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.