Daniel E. Eakins

Daniel E. Eakins
University of Oxford | OX · Department of Engineering Science

PhD

About

111
Publications
16,006
Reads
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1,386
Citations
Citations since 2017
42 Research Items
903 Citations
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150
Additional affiliations
May 2017 - present
University of Oxford
Position
  • Senior Researcher
January 2010 - September 2019
Imperial College London
Position
  • Lecturer
November 2007 - December 2009
Los Alamos National Laboratory
Position
  • Director's Postdoctoral Fellow
Education
August 2003 - May 2007
Georgia Institute of Technology
Field of study
  • Materials Science and Engineering
August 2001 - May 2003
Washington State University
Field of study
  • Materials Science and Engineering
August 1997 - August 2001
Washington State University
Field of study
  • Materials Science and Engineering

Publications

Publications (111)
Article
The relationship between the dynamic mechanical properties of stony meteorites and their microstructures was investigated in-situ for an L-type ordinary chondrite using a split-Hopkinson pressure bar apparatus and ultra-high speed phase-contrast X-ray radiography at the European Synchrotron Radiation Facility (ESRF). Synchrotron X-ray microtomograp...
Article
Full-text available
In this work the dynamic fracturing of an ultra-high strength cementitious material is probed with in-situ ultra-high speed X-ray phase-contrast diagnostics to investigate the phenomenology of dynamic fracture. Gas gun experiments were conducted on two characteristic samples with two different impact speeds, namely 80 and 190 m/s using the edge-on...
Article
Full-text available
The Photon Doppler Velocimetry (PDV) technique is used to capture simultaneously propagating elastic waves of longitudinal and shear nature in a Tension-Torsion Hopkinson Bar (TTHB) apparatus. The system uses a pair of probes per velocity measurement, which were taken on the opposite sides of the TTHB bar with a laser irradiated spot size of ~35 µm...
Conference Paper
The role of texture in the dynamic yielding behaviour of magnesium alloy AZ31B has been studied in a series of instrumented plate-impact experiments. Specimens with thicknesses between 0.45 and 2 mm were cut parallel and perpendicular to the material extrusion direction and shock loaded to impact stresses around 3 GPa. Frequency-shifted photon dopp...
Conference Paper
The phenomenon of cavity collapse has long been of interest because of the dramatic and highly localised increases in pressure and temperature that can occur during the collapse process. Due to the constraints imposed by optical imaging systems, existing experimental work has largely been limited to cylindrical cavities in transparent liquid and ge...
Conference Paper
Full-text available
This article presents results of plate impact experiments coupled to in situ X-ray radiography, performed on a polyurethane foam, to visualize its deformations during the propagation of a stress wave. A two-wave structure associated with the propagation of an elastic precursor and pores compaction has been observed. A phenomenological compaction mo...
Article
Head-to-head comparisons are made between calculations and experimental data on shock-driven pore collapse in the transparent material, poly(methyl methacrylate) (PMMA). Simulations are performed using SCIMITAR3D, an Eulerian sharp-interface multi-material code, while plate impact experiments are visualized using ultra-high speed x-ray imaging. The...
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Extraordinary states of highly localised pressure and temperature can be generated upon the collapse of impulsively driven cavities. Direct observation of this phenomenon in solids has proved challenging, but recent advances in high-speed synchrotron radiography now permit the study of highly transient, subsurface events in real time. We present a...
Chapter
Ceramic materials are widely used all around the world in protective solutions as front plate of bilayered configurations, a metallic or composite material being used as backing to absorb the kinetic energy of fragments. However, during the impact, an intense fragmentation process composed of numerous oriented cracks develops in the ceramic plate d...
Conference Paper
Full-text available
Additive manufacturing (AM) is an attractive approach for the design and production of complex structures not possible to realize with conventional methods. While the dynamic mechanical response of bulk material is object of extensive investigation, the dynamic behavior of mesostructured material is lacking attention. In this study, a series of dif...
Article
Pyrometry is one of the most prevalent techniques for measuring temperature in shock physics experiments. However, the challenges of applying pyrometry in such highly dynamic environments produces multiple sources of uncertainty that require investigation. An outstanding question is the degree of agreement between different pyrometers and different...
Article
This paper presents a description and the demonstration results of a custom-designed bespoke Split-Hopkinson Pressure Bar (SHBP) which has been installed at the ID-19 beamline at the European Synchrotron Radiation Facility (ESRF). Building upon recent advances in real-time x-ray imaging, this system enables the study of dynamic mechanical phenomena...
