CERES :: Browsing by Author "Hazell, Paul J."

Browsing by Author "Hazell, Paul J."

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Open Access
Advances in Applied Ceramics: Guest editorial
(Maney Publishing, 2010-12-31T00:00:00Z) Hazell, Paul J.
The development, engineering, and testing of ceramic armour systems and materials has been carried out during the past 50 years and dates back to the pioneering work of M. L. Wilkins and his colleagues [1]. Arguably, the first indications that such armour would be ballistically efficient were seen much earlier than Wilkins when, in 1918 Maj Neville Monroe‐Hopkins found that a thin layer of enamel improved the ballistic performance of a thin steel plate [2]. Indeed, many early designs employed a hard ceramic face backed by a relatively ductile material, thereby employing the disruptor (or ‘disturber’)/absorber recipe that is still used in modern armour systems today.
Open Access
The bactericidal effect of shock waves
(Institute of Physics, 2014-05-07) Leighs, James Allen; Appleby-Thomas, Gareth J.; Wood, David C.; Goff, Michael J.; Hameed, Amer; Hazell, Paul J.
There are a variety of theories relating to the origins of life on our home planet, some of which discuss the possibility that life may have been spread via inter-planetary bodies. There have been a number of investigations into the ability of life to withstand the likely conditions generated by asteroid impact (both contained in the impactor and buried beneath the planet surface). Previously published data regarding the ability of bacteria to survive such applied shockwaves has produced conflicting conclusions. The work presented here used an established and published technique in combination with a single stage gas gun, to shock and subsequently recover Escherichia coli populations suspended in a phosphate buffered saline solution. Peak pressure across the sample region was calculated via numerical modelling. Survival data against peak sample pressure for recovered samples is presented alongside control tests. SEM micrographs of shocked samples are presented alongside control sets to highlight key differences between cells in each case.
Open Access
Ballistic behaviour of explosively shattered alumina and silicon carbide targets
(Maney Publishing, 2011-12-31T00:00:00Z) Nanda, H.; Appleby-Thomas, Gareth J.; Wood, David C.; Hazell, Paul J.
The resistance offered by three ceramic materials of varying strength that have been subjected to explosive loading has been investigated by depth-of-penetration testing. Each material was completely penetrated by a tungsten carbide cored projectile and the residual penetration into a ductile aluminium alloy backing material was measured. The resulting ballistic performance of each damaged ceramic was found to be similar implying that the resistance offered to the projectile by the damaged ceramic is not dependent on the intrinsic strength properties of the intact material. This was taken as evidence that the important controlling parameter for enhancing the ballistic performance of a damaged ceramic material was not the strength of the ceramic but rather the fragment morphology.
Open Access
Crack softening damage model for ceramic impact and its application within a hydrocode
(American Institute of Physics (AIP), 1997-12-31T00:00:00Z) Hazell, Paul J.; Iremonger, Michael J.
A physically based crack softening damage model has been developed and used in a non-linear transient dynamic computer code (AUTODYN-2D). It is assumed that there is a finite number of orientated pre-existing flaws within the ceramic target. The mode I and mode II stress intensity factors are calculated in compression and tension and the strain energy release rate is then estimated and compared to a critical dynamic strain energy release rate. At initiation, a tension crack propagates at a velocity dependent on the mode I stress intensity factor and failure occurs in a computational cell when two neighbouring microcracks coalesce. The model was used to simulate two different plate impact experiments of alumina on alumina with encouraging results. The model was also used to analyze the impact of a steel sphere on alumina and shows strong correlation between experimental and predicted results.
