduce the initial investment required for discovery and performance uncertainty because existing energetic molecules with known properties serve as the constituents. The formation of a hydrogen peroxide (HP) solvate of CL‐20 was previously reported and has a density comparable to that of ϵ‐CL‐20, the densest and most stable polymorph of CL‐20. CL‐20/HP produces a second crystalline form, which was unexpected given the high density of the original CL‐20/HP solvate. Both forms were predicted to have improved detonation performance relative to that of ϵ‐CL‐20. In this work, the detonation velocity of a solvate of CL‐20/HP is measured and compared to that of CL‐20. Using the measured enthalpy of formation, the solvate was predicted to detonate 80 m s faster at a powder density of 1.4 g cm; however, experimentally, the solvate detonates 300 m s faster than CL‐20. Thermochemical predictions are also used to show that the solvate detonates 100 m s faster than ϵ‐CL‐20 at the theoretical maximum density, making it the first energetic cocrystal or solvate of ϵ‐CL‐20 predicted to detonate faster than CL‐20 at full density.


X‐Ray Phase Contrast Imaging of the Impact of a Single HMX Particle in a Polymeric Matrix

Kerschen, Nicholas E. ; Sorensen, Christian J. ; Guo, Zherui ; Mares, Jesus O. ; Fezzaa, Kamel ; Sun, Tao ; Son, Steven F. ; Chen, Weinong W.
Propellants, Explosives, Pyrotechnics, April 2019, Vol.44(4), pp.447-454


A complete understanding of the mechanisms by which high explosives (HEs) are shock initiated, especially at the particle scale, is still in demand. One approach to explain shock initiation phenomenon is hot spot theory, which suggests that distributed energy in energetic material is localized due to shock or impact to generate the high temperatures for ignition. This study focuses on the impact response of a HE polycrystalline particle, specifically HMX, in a polymer matrix. This represents a simplified analog of a traditional polymer‐bonded explosive (PBX) formulation. A light gas gun, together with high‐speed x‐ray phase contrast imaging (PCI), was used to study the impact response of a single particle of production‐grade HMX in a Sylgard‐184® matrix. The high‐speed x‐ray PCI allows for real‐time visualization of HE particle behavior. The experiments revealed that, at impact velocities of ∼200 m s, the energetic particle was cracked and crushed. When the impact velocity was increased to 445 m s, a significant volume expansion of the particle was observed. This volume expansion is considered to be the result of chemical reaction within the HE particle.


Dynamic imaging of the temperature field within an energetic composite using phosphor thermography

Casey, A.D. ; Roberts, Z.A. ; Satija, A. ; Lucht, R.P. ; Meyer, T.R. ; Son, S.F.
Applied Optics, 1 June 2019, Vol.58(16), pp.4320-4325


An improved understanding of energy localization ("hot spots") is needed to improve the safety and performance of explosives. We propose a technique to visualize and quantify the properties of a dynamic hot spot from within an energetic composite subjected to ultrasonic mechanical excitation. The composite is composed of an optically transparent binder and a countable number of octahydro 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystals. The evolving temperature field is measured by observing the luminescence from embedded phosphor particles and subsequent application of the intensity ratio method. The spatial temperature precision is less than 2% of the measured absolute temperature in the temperature regime of interest (23°C–220°C). The temperature field is mapped from within an HMX–binder composite under periodic mechanical excitation.


Mesoscale observations of the thermal decomposition of energetic composites under ultrasonic excitation

Roberts, Z. A. ; Wickham, J. A. ; Sorensen, C. J. ; Manship, T. D. ; Gunduz, I. E. ; Son, S. F. ; Rhoads, J. F.
Journal of Applied Physics, 07 June 2019, Vol.125(21)


Polymer bonded explosives (PBXs) have exhibited localized heating and, in some cases, subsequent reactions in response to ultrasonic excitation. The objectives of this work are to investigate the conditions for, and locations of, hot spot initiation of energetic crystals embedded within a polymer binder subjected to periodic mechanical excitation from a contacting transducer operating at 210.5 kHz. Crystal and binder interactions and events such as delamination, solid-solid phase change, and gas production were observed in real time via optical microscopy. We conclude that there are two main pathways of heat generation which are capable of driving an explosive to decomposition in the systems of interest: frictional heating from a delaminated and moving binder interface and viscoelastic heating in the binder near an embedded crystal. Formulations that address the vibration initiation sensitivity of PBX composites require knowledge of the key internal heat generation mechanisms. The results included here indicate that improving binder adhesion to energetic crystals or improving crystal morphology to reduce heating during cyclic loading may only address one of the available pathways of energy dissipation and that binder and crystal selection should be done concurrently. Furthermore, the results presented herein appear to indicate that rounded particles, in contrast to faceted crystals, with strong adhesion to the binder are expected to result in decreased heating rates under ultrasonic excitation.