Article
E. M. Escauriza’s appeared incorrectly on the original publication of this article. It is corrected here.
Article
Pressure–density relationships derived from the experimentally obtained shock and particle velocities are critical to define a material’s equation of state (EOS). Typically, impact experiments coupled with velocimetry are used to map a material’s Hugoniot. Limitations such as sample geometry and varying indices of refraction may prevent proper char...
Conference Paper
For several decades, ceramic materials have been widely used in bilayered protective configurations. However, the impact loading produces dynamic tensile stresses that spread out the ceramic tile leading to an intense fragmentation made of short oriented cracks. To improve the design of such configurations the fragmentation process needs to be bett...
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Full-text available
Interpreting and tailoring the dynamic mechanical response of granular systems relies upon understanding how the initial arrangement of grains influences the compaction kinetics and thermodynamics. In this article, the influence of initial granular arrangement on the dynamic compaction response of a bimodal powder system (soda-lime distributed thro...
Article
Impact-driven compaction is a proposed mechanism for the lithification of primordial bimodal granular mixtures from which many meteorites derive. We present a numerical-experimental mesoscale study that investigates the fundamental processes in shock compaction of this heterogeneous matter, using analog materials. Experiments were performed at the...
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Full-text available
Betatron radiation from laser wakefield accelerators is an ultrashort pulsed source of hard, synchrotron-like x-ray radiation. It emanates from a centimetre scale plasma accelerator producing GeV level electron beams. In recent years betatron radiation has been developed as a unique source capable of producing high resolution x-ray images in compac...
Conference Paper
Full-text available
Meteorites are classified by their relative exposure to three processes: aqueous alteration; thermal metamorphism; and shock processes. They constitute the main evidence available for the conditions in the early solar system. The precursor material to meteorites was bimodal and consisted of large spherical melt droplets (chondrules) surrounded by a...
Conference Paper
Pyrometry is an established technique used in high strain rate experiments (such as plate impact experiments) whereby the temperature of a sample is determined from the measurement of collected thermal radiation. By applying Planck’s Law, ra-diometry data can be used to determine temperature. A significant source of uncertainty in applying pyrometr...
Conference Paper
Full-text available
Understanding the dynamic mechanical behaviour of Additively Manufactured (AM) materials is important when designing components for real-world applications. A series of Taylor tests were carried out on AM and conventionally manufactured 316L stainless steel to evaluate differences in mechanical behaviour arising from manufacturing process. AM speci...
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Full-text available
A new generation of cameras has made ultra high-speed X-ray imaging at synchrotron light sources a reality , revealing never-before-seen details of sub-surface transient phenomena. We introduce a versatile indirect imaging system capable of capturing-for the first time-hundreds of sequential X-ray pulses in 16-bunch mode at the European Synchrotron...
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Full-text available
Primitive solar system solids were accreted as highly porous bimodal mixtures of mm-sized chondrules and sub-μm matrix grains. To understand the compaction and lithification of these materials by shock, it is necessary to investigate the process at the mesoscale; i.e., the scale of individual chondrules. Here we document simulations of hypervelocit...
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Full-text available
EPSRC under Established Career Fellowship grant EP/N025954/1. Trinity College Cambridge Institute of Shock Physics Research Board and the Faculty of Engineering Dean’s office at the American University of Beirut
Article
In this paper we demonstrate a new post-processing technique that allows straightforward identification of deformation mechanisms in molecular dynamics simulations. We utilise reciprocal space methods by calculating a per-atom structure factor (PASF) to visualise changes in volume, orientation and structure, thus allowing unambiguous discrimination...
Article
Quasi-Taylor wave loaded plate impact experiments have been used to study the effects of bulk grain size on the shock and spall response of pure copper samples. Using line-Velocity Interferometry System for Any Reflector velocimetry, an increased particle velocity dispersion was measured for larger bulk grain size samples resulting in lower mean pe...
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Chondritic meteorites are fragments of asteroids, the building blocks of planets, that retain a record of primordial processes. Important in their early evolution was impact-driven lithification, where a porous mixture of millimetre-scale chondrule inclusions and sub-micrometre dust was compacted into rock. In this Article, the shock compression of...
Article
Full-text available
This article offers a comprehensive experimental and theoretical study of the causes of thermal hardening in FCC Al and BCC Fe at high strain rates, with the aim to shed light on important mechanisms governing deformation and failures in materials subjected to shocks and impacts at very high strain rates. Experimental evidence regarding the tempera...
