Time-Temperature Superposition Principle in Shearing Tests Compared to Tension Conditions for Polymers Close to Glass Transition.

The well-known principle of time-temperature superposition (TTS) is of prime interest for polymers close to their glass transition. First demonstrated in the range of linear viscoelasticity, it has been more recently extended to large deformations in tension. However, shear tests were not yet addressed. The present study depicted TTS in shearing conditions and compared it to results in tensile conditions both for low and high strains for a polymethylmethacrylate (PMMA) of different molar masses. The main objectives were to enlighten the relevance of the principle of time-temperature superposition for shearing at high strain and to discuss the way shift factors should be determined. It was suggested that shift factors could be dependent on compressibility, which should be taken into account when addressing various types of complex mechanical loadings.