CERES :: Browsing by Author "Horsfall, Ian"

Browsing by Author "Horsfall, Ian"

Now showing 1 - 20 of 35

Open Access
3D printing, the future of cost effective biomechanical testing
(SAFE, 2017-04-06) Franceskides, C.; Arnold, Emily; Horsfall, Ian; Clasper, J.; Tozzi, G.; Zioupos, Peter
Open Access
Adequacy of test standards in evaluating blast overpressure (BOP) protection for the torso
(2016-11-18) Whyte, Tamlin; Horsfall, Ian
The blast wave emanating from an explosion produces an almost instantaneous rise in pressure which can then cause Blast Overpressure (BOP) injuries to nearby persons. BOP injury criteria are specified in test standards to relate BOP measurements in a testing environment to a risk of BOP injury. This study considered the adequacy of test standards in evaluating BOP protection concepts for the torso. Four potential BOP injury scenarios were studied to determine the likelihood of injury and the adequacy of test standards for appropriate protection concepts. In the case of vehicle blast, BOP injury is unlikely and test standards are adequate. In the scenario involving an explosive charge detonated within a vehicle, and the close proximity to a hand grenade scenario, test standards are not available. The demining scenario was identified as of importance as test standards are available, but do not mandate the evaluation of BOP protection. A prototype South African Torso Surrogate (SATS) was developed to explore this scenario further. The SATS was required to be relatively inexpensive and robust. The SATS was cast from silicone (selected to represent body tissue characteristics) using a torso mould containing a steel frame and instrumented with chest face-on pressure transducer and accelerometer. The SATS was subjected to an Anti-Personnel (AP) mine test and the Chest Wall Velocity Predictor and Viscous Criterion were used to predict that BOP injuries would occur in a typical demining scenario. This result was confirmed by applying the injury criteria to empirical blast predictions from the Blast Effects Calculator Version 4 (BECV4). Although limitations exist in the ability of injury criteria and measurement methods to accurately predict BOP injuries, generally a conservative approach should be taken. Thus, it is recommended that the risk of BOP injuries should be evaluated in demining personal protective equipment test standards.
Open Access
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.
Open Access
Ballistic and physical properties of highly fractured alumina
(Maney Publishing, 2010-11-01T00:00:00Z) Horsfall, Ian; Edwards, M. R.; Hallas, M. J.
It is known that ceramic materials in armour are often shattered by a penetrating projectile and the resistance to penetration is therefore dependent upon the properties of this failed material. A small explosive charge was used to shatter a confined 95% alumina tile by passing the stress wave from an explosive detonation through a steel cover plate and into the ceramic. This fractured material was shown to have an elastic modulus of 130 GPa compared to 330 GPa for the monolithic alumina. Impact indentation tests and ballistic depth of penetration tests were performed on the intact ceramic, shattered ceramic and a pressed ceramic powder compact. It was found that the fractured material had a ballistic efficiency approximately 70% of that of the monolithic alumina and was also able to cause significant erosion to the project
Open Access
Ballistic impact on composite armour
(2007-11-25T17:48:05Z) Bourke, Paul; Horsfall, Ian
Armoured vehicles in current military service are requiring ever more protection to enable them to carry out their mission in a safe, effective manner. This requirement is driving vehicle weight up to such an extent that the logistics of vehicle transport is becoming increasingly difficult. Composite materials are an important material group whose high specific properties can enable structures to be manufactured for a far lower weight than might otherwise be possible. Composite materials in an armoured vehicle will require structural performance as well as ballistic performance. The mechanical and ballistic performance of tl-kk armour and structural composites has been investigated against dcformable and armour-piercing ammunitions, over a range of impact velocities. Testing has indicated that heavy/coarse reinforcement weaves perform well against deformable ammunition and light/fine weaves well against armour piercing ammunition. The effect of individual mechanical properties on ballistic performance has been investigated as has the damage morphology of impacted materials. High tensile strength combined with low fracture toughness has been identified as an important requirement. Failure mechanisms have been identified from sections of ballistic impacts and through the use of mechanical test data the energy absorbed by each mechanism has been calculated. An energy audit has been carried out of all materials tested and a modelling procedure developed based on mechanical characteristics, damage morphology and failure mechanisms. This model has been tested against literature results and found to give very satisfactory performance.
