Browsing by Author "Knock, Clare"
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Item 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, ClareInjuries 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.Item Open Access The effect of breast size and bra type on comfort for UK female police officers wearing body armour(Elsevier, 2019-12-05) Malbon, Christopher; Knock, Clare; Critchley, Richard; Carr, Debra J.Within the Police service of England and Wales the wearing of ballistic and stab resistant body armour is common, with most police forces mandating its usage when away from the police station. Of all the serving police officers in England and Wales 29.1% are female (Hargreaves et al., 2017). A survey was developed and then distributed by the Police Federation of England and Wales to all servicing police officers up to the rank of Inspector. The survey returned 2633 responses after cleaning of the data. From the responses it was seen that the predominant bra type worn is underwired (71%) and the predominant UK bra size is 34B (9%). It was also determined that the predominant areas where the body armour either rubbed or caused discomfort were the left and right anterior mammary regions and the posterior lateral sacral region. By understanding the distribution of bra size, type of bra worn and areas of discomfort or rubbing it helps further understand the issues faced by female police officers and how body armour design could be improved.Item Open Access The effect of fabric mass per unit area and blood impact velocity on bloodstain morphology(Elsevier, 2019-05-09) Dicken, Anthony; Knock, Clare; Beckett, Sophie; Carr, Debra J.This paper discusses the effects of thickness, mass per unit area, sett, yarn linear density and twist of calico fabrics (100% cotton, plain woven) on the morphology of passive bloodstains. Horse blood was dropped vertically onto three calico fabrics with different mass per unit areas (85.1 g/m², 163.5 g/m² and 224.6 g/m²). Six different impact velocities were used (1.7 ms-1, 2.9 ms-1, 4.1 ms-1, 4.9 ms-1, 5.1 ms-1 and 5.4 ms-1). The dry bloodstains were largest on the calico with the lightest mass per unit area. The low yarn linear density and large inter-yarn spaces meant that the blood could wick into the yarns from all directions and along the intra-yarn spaces. The calico with the middle mass per unit area had the smallest mean dry bloodstain area for four out of the six velocities. The twist level for this calico was greater than for the calicos with a heavier or lighter mass per unit area. This reduced the amount of wicking which occurred along the yarns due to the tighter yarn structure. The calico with the heaviest mass per unit area had the highest yarn linear density resulting in a thicker fabric, so the blood could not as easily penetrate into the fabric. This resulted in a thicker wet blood layer remaining on the fabric surface, where it gradually wicked vertically into the yarns under gravity. Less wicking along the yarns occurred, resulting in a smaller bloodstain than on the fabric with the lightest mass per unit area. The correlation between impact velocity and mean dry bloodstain area was greater for the calicos with the medium and heaviest mass per unit area than for the calico with the lightest mass per unit area. For the calicos with the medium and heaviest mass per unit area, the distance the blood spread laterally at impact, which increased with the increase in impact velocity, had a greater influence on the dry bloodstain area than the amount of wicking.Item Open Access The effect of reactive dyeing of fabric on the morphology of passive bloodstains(Elsevier, 2022-04-30) Dicken, Lisa; Knock, Clare; Carr, Debra J.; Beckett, SophieThe majority of fabrics at crime scenes have been coloured in some way. The effect of such treatments on resultant bloodstains has not been considered. In this work, horse blood was dropped onto reactively dyed calico fabrics (100% cotton, plain woven) with three different masses of 91 g m-², 171 g m-² and 243 g m-² and the results compared to previous work on the not-coloured calico fabric. Five impact velocities were used from 1.7 ms−1 to 5.4 ms−1. The use of reactive dye increased the thickness (from 0.38 – 0.56 mm to 0.39 – 0.6 mm) and mass per unit area (from 85.1 – 224.6 g/m² to 91 – 243 g/m²) of the calico fabrics. The reactively dyed fabrics had larger bloodstains (e.g. lightest calico 41.2 – 78.6 mm²) compares to the not-coloured