Article
When designing a spectral-band pyrometer for use at high time resolutions (sub-μs), there is ambiguity regarding the optimum characteristics for a spectral filter(s). In particular, while prior work has discussed uncertainties in spectral-band pyrometry, there has been little discussion of the effects of noise which is an important consideration in...
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Full-text available
Cellular materials have potential application as absorbers of energy generated by high velocity impact. CTH, a Sandia National Laboratories Code which allows very severe strains to be simulated, has been used to perform very high resolution simulations showing the dynamic crushing of a series of two-dimensional, stainless steel metal structures wit...
Article
We describe the capability of a high-resolution three-dimensional digital image correlation (DIC) system specifically designed for high strain-rate experiments. Utilising open-source camera calibration and two-dimensional DIC tools within the MATLAB framework, a single camera three-dimensional DIC system with submicron displacement resolution is de...
Conference Paper
Laser-driven shock experiments were performed on fcc metals, aluminum and invar, at a range of initial temperatures from approximately 120-800 K to explore the effect of initial temperature on dynamic strength properties at strain rates reaching up to 10⁷ s⁻¹. In aluminum,velocimetry data demonstrated an increase of peak stress of the elastic wave,...
Conference Paper
Full-text available
Water can freeze upon multiple shock compression, but the window material determines the pressure of the phase transition. Several plate impact experiments were conducted with liquid targets on a single-stage gas gun, diagnosed simultaneously using photonicdopplervelocimetry (PDV) and high speed imaging through the water. The experiments investigat...
Conference Paper
The effectchemical composition on the shock response of two bulk metallic glass(BMG) alloys with slightly different elemental compositions (Zr55Cu10Ni5Al30 and Zr46Cu38Ag8Al8) has been investigated. Plate-impact experiments were conducted at a peak compressive stress of ∼10GPa, above the expected elastic limit of these alloys (∼7GPa). Velocity inte...
Conference Paper
Full-text available
We present a study on the dynamic fracture and fragmentation of Ti-6Al-4V cylinders at initial temperatures ranging from approximately 150 K to 750 K. Cylinders with an inner diameter of 50 mm and a wall thickness of 4 mm were driven into uniform axially-symmetric expansion at radial strain rates of 10⁴ s⁻¹ using the ogive-insert gas gun method. Di...
Conference Paper
Full-text available
Expanding cylinder experiments using a gas gun technique allow investigations into the ductility of metals and the fracture and fragmentation mechanisms that occur during rapid tensile failure. These experiments allow the radial strain-rate of the expansion to be varied in the range 102 to 104 s−1. Presented here is a comparative study of the fract...
Conference Paper
Full-text available
Calcite and sapphire were shock compressed along the 〈101¯0〉 direction (a axis) in a plate impact configuration. Polarimetery and Photonic Doppler Velocimetery (PDV) were used to measure the change in birefringence with particle velocity in the shock direction. Results for sapphire agree well with linear photoelastic theory and current literature s...
Conference Paper
Granular materials are widespread in nature and in manufacturing. Their particulate nature gives a compressive strength of a similar order of magnitude as many continuous solids, a vanishingly small tensile strength and variable shear strength, highly dependent on the loading conditions. Previous studies have shown the effect of composition, morpho...
Article
A gas-gun technique is described in which a thick-walled cylinder of a chosen solid may be collapsed over a wide range of effective strains, and at shear strain-rates of the order 104 s−1. Two variants of the basic concept are described. Initially a 70 mm bore gun was used to dynamically collapse stainless steel 304 cylinders to a wide range of fin...
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Full-text available
Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic inves...
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The short pulse duration, small effective source size and high flux of synchrotron radiation is ideally suited for probing a wide range of transient deformation processes in materials under extreme conditions. In this paper, the challenges of high-resolution time-resolved indirect X-ray detection are reviewed in the context of dynamic synchrotron e...
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High pressure solid state transformations at high strain rates are usually observed after the fact, either during static holding or after unloading, or inferred from interferometry measurements of the sample surface. The emergence of femtosecond X-ray diffraction techniques provides insight into the dynamics of short-timescale events such as shocks...
Article
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Adiabatic shear band (ASB) formation in textured HCP polycrystals has been investigated under regimes of high rate compression and shear loading using dynamic thermo-mechanically coupled, dislocation-based crystal plasticity modelling. The balance between rate of plastic dissipation leading to internal heat generation versus rate of thermal diffusi...