Open Access
The design of mosaic armour: the influence of tile size on ballistic performance
(2008-03-15T00:00:00Z) Hazell, Paul J.; Roberson, Colin J.; Moutinho, Mauricio
Silicon carbide square tiles of different areal geometries and manufactured via two different processing routes have been bonded to polycarbonate layers to evaluate their ballistic performance. Four ceramic tile sizes were tested: 85mm, 60 mm, 50 mm and 33 mm. In each case the residual depth-of-penetration into a polycarbonate semi-infinite backing was recorded. To elucidate the penetration and failure mechanisms, a computational model using the JH-1 ceramic model [Holmquist TJ, Johnson GR. Response of silicon carbide to high velocity impact. J Appl Phys 2002;91:5858–66] of the projectile used in the experimental study penetrating into a silicon carbide-faced polycarbonate was implemented in the hydrocode AUTODYN-2D. This paper shows that there is a critical dimension of tile that should be used in a silicon carbide-based ceramic-faced mosaic armour system design to ensure optimum system performance when each tile is struck centrally.
Open Access
Deviatoric response of an armour-grade aluminium alloy
(AIP American Institute of Physics, 2009-12-31T00:00:00Z) Appleby-Thomas, Gareth J.; Hazell, Paul J.; Millett, Jeremy C. F.; Bourne, Neil K.
Aluminium alloys such as 5083 H32 are established light-weight armour materials. As such, the shock response of these materials is of great importance. The shear strength of a material under shock loading provides an insight into its ballistic performance. In this investigation embedded manganin stress gauges have been employed to measure both the longitudinal and lateral components of stress during plate-impact experiments over a range of impact stresses. In turn, these results were used to determine the shear strength and to investigate the time dependence of lateral stress behind the shock front to give an indication of material response.
Open Access
The dynamic behaviour of a modified polyurethane resin
(2011-06-15) Appleby-Thomas, Gareth J.; Hazell, Paul J.; Stennett, Christopher; Cooper, G.; Cleave, R.
The dynamic response of both a pure and nano-reinforced polyurethane replacement resin (PRR) have been investigated using plate impact techniques. Similar U-P-U-S Hugoniot equations of state have been established for both materials, despite the altered cross-linking associated with the addition of inorganic polyhedral oligomeric silsesquioxane (POSS) blocks of c. 1.5 nm size to the resin matrix. At higher particle velocities a similar U-P-U-S response to that of polyurethane from the literature was observed. However, at lower particle velocities a non- linear response was noted in both forms of PRR, similar to that observed for polymers elsewhere. Ultrasonic measurements were also undertaken and indicated the presence of two distinct phases in the reinforced elastomer.
Open Access
The dynamic behaviour of ballistic gelatin
(AIP American Institute of Physics, 2009-12-31T00:00:00Z) Shepherd, C. J.; Appleby-Thomas, Gareth J.; Hazell, Paul J.; Allsop, Derek F.
In order to characterise the effect of projectiles it is necessary to understand the mechanism of both penetration and resultant wounding in biological systems. Porcine gelatin is commonly used as a tissue simulant in ballistic tests because it elastically deforms in a similar manner to muscular tissue. Bullet impacts typically occur in the 350–850 m/s range; thus knowledge of the high strain-rate dynamic properties of both the projectile and target materials are desirable to simulate wounds. Unlike projectile materials, relatively little data exists on the dynamic response of flesh simulants. The Hugoniot for a 20 wt.% porcine gelatin, which exhibits a ballistic response similar to that of human tissues at room temperature, was determined using the plate-impact technique at impact velocities of 75–860 m/s. This resulted in impact stresses around three times higher than investigated elsewhere. In US−uP space the Hugoniot had the form US = 1.57+1.77 uP, while in P−uP space it was essentially hydrodynamic. In both cases this was in good agreement with the limited available data from the literature.
Open Access
The effect of specimen thickness on the shock propagation along the in-fibre direction of an aerospace-grade CFRP laminate
(Elsevier, 2009-02) Hazell, Paul J.; Stennett, C.; Cooper, G.
In-fibre measurements of the Hugoniot have been carried out on a carbon fibre-reinforced polymer composite. For this material, we have shown at high shock stresses, a two component wave was formed consisting of a fast moving ramped portion and a slower moving shock wave. Changing the thickness of test specimen for a given shock stress resulted in a change in the magnitude and duration of the ramped portion of the wave front. As the shock stress imparted to the target was reduced, or the thickness of the target was increased, the steep shock wave in the rear surface gauge was no longer apparent. Instead a relatively slow rising wave was measured. Consequently, to establish a Hugoniot at lower shock stress levels, relatively thin specimens of target material are required.
