CERES :: Browsing by Author "Hazael, Rachael"

Browsing by Author "Hazael, Rachael"

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Open Access
An experimental method of determining explosive equivalency when scaled distance approaches zero
(International Society of Explosives Engineers, 2024-01-01) Alford, Roland; Hazael, Rachael; Critchley, Richard
The ability to compare explosives is fundamental. Numerous methods are used and while simple conversion factors are often used, the use of TNT Equivalency (TNTe) is not a simple subject as explosives exhibit very different equivalencies depending on whether the pressure or impulse are being considered as well as other conditions. The scaled distance has been found to have a significant effect on the TNTe but due to the difficulty of taking measurements at very close ranges, no TNTe have been quoted for charges in direct contact (Z=0). This paper describes the use of a ballistic pendulum to measure the impulse from contact charges and presents some surprising results that require a two-stage propulsion, as originally described by Backofen, to be explained.
Open Access
Are low-yield explosive ordnance disposal methods viable?
(IMCSE, 2022-10-01) Alford, Roland; Hazael, Rachael; Critchley, Richard
In 2021 reports began to appear online regarding a new underwater UXO clearance tech that produced a “low-yield” result. It claimed that the technology used did not cause deflagration (burning) but resulted in the munitions breaking up and scattering, causing the explosives to dissipate. The system used was referred to by the brand name Hydra-Jet.[1] Review of available material shows that at Seagreen Offshore Wind Farm, currently being constructed 27km off the Scottish coast in the North Sea [2], three sea mines were attacked using the Hydra-Jet and all three interventions either caused a detonation or a partial detonation. It is unlikely that this technology is 100% reliability and appears to show no improvement over proven low-order techniques such as shaped charges that use low-density reactive liners.[3] It is thought likely that the disruptive effect is produced by overpressure from the charge, placed at close range to the target causing high pressures that are designed to result in physical break-up of the munition rather than any more complex mechanism. The pressure readings taken of the events show that they strongly indicate that at least some of the explosives detonated. The published pressure measurements, indicating that there had been at least partial detonations, were reported to have presented a risk of harm to wildlife (harbour porpoise within approximately 4km) despite the results not having breached the operator’s licence thresholds.[4,5] The latest data from trials conducted by the national Physical Laboratories and Loughborough University might offer guidance for more stringent but achievable thresholds for future work.[6]
Open Access
Assessing the pressure losses during hydrogen transport in the current natural gas infrastructure using numerical modelling
(Elsevier, 2023-06-08) Thawani, Bonny; Hazael, Rachael; Critchley, Richard
The UK government aims to transition its modern natural gas infrastructure towards Hydrogen by 2035. Since hydrogen is a much lighter gas than methane, it is important to understand the change in parameters when transporting it. While most modern work in this topic looks at the transport of hydrogen-methane mixtures, this work focuses on pure hydrogen transport. The aim of this paper is to highlight the change in gas distribution parameters when natural gas is replaced by hydrogen in the existing infrastructure. This study uses analytical models and computational models to compare the flow of hydrogen and methane in a pipe based on pressure loss. The Darcy-Weisbach and Colebrook-White equations were used for the analytical models, and the k- ε model was used for the computational approach. The variables considered in the comparison were the pipe material (X52 Steel and MDPE) and pipe diameters (0.01m–1m). It was observed that hydrogen had to be transported 250–270% the velocity of methane to replicate flow for a fixed length of pipe. Furthermore, it was noted that MDPE pipes has 2–31% lower pressure losses compared to X52 steel for all diameters when transporting hydrogen at a high velocity. Lastly, it was noted that the analytical model and computational model were in agreement with 1–5% error in their findings.