fabrics (e.g. lightest calico 21.4 – 67.5 mm²) across all three mass per unit areas. The dyeing of the fabrics altered the intra-yarn spaces to a more optimum size for wicking blood, increasing the ease with which the blood could wick along the yarns in the dyed calico. The amount of wicking varied depending on individual variations within the fabrics and yarns. More variation in dry bloodstain area was seen among dyed calico specimens than for the not-coloured fabric. The amount of wicking which was seen on the dyed calico meant there was no correlation between dry bloodstain area and impact velocity, a correlation which was seen on the medium and heavy not-coloured calico in the previous work.Item Open Access The effect of the digital printing of fabric on the morphology of passive bloodstains(Elsevier, 2022-11-10) Dicken, Lisa; Knock, Clare; Carr, Debra J.; Beckett, SophieBloodstained fabrics found at crime scenes are likely to have had processing treatments, such as dyeing or printing, but the effect of the treatments on bloodstain morphology is not always considered. In order to study the effect of digital printing on bloodstain morphology, drip stains were created from five impact velocities (1.9–5.4 ms−1) on three different mass per unit areas (88–226 g/m²) of 100% cotton calico which had been digitally printed using reactive dye. Across all three printed fabrics, the bloodstains appeared visually similar, and no correlation was found between the dry bloodstain area and the impact velocity. When comparing the bloodstains on the printed fabric to those which had been created previously on the same fabric in a dyed and not-coloured state, the dry bloodstains on the printed fabric were statistically significantly larger (e.g. for the calico with the lightest mass per unit area, mean dry bloodstain area was 126.6, 64.4 and 44.3 mm² for the printed, dyed and not-coloured fabrics respectively). Examination of the larger bloodstains on the printed calico with the micro computed tomography scanner and scanning electron microscope, suggested that the printing process increased the wettability of the fabric, so the blood could spread more easily on the surface. This allowed the blood to coat the yarns, and wick into them before wicking along the intra-yarn spaces. The results presented in this paper showed that care must be taken when examining bloodstains at crime scenes. Depending on the fabric and the processing of the fabric the size of the blood stains may not increase with impact velocity as wicking may result in a larger bloodstain from a lower velocity. The bloodstain on the penetrated face of the fabric may be larger than on the impacted face and the same fabrics with different processing will produce different blood stain sizes and shapes.Item Open Access The effect of underwired and sports bras on breast shape, key anthropometric dimensions, and body armour comfort(Sage, 2021-04-23) Malbon, Christopher; Knock, Clare; Critchley, Richard; Carr, Debra J.This study follows on previous research which investigated the comfort and types of bras worn by UK female police officers when wearing body armour and performing typical activities. This controlled study involved a cohort of 31 female police officers and investigated three main areas. Firstly the effect of professional bra fitting on size and comfort, secondly the effect of wearing an underwired bra or a sports bra on comfort and ability to perform certain actions, and thirdly the effect of an underwired bra and sports bra on key anthropometric data in relation to the fitting of body armour.Item Open Access Effects of surface roughness on bloodstain spreading and spine formation(2016-08-19) Murray, R; Knock, ClareExpert witnesses employ bloodstain pattern analysis (BPA), to provide objective analysis of bloodstain evidence in criminal cases. This thesis added to the scientific understanding of BPA by generating and analysing a large data set of 785 horse blood experiments. The experiments produced impact velocities, u0, of 2:89ms-1 to 6:54ms-1, with impact angles, [theta]f , 90°, 72°, 54°, 36°, and 18°. Different surface roughnesses were investigated: conditioned and unconditioned paper, smooth steel, and three roughened steel substrates with roughness values, Ra, 1:6x10-6 m, 3:2x10-6m, and 6:3x10-6 m. To analyse the data, two computational tools were developed. The first tool extracted the diameter and velocity of a droplet from high-speed videos. The second tool