Atomistic to continuum scale investigations on mechanical properties of epoxy bonded fiber reinforced polymer composite systems under hygro-thermal exposures

Abstract Epoxy polymers are widely used as adhesives in bonded composite systems. In this study, multi-scale computational investigations from molecular dynamics (MD) to finite element (FE) simulations are carried out to understand the material behaviour at atomistic level and to evaluate the performance at macro level. MD investigations are carried out to understand the extent of degradation of mechanical (such as strength, modulus) and transport properties (such as moisture diffusion coefficient) due to different environmental conditions like moisture ingress and high temperature. The influence of degree of curing of epoxy (diglycidyl ether of bisphenol-A) and type of hardener (diethyltoluene diamine, diethylene triamine, trimethylene hexadiamine) on the mechanical performance of the cross-linked epoxy polymer systems is also investigated. In-depth investigations are also carried out to identify the factors contributing to the total potential energy of cross-linked epoxy polymers and their role during the process of curing. Diffusion coefficient (key transport property) of epoxy polymer under moisture exposure is also determined using MD simulations. It has been demonstrated that high temperature causes the increase in diffusion in epoxy polymer systems. The observations on the performance of the epoxy system under moisture exposure obtained from MD simulations are translated to the higher length scale. The moisture ingress (in turn, significant reduction in mechanical properties) in epoxy polymer used for bonded composite system is also investigated using FE simulations. It is found that the extent of moisture ingress in the epoxy adhesive increases rapidly when epoxy polymer is environmentally exposed (under high temperature), and thus, the whole system gradually loses its effectiveness due to mechanical degradation. The findings of this study will help in understanding crucial parameters and aid to better use/engineering of epoxy polymers.