Browsing by Author "Watson, Celia H."

Now showing 1 - 9 of 9
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    Assessment and Measurment of Potential Blunt Trauma Under Ballistic Helmets
    (2008-09-22T00:00:00Z) Watson, Celia H.; Webb, Annette; Horsfall, Ian; Bless, S.; Walker, J.
    This paper investigates measurement techniques to evaluate ballistic impact protection in terms of head contact loads from non penetrating impacts on helmets. An aluminium head form instrumented with piezo-electric transducers, film sensors and accelerometers was used to measure impact forces applied by the back face deformation of helmets after ballistic impacts. The head form and an instrumented accelerated weight machine are also used to measure impact forces applied to the helmet and forces transmitted behind the helmet.Radius of curvature of back face deformation data were also collected from ballistic impacts on helmets mounted on conditioned plastilina® and was shown to correlate with published studies from Wilber [4] and Byers [5] which established a correlation between the force required to fracture a human skull and radius of curvature of the striker. It is shown that backface deformation of potentially damaging levels can be generated behind typical ballistic helmets.
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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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    A comparison of the behind armour blunt trauma effects between ceramic faced and soft body armours caused by ballistic impact
    (2002-11-18T00:00:00Z) Lewis, E. A.; Horsfall, Ian; Watson, Celia H.; van Bree, J. L. M. J.
    Recently published research has characterised the behind armour blunt trauma (BABT) effects associated with high velocity ballistic impact on textile-based armour faced with a ceramic plate. Subsequently dynamic displacements, accelerations and pressures have been characterised both in Gelatine experiments and animal experiments and used to provide test methodologies. High velocity armour consists of a ceramic plate usually backed with a composite panel, which is worn over the conventional textile body armour. The purpose of the plate is to disrupt and spread the energy of the high velocity projectile such that the resulting displacement can beaccommodated and partially absorbed by the textile armour. On its own, the textile armour isonly capable of preventing penetration by low kinetic energy density projectiles such as fragments, which are of a similar magnitude to hand gun bullets. For police officers, civilian security personnel and for the military, in operations other than war, there is a need to protect against low-velocity handgun bullets such as 9mm and 0.375 Magnum; these being the rounds typically used in ballistic test standards. As the purpose of the ceramic plate is to reduce the energy density of a high-velocity projectile to that which can be arrested bya soft armour; it follows that there may be a relationship between the impact of a low-velocity projectile on soft armour and a high velocity projectile on a ceramic faced soft armour .The purpose of this work was to gather data on the back-face deformation behaviour of soft body armour and compare it to that of hard armour by determining whether there was a correlation between previous ceramic plate data and soft armour tests, and also to determine whether backface pressure data could be used to rank other simulant materials.
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    Ergonomics, design and reliability of body armour
    (2011-09-08) Watson, Celia H.
    The wearing of body amour has become a necessity for many professions and much work has gone into the optimisation of the mechanics of protection. In the present study a broader view of the effects of ergonomics, design, reliability and protection has been taken. Three background topics are examined by reference to the literature. First, as an example of the threats and injury mechanisms that prevail in modern conflicts, the effects of blast injury to the head are investigated. This is followed by a review of ergonomic test methods and is completed by a study exploring the influence of history on modern body armour design. Solutions to some of these problems are then considered. The problem of accurately measuring impact loads to the head is investigated and a rigid instrumented head form is demonstrated. This work showed that the filtering techniques derived from crash tests used in the current helmet standards are not applicable to ballistic impact events. A one day wearer trial for police armour based on typical actions carried out by police officers in the performance of their normal duties is developed and demonstrated. A mechanical flexibility test is shown to give quantitative data but a direct link between ergonomic rankings and flexibility could not be established. Reliability of both soft and hard body armour is investigated and for typical armour types it is demonstrated that a minimal deterioration takes place with time and existing inspections techniques can highlight armour that is below standard. This study has introduced measurement techniques in an attempt to quantify some of the effects investigated with the intention of using quantitative methods to improve armour design and minimise some of the negative effects of wearing body armour.
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    An evaluation of the hypodermic needle threat against body armour
    (2004-09-06T00:00:00Z) Watson, Celia H.; Horsfall, Ian; Luk, Edwina; van Bree, J. L. M. J.
