Fiber Reinforced Polyurethane Composites: Shock Tolerant Components With Particular Emphasis on Armor Plating

Structures fabricated with composite materials, such as graphite fibers in thermoset or thermoplastic resins, are typically brittle and have high stiffness. There are many military situations where high-g shock loading and ballistic impacts mean using these composites may be unsatisfactory. The U.S. Army is designing a new high-performance armored personnel carrier, and composite materials will be used for armor plating, replacing traditional heavy metal armor. This paper describes a fiber reinforced polyurethane matrix composite panel investigated for its suitability as armor plating. When a projectile hits conventional composite armor, its energy is dissipated through delamination of the composite. This causes a reduction in the structural properties of the composite. Additionally the moving debris inside the vehicle can result in injury to personnel. The new material system reported here consists of 24-oz 5x5 S-2 glass fabric infiltrated with a polyurethane having a tensile modulus of 1100 psi and a strain to failure of 400%. The system is mechanically flexible, and has a high inherent energy dissipation potential. When impacted with a high-velocity projectile, delamination is insignificant and its structural characteristics are not significantly degraded. Spalling is eliminated. Also, the high attenuation of the resulting mechanical shock wave within the armor plating reduces the perceived severity of the impact. This is beneficial in raising the crew’s level of confidence, and therefore their performance under adverse conditions. The extensive reinforcement and thick section requirements present some unique challenges. This paper discusses the design and fabrication of a prototype flexible composite panel. Additionally, the experimental results of a dynamic evaluation of two panels and the possible bearing on perceived severity of impact are presented and discussed.