Open Access
An assessment of a non-destructive magneto-optical imaging technique for the recovery of laser engraved marks from steel plates and firearm components
(Elsevier, 2023-10-22) Henwood, Bailey; Helliker, Aimée; Hazael, Rachael; Hewins, Katherine
The International Tracing Instrument (ITI) is a document adopted by United Nations Member States in 2005, which outlines challenges faced in the tracing of illicit weapons and offers suggestions to increase the success of tracing operations. A key provision of the ITI states that serial numbers must be recoverable if obliterated. This research, therefore, investigates two methods of recovering laser engraved marks on steel, due to the increase in firearms manufacturing relying on lasers to apply critical markings. This work uses 20 steel plates (CR4 grade), 6 AK-pattern rifle top covers, and a steel pistol slide to investigate the potential for visualising laser engraved marks. All samples had marks applied using a BWM-30F Fibre laser marking machine, in addition to any original manufacture’s stamped marks on the pistol. All marks were removed using a grinding belt (plates) and a Dremel® rotary tool (slide and top covers) to average depths of 1200 µm (stamped) and 240 µm (laser engraved). Recovery of the marks was attempted using two techniques to compare the two techniques in their ability to recover laser engraved marks; Regula Forensics® Eddy Current Recovery kit, followed by traditional Fry’s reagent. Both recovery techniques recovered 100 % (n = 6) of the stamped characters on the pistol slide, and 0 % (n = 509) of the laser engraved characters on the pistol, top covers and steel plates. Recommendations are made for forensic firearms examiners to avoid attempting the recovery of laser engraved marks using Fry’s reagent to preserve the integrity of evidence. It is also suggested that manufacturers avoid laser engraving unique identifying marks on firearms, and to use more permanent methods, such as stamping, to remain compliant with politically binding documents such as the ITI.
Open Access
Bacterial survival following shock compression in the GigaPascal range
(Elsevier, 2017-09-01) Hazael, Rachael; Fitzmaurice, Brianna C.; Foglia, F.; Appleby-Thomas, Gareth J.; McMillan, P. F.
The possibility that life can exist within previously unconsidered habitats is causing us to expand our understanding of potential planetary biospheres. Significant populations of living organisms have been identified at depths extending up to several km below the Earth's surface; whereas laboratory experiments have shown that microbial species can survive following exposure to GigaPascal (GPa) pressures. Understanding the degree to which simple organisms such as microbes survive such extreme pressurization under static compression conditions is being actively investigated. The survival of bacteria under dynamic shock compression is also of interest. Such studies are being partly driven to test the hypothesis of potential transport of biological organisms between planetary systems. Shock compression is also of interest for the potential modification and sterilization of foodstuffs and agricultural products. Here we report the survival of Shewanella oneidensis bacteria exposed to dynamic (shock) compression. The samples examined included: (a) a "wild type" (WT) strain and (b) a "pressure adapted" (PA) population obtained by culturing survivors from static compression experiments to 750 MPa. Following exposure to peak shock pressures of 1.5 and 2.5 GPa the proportion of survivors was established as the number of colony forming units (CFU) present after recovery to ambient conditions. The data were compared with previous results in which the same bacterial samples were exposed to static pressurization to the same pressures, for 15 minutes each. The results indicate that shock compression leads to survival of a significantly greater proportion of both WT and PA organisms. The significantly shorter duration of the pressure pulse during the shock experiments (2-3 μs) likely contributes to the increased survival of the microbial species. One reason for this can involve the crossover from deformable to rigid solid-like mechanical relaxational behavior that occurs for bacterial cell walls on the order of seconds in the time dependent strain rate.
Open Access
Ballistic impact of hollow-point ammunition on porcine bone
(Wiley, 2023-05-06) Watson, Kayla E.; Henwood, Bailey; Hewins, Kate; Roberts, Andrew; Hazael, Rachael
Identifying failure mechanisms in skeletal tissue allows a deeper understanding of the effects of specific projectile impacts on bone. While ballistic trauma in flat bones is largely researched, knowledge of how long bones react to gunshot impacts is limited in the literature. The impacts of deforming ammunition appear to produce higher levels of fragmentation; however, these have not been studied in depth. This study compares the damage to femora bone by HP 0.357 and 9 mm projectiles constructed with both full and semi-metal jackets. Impact experiments were undertaken on a single-stage light gas gun involving the use of a high-speed video camera and full reconstruction of the bones to ascertain fracture patterns occurring in the femora. Higher degrees of fragmentation are likened to the presence of semi-jacketed HP projectiles than jacketed HP projectiles. The observations of external facing beveled edges are believed to be associated with the increased separation of the jacket and lead core of projectiles. Additionally, experimentation has shown that the amount of kinetic energy lost postimpact is likely related to the presence or the absence of a metal jacket on an HP projectile. The observed data, therefore, suggest that the composition, rather than the configuration, of a projectile affects the type and extent of the damage.
