R. Hart, D. Tzelepis, M. Haq
US Army CCDC Ground Vehicle Systems Center,
Keywords: structural adhesives, multiscale modeling, carbon nanotubes
Summary:As the US Army looks to modernize the ground vehicle fleet with lightweight, expeditionary vehicles, new integration challenges arise. Advanced joining techniques are required to build these lightweight, multi-material vehicle platforms. Adhesive bonding offers an attractive option for joining lightweight composites, alloys, and ceramics. For military ground vehicle applications, adhesives must offer high strength but also must be tolerant to extreme dynamic loads such as ballistic shock and blast loads. The Army Research Lab has classified adhesive joints based on their strengths and elongations at failure. Past research has shown that many high strength adhesives exhibit low elongations to failure and therefore are unable to sufficiently absorb energy and resist failure during ballistic and blast events. Conversely, adhesives with high ductility generally exhibit low strength and are inadequate for structural applications. Very few adhesives have the desirable balance of strength and elasticity needed for military vehicle applications, and moreover the low production scales of military ground vehicles do not necessarily justify the development new adhesive system each individual application. This paper develops a novel technique for optimizing the strength and elongation characteristics of traditional elastomeric adhesives through the addition of carbon nanotube reinforcements. In this work, the adhesive was characterized through experimental techniques and used as an input to the multiscale modeling software. A multi-scale modeling approach was used to determine the effects of carbon nanotubes on the strength and elongation. Representative volume elements were created for various concentrations of carbon nanotubes to determine the influence of the reinforcements on the overall material properties. Computational simulations of a single lap-shear joint were used to assess the influence of the reinforcements on the strength and elongation performance of the enhanced adhesive systems. Finally, computational data points were then used to develop a design frontier which can be used to optimize both the performance and cost of future adhesive systems for a given military or commercial application.