The Effects of Combined Compression and Aging on the Properties of Glassy Polycarbonate

Physical aging and plastic flow are known to cause changes in the properties of glassy polycarbonate (PC). Although the individual effects of physical aging and plastic flow have been studied, the combined mechanical and thermal effects have yet to be evaluated for PC at large plastic strains. This work is the first characterization of the combined effects in PC of large plastic flow followed by thermal (physical) aging. To conduct this study, samples were prepared with different extents of plastic compressive strain, up to approximately 50 % engineering strain, followed by thermal aging up to 135 °C, with various aging times up to 6000 hours. These samples were then studied by conducting Charpy impact, quasi-static single-edge notched bending (SENB), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and temperature-modulated DSC (TMDSC) tests. The main content of this thesis is the description of the experimental setup and its evaluation, and a preliminary study of the results. The Charpy impact, quasi-static SENB, DSC, DMA, and TMDSC results are the first for PC at large plastic flow in the glassy state followed by physical aging. Charpy impact and quasi-static SENB tests provide information about crack initiation and propagation, and were conducted on PC to study the effect on failure of plastic flow followed by physical aging. For these tests, samples were cut with two orientations relative to the axis of the initial compression, labeled as TA and TT samples. The first letter denotes that the sample is cut with its long axis oriented transversely (T) to the axis of compression and the second letter denotes the direction of crack propagation, either axial (A) or transverse (T) to the axis of compression. Even though preliminary, this study shows a distinct anisotropic characteristic to the sample response during failure, with a measurable effect from both plastic deformation and from physical aging. As expected, the Charpy impact results show that plastic compression increases the toughness while physical aging has a large effect in increasing the brittleness. The quasi-static SENB tests provide more detailed information, yet provide similar results. DSC tests were performed on PC samples with plastic compressions up to 40 % engineering strain followed by physical aging at 105 °C, 125 °C, and 135 °C for aging times up to 6000 hours, 700 hours, and 300 hours, respectively. A LabView program was developed to calculate the relevant thermal parameters for these tests, which has been …