measured stain properties and counted spines of stains resulting from 90° and 72°. The results of these experiments are investigated, extracting relationships between impact properties of droplets to stain properties. Each of the stain properties were related to some combination of a non-dimensional number (Bond number, Bo, Froude number, Fr, or Reynolds number, Re) and impact angle. It was found that the stain area and stain perimeter are proportional to Bo(sin[theta]f )-1. The numberof spines and/or tails on a stain is dependent on Fr(sin[theta]f )2. The major diameter is proportional to Re(sin[theta]f )2 and conversely the minor diameter is proportional to Re(sin[theta]f)2. The full length of the stain is proportional to Bo(sin[theta]f)-2. The results showed that increased surface roughness, promotes increased variability in the bloodstains, up to a limit of Ra = 6:3x10-6m. The roughest steel is statistically the same as paper in almost all stain properties. The results proved a need to account for surface roughness in modelling the spreading of a droplet on a substrate. Starting from the laws of conservation of energy, a new model for predicting spread factor was derived which accounts for the impact angle and substrate roughness. This model uses a coefficient based on properties from the stain and is able to predict the experimental spread factors in this thesis more accurately than the spread factor models in literature. Two new equations were derived that calculate the impact velocity and droplet diameter using only stain properties, not experimental fitting constants, making the expressions more robust.Item Open Access Female police body armour : improving comfort, protection, and testing.(2021) Malbon, Christopher; Carr, Debra J.; Knock, Clare; Critchley, RichardThere is a paucity of published research into female body armour resulting in a lack of evolution in design and testing solutions. A series of surveys and experiments were designed to extend the knowledge relating to female body armour, focusing on comfort, protection, and testing. Comfort was shown to be improved through professional fitting and sizing of new bras, with a sports bra being reported as most comfortable after refitting by 77% of participants. Statistically significant differences in key anthropometric measurements around the breast area were identified between bra types, including bust to bust length, bust circumference, and bust prominence. Exposure of the anterior lateral region of the body was greater compared to the posterior lateral region for female police officers, particularly around the breast area, (exposed anterior lateral breast area – underwired bra: mean 55%, max 72%; sports bra: mean 57%, max 75%). A comparison of three backing materials used for the assessment of back face signature (BFS): Roma Plastilina No1 (RP1); 10% ballistic gelatine; SEBS gel; showed that there were statistically significant differences between the three materials. 10% ballistic gelatine had the greatest variation in measured BFS with both projectiles (9mm; BFS 21.5 – 42.3mm: 0.357”; BFS 31.5 – 67.3mm). RP1 had the smallest variance in measured BFS with both projectiles (9mm; BFS 17.6 – 30.9 mm: 0.357”; BFS 18.9 – 32.5 mm), however, there were statistically significant differences in the spread of results for RP1. The knowledge gained is enabling the development of new guidance for female police officers on improvement in comfort when wearing body armour by the Police Federation. Designers of body armour have information on the effects of bra type on breast shape enabling future designs of body armour to be more tailored to shape, enable a better fit, and reduce the risk of air gaps under the armour. Understanding of the differences in three backing materials will enhance the development of future testing methods for female body armour, which will deliver improvements in the safety of body armour.Item Open Access Investigating bloodstain dynamics at impact on the technical rear of fabric(Elsevier, 2019-05-19) Dicken, Lisa; Knock, Clare; Carr, Debra J.; Beckett, SophieUsing high speed video, the impact of blood drops falling at three velocities (1.9, 4.2 and 5.8 ms−1) were filmed from both the technical face and for the first time the technical rear of three different mass per unit areas (85.1, 163.5 and 224.6 g/m²) of 100% cotton calico. It was seen that there were two stages in the creation of a bloodstain on fabric; the impact dynamics, followed by wicking