Spall occurs when materials are subjected to shock impacts; under this loading, the material properties can be modified through microstructural changes and phase transitions. The effect of these changes on subsequent spall has been under-explored. The anisotropy of tin's ambient crystal structure and the accessibility of the beta -> gamma solid-solid phase transition under shock loading mean that tin offers a rich domain in which to study spall failure. Through testing single-crystal and polycrystal samples shocked above and below this transition, the effects of these variables on the deformation behavior of tin can be determined. Although no orientation dependent spall behavior is observed, unusual strain-rate-dependent behavior is observed, indicating likely mechanisms for the high-rate behavior of tin.

Tin is known for its asymmetric crystal structure and numerous solid phase transitions, with molecular dynamics studies suggesting the beta to gamma phase transition exhibits a strong orientation dependence. In this study, shock compression experiments are conducted on tin single crystals and polycrystals to probe the effects of the crystal orientation on this phase transition through Hugoniot measurements, with peak pressures between 9 and 13 GPa. A strong order-of-magnitude orientation dependence of the elastic limit is found; however, the transition and post-transition behavior show at best only qualitative differences to the velocimetry profiles, with no quantitative variation. A dependence of the transition on the peak pressure is also observed. Explanations of these results based on potential transformation pathways identified through prior static high pressure work are discussed.

Polycarbonate composites are widely used in applications subjected to compression loading at varying strain rates, benefiting from their ability to withstand large deformations due to the ductile nature of polycarbonate. However, the deformation and failure mechanisms, and the effects of fibre orientation, during large strain deformation are poorly understood. This study examines the rate-dependent properties of 20 wt % short glass fibre reinforced polycarbonate loaded in different orientations relative to the fibre flow and at strain rates from 0.01 to 2350 s- 1. High-speed optical and infrared imaging are used to aid interpretation of the deformation and failure arising from the formation of adiabatic shear bands. Novel experimental approaches are used to qualify and quantify the deformation mechanism: load-reload tests, final strain-controlled split Hopkinson bar experiments with ex-situ tomography. These are supported by dynamic in-situ X-ray measurements published previously. These comprehensive datasets establish a deep understanding of the constitutive behaviour of this ductile composite material that will enhance its use in a wide range of applications.

Polycarbonate is a widely used ductile glassy polymer that can undergo large strain deformation before failure. During the plastic deformation process, some mechanical energy is converted to heat, which, if the specimen is loaded at rates sufficient that the heat cannot conduct out of the material, can result in significant temperature rises that affect the mechanical response. Typically, this is expected to result in a reduction in stress at large strain, compared to the behaviour under isothermal conditions; however, compared to other glassy polymers, it has been observed that less softening than expected is experienced in polycarbonate at high strain rates. The current paper describes a thorough investigation of temperature rises in polycarbonate. Compression experiments are performed using a screw-driven machine, a hydraulic machine, and a long split Hopkinson bar, all instrumented with a high-speed infrared camera to measure temperature rises at strain rates between 0.01 and 2600 s- 1 at a starting temperature around 20 degrees C. Further, temperature rises in compression experiments at 0.5 s- 1 and starting temperatures between -80 to 150 degrees C are measured using embedded thermocouples. These span the range of the secondary- to glass-transitions of polycarbonate, allowing investigation of the effect of these transitions. These experiments are supported by finite element simulations, which use a phenomenological viscoplastic model, to ensure the thermal boundary conditions are adiabatic. Temperature rises are observed in both temperature and rate-dependent tests: experiments at higher strain rates and lower temperatures experience a greater temperature rise because of the higher yield stress; however, there are differences in the conversion ratio between plastic work and heat (Taylor Quinney coefficient), which is both temperature and rate dependent, and strongly affected by both the secondary and glass transitions.