Open Access
The failure of a tungsten carbide-cobalt cored projectile penetrating a hard target
(2010-11-08) Woolmore, Nicola J.; Hazell, Paul J.
Experimental results are presented from an investigation of the parameters of a ceramic-faced armour system that are required to induce damage in a tungsten carbide - cobalt (WC-Co) penetrator. A WC-Co material model has been successfully developed and implemented within the numerical hydrocode AUTODYN 2D. The understanding of penetration mechanisms was used to guide a parametric investigation, validating the WC-Co material failure model with experimental results. A series of experiments has been conducted firing the Russian 14.5 mm BS41 WC-Co cored projectile into various thicknesses and types of alumina (Al2O3) and silicon carbide (SiC), backed by aluminium alloy or mild steel semi-infinite witness blocks. Results demonstrated that SiC B out-performed standard monolithic armours and a selection of other armour ceramics including PS 5000 SiC and Sintox-CL. After comminution, the SiC B consisted of particles of closely interlocked grains. These appeared to provide considerable resistance to deviatoric stresses. Results suggest that it is not only increased hardness but also the nature of the fracture of the ceramic ahead of the penetrator that improves the armour’s ballistic performance at defeating WC-Co penetrators. If such superior ballistic response can be controlled and incorporated into practical armour systems, it will provide the basis for an advance in armour protective capability against WC-Co penetrators. In addition, a numerical material model derived from experimental data was developed to provide a preliminary tool to study the WC-Co failure. It was demonstrated that the numerical estimation of WC-Co behaviour using a shock Equation Of State (EOS), a piecewise linear strength model and a principle stress failure model provides a good method to estimate spall behaviour under dynamic loading in AUTODYN 2D. Successful numerical simulation of the material model used demonstrated the future potential of the technique.
Open Access
Gas gun ramp loading of Kel-F 81 targets using a ceramic graded areal density flyer system
(Elsevier, 2015-03-06) Goff, Michael J.; Hazell, Paul J.; Appleby-Thomas, Gareth J.; Wood, David C.; Stennett, Christopher
Kel-F 81 (PCTFE/Polychlorotrifluoroethylene) polymer targets were subjected to ramp loadings generated by a ceramic flyer accelerated into the targets by a gas gun in the plate impact configuration. This approach used a ceramic graded areal density flyer in conjunction with a ceramic buffer plate to induce a ramp loading in the target. The flyer was comprised of a rapid prototyped alumina ceramic. The loading was observed with embedded electromagnetic particle velocity gauges (PV gauges) with the results compared with ANSYS Autodyn™ hydrocode simulations. Experimental results show that ramp loadings of varying duration and magnitude were induced into the target. These loadings can be described as shockless compressions leading to shocked states within the material. In addition, numerical simulations provided further insight into the loading approach – with good agreement found with experimental data, opening the potential to design more complex loading systems in future.
Open Access
Impact, penetration, and perforation of a bonded carbon-fibre-reinforced plastic composite panel by a high-velocity steel sphere: an experimental study
(Professional Engineering Publishing, 2010-12-31T00:00:00Z) Hazell, Paul J.; Appleby-Thomas, Gareth J.; Kister, Guillaume
In this work, the response of a bonded CFRP composite panel, manufactured by bonding two laminates together, to impact, penetration and perforation by a high-velocity steel sphere has been studied. The response of a relatively thick (c.a. 12 mm) laminate has been compared to similar data from [1] where relatively thin monolithic laminates were impacted by the same type of projectile. It was found that the ballistic performance of the system was increased over the impact energy range of interest when compared to these similar relatively thin composite laminates. Furthermore, both the energy absorbed per-unit-thickness of laminate and the level of damage as measure by C-Scan was similar when the panels were perforated at normal and oblique incidence. This raises the prospect of reducing experimental testing at oblique angles, if the behaviour at normal incidence is known.