Open Access
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.
Open Access
Causes of scatter in high rate fracture testing of polymers
(Elsevier Science B.V., Amsterdam., 2013-12-31T00:00:00Z) Agnelli, S.; Horsfall, Ian
A method based on the measurement of failure time is being developed by the European Structural Integrity Society to determine high rate fracture toughness of polymers. The test method appears reasonably straightforward but produced unacceptably high scatter, due to failure time data scatter. In this work an experimentally based sensitivity study was performed by fracture tests at 1ms-1 in order to determine the causes of scatter and to seek to improve the test protocol. No single cause of scatter was identified but the quality and repeatability of the notching technique was identified as a major contributor.
Open Access
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.
Open Access
Development of models to assess penetrating injury from ballistic projectiles
(United Kingdom Defence Academy/Cranfield University, 2020) James, Gregory R.; Horsfall, Ian; Knock, Clare
Injuries from penetrating ballistic projectiles, such as fragments and bullets, are the major cause of military (and civilian) casualties in conflict, as well as casualties in terrorist incidents. This research project had the primary aim of developing models that facilitate the assessment of injury from penetrating ballistic projectiles, in both a physical and virtual environment. Existing models and literature in this area has been limited to a narrow range of scenarios (such as specific projectile types) or with limited validation of the models. Collation of ballistic data for muscle tissue and simulants from the literature, in addition to an extensive original dataset and novel data analysis techniques allowed a definitive assessment of the validity of skin and muscle tissue simulants for wound ballistics research, relevant to fragments and bullets. A range of physical and virtual models were developed and are applicable to assessing the risk of penetrating projectiles in ballistic and blast scenarios. Considered particularly novel was the development of a new fragment witness pack to assess the hazard from low density and low energy fragments by predicting the risk of eye penetration, skin perforation and to estimate the impact velocity of the projectile. The range of physical and virtual models developed have been used to provide insights to (and describe implications of) the target factors that influence the outcomes of physical testing when using real tissue or tissue simulants. The exploitation of these models has led to improvements in tactics, techniques, and procedures and equipment for UK Armed Forces and police, ultimately reducing injuries and saving lives.
Open Access
Evaluation of bone excision effects on a human skull model - I: Mechanical testing and digital image correlation.
(Sage, 2019-12-06) Franceskides, Constantinos; Leger, Thibault; Horsfall, Ian; Tozzi, Gianluca; Gibson, Michael C.; Zioupos, Peter
The mechanisms of skull impact loading may change following surgical interventions such as the removal of bone lesions, but little is known about the consequences in the event of subsequent head trauma. We, therefore, prepared acrylonitrile butadiene styrene human skull models based on clinical computed tomography skull data using a three-dimensional printer. Six replicate physical skull models were tested, three with bone excisions and three without. A drop tower was used to simulate the impact sustained by falling backwards onto the occipital lobe region. The impacts were recorded with a high-speed camera, and the occipital strain response was determined by digital image correlation. Although the hole affected neither the magnitude nor the sequence of the fracture pattern, the digital image correlation analysis highlighted an increase in strain around the excised area (0.45%–16.4% of the principal strain). Our approach provides a novel method that could improve the quality of life for patients on many fronts, including protection against trauma, surgical advice, post-operative care, advice in litigation cases, as well as facilitating general biomechanical research in the area of trauma injuries.