In-situ X-ray observations of ultrasound-induced explosive decomposition

Mares, Jo ; Roberts, Za ; Gunduz, Ie ; Parab, Nd ; Sun, T ; Fezzaa, K ; Chen, Ww ; Son, Sf ; Rhoads, Jf
Applied Materials Today, 2019 Jun, Vol.15, pp.286-294


Ultrasound is used to study “hot spot” formation and explosive initiation. This work details observations of the heating and decomposition of an explosive. Interfacial friction is shown to be a dominant heating mechanism. High-strain mechanical loading of polymer-bonded explosives can produce significant stress concentrations due to microstructural heterogeneities, resulting in localized thermal “hot spots”. Ultrasound produces similar effects and has been proposed as a tool to study the thermomechanical interactions related to explosive initiation. Detailed observations of the processes governing the generation of heat in these materials are severely lacking, yet they are vital for identifying salient physics, improving the modeling tools used to predict mechanical response, improving explosives safety, and providing insight into the initiation mechanisms of explosion. Here we report on high-speed, high-resolution in-situ observations, obtained via synchrotron X-ray phase contrast imaging and diffraction, of the heating and decomposition of an explosive material under ultrasonic excitation. We demonstrate that interfacial friction is a dominant heating mechanism and can lead to a violent reaction in the explosive particles. Furthermore, sub-surface particle temperatures are estimated via diffraction.


A benchtop shock physics laboratory: Ultrafast laser driven shock spectroscopy and interferometry methods

Powell, Michael Stephan ; Bowlan, Pamela Renee ; Son, Steven F ; Bolme, Cynthia Anne ; Brown, Kathryn Elizabeth ; Moore, David Steven ; Mcgrane, Shawn David
Review of Scientific Instruments, 19 June 2019, Vol.90(6)


Common Ti:sapphire chirped pulse amplified laser systems can be readily adapted to be both a generator of adjustable pressure shock waves and a source for multiple probes of the ensuing ultrafast shock dynamics. Here, we detail experimental considerations for optimizing the shock generation, interferometric characterization, and spectroscopic probing of shock dynamics with visible and mid-infrared transient absorption. While we have reported results using these techniques elsewhere, in this work we detail how the spectroscopies are integrated with the shock and interferometry experiment. The interferometric characterization uses information from beams at multiple polarizations and angles of incidence combined with thin film equations and shock dynamics to determine the shock velocity, particle velocity, and shocked refractive index. Visible transient absorption spectroscopy uses a white light supercontinuum in a reflection geometry, synchronized to the shock wave, to time resolve shock-induced changes in visible absorption such as changes to electronic structure or strongly absorbing products and intermediates due to reaction. Mid-infrared transient absorption spectroscopy uses two color filamentation supercontinuum generation combined with a simple thermal imaging microbolometer spectrometer to enable broadband single shot detection of changes in the vibrational spectra. These methods are reflected here in the study of shock dynamics at stresses from 5 to 30 GPa in organic materials and from a few GPa to >70 GPa in metals with spatial resolution of a few micrometers and temporal resolution of a few picoseconds. This experiment would be possible to replicate in any ultrafast laser laboratory containing a single bench top commercial chirped pulse amplification laser system.


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.