Open Access
Blast mitigation using polymeric 3D printed auxetic lattice structures - a preliminary study
(SAGE, 2021-10-18) Critchley, Richard; Hazael, Rachael; Bhatti, Kamran; Wood, David; Peare, Alan; Johnson, Stephen; Temple, Tracey J.
Protection of critical infrastructure in an urban environment is a challenging task, specifically against the vehicle bourne improvised explosive device threat. To design infrastructure to withstand this evolving threat, novel solutions and advanced materials need to be developed. One such material of interest are auxetics. This study experimentally analysed the mitigation of blast response of auxetic re-entrant honeycomb structures, with geometries varying between −ve 30° and +ve 30° using additive manufacturing (3D printing) techniques and non-explosive loading via shock tube. Re-entrant auxetic structures (−ve 15°) exhibited repeatable blast mitigation of 23% and reduced the transmitted pressure and impulse of the blast wave. Further highlighting their potential application as a protective measure to enhance a structures blast survivability.
Open Access
Blast wave ingress into a room through an opening – review of past research and US DoD UFC 3-340-02
(SAGE Publications, 2024-10-19) Eytan, Alex; Forth, Shaun A.; Pickering, Erik G.; Hazael, Rachael; Burrows, Stephanie J.
Blast wave ingress into a room through a facade opening results in complex pressure-time loadings on interior surfaces due to shock diffraction and interior reflections. The U.S. DoD UFC 3-340-02 Structures to Resist the Effects of Accidental Explosions includes a method to predict internal loading for such cases. Parameters such as the opening size, room dimensions and the external pressure wave characteristics influence the interior loading. Recent work suggests that the UFC methodology might overpredict the interior loading by some 600%. Such conservatism can result in over-engineered or prohibitively expensive protective solutions. In this paper we critically review the methodology of the UFC, that of Kaplan’s preceding work (on which the UFC relies), and the experimental data that informed both these works. Through a series of 45 case-studies we compare the UFC and Kaplan’s predictions with those of a computational fluid dynamics (CFD) model. The UFC consistently overpredicts the CFD area-averaged peak pressure of the back wall by up to 290% and the side-wall by up to 425%. Similarly, the UFC overpredicted the CFD side wall positive phase impulse by up to 565%. By contrast, the UFC predicted back wall positive phase impulse was similar to the CFD results. As our CFD results for side and back walls are area averaged, and not solely for the wall centre-point, as in other recent work, our paper gives support for the use of CFD prediction over the UFC for cost-effective design of structures to resist blast ingress.
Open Access
Comparative analysis of blast prediction software for far-field shock wave effects behind a blast wall
(SAGE, 2024-12-31) Chester, Alastair; Hazael, Rachael; Critchley, Richard
This paper investigates a selection of current and emerging software used in the prediction of overpressure generated through the detonation of a high explosive in the far field behind a blast wall. In particular, this paper compares the software Autodyn, blastFoam, ProSAir, Viper::Blast and WALAIR++. These packages are compared by simulating a 100 kg TNT explosive charge at a stand-off distance of 25 m from a complex structure, then reviewing the performance in terms of the overpressure results, speed of each modelling package, the degree of effect from mesh, and domain sizes and ease of use. A live experimental trial representing the simulation was also performed, although it used a similar but different explosive, for a high-level comparison. The live-trial instrumentation design details are reviewed and compared with best practice. The choice of software is found to lead to variations in peak pressure predictions of 28%, specific impulse by 10% and the simulation speed can vary by a factor of up to 1600 for this type of study. This shows that the choice of blast software package can have a significant impact on the accuracy and attainability of blast predictions.
