Large strain/time dependent mechanical behaviour of PMMAs of different chain architectures. Application of time-temperature superposition principle

Abstract : The relevance of equivalent strain rate at reference temperature derived from time/temperature superposition principle is validated as a constitutive parameter at large strain for PMMAs of different chain architecture. Shift factors were obtained from DMTA at infinitesimal strain, then identified according to Williams-Landel-Ferry or Arrhenius equations and finally extended to large deformations. Mechanical behaviour was characterized under cyclic tensile loading. So-called 3D digital image correlation was used to measure local strain. It is demonstrated that for different experimental conditions having same equivalent strain rate, the macroscopic behaviour will be the same. This was validated for elastoplastic, viscoelastic and rubbery behaviours. Such experimental observations indicate that time/temperature superposition at low strain can be extended for large deformation for PMMA. Additionally, the study opens a new way of addressing the temperature and strain rate dependencies in constitutive model by using the equivalent strain rate at reference temperature as a unique parameter.