Observation of Damage During Dynamic Compression of Production and Low-Defect HMX Crystals in Sylgard® Binder Using X-Ray Phase Contrast Imaging

Paulson, S.C. ; Roberts, Z.A. ; Sorensen, C.J. ; Kerschen, N.E. ; Harr, M.H. ; Parab, N.D. ; Sun, T. ; Fezzaa, K. ; Son, S.F. ; Chen, W.W.
Journal of Dynamic Behavior of Materials, October, 2019


Polymer bonded explosives (PBX) have many applications in both the military and civilian sectors, making their safety and behavior predictability of the utmost importance. Most explosive devices are typically initiated by some external stimulus; however, initiations can also occur via localized mechanical conversion of energy during impact, called ‘hot spots’. These unintended loads can lead to crystal fracture and frictional heating, amongst other mechanisms, in the energetic crystals of a PBX. In order to visualize the behavior of these crystals, high-speed phase contrast imaging experiments were conducted using synchrotron X-ray radiation to observe the internal crack behavior of simplified PBXs subjected to low velocity impact. The PBX samples used in these experiments were composed of single production-grade and recrystallized octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystals embedded in a Sylgard® 184 binder doped with iron (III) oxide. We observed a clear distinction in the qualitative behavior of production-grade versus recrystallized ‘low-defect’ HMX crystals which lacked significant internal voids. Production grade crystals exhibited consistent cracking behavior in the crystals, while the recrystallized crystals exhibited debonding from the surrounding binder material and cracked much less frequently. We assert that there is a clear effect of crystal quality on the behavior of PBX, which should influence future insensitive munition formulation design choices.


Probing the Reaction Mechanisms Involved in the Decomposition of Solid 1,3,5-Trinitro-1,3,5-triazinane by Energetic Electrons

Singh, Santosh K ; Zhu, Cheng ; Vuppuluri, Vasant ; Son, Steven F ; Kaiser, Ralf I
The journal of physical chemistry. A, 07 November 2019, Vol.123(44), pp.9479-9497


The decomposition mechanisms of 1,3,5-trinitro-1,3,5-triazinane (RDX) have been explored over the past decades, but as of now, a complete picture on these pathways has not yet emerged, as evident from the discrepancies in proposed reaction mechanisms and the critical lack of products and intermediates observed experimentally. This study exploited a surface science machine to investigate the decomposition of solid-phase RDX by energetic electrons at a temperature of 5 K. The products formed during irradiation were monitored online and in situ via infrared and UV–vis spectroscopy, and products subliming in the temperature programmed desorption phase were probed with a reflectron time-of-flight mass spectrometer coupled with soft photoionization at 10.49 eV (ReTOF-MS-PI). Infrared spectroscopy revealed the formation of water (H2O), carbon dioxide (CO2), dinitrogen oxide (N2O), nitrogen monoxide (NO), formaldehyde (H2CO), nitrous acid (HONO), and nitrogen dioxide (NO2). ReTOF-MS-PI identified 38 cyclic and acyclic products arranged into, for example, dinitro, mononitro, mononitroso, nitro–nitroso, and amines species. Among these molecules, 21 products such as N-methylnitrous amide (CH4N2O), 1,3,5-triazinane (C3H9N3), and N-(aminomethyl)methanediamine (C2H9N3) were detected for the first time in laboratory experiments; mechanisms based on the gas phase and condensed phase calculations were exploited to rationalize the formation of the observed products. The present studies reveal a rich, unprecedented chemistry in the condensed phase decomposition of RDX, which is significantly more complex than the unimolecular gas phase decomposition of RDX, thus leading us closer to an understanding of the decomposition chemistry of nitramine-based explosives.


Altering Agglomeration in a Composite Propellant with Aluminum–Silicon Eutectic Alloy

Terry, Brandon ; Rubio, Mario ; Gunduz, I ; Son, Steven ; Groven, Lori
Journal of Propulsion and Power, Nov/Dec 2019, Vol.35(6), pp.1048-1056


Although aluminum alloys are generally employed for their structural and mechanical properties, the low-level inclusion of secondary metals and metalloids may also make alloy powders advantageous in propellant formulations and have not been fully considered. In this work, the aluminum–silicon (Al–Si) eutectic alloy, which has a lower melting point (577°C) than either constituent, was evaluated as a potential solid composite propellant fuel. Equilibrium calculations showed that Al–Si-based propellants had slightly lower theoretical ideal performance to equivalent aluminum-based propellants, with a typical specific impulse reduction of roughly 2.5 s for most mixture ratios of interest. However, if product agglomerate size could be reduced, improved performance could result. Neat and composite Al–Si/polymer powders were studied in solid propellant formulations. Burning rate experiments were performed in a windowed pressure vessel, and condensed phase combustion products were collected. It was found that the Al–Si-based propellants followed the same trends (burning rate exponent) but at a lower magnitude (burning rate coefficient) as neat aluminum-based propellants. However, the coarse product agglomeration of the Al–Si-based propellants was found to be larger than the neat aluminum-based propellants, which may be due to the high fluidity of Al–Si eutectic alloy.