Polyamide 6 and its composites are widely used in engineering applications that are exposed to high strain rate deformation. This paper investigates the thermomechanical properties of two polyamide 6 composites, both reinforced with 30 wt% short glass fibres, and one of which additionally contains an impact modifier, to provide an understanding of the mechanical response over a wide range of strain rates and temperatures. Compression experiments were performed at rates between 2 and 3000 s-1, with high speed optical and infrared cameras to aid interpretation of the rate-dependent failure arising from the formation of adiabatic shear bands. Further high strain rate experiments were performed with ultra-fast X-ray phase-contrast imaging to provide in-situ internal damage evaluation. These data will improve the utilization of these composites and aid in development of advanced thermomechanical models.

The intersection of dynamic compression, high-rate material response and X-ray science has seen rapid growth, leading to the establishment of specialized end-stations at international facilities such as Linac Coherent Light Source LCLS (Matter at Extreme Conditions - MEC) and Advanced Photon Source APS (Dynamic Compression Sector - DCS), both USA. Although these facilities excel in working with X-rays tailored for small material volumes (i.e. <1mm(3)), it needs a different approach to delve into subsequent processes. This is particularly the case in the transition from the micro- to mesoscale: here the ESRF distinguishes itself. The large beam size (several cm(2)) of the ID19 beamline, in conjunction with a strong high energy component, source flux density, and outstanding imaging sensitivity, enables sub-surface visualization of engineering-scale structures as well as natural systems in representative volume, under high rate and shock. This is particularly valuable when studying materials with complex mesostructures and heterogeneities on relevant volumetric scales, which often dominate the dynamic material response. The study of the behavior of materials under dynamic loading presents a unique challenge due to inherently spanning over multiple lengths- and timescales. The evolution of sudden (thermo)mechanical excitation, starting from the lattice scale and progressing through grains, phase domains, and ultimately to structures, exhibits a spectrum of responses spanning from the microscopic to bulk length scales. Consequently, a diverse range of diagnostics as well as driver instrumentation is required to identify, study, and characterize this material response spectrum. This article shall introduce platforms available at beamline ID19 and underline their potential by selected showcase applications. Community access proposals such as the beamtime Block Allocation Group (BAG) allow for access in a routine manner.

Each year approximately 99% by mass of energetic material use takes place in the quarrying, mining, construction and petrochemical industries. The coupling of explosively driven shock waves to heterogeneous geological materials is of scientific and industrial relevance. Here we report the first experiments conducted with energetic materials at the ID19 beamline at the European Synchrotron Research Facility, Grenoble, France. The experiments used commercial detonators to explosively load sand samples and glass spheres. Time resolved images showing the compaction wave produced by the explosive loading of both coarse- and fine-grained sand as well as large and small diameter glass spheres.

Polyamide 6 is a widely used engineering plastic; however, its thermomechanical properties are not well understood, particularly at medium and high strain rates. In this research, the thermomechanical properties of Polyamide 6 were extensively characterized. Differential Scanning Calorimetry was performed to investigate the glass transition temperature and crystallinity. Frequency sweep Dynamic Mechanical Analysis was carried out through the secondary- and glass-transitions, and the temperature dependent storage moduli obtained from different sweep frequencies were used to construct a master curve. Quasi-static tensile tests at two loading speeds were conducted with digital image correlation for full-field strain mapping. Compression properties were measured at strain rates between 0.001 and 6000 s-1 at room temperature, and temperatures between -60 and 200 degrees C at 0.01 s-1. The mechanical response is highly rate- and temperature-dependent; at large strains and elevated rates, apparent softening occurs owing to heat generation, which was quantified using an infrared camera.

Polycarbonate composites are widely used in products exposed to high strain rate deformation. This paper investigates the thermomechanical properties of polycarbonate and 20 wt% glass fibre reinforced polycarbonate to provide characterisation data and improved mechanistic understanding of the response to load, supported by Dynamic Mechanical Analysis and time-temperature superposition. Compressive behaviour is characterised from 0.001 to 5000 s- 1 at room temperature and from -60 to 120 degrees C at 0.01 s- 1; and a thermal imaging camera used to obtain temperature rise data. Quasi -static tensile experiments were also performed in different orientations relative to the injection flow direction. High -rate compression experiments are performed with X-ray imaging. As well as information about rate dependence of yield stresses and softening in the two materials, these data show how adiabatic shear band formation can cause significant softening in the composite. These data will enhance application of these polymers and facilitate development of advanced thermo-mechanical models.

