Torsion and normal force responses of glassy polymers in the sub-yield regime

While there is a major body of literature relating the non-linear response of both elastomers and polymer melts with the molecular structure and topology of the chains, the same cannot be said of the non-linear response, especially that below the yield point, for polymer glasses. Here we take an approach that uses ideas of finite deformation elasticity and apply them to the isochronal response of glassy polymers in torsional deformations. We find that, while the torsional (shear) responses are similar for different molecular structures, there seems to be a strong effect of side group relaxations on the normal forces. The results are discussed in terms of the strain energy density function and the opportunities for future research.