Modelling strain rate and temperature dependent mechanical response of PMMAs at large deformation from below to above Tg

The potential and the interest of the development of mechanical approach based on concepts issued from the physics of polymers, as well as of the use of the time temperature equivalence principle, are illustrated. To achieve that point, a revisited constitutive model [1], [2] was used to model the mechanical behaviour of amorphous PMMA with different molecular weights. The model accounts for the elastic contribution of an equivalent network which experiences inelastic mechanisms coming from the evolution of internal state variables when the polymer is deformed. The experimental database included non-monotonic tensile tests at targeted equivalent strain rate at reference temperature coupled with DIC for obtaining local boundary conditions. Model exhibited good capabilities to capture the mechanical response of the material at different temperatures and strain rates corresponding to material state ranging from the end of the glassy state to near-liquid state going through viscoelastic and rubbery regime. Analysis of the parameters allowed introducing empirical equations to consider the time/temperature dependence into the model. It was possible to pretty well reproduce the behaviour of PMMAs from rubbery like domains to their glassy state with one unique formalism and one unique and of reduced number set of parameters. Effect of molar mass and crosslinking are discussed.