(576d) Multiscale Modeling of Hyperelastic Deformation and Related Microstructural Properties of Random Cross-Linked Elastomers

Hyperelastic behaviours of elastomers are characterized by non-linear mechanical response and microstructural changes at large deformations. In this study we have done multiscale modeling investigation of unfilled and nanoparticle-filled crosslinked-SBR rubber systems involving all atomistic molecular dynamics (MD), coarse-graining molecular dynamics (CGMD) and constitutive analytical modeling (CAM). All atomistic MD simulations can produce the equilibrium density, glass transition temperature and two lower length scale parameters – volumetric segment density of chains (N) and the average number of Kuhn segments between two cross-linking points (n). These all atomistic MD obtained parameters were fed into CGMD and CAM models for predicting properties of larger length-scale structures. Molecular network scale dynamics of polymeric chains by MD can catch the chemical cross-linking and Langevin chain dynamics in rubber stretching. Here the rubber material was taken as random co-polymer of SBR 1502 and effective crosslinking agent as S₃ molecules. The parameters N and n fed into a CAM modeling framework based on Arruda-Boyce model could reproduce the hyperelastic stress-strain behaviour closely. CGMD simulations also confirm the limiting chain extensibility behavior like CAM and shows the relative microstructural changes under large deformation of filled rubber. It was found in both MD and CGMD simulations that nano-voids appear and grow in the rubber matrix under hyperplastic tension. Additionally, CGMD simulations show that under stretching, the nano-particles can rearrange and locally agglomerate with 2-3 particles. At the point of fracture, the nanoparticles also show a tendency to come out to the internal void surfaces. This multiscale modeling study shows the use of different methods towards a deeper understanding of the behaviour of elastomers in general.