along the intra-yarn spaces. In the first stage, once the blood impacted the fabric, blood was visible on the technical rear of the fabrics with the medium and lightest mass per unit area within as little as 0.067 ms after impact. No blood was visible on the technical rear of the fabric with the heaviest mass per unit area following impact or the medium mass per unit area from 1.7 ms−1 impacts. On the technical face of the fabric, the blood drop spread laterally and then receded for 8 ms following impact. The dynamics on the technical face were not affected by what was occurring on the technical rear of the fabric. The bloodstain on the technical rear initially only increased until 0.8 ms following impact. The increase in technical rear bloodstain area was caused by continued movement of the blood through to the rear of the fabric as the blood drop spread on the technical face. Once the impact dynamics were concluded within 8 ms of impact, there was no further change in the bloodstain for the remaining 67 ms of high speed video. Following this the blood wicked into and along the yarns, resulting in a dry technical rear bloodstain on all fabrics at all velocities.Item Open Access Passive bloodstains on cotton fabrics(Cranfield University, 2019) Dicken, Lisa; Knock, ClareBloodstains on finished fabrics are frequently found at crime scenes, however there has been limited work on the creation mechanisms and interaction of blood and fabric. The initial aim of this research was to verify the use of a micro computed tomography (μCT) scanner for blood pattern analysis (BPA) research. The pilot study confirmed it was possible to visualise the form of the bloodstain inside the fabric in the CT scans, providing additional information to what could be learnt from examination of the external bloodstains alone. Bloodstains were created on three mass per unit areas (85.1, 163.5 and 224.6 g/m²) of laundered 100% cotton plain woven calico from six impact velocities (1.7, 2.9, 4.1, 4.9, 5.1 and 5.4 ms-1). The bloodstains were examined with external photographs, area measurements, a μCT scanner and a scanning electron microscope (SEM). The fabric with the lightest mass per unit area (85.1 g/m²) generally produced the largest bloodstains. The blood was able to coat the yarns owing to the high porosity of the fabric and wick along the low linear density yarns. For the fabrics with the middle (163.5 g/m²) and heaviest (224.6 g/m²) mass per unit areas less wicking occurred. Dry bloodstain area increased with impact velocity due to the increase in lateral spreading at impact with greater impact velocities. The yarn linear density, sett and yarn twist altered the way in which blood interacted with the fabrics. Bloodstains were then created on the calico fabrics following reactive dyeing or digital printing. The dry bloodstain areas increased for the dyed fabric owing to the swelling of the fibres following dyeing, reducing the intra-yarn spaces to a more optimum size for wicking. The digital printing increased the wettability of the fabric, most likely with a reduction in surface roughness. This allowed the blood to spread more easily on the surface of the fabric, before wicking into and along the intra-yarn spaces. The differences seen among the dry bloodstains for the different treatments emphasise the importance of not comparing bloodstains between fabrics with different finishing treatments.Item Open Access Post-mortem dismemberment using chainsaws(Taylor and Francis, 2019-08-25) Knock, Clare; George, AlisonExperiments were carried out to quantify the size of the tissue spatter distribution from post-mortem dismemberment. Pig joints were used with the same diameters as human arms. Two chainsaws were used: a petrol chainsaw and an electric chainsaw. For both chainsaws and all joint sizes, the tissue spatter distribution showed three distinct regions: i) a line of tissue in front of the cut, ii) tissue particles either side of the line of tissue in front of the cut and iii) a line of tissue behind the cut. The size of the tissue spatter distribution differed between the two chainsaws. The tissue pattern distribution was longer for the petrol chainsaw. The size of the tissue spatter distribution did not depend on joint size for joints with a cross-sectional area greater than 300 cm2.Item Open Access Predicting blast waves from the axial direction of a cylindrical charge(Wiley, 2014-12-10) Knock, Clare; Davies, Nigel; Reeves, ThomasBare, cylindrical, explosive