Investigation of Polymer Matrix Nano‐Aluminum Composites with Pulsed Laser Heating by In‐Situ TEM

Isik, Tugba ; Xu, Xiaohui ; Son, Steven F. ; Gunduz, I. Emre ; Ortalan, Volkan
Propellants, Explosives, Pyrotechnics, December 2019, Vol.44(12), pp.1608-1612


Nanocomposites of aluminum and fluoropolymers react rapidly due to highly exothermic aluminum fluorination because of the high specific surface area nanoscale particles. In‐situ transmission electron microscopy (TEM) techniques are invaluable for real time monitoring of the reactions in these systems at the nanoscale. Here, we investigated the reactions in nanoscale Al (nAl) and THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride) and nAl‐LDPE (low density polyethylene) composites, heated using a pulsed laser in a TEM. Results show that reactions are initiated at about 720 K, when THV starts to decompose, and proceed with the formation and growth of a hollow aluminum fluoride (AlF3) shell. Diffraction patterns revealed that this phase is the rare η‐phase AlF3. In contrast, no reactions were observed in the inert nAl‐LDPE composites. The experimental and theoretical results reveal that rapid pulsed laser heating and subsequent cooling of a nanoscale sample influences the phases that can form, and can be utilized to investigate other systems.


Void Collapse in Shocked β ‐HMX Single Crystals: Simulations and Experiments

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.


X‐ray Phase Contrast Imaging of the Impact of Multiple HMX Particles in a Polymeric Matrix

Kerschen, Nicholas E. ; Drake, Jonathan D. ; Sorensen, Christian J. ; Guo, Zherui ; Mares, Jesus O. ; Fezzaa, Kamel ; Sun, Tao ; Son, Steven F. ; Chen, Weinong W.
Propellants, Explosives, Pyrotechnics, April 2020, Vol.45(4), pp.607-614


The initiation of high explosives (HEs) under shock loading lacks a comprehensive understanding: particularly at the particle scale. One common explanation is the hot spot theory, which suggests that energy in the material resulting from the impact event is localized in a small area causing an increase in temperature that can lead to ignition. This study focuses on the response of HMX particles (a common HE) within a polymer matrix (Sylgard‐184®), a simplified example of a polymer‐bound explosive (PBX). These PBXs consist of multiple HMX particles in a single polymer‐bound sample. A light gas gun was used to load the samples at impact velocities above 400 m/s. The impact events were visualized using X‐ray phase‐contrast imaging (PCI) allowing real‐time observation of the impact event. The experiment used two different types of samples (multi‐particle and two crystals) and found evidence of cracking and debonding in both sample types. In addition, it was found that the multiple particle samples showed similar evidence of damage at lower velocities than that of single particle samples. This is an expected result as the multiple particles add additional interfaces for stress concentration and frictional heating.


Dynamic stress-strain response of high-energy ball milled aluminium powder compacts

Justice, A.W ; Beason, M.T ; Gunduz, I.E ; Chen, W ; Son, S.F
Mechanics of Materials, April 2020, Vol.143


Ball milling is a bulk powder manufacturing process used in the creation of dispersion strengthened and nanostructured materials. Fundamentally, these powders have not been dynamically characterized in a green state prior to hot consolidation. The understanding of high strain-rate compaction on void collapse and particle interaction for such systems can help the development of predictive models for impact events of porous metallic structures that may be employed as energy absorbers, reactive structures, and intermetallic materials. This study investigates high strain-rate impact of porous green compacts of as-received and high-energy ball milled (HEBM) aluminium powders characterized under dynamic compression using a split-Hopkinson pressure bar (SHPB) in a passive confinement configuration. The plastic deformation of the powder compacts and crush up were shown to be strain-rate insensitive within the strain rate range of 1000–2100 s−1 and as a result, were modelled adequately with a second order P-α model. The as-received aluminium and HEBM aluminium powders appear to have the same strain-hardening coefficient and strength index as solid aluminium after yielding. The respective stress-strain responses of green compacts follow the same trend but differ only in strength as result of porosity and pre-strain experienced prior to dynamic compression. The HEBM powder was found to be twice as strong as the untreated as-received aluminium powder.