Investigation of the effect of adhesive type for ballistic armor applications

Functional optimization is necessary in ballistic armor applications to overcome threat penetration. Multi-layer armor systems have been developed by combining several types of material to achieve high-performance protection. One of the most effective ways of building layered structures is application of adhesive in between intermediate layers. In this present study, five different commonly used adhesives have been used for determination of effect of the mechanical properties on ballistic protection. Tensile and bending test samples were prepared and tested to characterize their mechanical properties. Furthermore, armor plates were prepared by bonding 99.7% pure hexagonal alumina ceramic tiles together with the Al6061 backing plate. Prepared armor plates were ballistically tested by using STANAG 4569 Level three threat 7.62 mmx54R B32 (854 ± 20 m/s) ammunition. The tensile stress and impedance ratio of the adhesive layer are directly correlated. In the polyurethane-based adhesive, the mechanical impedance ratio was calculated as the highest value. In addition, higher back plate deformation was caused by low toughness and flexural stress. The ratio of adhesive flexural stress to tensile stress affected ballistic efficiency, so when the ratio was less than 2.5, partial penetration was observed. Tensile and flexural stress values are found associated with impedance ratio, playing a crucial role in elastic energy absorption during the impact. Also, ballistic impact-induced damage mechanisms were observed and correlated with adhesive toughness and flexural stress. Furthermore, damage area of each type of armor plates was associated with ratio between tensile and flexural stresses of adhesives.