Modelling the finite deformation of thermoplastic polymers via hyperinelasticity, Part II: An amorphous polymer with varying rubber content-, rate- and temperature-dependency

In Part I we presented the application of the hyperinelasticity modelling approach to the large elastic and inelastic deformations of semi-crystalline polymers. In this sequel we extend the application of this model to the finite strains of amorphous polymers, by studying Poly(methyl methacrylate), i.e., PMMA, and rubber-toughened PMMA (RT-PMMA) polymer systems. The effects of variation in rubber particle content, temperature and deformation rate on the elastic and inelastic mechanical behaviour of the specimens will be examined and modelled, under large uniaxial compression. The core model will be calibrated using base-line behaviours (i.e., quasi-static deformation, zero particle content, ambient temperature etc.), and the augmented model will be shown to favourably capture the effects of the foregoing inelasticity-inducing factors on the deformation behaviour of the samples. The augmentation of the core model is achieved by considering a linear evolution of the core model parameters, as the function of, e.g., particle content, deformation rate, temperature etc. Predictions of the elastic and inelastic behaviours at intermediary values of temperature/rubber content etc will also be made, and will be verified against experimental data to demonstrate the close match between the two. Given the success of the modelling approach in these applications and in Part I, this two-part contribution concludes a unified modelling tool for application across various thermoplastic polymers, from semi-crystalline to amorphous polymer types. Such a model allows exploration and prediction of the shift in the material response of semi-crystalline polymers from a thermoplastic-like to a rubber-like behaviour, and the reshaping of the amorphous matrix response in the presence of inelasticity-inducing effects for amorphous polymers, using a unified modelling approach.