Open Access
A comparison of far-field explosive loads by a selection of current and emerging blast software
(Sage, 2024-04-29) Chester, Alastair; Critchley, Richard; Hazael, Rachael
In blast resistant design, simulation data may be used to generate the explosive loads that would be witnessed by the detonation of a high explosive device. There are many software packages available to simulate explosions, and this study aims to provide a comparison of a selection of them, including some recently available, with the aim of forming an understanding of the potential accuracies and speed of these in far-field explosive prediction. Software selection criteria were formed by a literature survey to highlight the commonly commercially used programmes. Each software package was used to predict the far-field effects of overpressure and specific impulse from two explosive charges against a reflective target. The data generated by these simulations were then critically compared and reviewed, both with respect to each other and, for the 100 kg charge size, with respect to experimental data. It shows that for the simulated scenarios, after domain and cell size fidelity studies have been performed, the choice of software may lead to a variance in prediction in the peak overpressure of up to 50%, specific impulse of up to 15%, and simulation run times by a factor of 600.
Open Access
Design of multi-layered protection against guided mortar threats through numerical modeling
(Elsevier, 2023-01-28) Thawani, Bonny; Lim, Seng Kiat; Brown, Laura; Critchley, Richard; Hazael, Rachael
The trade – off between protection and weight is a constant consideration when designing a portable protective solution. Greater mobility is a desirable attribute and protection must therefore adapt, prompting a demand for lightweight, simple to construct, low-cost and effective ballistic protection systems. High strength and ductility, wave spreading capability and good energy absorption are key properties for ballistic protection. Four materials, polycarbonate, Kevlar®-epoxy, polyurethane foam, and aluminium alloy, possess these properties and were selected for analysis by numerical simulation. Multi-layered configurations were proven to be an optimal solution, by exploiting the advantages of each material without having large penalties of mass and cost. Numerical modelling using ANSYS AUTODYN® is used to simulate monolithic and multi-layered target configurations, to obtain the penetration mitigation performance. The results are analysed to select configurations based on different requirements, such as lowest cost, lowest mass, best performance, and optimal configuration which balanced the three key parameters mentioned. The optimal configuration of Aluminium, Kevlar-Epoxy, Polyurethane, and Polycarbonate has layers with thickness of 7, 3, 38, 2 mm respectively with a total mass of 7.97 kg, total cost of $39.86 and penetration of 29.34% (14.67 mm). Polynomial relationships between performance and mass/cost are also determined.
Open Access
The effects of quasi-one-dimensional shock on Escherichia coli while controlling pressure and temperature
(Elsevier, 2020-11-28) Fitzmaurice, Brianna C.; Appleby-Thomas, Gareth J.; Painter, Jonathan; Wood, David C.; Hazael, Rachael
The response of microorganisms to high pressures is of growing interest in the literature, regarding areas of research including the sterilisation of foodstuffs, panspermia and, more generally, the study of extremophiles. When examining organisms under shock pressure, there are a number of caveats that need to be considered, including temperature and the nature of the shock wave front. Both of these caveats have been explored in this study through the application of the plate impact technique to create quasi-one-dimensional shock waves with controlled shock fronts through bacterial targets. This was achieved using typical planar flyer plates to study the dynamic pressure response of the bacterium, Escherichia coli NCTC 10538. Additionally, in order to create an adiabatic, off-Hugoniot loading path, a novel graded areal density flyer produced by the Surfi-Sculpt® approach was used to assess the effects of lowering temperature during shock on E. coli growth rates. The maximum temperature generated by a Surfi-Sculpt® flyer impact was 5 K less than that produced by the planar flyer analogue. Higher growth rates of bacterial colonies post-impact by the Surfi-Sculpt® flyer compared to those by the planar flyer were observed, with this behaviour determined to be a possible function of the nature, although temperature was also decreased with the use of this adiabatic ramp loading technique. In an effort to purposefully increase pressure and temperature for the E. coli samples, a modified form of a previously developed bacterial encapsulation system was also employed in this study, allowing pressures of up to 10 GPa and growth rates of up to 0.09% to be reached.