Open Access
Evaluation of bone excision on occipital area of simulated human skull
(2016-07-13) Franceskides, Constantinos; Leger, T.; Horsfall, Ian; Shanker, Tobias; Adams, George John; Clasper, J.; Zioupos, Peter
Surgical effects of bone and soft tissue tumours, whether for biopsy or full excision have been researched from as early as the 1970’s [1]. These researches though have as main focus the biological (histological) rather the mechanical aspects of the effects [2]. With technological advances in biomedical and biomechanical modelling, a plethora of researchers have been exploring the possibilities of understanding [3] or even predicting musculoskeletal behaviour under different loading conditions [4]. This research is seeking to bridge these two different facets by looking into the mechanical effects bone tumour surgery might have to the structural rigidity of a simulated human skull.
Open Access
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.
Open Access
Fabrication procedure and performance of 3D printed X-band horn antenna
(IET, 2019-02-18) Wirth, Sebastian G.; Morrow, Ivor L.; Horsfall, Ian
This paper presents the design, fabrication and performance of fusion deposition modeled 3D printed X-band horn antennas. The WR90 waveguide feed and pyramidal horn flare are printed as one piece from Acrylonitrile Butadiene Styrene (ABS). Different metallisation techniques are assessed to provide a uniform 40 micron coat on the ABS surfaces. Uniquely, the coaxial waveguide launcher is integrated with the waveguide section in a single interference fit operation. The measured and simulated radiation patterns showed good correlation and the antenna return loss was ≤−10dB over the 8.212.4GHz operating range. The measured and simulated antenna gain was in good agreement and increased monotonically from 10–17 ± 1.0dBi across the operating frequency.
Open Access
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.
Open Access
Glass ceramic armour systems for light armour applications
(2001-05-07T00:00:00Z) Horsfall, Ian; Crewther, I. R.
This paper descries an experimental evaluation of lithium-zinc-silicate glass ceramics when used as the strike face of an armour system. It is shown that against soft cored 7.62mm rounds (lead or mild steel cores) glass ceramics offer protection at an areal density which is equal to or better than alumina faced systems. The lithium zinc silicate system has a relatively low hardness (Hv 600) when compared to conventional ceramics such as alumina (typically Hv1300-1500). Consequently the performance of the glass ceramic system against hard cored projectiles is poor.
Open Access
A gun based test method to simulate mine blast against boots
(2016-11-18) Pinto, Ryan Keith; Horsfall, Ian
Blast mines have played a major role in almost every conflict from the two world wars to the most recent skirmishes. They provide a psychological threat in addition to denying access to areas and exerting a huge toll on the logistic and medical capabilities in conflict zones. Due to the lack of inexpensive and reliable mechanical technique that would work consistently and without the danger of mines being missed, human deminers are often preferred. This means that deminers are under constant threat of serious traumatic injuries to lower extremities, potentially leading to amputation and death. A limited number of studies have been published in the open literature regarding the performance of boots both commercially available and those that are specifically designed to deal with anti – personnel mines. The issue with these studies is that while they have followed a common test method, they have been unable to agree on the variables involved. This has resulted in studies that produce vastly different results making them difficult to compare. However, while all of them have concluded that none of the commercial boots tested provided adequate protection against even a small mine, there have been varied results observed with respect to certain mine resistant boots with some reporting adequate protection while others reporting outright failure. Blast testing involves a large number of variables making it difficult to produce repeatable, consistent and conclusive results, and therefore difficult to prove the claims of different boots. The aim of the research project was i) to investigate the reliability and reproducibility of current blast test methods while testing the performance of commercially available boots and ii) to develop a new test method that is able to replicate the performance of blast test methods that is capable of producing more consistent and reproducible results while being cheaper, quicker and flexible. To address these challenges, blast testing was conducted using a variety of commercially available boots – i) to test their performance and if the results observed line up with the literature and ii) to obtain baseline data for further analysis. Blast testing demonstrated that none of the commercially available boots offer adequate protection even against a small mine. They additionally highlighted issues with this type of testing regarding their accuracy and repeatability. This was compared to an analysis of the effect that foams have on reducing loads, which showed that by increasing the number of layers it was possible to reduce the loads measured. However, the total impulse measured remained the same irrespective of the foam thickness. The baseline data from the blast test was used to develop a new gun based test in order to address the limitation observed during blast testing. The final version of this test was able to match the performance of the blast test while being able to produce penetration. A subsection of the research tested the effectiveness of socks as a means of preventing contamination. Two different types of socks were used in three different arrangements and testing revealed that socks have a positive effect on preventing contamination.