Photon Doppler velocimetry (PDV) has become a standard diagnostic in impact and shock experiments, due to its relative flexibility and ease in alignment compared to other optical diagnostics. The conventional approach to fielding PDV in plate-impact experiments is to place probes directly down-range from the projectile and target. In experiments such as these, probes are almost certainly destroyed, resulting in significant replacement cost particularly when multiple probes are used. To overcome these shortcomings, a free-space optical relay system has been developed to focus multiple channels of PDV from outside an experimental tank onto a target of reduced size than the probe array. This system has been successfully tested on plate-impact experiments measuring a Hugoniot state of polycrystal tin, and the peak elastic stress and spall strength in 6082 aluminium alloy, in both cases adding information about the shock tilt to the experimental data generated.

The effects of cold work on dynamic flow strength is studied through measurements of dislocation density and elastic precursor attenuation in shocked aluminium. High-purity aluminium and Al 6082 alloy samples are subjected to up to three passes of rotary swaging, a severe plastic deformation (SPD) technique, in order to produce large variations in starting material conditions. Detailed material characterisation is performed using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) to determine the initial dislocation density, texture, grain boundary density and misorientation distribution. Variations in dynamic strength are studied through the evolution of the elastic precursor amplitude with propagation distance in specimens with thicknesses between 0.2 and 1 mm, shock loaded to impact stresses of about 4.6 GPa. It is shown that dynamic strength decreases with increasing initial dislocation density in both materials, demonstrating rare, quantified measurements of a reversal in the effect of dislocation density on yield strength at strain rates around 10 ^4 s ^-1 and above.

The present study demonstrates experimental evidence of subsurface mesoscale damage initiation and evolution in angle-ply CFRP laminates under high strain-rate loading at low temperatures using synchrotron-based X-ray MHz radiography. A bespoke set of loading, temperature control and in-situ X-ray imaging systems were applied to simultaneously correlate high strain-rate mechanical response with observed subsurface damage in a time-resolved manner. The results demonstrate that independent of temperature, damage evolved following a specific sequence; firstly intra-ply shear cracking along the fibre direction, developing into multi-layer cracking with continued deformation, and finally culminating in inter-ply delamination and complete failure of the specimen. The timescale for this sequence, however, was observed to strongly depend upon temperature, with low temperatures resulting in more rapid damage evolution and loss of mechanical strength.

A range of concrete types, representing commercially important formulations, were characterised under shock loading and release, using a large-bore single-stage light-gas gun. The plate impact experiments used a wave reverberation technique and an array of optical velocimetry probes to measure Hugoniot data and the subsequent release states for shocks from 2 to 11 GPa. The use of multiple velocimetry probes enabled quantification of the variation in particle velocity arising from the heterogeneous nature of concrete. Four types of concrete were investigated; a regular concrete, a fibre reinforced concrete using poly-propylene fibres, fibre concrete with steel fibres and, lastly, ultra-high performance fibre-reinforced concrete. Despite the compositional complexity, and range of quasi-static compressive strengths and reinforcement methods, the average Hugoniot data were remarkably similar between compositions.

The modelling of energetic materials is usually performed within an Eulerian framework, inherently well suited to simulate fluid-like behaviour of the reaction products and the propagation of pressure waves in the surrounding fluid media (e.g. air or water). However, the Lagrangian framework becomes more attractive in the effort to reproduce the unreacted mechanical response of the material, especially as we move towards trying to capture better the response of damaged explosives. In this paper the implementation of the History Variable Reactive Burn (HVRB) model in the Lagrangian explicit software LS-Dyna is presented. The HVRB reaction rate parameters are verified against simple ratestick tests before being used to simulate the detonation of hemispherical charges from an ignition point located at the pole of the hemisphere. The numerical results are directly compared against high-speed video from the experimental tests, illustrating reasonable agreement given the simplicity of the HVRB formulation. This paves the way for developing deeper understanding by incorporating more complex reactive burn models, e.g. Damage Initiated Reaction (DMGIR), which can consider the role of mechanically induced damage upon the response of explosives.