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The dynamic fracture of a body is a late-stage phenomenon typically studied under simplified conditions, in which a sample is deformed under uniform stress and strain rate. This can be produced by evenly loading the inner surface of a cylinder. Due to the axial symmetry, as the cylinder expands the wall is placed into a tensile hoop stress that is...
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Homogeneous nucleation of dislocations is the dominant dislocation generation mechanism at strain rates above 10^8/s; at those rates, homogeneous nucleation dominates the plastic relaxation of shock waves in the same way that Frank-Read sources control the onset of plastic flow at low strain rates. This article describes the implementation of homog...
Article
Full-text available
When a metal is subjected to extremely rapid compression, a shock wave is launched that generates dislocations as it propagates. The shock wave evolves into a characteristic two-wave structure, with an elastic wave preceding a plastic front. It has been known for more than six decades that the amplitude of the elastic wave decays the farther it tra...
Article
Full-text available
Ramp loading using graded density impactors as flyers in gas-gun-driven plate impact experiments can yield new and useful information about the equation of state and the strength properties of the loaded material. Selective Laser Melting, an additive manufacture technique, was used to manufacture a graded density flyer, termed the “bed-of-nails” (B...
Article
Full-text available
Gas guns are traditionally used as platforms to introduce a planar shock wave to a material using plate impact methods, generating states on the Hugoniot. The ability to deliver a ramp wave to a target during a gas gun experiment enables access to different regions of the equation-of-state surface, making it a valuable technique for characterising...
Chapter
This chapter concerns with dynamic discrete dislocation plasticity (D3P), a two-dimensional method of discrete dislocation dynamics aimed at the study of plastic relaxation processes in crystalline materials subjected to weak shock loading. Traditionally, the study of plasticity under weak shock loading and high strain rate has been based on direct...
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Full-text available
In this paper, we describe a new approach enabling study of subsurface dynamics in high-Z materials using the unique combination of high-energy synchrotron X-rays, a hybrid bunch structure, and a new dynamic loading platform. We detail the design and operation of the purpose-built, portable small bore gas-gun, which was installed on the I12 high-en...
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Full-text available
A technique has been developed to measure the change in birefringence along the axis of shock propagation, probing the relative refractive indices of the material perpendicular to shock propagation. Experiments were performed on calcite single crystals and the results compared to previous literature studies on calcite quasi-static behaviour. Interf...
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Full-text available
Precise measurement of the free-surface velocity can be a rich source of information on the effects of time and strain on material strength. With this objective, we performed a careful comparative measurement of the free-surface velocity of shock loaded aluminium AD1 and magnesium alloy Ma2 samples of various thicknesses in the range 0.2 mm to 5 mm...
Article
Full-text available
Ramp loading using graded-density-impactors as flyers in gas-gun-driven plate impact experiments can yield new and useful information about the equation of state and the strength properties of the loaded material. Selective Laser Melting, an additive manufacture technique, was used to manufacture a graded density flyer, termed the "bed of nails" (B...
Article
Full-text available
The mechanisms of stress relaxation in metallic glasses under high strain rates are an area of active study. The lack of extended structure forces strain accommodation through alternative modes to slip For example, amorphous Ce3Al has been shown to undergo a phase transition to the crystalline FCC Ce3Al at 25 GPa under quasistatic loading. Whether...
Article
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The high strain-rate behaviour of multi-component systems is often dominated by mediation at material interfaces. The extent to which a materials microstructure influences dynamic friction and relative sliding response remains an area of active study. Initial results from a study on the behaviour of dry metallic interfaces under the passage of a co...
Article
Full-text available
The dynamic fracture and fragmentation of a material is a complex late stage phenomenon occurring in many shock loading scenarios. Improving our predictive capability depends upon exercising our current failure models against new loading schemes and data. We present axially-symmetric high strain rate (104 s−1) expansion of Ti-6Al-4V cylinders using...
Article
Full-text available
Often the velocity measured at the rear surface of a dynamic compression target varies spatially, caused for instance by the tilt/curvature of a gas gun flyer, asymmetries in the magnetic field on a pulsed power driven experiment, or meso-scale heterogeneous targets. One way to monitor this in an experiment is to employ multiple point velocimetry t...
Article
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Porous materials are of great interest because of improved energy absorption over their solid counterparts. Their properties, however, have been difficult to optimize. Additive manufacturing has emerged as a potential technique to closely define the structure and properties of porous components, i.e. density, strut width and pore size; however, the...
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Full-text available