Ballistic performance body armour

Experimental work is based on the data obtained from ballistic tests and is an integral part of soft body armour engineering. From a research point of view, results from the experimental tests and observations not only directly indicate the performance and usability of materials in ballistic applications, but provide empirical data to test the validity of the theories that are put forward in this field as well. This section will list the methods and approaches adopted to study fabric response and evaluate its performance upon ballistic impact. 

A ballistic panel can be made from a single ballistic material or from two or more materials in combination. Where more than one ballistic fibre is used, the vest is often referred to as a hybrid . The location and number of layers of each material within the multiple-layer protective panel ate critical to the overall performance of the panel. If a manufacturer uses insufficient ballistic material, the body armour will offer insufficient protection. It is thus indispensable that sufficient material and a suitable margin of safety be incorporated into well-designed, properly manufactured body armour (McConnell, 2006). 

All the firing tests have been performed with respect to the NIJ norm level n (NH Standard 0101.04, 2011), which corresponds to 9 mm ammunition at a speed of 358 m/s. Six shots have been carried out, two on the right flank, two on the left flank, one in the middle of the body armour and one on the nipple. To better measure the blunt trauma effect after impact, plastiline clay of the type Roma no. 1 has been shaped in 3D to represent the wearer s body. The body armour was fitted onto the 3D plastiline clay during the ballistic tests, ensuring that the vest behaved in the way it would on a real female body (Fig. 8.17). 

Composite materials and hybrid structures are usually employed to provide multiple functions in addition to cut resistance requirements. Composite cord threads using stainless steel filaments as core, and other high performance fibres as sheath, are used in cut resistance fabrics to provide both flexibility and cut protection. A flexible body armour vest made from a combination of Dyneema high performance polyethylene fibre from Royal DSM (Dutch State Mines), and Steelskin steel cord material from Bekaert, offering both ballistic-proof and stab-proof protections from gunshots, shrapnel and knives stabs has been reported. 

Before the 1970s, many different materials had been used as body armour material such as cotton, silk and nylon. Only in the last 30 years, have high-performance materials such as Kevlar and Dyneema been introduced in the body armour industry. Apart from fibre am properties, fabric construction parameters, including fabric weave, yam counts, density and fabric width have also had a significant effect on ballistic performance of body armour. On top of this, fabric (yam) surface treatments are additional parameters that can be considered for the optimum conditions for ballistic application. 

Apart from yam properties and fabric stmcture, yam count and yam density in a fabric are also factors influencing ballistic performance of body armour. It was found that the fabrics constmcted of finer yams performed better than the fabrics constructed of thicker yams (Bhatnagar, 2006). This result indicates that the detrimental effect of crimp can be overcome by increasing the number of yams involved in the resistance to projectile penetration. Basically the numbers of fibre breakage on ballistic impact is the mean source of kinetic energy absorption, and it is greater for the fine yam-based fabric systems than thick yam-based systems. 

The overall thickness of fabrics for ballistic protection must be high to achieve the desired level of performance. In turn, the increased bulk and thickness of body armour reduces the level of thermal comfort. However, the performance of these textiles for ballistic protection is still the essential requirement. 

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