Shock waves from hollow cylinders

Hollow 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

Radial blast prediction for high explosive cylinders initiated at both ends

This 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

Predicting blast waves from the axial direction of a cylindrical charge

Bare, 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)

Post-mortem dismemberment using chainsaws

Experiments 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

The effect of fabric mass per unit area and blood impact velocity on bloodstain morphology

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

Investigating bloodstain dynamics at impact on the technical rear of fabric

Using 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

The effect of underwired and sports bras on breast shape, key anthropometric dimensions, and body armour comfort

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

The effect of reactive dyeing of fabric on the morphology of passive bloodstains

The 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

The effect of the digital printing of fabric on the morphology of passive bloodstains

Bloodstained 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

The effect of breast size and bra type on comfort for UK female police officers wearing body armour

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