Cohesive zone failure modeling of polymeric adhesives used in ceramic/metal armor

Abstract

In this paper, a trilinear cohesive zone modeling approach available in the explicit nonlinear finite element software LS-DYNA is used to model the dynamic impact failure of an adhesive layer. This approach is an improvement over simpler cohesive zone models presented in the literature. The model is validated for the SikaForceTM6 7752-L60 polyurethane adhesive using force–displacement curves of double cantilever beam and end-notched flexure tests extracted from the literature. The trilinear cohesive zone model was then implemented to simulate the behavior of the adhesive bonding a ceramic alumina tile to an aluminum backing. Simulations were performed to explore the effect of the adhesive layer thickness, manufacturing defects (air bubbles simulated through deleted elements), and strain rates. It was found that: (1) a thicker adhesive layer decreased the ceramic/metal armor performance for a single hit, but resulted in a reduction of the damage area of the top ceramic tile in simulations; (2) an increase in the amount of defects resulted in greater depth of penetration and increased delays to stop the projectile, resulting in a reduction of simulated armor performance; and (3) including strain rate effects in the model resulted in predictions of a reduced depth of penetration and an increase in the damage region of the interlayer after the impact event for all of the simulated impact velocities, thereby predicting a decreased performance for multi-hit impact conditions of the armor system.