Open Access
Evaluation of soft tissue simulant performance against economic and environmental impact
(Royal Society of Chemistry, 2024-02-22) Read, James; McNaught, Ken R.; Hazael, Rachael; Critchley, Richard
Soft tissue simulants are traditionally used to provide a post impact medium suitable for replicating human anatomy. Performance of materials is therefore paramount, and the analysis of such experimentation relies on responses that mimic the various tissue, bone and muscle groups contained within the human body. However, with an increasing global push to reduce carbon emissions and increase sustainability, current materials require examination to ensure research establishments remain at the forefront of environmentally friendly practices. To date, the literature contains little in relation to how environmentally friendly the use and supply of soft tissue simulants is. The aim of the research is to provide researchers with primary data to support decisions on material selection for ballistic simulation research. The need arises due to the high cost and environmental impact of existing materials. To explore this research gap, a series of 5.5 mm ball bearings were fired from a gas gun at velocity ranges between 122 and 526 m s−1 to examine the performance characteristics of six commercially available soft tissue simulants and a foodstuffs grade gelatine that represented a more cost effective environmentally friendly alternative. A structured multi-criteria decision analysis approach was employed to compare the overall effectiveness of the alternative materials. It was found that whilst PermaGel, 20 and 10% ballistic gelatine performed the most advantageously respectively during experimental testing, qualitative environmental assessment showed ballistic soap, PermaGel and foodstuffs gelatine to be most advantageous. The information provided within this study will enable researchers to make more informed decisions on both economic and environmental implications when sourcing materials for use within survivability assessment, whilst further work would increase awareness and viability of alternative materials.
Open Access
Fragmentation studies by non-explosive cylinder expansion technique
(Elsevier, 2020-09-04) Rao, Prakash; Painter, Jonathan; Appleby-Thomas, Gareth J.; Critchley, Richard; Wood, David; Roberts, Andrew; Hazael, Rachael
Expansion and fragmentation of metallic cylinders is an important area of study both for designing munitions and mitigation techniques against fragments as well as in the failure of pressurised pipes in industry. Most of the reported studies on fragmentation have been carried out by detonating explosively filled metallic cylinders. However, this approach has inherent limitations in terms of both safety and repeatability – not least due to packing issues with explosive fills. Fragmentation studies on hollow metallic cylinders of both mild and stainless steel of various thicknesses (2–4 mm) were carried out by firing a polycarbonate projectile from a single-stage light gas gun. Strain rates of the order of 2 × 104 s−1 were observed at cylinder expansion velocities of 400–450 m s−1, calculated from flash X-ray radiographs. The differences in fragmentation behaviour of both materials was observed, attributed to their different response to high strain-rate loadings. Microscopic analysis of mild steel fragments showed interesting alignment of ferrite and pearlite grains, similar to reported effects of explosive loading. This suggests the potential to employ this technique to simulate explosive cylinder expansion in a non-explosive laboratory environment enabling a convenient recovery of fragments. Numerical modelling with using ANSYS AUTODYN® allowed for a better understanding of the various parameters controlling expansion and fragmentation. Analysis of recovered fragments by a Fragment Weight Distribution Map (FWDM), a method generally used for characterising pipe bombs, could clearly demonstrate the effect of casing material and thickness.
Open Access
In Vivo water dynamics in Shewanella oneidensis bacteria at high pressure
(Nature Publishing Group, 2019-06-18) Foglia, Fabrizia; Hazael, Rachael; Meersman, Filip; Wilding, Martin C.; Sakai, Victoria García; Rogers, Sarah; Bove, Livia E.; Koza, Michael Marek; Moulin, Martine; Haertlein, Michael; Forsyth, V. Trevor; McMillan, Paul F.
Following observations of survival of microbes and other life forms in deep subsurface environments it is necessary to understand their biological functioning under high pressure conditions. Key aspects of biochemical reactions and transport processes within cells are determined by the intracellular water dynamics. We studied water diffusion and rotational relaxation in live Shewanella oneidensis bacteria at pressures up to 500 MPa using quasi-elastic neutron scattering (QENS). The intracellular diffusion exhibits a significantly greater slowdown (by −10–30%) and an increase in rotational relaxation times (+10–40%) compared with water dynamics in the aqueous solutions used to resuspend the bacterial samples. Those results indicate both a pressure-induced viscosity increase and slowdown in ionic/macromolecular transport properties within the cells affecting the rates of metabolic and other biological processes. Our new data support emerging models for intracellular organisation with nanoscale water channels threading between macromolecular regions within a dynamically organized structure rather than a homogenous gel-like cytoplasm.