Open Access
Impact perforation testing of stab-resistant armour materials
(1995-12-31T00:00:00Z) Horsfall, Ian; Pollitt, S. M.; Belk, J. A.; Angood, C.; Williams, J.G.; Pavan, A.
This paper describes the development of a method for the investigation and comparison of materials for use in stab resistant body armour. A number of polymer composite panels of different thicknesses and construction have been tested. A dynamic test which simulated the real threat has been used and the results compared to a simpler quasi-static test that might be used in initial materials selection. The materials tested were glass-epoxy, and glass-nylon composite panels of several thicknesses between 1.8 and 5.8mm. Additional tests were also performed on similar composites containing tungsten wires. An accelerated instrumented drop-tower was used to drive a knife through composite panels and record the force resisting penetration by the knife. The final penetration of the knife through the armour into a soft backing was also measured. For comparison,a similar geometry quasi-static test was carried out on the same specimens. It was found that energy absorbtion took the form of an initial resistance to perforation and then by a resistance to further penetration. This is thought to stem from resistance to cutting ofthe panel material and gripping of the knife blade. The energy required to produce a given penetration in dynamic tests was found to be in good agreement with the penetration achieved at similar energies under quasi-static conditions. For the materials tested there was no significant difference between the penetration resistance of single or two layer systems. The penetration achieved through a panel of a given material was approximately proportional to the inverse square of the panel's thickness. The relative performance of different armour materials was assessed by plotting the energy required to penetrate a fixed distance against the areal density of the panel.
Open Access
Key issues in body armour: threats, materials and design
(2012-06-30T00:00:00Z) Horsfall, Ian; Sparks, E.
This chapter will examine the mechanics and materials of body armour in military, police and some security related applications to protect the wearer from penetrative threats. These threats will include battlefield threats such as shell fragments and high velocity bullets, and threats to law enforcement personnel such as handgun bullets and knives. Regardless of whether the threat is a high velocity bullet, or a knife, the essential requirements of body armour are the same; first an interaction must be established to capture the projectile and extract its kinetic energy; second this energy must be dispersed without undue damage to the armour or wearer. Both these aims need to be achieved without significant rearwards protrusion into the wearer. In addition to these protection requirements it is also clear that the armour must be as comfortable as possible and reasonably light. This chapter reviews some of the approaches used to provide protection based on the all these needs.
Open Access
Near-field microwave imaging using a polarimetric array of 3D printed antennas and lenses
(IET, 2019-02-18) Wirth, Sebastian G.; Morrow, Ivor L.; Horsfall, Ian
A novel near-field microwave imaging system was designed and fabricated using the three-dimensional (3D) printing technique to manufacture X-band Pyramidal horn antennas and planar graded-index (GRIN) lenses. The flat lens focusing profile is synthesised by varying the refractive index radially in incremental steps that adjust the air-dielectric mixture. The lens is designed for direct attachment to the antenna aperture and transforms spherical waves emanating from antenna phase center into plane radiating waves. Simulated and measurement results show the antenna lens system input impedance is ≤ -10 dB, radiation pattern gain is between 17-20dBi over the 8.2-12.4GHz frequency band and when arrayed for polarimetry sensing has a polarisation cross-talk of ≤-50 dB. A ground penetrating radar system using the nearfield array was scanned over buried targets. The SAR results demonstrated high resolution and polarisation discrimination imagery capable of detecting subsurface objects.
Open Access
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.