Browsing by Author "Wood, D. C."
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Item 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, D. C.; Hazell, P. 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.Item Open Access The effects of changing chemistry on the shock response of basic polymers(2016-07-11) Millett, J.; Brown, E. N.; Gray III, G. T.; Bourne, Neil K.; Wood, D. C.; Appleby-Thomas, Gareth J.The shock response of four common semicrystalline thermoplastic polymers—polyethylene (PE), polyvinylchloride (PVC), polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE)—have been studied in terms of their Hugoniots, release velocities and shear strengths. Through the variations in behaviour caused by changes to the attached atoms to the carbon backbone, it has been possible to suggest that there are two main factors in play. The first is an electrostatic repulsion between adjacent polymer chains. Where this force is large, for example in PTFE with highly electronegative fluorine atoms, this results in this force dominating the shock response, with low shock velocities, high release velocities and little if no hardening behind the shock front. In contrast, in materials such as PE, this force is now weaker, due to the lower electronegativity of hydrogen, and hence this force is easier to overcome by the applied shock stress. Now the main factor affecting shock behaviour is controlled by the shape of the polymer chain allowing inter chain tangling (tacticity). This results in higher shock velocities, lower release speeds and significant hardening behind the shock front as the chains are forced together. This is prevalent in materials with a relatively open structure such as PE and is enhanced with the presence of large side groups or atoms off the main polymer chain.Item Open Access Investigation of the high-strain rate (shock and ballistic) response of the elastomeric tissue simulant Perma-Gel®(Elsevier, 2016-04-01) Appleby-Thomas, Gareth J.; Wood, D. C.; Hameed, Amer; Painter, Jonathan; Le-Seelleur, V.; Fitzmaurice, Brianna C.For both ethical and practical reasons accurate tissue simulant materials are essential for ballistic testing applications. A wide variety of different materials have been previously adopted for such roles, ranging from gelatin to ballistics soap. However, while often well characterised quasi-statically, there is typically a paucity of information on the high strain-rate response of such materials in the literature. Here, building on previous studies by the authors on other tissue analogues, equation-of-state data for the elastomeric epithelial/muscular simulant material Perma-Gel® is presented, along with results from a series of ballistic tests designed to illustrate its impact-related behaviour. Comparison of both hydrodynamic and ballistic behaviour to that of comparable epithelial tissues/analogues (Sylgard® and porcine muscle tissue) has provided an insight into the applicability of both Perma-Gel® and, more generally, monolithic simulants for ballistic testing purposes. Of particular note was an apparent link between the high strain-rate compressibility (evidenced in the Hugoniot relationship in the Us-up plane) and subsequent ballistic response of these materials. Overall, work conducted in this study highlighted the importance of fully characterising tissue analogues – with particular emphasis on the requirement to understand the behaviour of such analogues under impact as part of a system as well as individually.Item Open Access Lateral stress evolution in chromium sulfide cermets with varying excess chromium(2016-07-01) Petel, O. E.; Appleby-Thomas, Gareth J.; Wood, D. C.; Capozzi, A.; Nabavi, Seyed Ali; Goroshin, S.; Frost, D. L.; Hazell, P. 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 contentsItem Open Access On the dynamic behavior of three readily available soft tissue simulants(American Institute of Physics, 2011-12-31T00:00:00Z) Appleby-Thomas, Gareth J.; Hazell, P. J.; Wilgeroth, J. M.; Shepherd, C. J.; Wood, D. C.; Roberts, A.Plate-impact experiments have been employed to investigate the dynamic response of three readily available tissue simulants for ballistic purposes: gelatin, ballistic soap (both subdermal tissue simulants), and lard (adipose layers). All three materials exhibited linear Hugoniot equations-of-state in the US-uP plane. While gelatin behaved hydrodynamically under shock, soap and lard appeared to strengthen under increased loading. Interestingly, the simulants under test appeared to strengthen in a material-independent manner on shock arrival (tentatively attributed to a rearrangement of the amorphous molecular chains under loading). However, material-specific behavior was apparent behind the shock. This behavior appeared to correlate with microstructural complexity, suggesting a steric hindrance effect.Item Open Access On the effects of powder morphology on the post-comminution ballistic strength of ceramics(Elsevier, 2016-10-29) Appleby-Thomas, Gareth J.; Wood, D. C.; Hameed, Amer; Painter, Jonathan; Fitzmaurice, Brianna C.In this paper in order to try and elucidate the effects of particle morphology on ballistic response of comminuted systems, a series of experiments were carried out via the use of powder compacts with differing initial particle morphologies. This approach provided a route to readily manufacture comminuted armour analogues with significantly different microstructural compositions. In this study pre-formed `fragmented-ceramic' analogues were cold-pressed using plasma-spray alumina powders with two differing initial morphologies (angular and spherical). These compacts were then impacted using 7.62-mm FFV AP (Förenade Fabriksverken Armour Piercing) rounds with the subsequent depth-of-penetration of the impacting projectile into backing Al 6082 blocks used to provide a measure of pressed ceramic ballistic response. When material areal density was accounted for via differing ballistic efficiency calculations a strong indication of particle morphology influence on post-impact ceramic properties was apparent. These