Open Access
Inelastic deformation and failure of tungsten carbide under ballistic-loading conditions
(Elsevier , 2010-12-31T00:00:00Z) Hazell, Paul J.; Appleby-Thomas, Gareth J.; Herlaar, K.; Painter, Jonathan
High-speed photography has been used to investigate the dynamic behaviour of similar grades of WC-Co hardmetals during ballistic impacts with velocities in the range of 28-484 m/s. Key features of the failure of similar grades of WC-Co materials during complimentary impacts have been observed and discussed. In particular, fast moving fragments were observed to emanate from the point of impact and flow radially across the target's surface analogous to the processes of interface defeat. Further, as the velocity of impact was increased a non-linear increase in the indentation depth was observed that corresponded with an apparent onset of trans-granular fracture in the WC crystallites. Comparisons with ANSYS AUTODYN™ simulations were made and good correlation has been established between the measured inelastic deformation and computations using a simple strain-hardening model.
Open Access
Initiation of secondary explosives measured using embedded electromagnetic gauges
(AIP American Institute of Physics, 2009-12-31T00:00:00Z) Stennett, Christopher; Cooper, G. A.; Hazell, Paul J.; Appleby-Thomas, Gareth J.
There is considerable evidence that secondary explosive materials having a relatively large (10-12%) proportion of HTPB binder do not exhibit DDT under cook-off. However, the understanding of the mechanisms controlling the growth of reaction in such experiments is incomplete. Most importantly, it is not known whether a mechanistic reason exists to preclude DDT; it is possible that existing techniques to explore cook-off simply do not offer the correct conditions to allow DDT to occur. We present experiments in which impacts were made against a RDX/HTPB PBX using a single-stage light gas gun. Electromagnetic particle velocity gauges were embedded within the targets at different distances from the impact face to record the onset of reaction, and in some cases detonation. These experiments were also performed against RDX/TNT targets. The time-resolved particle velocity histories have allowed comparison of some of the factors governing growth of reaction, and have provided run-to-detonation distance data for different impact stresses.
Open Access
Lateral stress evolution in chromium sulfide cermets with varying excess chromium
(2016-07-01) Petel, Oren E.; Appleby-Thomas, Gareth J.; Wood, David C.; Capozzi, Alexander; Nabavi, Seyed Ali; Goroshin, Samuel; Frost, David L.; Hazell, Paul J.
The shock response of chromium sulfide-chromium, a cermet of potential interest as a matrix material for ballistic applications, has been investigated at two molar ratios. Using a combustion synthesis technique allowed for control of the molar ratio of the material, which was investigated under near-stoichiometric (cermet) and excess chromium (interpenetrating composite) conditions, representing chromium:sulfur molar ratios of 1.15:1 and 4:1, respectively. The compacts were investigated via the plate-impact technique, which allowed the material to be loaded under a onedimensional state of strain. Embedded manganin stress gauges were employed to monitor the temporal evolution of longitudinal and lateral components of stress in both materials. Comparison of these two components has allowed assessment of the variation of material shear strength both with impact pressure/strain-rate and time for the two molar ratio conditions. The two materials exhibited identical material strength despite variations in their excess chromium contents
Open Access
Measuring the strength of brittle materials by depth-of-penetration testing
(Maney Publishing, 2010-12-31T00:00:00Z) Hazell, Paul J.
Based on an energy conservation model, the strength offered by a number of brittle materials has been calculated from depth-of-penetration (DOP) test results. Each material was completely penetrated by a tungsten carbide cored projectile of known kinetic energy and the residual penetration into a ductile aluminium alloy backing material was measured. The energy transferred to the tile by the projectile has been calculated and has been shown to vary linearly with the tile thickness. From the energy transferred to the armour tile, the mean resisting stress that was offered to the penetrator was calculated and for the materials tested, scaled with the material hardness. This work shows that for DOP testing, where the projectile remains intact, the measured DOP is merely a facet of the ceramic’s hardness and not its true ballistic performance. The possibility of using this method to measure the strength of damaged ceramic is also discussed.
