Relaxação não-linear de tensões do poli(metacrilato de metilo)

Abstract

Nonlinear stress relaxation is much more difficult to model than creep. This model, although still simplified, describes a clearly non-linear (strain-dependent) behavior that only becomes linear for very low strains; is the first to explain the effect of small differences between the level of the initial and final moduli, as is the case in semi-crystalline materials; explicitly quantifies the effect of temperature, when considering the distribution of relaxation times; can be extended to also take into account the effect of changes in free volume; and ensure a very fast calculation of relevant physical parameters and extrapolate long-term behavior at any temperature, from experiments close to room temperature, lasting just a few hours. The model can, however, still be updated and, eventually, also take into account the effect of the rapid initial deformation ramp up to its nominal value. The work also analyzes in detail the meaning of the values and physical characteristics of the model parameters, applied to poly(methyl methacrylate) – PMMA, with temperatures of 30, 40 and 50 ºC, and deformations of 3, 4 and 5%.