Browsing by Author "Champion, Stephen M."

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    Blade Sharpness and its Effect on the Testing of Body Armours
    (2002-11-22T00:00:00Z) Watson, Celia H.; Horsfall, Ian; Champion, Stephen M.; Harrod, I. C.; van Bree, J. L. M. J.
    Factors such as edge sharpness and tip sharpness have been identified by Horsfall,1 as keyvariables in the testing of stab and slash resistant armours. This paper evaluates the influenceof blade sharpness on the mechanics of penetration and its relationship with a variety ofmaterials used for body armour systems. The differences in performance between blunt andsharp blades are compared by dynamic tests using an instrumented drop tower, measuringpeak loads and energy to penetration. Variance in the initial impact forces required topenetrate body armour between blunt and sharp blades is shown. However, the total energyto penetration for both sharp and blunt knives was found to be similar for a specific bodyarmour system. Dynamic tests were also used to evaluate the effect of wear on bladeperformance by the comparison of the initial loads for puncture and depth of penetration onaramid and metallic armour systems. The effect of sharpness on the reproducibility of testresults is also investigated and discussed. Various test methods are described for themeasurement of sharpness for both stab and slash and compared. The recent development ofa new non-destructive proof test method to measure tip and edge sharpness is also described.
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    Comparison of porcine thorax to gelatine blocks for wound
    (2016-02-04) Mabbott, A.; Carr, Debra J.; Champion, Stephen M.; Malbon, Christopher
    Tissue simulants are typically used in ballistic testing as substitutes for biological tissues. Many simulants have been used, with gelatine amongst the most common. While two concentrations of gelatine (10 and 20 %) have been used extensively, no agreed standard exists for the preparation of either. Comparison of ballistic damage produced in both concentrations is lacking. The damage produced in gelatine is also questioned, with regards to what it would mean for specific areas of living tissue. The aim of the work discussed in this paper was to consider how damage caused by selected pistol and rifle ammunition varied in different simulants. Damage to gelatine blocks 10 and 20 % in concentration were tested with 9 mm Luger (9 × 19 full metal jacket; FMJ) rounds, while damage produced by .223 Remington (5.56 × 45 Federal Premium® Tactical® Bonded®) rounds to porcine thorax sections (skin, underlying tissue, ribs, lungs, ribs, underlying tissue, skin; backed by a block of 10 % gelatine) were compared to 10 and 20 % gelatine blocks. Results from the .223 Remington rifle round, which is one that typically expands on impact, revealed depths of penetration in the thorax arrangement were significantly different to 20 % gelatine, but not 10 % gelatine. The level of damage produced in the simulated thoraxes was smaller in scale to that witnessed in both gelatine concentrations,though greater debris was produced in the thoraxes.
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    Early spears as thrusting weapons: Isolating force and impact velocities in human performance trials
    (Elsevier, 2016-10-01) Milks, Annemieke; Champion, Stephen M.; Cowper, Elizabeth J.; Pope, Matt; Carr, Debra J.
    Human hunting has been a cornerstone of research in human evolutionary studies, and decades worth of research programmes into early weapon systems have improved our understanding of the subsistence behaviours of our genus. Thrusting spears are potentially one of the earliest hunting weapons to be manufactured and used by humans. However, a dearth of data on the mechanics of thrusting spear use has hampered experimental research. This paper presents a human performance trial using military personnel trained in bayonet use. Participants thrusted replicas of Middle Pleistocene wooden spears into PermaGel™. For each spear thrust, impact velocity was recorded with high-speed video equipment, and force profiles were recorded using a force transducer. The results demonstrate that training improves performance when compared with previous experimental results using untrained participants, and that the mechanics and biomechanics of spear thrusting are complex. The trial confirms that previous spear thrusting experiments firing spears as projectiles are failing to replicate the entire spear thrusting event, and that crossbows are too powerful to replicate the low velocities involved in spear thrusting. In order to better understand evidence of spear thrusting in the archaeological record, experimental protocols accurately replicating and recording the mechanics of spear thrusting in the past are proposed.
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    Investigation into the impact of integral suppressor configurations on the pressure levels within the suppressor
    (DEStech Publications Inc., 2016-05) Helliker, A.; Champion, Stephen M.; Duncan, A.
    This paper reports on an experimental investigation supported by basic modeling in to the performance of an integral suppressor on a low power firearm. A model was developed to determine the pressure within a suppressor chamber using iterative empirical calculations of the gas properties and flow within the system. The design of a reconfigurable suppressor chamber has been undertaken allowing suppressor chamber volume to be varied through the use of baffles. Pressure transducers were used to determine the pressure within the suppressor chamber for a series of firings. The results of the firings with different configurations within the suppressor are presented allowing trends to be established. The modeling and experimental results show an increase in suppressor chamber volume results in a reduction of recorded pressure within the suppressor chamber.
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    Optimizing the stacking sequence in dual-purpose body armors
    (American Society Mechanical Engineers, 2013-05-01T00:00:00Z) Horsfall, Ian; Watson, Celia H.; Champion, Stephen M.