charges produce secondary shock waves in the direction of least presented area. Whilst the source of these shock waves was explored in the 1940’s, no attempt was made to predict them. This paper describes the detonation of bare, cylindrical charges of PE4 (RDX binder 88/12 %), mass 0.2 to 0.46 kg and with a length to diameter ratio of 4 to 1. High speed camera footage showed (i) the formation of the separate, primary, shock waves from the sides and ends of the charge, (ii) Mach reflection of these separate shock waves, giving rise to reflected, secondary shock waves, and (iii) the secondary shock waves catching and merging with the primary shock wave. In the axial direction, the secondary shock wave’s peak overpressure and impulse exceeded that of the primary shock wave for scaled distances, Z=R/M1/3 ≥3.9 m kg−1/3, where M is the mass in kg and R the distance from the charge in m. It was found possible to predict the primary peak overpressure, P, at all distances in the axial direction, for a constant length to diameter ratio, using P=3075 Z−3−1732 Z−2+305 Z−1. Close in the primary peak overpressure is proportional to M/R3 in the axial direction. It was not possible to predict the secondary peak overpressure with the data obtained. The total impulse from both shock waves, I, in the axial direction can be predicted using I=746(M2/3/R)3−708(M2/3/R)2+306(M2/3/R).Item Open Access Radial blast prediction for high explosive cylinders initiated at both ends(2016-07-11) Anastacio, A.; Knock, ClareThis paper presents experimental results for the double ended initiation of cylindrical, explosive charges. Bare cylindrical charges of PE4 (RDX/binder 88/12 %) were used with length to diameter ratios of 1/3.7 to 5.75/1 and masses of 0.25 to 0.45 kg. Pressure measurements were taken at distances of 1 to 3.5 m in the radial direction. It was found that it was possible to predict the peak overpressure in the radial direction using P=K′M(L/D)1/3R−3. M is the mass of explosive, L the length of the explosive charge, D the diameter of the explosive charge, and R the distance from the charge. For PE4, K′=2251 kPa m3 kg−1 for all length to diameter ratios. The double ended initiation gives a peak overpressure 1.6 times that for single ended initiation. The impulse for double ended initiation was found to be the same as for single ended initiated charges.Item Open Access Shock waves from hollow cylinders(2016-08-02) Knock, ClareHollow cylindrical charges of PE4 were detonated. The charges had masses of 0.16 to 0.49 kg and a length to diameter ratio of 1/1 to 1/6. The circular hollows were of diameter 0, 0.01, 0.02 and 0.04 m. The charges were detonated from one end. The results showed that provided the correct ratio of charge mass, charge length to diameter ratio and distance are maintained the peak overpressure and impulse remain constant. This means that it is not necessary to know the size of the hole to predict the peak overpressure and impulse in the radial direction. For PE4 the peak pressure, P, is given by P = -251 (M(L/D)1/3R-3)2 +1677 M(L/D)1/3R-3 and the impulse, I, by I = 150 M2/3 R-1. M is the charge mass, L the charge length, D the charge diameter and R the distance from the charge.Item Open Access The use of micro computed tomography to ascertain the morphology of bloodstains on fabric(Elsevier, 2015-10-23) Dicken, Lisa; Knock, Clare; Beckett, Sophie; de Castro, Therese C.; Nickson, Tania; Carr, Debra J.Very little is known about the interactions of blood and fabric and how bloodstains on fabric are formed. Whereas the blood stain size for non-absorbent surfaces depends on impact velocity, previous work has suggested that for fabrics the blood stain size is independent of impact velocity when the drop size is kept constant. Therefore, a greater understanding of the interaction of blood and fabric is required. This paper explores the possibility of using a micro computed tomography (CT) scanner to study bloodstain size and shape throughout fabrics. Two different fabrics were used: 100% cotton rib knit and 100% cotton bull drill. Bloodstains were created by dropping blood droplets from three heights; 500 mm, 1000 mm and 1500 mm. Results from the CT scanner clearly showed the bloodstain shape throughout the fabric. The blood was found to form a diamond shaped stain, with the maximum cross-sectional area 0.3–0.5 mm below the surface. The bloodstain morphology depended on both the impact velocity and fabric structure.