|
Abstract
|
Flexible stab- and puncture-resistant materials are required for a range of applications, including industrial safetywear, needle-resistant gloves and garments for medical workers, inflatable structures and, tamper-proof packaging, and ruggedized soft carriers. One particularly challenging application is stab-resistant body armor. Flexible, comfortable systems are required to protect law enforcement and security personnel against stab attacks. These concerns are of particular concern in European countries, where stab assaults are much more likely than firearm attacks.
"Stab" attacks refer to impacts in which the direction of thrust of the stabbing weapon is perpendicular to the target. In contrast, "slash" attacks refer to cases where the weapon is swept in a direction parallel to the target during engagement. In general, preventing penetration from stab attacks is significantly more difficult than providing protection from slash attacks.
Stab weapons can be classified as edged or pointed. Edged weapons, or knives, include a long continuous cutting edge. In contrast, pointed weapons consist of a slender rod with a pointed tip. Pointed weapons, also referred to as spikes, include ice picks and awls. General purpose stab vests, such as for police officers, require both knife and spike protection. Specialty applications, such as for corrections officers, require only spike protection.
Stab-resistant body armors can be characterized according to the National Institute of Justice (NIJ) Standard 0115.00. This standard defines two edged weapons and one pointed weapon. The weapons are individually mounted on a damped two-part drop mass, designed to replicate the dynamics of a stab attack. The drop mass is dropped onto targets to achieve six discrete impact velocities, generating stab energies that represent likely stab attacks of increasing severity. Armors are mounted on a prescribed stack of foams and elastomers that provide a damped target response similar to armor mounted on a human torso. Penetration through the armor, and into the target backing, is measured for each stab event. In order to meet NIJ requirements, the penetration through the armor must fall below prescribed maximum values, over multiple impacts, and under both normal and oblique impact directions.
The cut and puncture resistance of thermoplastic (TP) impregnated, woven aramid fabric is characterized under quasi-static and dynamic stab testing conditions. Polyethylene, Surlyn®, and co-extruded polyethylene-Surlyn films of various thicknesses are laminated into fabrics and compared with neat fabrics at equal weights and layer counts. The results show that TP-laminated fabrics improve the stab and puncture resistance of the fabrics, through a combination of increased cut resistance and reduced windowing. All films are shown to be effective, although thin Surlyn films appear to provide the best overall performance. The results also show that the TP films need to be integrally bonded to the fabrics in order to achieve synergistic property enhancement. |