    Previous work has addressed protection against stab attacks [1, 2], and slash attacks [3, 4] this has resulted in body armour that is suitable for protecting the torso against knives. Whilst this armour combats the primary lethal injuries to the torso it does not protect against minor injuries to the limbs and hands from items such as hypodermic needles and other sharp weapons. To reduce injuries to the hands from sharp weapons and needles there is a need for an effective protective glove and also a protective sleeve for the arms. This paper investigates the threats posed by hypodermic needles and examines the effectiveness of various possible needle proof systems. In order to determine the contact loads from needles that might be encountered whilst conducting body searches, male and female volunteers used an instrumented impact system to measure the average impact forces of human hand against a fixed object. The compressive loads a hand imparts as it grips an object to pick it up were also measured. A range of sizes of hypodermic needles were used to measure the puncture resistance of several lightweight armour materials and the buckling loads of the needles were also determined. This study showed that the buckling loads for hypodermic needles were much lower than typical loads measured in the human tests for accidental contact or gripping. Although a hypodermic needle is able to puncture skin easily, when puncturing armour materials the needles tended to buckle.
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    Feasibility of using damage to body armour as evidence to prove the degree of intent of wounding
    (2008-10-06T00:00:00Z) Watson, Celia H.; Parker, Fiona; Horsfall, Ian; Fenne, Paul
    It has become standard practice for Police Authorities to issue stab resistant body armour to all officers who are placed at risk of knife assault. Subsequently if the officer is subjected to a knife attack it has been difficult to prove the degree of intent of wounding by a suspect. Arguments that no real harm could be intended, as the officer was protected by armour, are presented in court to mitigate any sentence of intent to wound. Several Police Forces have requested that damaged armour from attacks be forensically examined to determine the extent of damage and directly relate this damage to the forces of the impacts in an attack.This paper assesses the feasibility of using damage to body armour worn during an incident as evidence to prove the degree of intent of wounding. The study compares the different weapons used, variation in damage caused by blades of different dimensions and damage related to tip and blade sharpness. The relationships between force, energy and damage, the effect of armour construction and how all these factors effect the type of damage expected are also investigated. This work highlights the fundamentals necessary for the development of a forensic protocol to investigate damage to stab resistant armours so that the results could be accepted in evidence.
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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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    A statistical approach to proof testing
    (2008-10-06T00:00:00Z) Horsfall, Ian; Ringrose, Trevor J.; Watson, Celia H.
    Police body armour has undergone rapid evolution, and this is due in part to a relatively simple type approval process which matches relatively small numbers purchased by individual police forces. However, as body armour technology and usage has increased there has been a gradual change of emphasis from solving the immediate protection problems of highly specialised systems towards quality assurance towards of a standard item of equipment. In addition, as the amount and age of armour in service increases, concerns have been raised about methods for ensuring the continued performance over long periods of use or over long production runs. These factors have drawn attention to the statistical significance of existing proof tests, in which armour systems are subjected to small numbers of stabs or ballistic tests. A number of approaches have been suggested including the addition of a V50 ballistic limit test to provide a fully quantitative measure of performance [1]. However this approach also lacks statistical rigour and further enhancements such as regression analysis [2,3] have been suggested to remedy this. In the current work a different statistical approach is suggested in which conventional proof tests can be used to produce statistically robust data of known significance. Initial trials on current police body armour showed that ballistic penetration and knife penetration were similar as the data was highly random and it was difficult to statistically predict individual test results. Ballistic blunt trauma followed a more predictable pattern with simple and easily predicted test-to-test variation allowing good predictions to be made. For the knife and ballistic penetration tests two approaches have been investigated. One method is a point estimate approach that determines failure probability as a simple ratio of pass or fail. Therefore to achieve a failure probability of lower than 0.1 (10%) no more than 1 failure in 10 would be allowed. The second option would be determine how many successful tests were needed to be sure (for instance to 95% probability) that the failure rate was no more than 0.1. This second approach is more severe and it has been shown that at least 28 successful tests are required in order to be reasonably sure that the failure rate is less than 0.1. This paper will demonstrate the development of the statistical model which has been used within 2007 HOSDB body armour standards and shows how it is applied in both type approval and batch testing.
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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.