results were reinforced by a separate small series of plate-impact experiments, whose results indicated that powder morphology had a strong influence on the nature of compact collapse.Item Open Access On the interpretation of lateral manganin gauge stress measurements in polymers(American Institute of Physics, 2010-12-31T00:00:00Z) Appleby-Thomas, Gareth J.; Hazell, P. J.; Wilgeroth, J. M.; Wood, D. C.Encapsulated wire-element stress gauges enable changes in lateral stress during shock loading to be directly monitored. However, there is substantial debate with regards to interpretation of observed changes in stress behind the shock front; a phenomenon attributed both to changes in material strength and shock- dispersion within the gauge-encapsulation. Here, a pair of novel techniques which both modify or remove the embedding medium where such stress gauges are placed within target materials have been used to try and inform this debate. The behavior of three polymeric materials of differing complexity was considered, namely polystyrene, the commercially important resin transfer moulding RTM 6 resin and a commercially available fat lard. Comparison to the response of embedded gauges has suggested a possible slight decrease in the absolute magnitude of stress. However, changing the encapsulation has no detectable effect on the gradient behind the shock in such polymeric systems.Item Open Access On the interpretation of lateral manganin gauge stress measurements in polymers(2010-09-17) Appleby-Thomas, Gareth J.; Hazell, P. J.; Wilgeroth, J. M.; Wood, D. C.Encapsulated wire-element stress gauges enable changes in lateral stress during shock loading to be directly monitored. However, there is substantial debate with regards to interpretation of observed changes in stress behind the shock front; a phenomenon attributed both to changes in material strength and shock-dispersion within the gauge-encapsulation. Here, a pair of novel techniques which both modify or remove the embedding medium where such stress gauges are placed within target materials have been used to try and inform this debate. The behavior of three polymeric materials of differing complexity was considered, namely polystyrene, the commercially important resin transfer moulding (RTM) 6 resin and a commercially available fat (lard). Comparison to the response of embedded gauges has suggested a possible slight decrease in the absolute magnitude of stress. However, changing the encapsulation has no detectable effect on the gradient behind the shock in such polymeric systems. © 2010 American Institute of Physics.Item Open Access Shock behaviour of a phenolic resin(Springer Science Business Media, 2011-12-31T00:00:00Z) Wood, D. C.; Hazell, P. J.; Appleby-Thomas, Gareth J.; Barnes, N. R.Phenolic resins are used in many aspects of everyday life, e.g. as the matrix material for carbon fibre laminates used in the aerospace industry. Consequently detailed knowledge of this material, especially while under shock loading, is extremely useful for the design of components that could be subjected to impact during their lifespan. The shock Hugoniot equation of state for phenolic resin (Durite SC-1008), with initial density of 1.18 gcm −3 have been determined using the plate-impact technique with in situ manganin stress gauges. The Hugoniot equation in the shock velocity-particle velocity plane was found to be non- linear in nature with the following equation: Us = 2.14 + 3.79up - 1.68up2. Further, the Hugoniot in the pressure-volume plane was observed to largely follow the hydrostatic curve. Lateral gauge measurements were also obtained. An ANSYS Autodyn TM 2D model was used to investigate the lateral stress behaviour of the SC-1008. A comparison of the Hugoniot elastic limit calculated from the shear strength and measured sound speeds gave reasonable agreement with a value of 0.66 ± 0.35 GPa obtainItem Open Access Shock propagation in a complex laminate(2014-06-10) Wood, D. C.; Hazell, P. J.; Appleby-Thomas, Gareth J.The shock response of a complex laminate has been investigated using a single stage gas gun, with manganin pressure gauges employed to investigate the shock profile. The complex laminate investigated was known by the acronym TWCP and is a tape wrapped carbon fibre composite with phenolic resin matrix. Carbon fibre composites are used in the aerospace industry due to their high strength to weight ratio, so understanding of different loading conditions is needed. To investigate the shock response of the TWCP, four weave orientations were studied. The orientations investigated with respect to the shock front were 0◦ (parallel to the shock front or perpendicular to the direction of travel), 25◦, 45◦ and 90◦ (perpendicular to the shock front or parallel to the direction of travel). As well as the TWCP the shock response of the matrix material, a phenolic resin Durite SC-1008 was also investigated. For the phenolic resin matrix material a non-linear Hugoniot was found in the US-up plane with the equation of US = 2.14 + 3.79up - 1.68u2 p. Such non-linear Hugoniot behaviour has been seen in other polymeric materials, e.g. PMMA. In the pressure-volume plane deviation was seen in the higher pressure data most likely due to the materials non-linear response. For the TWCP composite, linear Hugoniots were found for all four orientations with the corresponding equations shown below. • 0◦ US = 3.69 + 0.59up • 25◦ US = 3.45 + 0.73up • 45◦ US = 3.44 + 1.12up • 90◦ US = 3.96 + 0.46up The four Hugoniots are comparable in nature and it is possible to assign a single Hugoniot with the equation US = 3.56 + 0.84up through the majority of data points. The largest deviation from this “average” response was obtained from the 90◦ orientation due to the high elastic sound speed of this weave angle. Convergence was also seen between the Hugoniots in the US-up plane towards the higher up values (approximately 1 mm μs−1). In the pressure-up plane there was very little difference between all of the experimental data, meaning that for the stress in this material, orientation makes no difference.