Large deformation response of polycarbonate: Time-temperature, time-aging time, and time-strain superposition

Data are presented from tests of the stress relaxation response of a polycarbonate under torsional deformations. Tests were performed on samples over a range of strains from 0.0025 to 0.08, temperatures from 30 to 135°C and aging times from 1800 to 64,800 s. Individual data sets at each strain, temperature and aging time could be described using a stretched exponential form relaxation function, and time-aging time superposition was found to be applicable to the data under all test conditions. The double logarithmic aging time shift rate, μ, was found to vary significantly with both temperature and strain. Over the range of temperatures studied the data could be superimposed using conventional time-temperature superposition. However, the master curve was found not to be described by a stretched exponential function. For strains up to 0.07, the data at each temperature could also be superimposed to form a master curve following the principle of time-strain superposition. Interestingly, the master curves found from time-strain and time-temperature superposition did not have the same form. In both the time-aging time and time-temperature superposition analyses it was found that the application of vertical shifts was required for superposition of data.