The role of adhesive in the ballistic/structural performance of ceramic/polymer–matrix composite hybrid armor

Transient non-linear dynamics computational finite-element analyses are employed to investigate the role of the adhesive used in ceramic strike-face/composite back-face hybrid armor. The role of the adhesive is investigated under: (a) high loading-rate conditions accompanying impact of an armor-piercing projectile onto the armor structure; and (b) low loading rate conditions associated with the ingress of the loads which are generated at the road/tire contact interfaces and transmitted into the armor structure through the vehicle frame. The high loading-rate conditions were analyzed since they reveal the role of the adhesive under ballistic impact scenarios which controls the overall penetration resistance of the armor. On the other hand, the low loading-rate conditions were analyzed since they may reveal the potential structural damage that armor may experience due to sustained in-service loads. Since structural thermoset-polymer-based adhesives suffer from inadequate ductility, only the case of flexible (elastomer-based) adhesives was considered. The following two specific aspects of the adhesive mechanical response are given special attention: (a) strain rate sensitivity and (b) the degree of volumetric compressibility. The results obtained show that while significant improvements in the ballistic protection performance and durability of hybrid armor can be attained by proper modifications in the adhesive layer mechanical properties, there is no single combination of these properties which simultaneously optimizes all the performance requirements.