    Many police body armor systems are dual purpose, offering both ballistic and knife resistanceby combining a flexible ballistic textile pack with a stiffer knife resistant layer.The two types of protection differ in materials and mechanisms such that each individualcomponent may help or interfere with the function of the other. This paper investigatesthe effect on knife and ballistic penetration resistance when a single thin metal plate wasplaced at various different positions within an aramid textile armor pack. Two metalliclayers were used: aluminum 7075 and commercial purity titanium; these had similarareal densities and were positioned in the front, middle, and back of a 20 layer pack ofwoven KevlarVR 49. An instrumented drop weight machine was used to deliver a repeatableknife blade impact at comparable energy levels to those specified in the UK HomeOffice test standards for knife resistance. Ballistic tests were used to determine the V50ballistic limit velocity against typical 9mm and 0.357 Magnum handgun threats. Againsta stabbing threat, it was found that positioning the metal plate in the middle of the packprovided the greatest resistance to knife penetration by a factor of almost two, while aplate at the front of the pack provided less resistance and plates positioned at the rear ofthe pack provided the least resistance to penetration. Against the ballistic threat, the penetrationresistance of the textile pack can be significantly improved when a metal plate isat the front of the pack, while for all other positions the effect is negligible. However, thiseffect is sensitive to both the ammunition type and the metal plate composition. When themetal plate is positioned at the rear of the pack there is a significant decrease in theback-face deformation of the armor pack although, again, this effect is only present forcertain ammunition and metal combinations. The overall effect of combining soft andhard elements was that specific performance parameters could be substantially increasedby the correct combination. There were no significant negative effects, however, in anumber of cases, the combined systems performance was no greater than that of a singleelement type, despite the added weight.
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    The overmatching of UK police body armour
    (2016-09-12) Mabbott, A J; Carr, Debra J.; Champion, Stephen M.
    Police officers and other personnel in the UK routinely wear body armour that provides protection from specific threats. Typically, 'soft' armours, usually formed from multiple layers of fabric, can protect wearers from fragmentation and low velocity (handgun) ballistic threats, while ‘hard’ armours, formed from ceramic and composite plates, offer protection from high velocity (rifle) threats. Protection from stab and/or slash attack is predominantly provided by utilising chain mail and laminated solutions. The question has been raised however, of what would happen when armour is overmatched with a greater threat than it is designed to protect against. A limited number of studies have been published in the open source literature regarding the overmatching of soft body armour. This research aims to increase the understanding of overmatching, by investigating the effect of both i) soft fabric body armour designed to protect from handgun ammunition being challenged by high velocity rifle projectiles and ii) knife and spike resistant armour protecting against low velocity handgun projectiles. A subsection of the research considered three tissue simulants in order to find the most suitable for investigating the effects of overmatching armour. A method for recording the damage produced in the simulants was also developed; from which comparison of damage to different targets was possible. Following the tissue simulant investigation, gelatine blocks 10% in concentration were selected and used to investigate the overmatching of two types of UK police body armour. Three different arrangements were setup, namely 10% gelatine blocks 500mm, 10% gelatine blocks 250mm in length, and porcine thoracic walls arranged to simulate a thorax. Testing blocks 500mm in length was a set-up typical to ballistic investigations; the blocks were capable of capturing the majority of the projectiles’ damage, with the damage produced in both unprotected and protected (on the front face only) targets compared. Based on anthropometric measurements, testing 10% gelatine blocks 250mm in size was more representative of a torso sized target. With the blocks smaller, armour was placed on both the front and back face of targets. This is more representative of how armour would be worn in a real life scenario; patrolling UK police officer wearing armour that protects both the front and back of their torso. Finally, the use of porcine samples arranged to simulate both protected and unprotected thoraxes enabled comparisons of the damage seen in homogenous tissue simulants to damage in non-homogenous material typical to those found in the human torso. The outcomes from testing three different targets with two ammunition and armour combinations revealed the effect of overmatching armour is not one that can be generalised and predicted for all overmatching scenarios. The presence of armour on the rear face of targets based on typical measurements of human chest depth, increased the chances of the projectiles tested remaining within the targets.
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    Wounding patterns and human performance in knife attacks: optimising the protection provided by knife-resistant body armour
    (2016-01-06) Bleetman, A; Watson, Celia H.; Horsfall, Ian; Champion, Stephen M.
    Stab attacks generate high loads,1 and to defeat them, armour needs to be of a certain thickness and stiffness.2,3 Slash attacks produce much lower loads and armour designed to defeat them can be far lighter and more flexible.Methods and subjects: Phase 1: Human performance in slash attacks: 87 randomly selected students at the Royal Military College of Science were asked to make one slash attack with an instrumented blade on a vertically mounted target. No instructions on how to slash the target were given. The direction, contact forces and velocity of each attack were recorded. Phase 2: Clinical experience with edged weapon attacks: The location and severity of all penetrating injuries in patients attending the Glasgow Royal Infirmary between 1993 and 1996 were charted on anatomical figures.Results Phase 1: Two types of human slash behaviour were evident: a ‘chop and drag’ blow and a ‘sweep motion’ type of attack. ‘Chop and drag’ attacks had higher peak forces and velocities than sweep attacks. Shoulder to waist blows (diagonal) accounted for 82% of attacks, 71% of attackers used a long diagonal slash with an average cut length of 34 cm and 11% used short diagonal attacks with an average cut length of 25 cm. Only 18% of attackers slashed across the body (short horizontal); the average measured cut length of this type was 28 cm. The maximum peak force for the total sample population was 212 N; the maximum velocity was 14.88 m s−1. The 95 percentile force for the total sample population was 181 N and the velocity was 9.89 m s−1. Phase 2: 431 of the 500 patients had been wounded with edged weapons. The average number of wounds sustained by victims in knife assaults was 2.4. The distribution of wounds by frequency and severity are presented.Conclusions Anti-slash protection is required for the arms, neck, shoulders, and thighs. The clinical experience of knife-attack victims provides information on the relative vulnerabilities of different regions of the body. It is anticipated that designing a tunic-type of Police uniform that is inherently stab and slash resistant will eventually replace the current obvious and often bulky extra protective vest. Attempts at making a combined garment will need to be guided by ergonomic considerations and field testing. A similar anatomical regional risk model might also be appropriate in the design of anti-ballistic armour and combined anti-ballistic and knife-resistant armour.