The effect of grain orientation distribution on the dynamic strength of highly textured magnesium alloy AZ31B has been studied in a series of plate-impact experiments. Specimens with thicknesses between 0.45 mm and 2 mm were cut parallel and perpendicular to the material extrusion direction and shock loaded to impact stresses between 1.4 GPa and 3.4 GPa. The dynamic strength is found to be highly dependent on the loading direction, with loading along the extrusion direction exhibiting significantly higher Hugoniot elastic limits than the transverse direction, including a much slower precursor decay rate. Application of an orientation-based analysis framework shows that the yield point of the polycrystalline material can be predicted reasonably well from its grain orientation distribution, predicated upon the use of dynamic critical resolved shear stress values from single-crystal data modified by a fitted strengthening factor. It is shown that the strong dependence on loading orientation in Mg AZ31 is caused by the relative differences in slip system activity and the slip anisotropies inherent to the hexagonal close packed crystal structure.

We have carried out a series of experiments to measure the Cl K-absorption edge for shock-compressed samples of chlorinated parylene. Colliding shocks allowed us to compress samples up to four times the initial density with temperatures up to 10 eV. Red shifts in the edge of about 10 eV have been measured. We have compared the measured shifts to analytical modelling using the Stewart–Pyatt model and adaptions of it, combined with estimates of density and temperature based on hydrodynamic modelling. Modelling of the edge position using density functional theory molecular dynamics (DFT-MD) was also used and it was found that good agreement was only achieved when the DFT simulations assumed conditions of lower temperature and slightly higher density than indicated by hydrodynamic simulations using a tabular equation of state.

Wetted-foam layers are of significant interest for inertial-confinement-fusion capsules, due to the control they provide over the convergence ratio of the implosion and the opportunity this affords to minimize hydrodynamic instability growth. However, the equation of state for fusion-relevant foams are not well characterized, and many simulations rely on modeling such foams as a homogeneous medium with the foam average density. To address this issue, an experiment was performed using the VULCAN Nd:glass laser at the Central Laser Facility. The aim was to measure the principal Hugoniot of TMPTA plastic foams at 260mg/cm^{3}, corresponding to the density of liquid DT-wetted-foam layers, and their "hydrodynamic equivalent" capsules. A VISAR was used to obtain the shock velocity of both the foam and an α-quartz reference layer, while streaked optical pyrometry provided the temperature of the shocked material. The measurements confirm that, for the 20-120 GPa pressure range accessed, this material can indeed be well described using the equation of state of the homogeneous medium at the foam density.

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 microtomography (mu CT) was performed both prior to and immediately following dynamic compression to correlate key structural features between the initial microstructure and recovered fragments as well as to identify the leading mechanisms for fracture and fragmentation. Real-time visualisation of damage evolution in the specimens revealed the very first cracks to be initiated at the sites of FeNi-metal nodules. These cracks propagated rapidly through the largest group of chondrules (the porphyritic olivine type chondrules) along the loading direction, which led to the formation of column-like fragments. mu CT analysis of the collected fragments confirmed the dominant mode of fracture to be transgranular with a clear link between FeNi-metal nodule statistics and the size distribution of fragments, emphasising their role in mechanical failure and fragmentation process. The resulting fragmentation was used to validate the predictions of brittle fragmentation models, and found to be in good agreement with the laboratory-scale impacts. In turn, these models can help unravel the consequences of impact-induced fragmentation processes that have helped shape the solar system.

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 impact test configuration. The samples were placed within the intense X-ray beam providing an observation field of 12.8 mm in width and 8 mm in height. Thanks to equispaced 16 bunches of short X-ray pulses, the samples were imaged through an indirect detector arrangement using the Shimadzu HPV-X2 camera lens-coupled to a fast scintillator capturing through-thickness measurements with an interframe time of 1.06 µs. The comparison of fragmentation patterns between two samples revealed an important insight into velocity dependant spall formation as well as the effects of crack closure and bridging.