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Woven Fabrics and Composite Laminates for Armour Applications
Published in Paul J. Hazell, Armour, 2023
One such fibre that has the strength potential and has already been used in body armour applications with controversial outcomes is poly p-phenylene-2, 6-benzobisoxazole (PBO) currently manufactured under the trade name Zylon®. This fibre has a tensile strength of 5.2 GPa and, according to Table 9.2, will perform as an excellent ballistic-grade material. However, a report from the National Institute of Justice (United States) suggested that it degrades due to environmental conditions (moisture and heat; see Walsh et al., 2006a) and this, it is thought, was a contributing factor to the failure of a vest worn by a police officer who was mortally wounded. Furthermore, the report implied that a visual inspection of a Zylon-based body armour would not indicate whether the intended ballistic performance was maintained (Hart, 2005). There have been subsequent attempts to stabilize PBO fibres, but to date, these have been deemed as not being successful (Walsh et al., 2006b).
Fibre reinforcements
Published in A.R. Bunsell, S. Joannès, A. Thionnet, Fundamentals of Fibre Reinforced Composite Materials, 2021
R. Bunsell, S. Joannes, A. Thionnet
Other polymers with heterocyclic structures have been developed which have remarkable properties. The Zylon® fibre is made from poly-p-phenylenebenzobisoxazole, which is one of the polybenzazoles (PBO) class of polymers developed by the US Air Force as polymers to resist heat better than Kevlar®. It was first produced commercially in 1998 by Toyobo in Japan. It possesses the highest stiffness of all commercial organic fibres. This fibre is forty percent stiffer than steel for a fifth of the density. As the molecule is straight, the Zylon® fibre, as shown in Table 2.5 has a tensile stiffness twice as great as that of Kevlar®. Zylon® fibres absorb very little water (0.2wt%) which fits into residual porosity left behind by the evaporation of the solvent. Lateral cohesion is dominated by Van der Waals bonds which explains both its hydrophobic character and also its anisotropy leading to low compressive properties and fibrillation on failure.
Soft body armour
Published in Textile Progress, 2019
Unsanhame Mawkhlieng, Abhijit Majumdar
PBO is probably the strongest fibre having tensile strength of 5.8 GPa and modulus of 270 GPa, which are higher than those of aramids or UHMWPEs. However, the density (1.56 g/cc) of PBO fibre is higher than that of aramids or UHMWPEs. Zylon® was considered to have a high prospect of being a good ballistic material until 2003, when the failure of some Zylon® vests to protect a couple of police officers from gunshot injury put the material into question [29]. Soon after, it was revoked by the US army. It is believed that the fibre lost its strength upon exposure to a humid environment. As a matter of fact, Zylon® can withstand very high temperature (75% strength retention at 400 °C) when dry. However, when subjected to an even lower temperature condition (250 °C) in the presence of moisture (saturated steam), the strength dropped down drastically (20% of the strength tested at standard conditions) [27]. Zylon® is also susceptible to UV radiations and will quickly lose its strength when exposed for a longer duration. As such, for effective utilization of its property, Zylon® material has to be kept in dry and UV-free environment [23]. Yet another disadvantage of Zylon® is its very low compressive strength, restricting its use as reinforcement in composite structures. However, it is superiorly resistant to creep, abrasion as well as chemical attacks. More importantly, its toughness (area under the load-extension curve), as a measure of energy absorption capacity, is even higher than that of Kevlar® [19].