Open Access
Modelling and characterization of cell collapse in aluminium foams during dynamic loading
(Elsevier, 2016-07-01) Kader, Md Abdul; Islam, Md A.; Hazell, Paul J.; Escobedo, Juan P.; Saadatfar, Md; Brown, Andrew David; Appleby-Thomas, Gareth J.
Plate-impact experiments have been conducted to investigate the elastic–plastic behaviour of shock wave propagation and pore collapse mechanisms of closed-cell aluminium foams. FE modelling using a meso-scale approach has been carried out with the FE software ABAQUS/Explicit. A micro-computed tomography-based foam geometry has been developed and microstructural changes with time have been investigated to explore the effects of wave propagation. Special attention has been given to the pore collapse mechanism. The effect of velocity variations on deformation has been elucidated with three different impact conditions using the plate-impact method. Free surface velocity (ufs) was measured on the rear of the sample to understand the evolution of the compaction. At low impact velocities, the free-surface velocity increased gradually, whereas an abrupt rise of free-surface velocity was found at an impact velocity of 845 m/s with a copper flyer-plate which correlates with the appearance of shock. A good correlation was found between experimental results and FE predictions.
Open Access
Normal and oblique penetration of woven CFRP laminates by a high velocity steel sphere
(Elsevier , 2008-05-31T00:00:00Z) Hazell, Paul J.; Kister, Guillaume; Stennett, Christopher; Bourque, P.; Cooper, G.
In this research, two thicknesses of a woven CFRP laminate have been subjected to impact by a steel sphere in a velocity regime ranging from 170 to 374 m/s. Impact and penetration of targets at normal and oblique incidence were studied using high speed video. For the normal incidence targets at the higher velocities of impact, a conical mass of laminate was ejected ahead of the projectile. Furthermore, despite the energy transferred to the plate increasing with impact energy, the degree of delamination in the thicker targets decreased indicating a change in projectile penetration mechanism. Eventually, the degree of delamination in the thicker targets appeared to approach an asymptotic level whereas for the thinner targets the degree of delamination appeared constant regardless of impact energy. For oblique targets, more of the kinetic energy was transferred from the projectile when compared to the same thickness of target that had been subjected to a normal incidence impact. However, this was merely due to a geometrical effect. Further, thicker panels appeared to behave more efficiently by absorbing more kinetic energy per effective linear thickness at the lower impact energies where petalling is a dominant factor in the penetration. This advantage appeared to disappear as the impact energy was increased.
Open Access
A note on the behind armour effects from perforated alumina/aluminium targets
(Elsevier , 1998-12-31T00:00:00Z) Hazell, Paul J.; Fellows, Neil A.; Hetherington, John G.
A thin, ceramic-faced armour, separated from a thick metal block, has been subjected to high-velocity impact by a 6.35 mm diameter steel sphere. Experimental work was carried out which compared firings into ceramic-faced aluminium armour, separated from thick aluminium witness blocks, with firings into the thick aluminium blocks alone. The depth of penetration and the area of damage were measured and an estimated percentage weight saving due to the inclusion of the ceramic-faced armour was calculated at varying velocity. This note yields useful information for the design and application of ceramic applique systems.
Open Access
The numerical analysis of dynamically loaded ceramic: a crack softening approach
(Wiley, 2000-12-31T00:00:00Z) Hazell, Paul J.; Iremonger, Michael J.
A physically based crack softening approach to modelling the failure of brittle materials that have been subjected to dynamic loading is presented and applied to a two-dimensional non-linear transient dynamic hydrocode. It is assumed that there are a number of evenly distributed and orientated micro flaws within the brittle material that are activated by a dynamically applied stress. Modes I and II stress intensity factors are calculated and compared to critical values, at which point the cracks grow at a velocity dependent on mode I stress intensity factor. The strength of the ceramic is degraded according to the length of the cracks. A simulation of a steel sphere impacting and penetrating a ceramic target at 1500 m/s is presented. Comparisons are drawn from experimental data.