Open Access
Internally bevelled conoidal entry wounds in sandwich bones; their genesis, impact dynamics and macroscopic and microscopic morpholog
(Cranfield University, 2021-01) Rickman, John; Painter, Jonathan; Hazael, Rachael
Projectile trauma to the sandwich bones of the neurocranium is of considerable forensic anthropological importance due to the high lethality associated with gunshot wounds to this anatomical region. The internally bevelled conoidal wound that typically results from perpendicular projectile impact has long been considered diagnostic of bullet involvement and is utilised in both differential diagnosis of gunshot trauma and in making trajectory determinations using the direction of bevel asymmetry as an indicator. However, despite the importance of these activities in forensic anthropological casework the fracture mechanisms underlying bevel formation have remained elusive, with multiple hypotheses presented but few empirical investigations carried out to test them. Further diagnostic complexity has been introduced by the recognition that bevelling also results from low-velocity impacts and that taphonomic agencies can both modify and create internally bevelled fractures. Despite the fact that bone is a complex hierarchical material the majority of analyses of projectile entry wounds in sandwich bones have been conducted at the macroscopic scale, leaving important questions as to whether lower scales of organisation may yield signatures of diagnostic importance. This thesis presents the findings of an experimental investigation into the fracture mechanisms that underlie internal bevelling and presents an analysis of the relationships between the dynamics of impact and quantitative wound morphology. A refined nomenclature for the components of internally bevelled fractures is presented and the layers composing the bevel formally defined. This thesis also presents a Scanning Electron Microscope (SEM) analysis of the effects of projectile impact on compact bone at lower hierarchical scales of bone organisation. Examination of fracture morphology with micro-computerised tomography (µ-CT) coupled with high-speed videography of the impact events revealed a novel cone cracking mechanism that fundamentally changes our understanding of bevel morphology. This mechanism explains how internal bevelling results from both low- and high-velocity impact events and suggests caution should be applied to trajectory determinations made using bevel asymmetry alone. Quantitative analysis of the perforation event revealed, for the first time in sandwich bones, a power relationship between incident velocity and absorbed kinetic energy. SEM analysis of cortical bone around the entry captured the early genesis of conoidal wounds through ring crack formation. Analysis of the periphery of the entry revealed two types of plastic deformation that are suggestive of changes to hydroxyapatite (HA) crystal structure that may be of diagnostic utility. Collectively, the findings presented in this thesis will enhance the diagnosis and interpretation of conoidal wounds in both forensic and archaeological contexts.
Open Access
Introducing Bayesian belief updating as a method to counter improvised explosive devices: a qualitative case study on identifying human behaviours associated with explosive chemical precursor diversion
(Springer, 2023-08-21) Collett, Gareth; Ladyman, Melissa; Temple, Tracey; Hazael, Rachael; McNaught, Ken R.
Countering improvised explosive devices (C-IED) is a significant theme of the twenty-first century, particularly in regions with limited governance and a fragile rule of law. Many strands of activity are involved, with human interaction proving difficult to predict. However, Bayesian belief updating (used across several academic fields to provide insight into human behaviours) has never been considered. Given the breadth of C-IED, this research focusses on a state affected by conflict, and where illicit diversion of explosive chemical precursors (ECP) for IED manufacture is supported by the population. It aims to represent (both visually and probabilistically) a methodology by which human relationships could be better understood, thereby promoting belief updating as new evidence becomes available. Such belief updating would refine focus and improve resource mobilisation.
Open Access
Introducing the combustion continuum to define the transition points between burning, deflagration, and detonation regimes of energetic materials
(Taylor and Francis, 2024-12-28) Alford, Roland; Hazael, Rachael; Critchley, Richard
This paper introduces what the authors term Combustion Continuum which treats oxidation reactions of energetic materials as lying on a continuum in which the variable is the speed of reaction. It divides the continuum into three regions, burning, deflagration, and detonation (BDD) and defines the transition points between each region and describes various observable effects that allow definitive identification of the type of reaction. The transition point between combustion and deflagration is defined as the onset of an atmospheric shock wave, which is the first time deflagration has been defined in such a way that the point of transition can be observed and fixed. The transition point between deflagration and detonation is well defined elsewhere and is the point at which the reaction shocks-up to produce a shock wave driven detonation front. This approach contrasts with most literature that treats burning, deflagration and detonation as interrelated forms of energetic reaction with none giving precise definitions that allow a full understanding of the difference between them and most critically, how to determine whether a reaction is burning or deflagration.
Open Access
Material strength evolution of FCC metals under high strain rates
(2020-12) Gilroy-Hirst, Caitlin; Hazael, Rachael; Wood, David; Akhavan, Jacqueline
Copper and stainless steel 21-6-9, two face-centred cubic (FCC) materials, were shock loaded in partially recovered uniaxial strain flyer-plate impact experiments at varying impact pressures (6 GPa - 16 GPa). These samples were collected post impact via three differing recovery configurations: (1) standard or ‘free boundary’; (2) partial shock recovery, i.e. using both ‘momentum trapping’ and ‘soft recovery’ techniques but with a flyer plate thickness of 10 mm to see the effects on partial tensile release in the rear spall plates of an established recovery target design; finally (3) a traditional full recovery comparison with a 2 mm flyer impact. These samples were then analysed using a suite of analytical techniques including X ray diffraction, optical microscopy, hardness testing and compression after impact testing, to observe the material deformation characteristics in the simplified partially recovered shock and release condition compared to the more complex ‘standard’ release wave situation. A control sample of a ‘ fully recovered’ sample was also carried out for comparative purposes. The rear spall plates were modified on these partially recovered samples to see the effect that this had on the tensile release waves and how this changed the material deformation properties overall. Results for the stainless steel 21-6-9 demonstrated the ability of the partial shock recovery technique (hereafter called ‘partial-recovery’) to mitigate the reverberations compared to that of the standard samples. Upon analysis of the targets, it was observed that the dislocation density was generally lower for the partially recovered samples but varied with impact pressure for both the standard and recovered configuration. For the stainless steel recovery experiments an increasing dislocation density from 4 x 1015 m-2 at 6 GPa to 6.5 x 1015 m-2 at 12 GPa was observed which then decreased to 5.5 x 1015 m-2 at 16 GPa. The twinning density to grain ratio obtained from optical microscopy showed a linear increase (y= 1.5345x - 8.3508) with an R2 value of 0.8295 from 7 GPa at 4 twins per grain to 17 twins per grain at 16 GPa. Twinning density is indicative of a successful recovery, where a successful recovery is a reduction in reverberations in the sample and in a full recovery is a 1D shock. The dataset both verifies the use and success of the recovery technique as well as demonstrating the materials characteristics under partial-recovery, while observing reverberation effects.
Open Access
Metal β-diketoiminate precursor use in aerosol assisted chemical vapour deposition of gallium- and aluminium-doped zinc oxide
(Elsevier, 2017-11-02) Knapp, Caroline E.; Dyer, Caragh; Chadwick, Nicholas P.; Hazael, Rachael; Carmalt, Claire J.
Aerosol assisted chemical vapour deposition (AACVD) has been used to deposit thin films of ZnO from the single-source precursor [Zn(OC(Me)CHC(Me)N(iPr))2] (1) affording highly transparent (>80%) and conductive films (sheet resistance ∼70 KΩ/sq). Extension of this AACVD method whereby related precursors of the type, [R2M(OC(Me)CHC(Me)N(iPr))] (R = Et, M = Al (2); R = Me, M = Ga (3)), isolated as oils, were added to the precursor solution allowed for the deposition of aluminium- and gallium-doped ZnO (AZO and GZO) films, respectively. Complexes 1–3 were characterised by elemental analysis, NMR and mass spectrometry. Films were deposited in under 30 min at 400 °C, from CH2Cl2/toluene solutions with a N2 carrier gas. Herein we report the bulk resistivity, ρ, of AZO (0.252 Ω cm) and GZO (0.756 Ω cm) films deposited from this novel approach. All the films transparency exceeded 80% in the visible, X-ray diffraction (XRD) showed all films to crystallise in the wurtzite phase whilst X-ray photoemission spectroscopy (XPS) confirmed the presence of the Al and Ga dopants in the films, and highlighted the low C-contamination (<5%) this route offers. Investigation of a mechanism analogous to the Kirkendall effect confirmed that heating of GZO films at 1000 °C produced the spinel structure GaZn2O4.