Effects of aging on fracture behavior of polycarbnate

摘要

Polycarbonate (PC) is one of the toughest, most versatile engineering thermoplastics. However, due to physical aging phenomenon, the polymer can break in a brittle manner at normal temperature with relatively low loading rates. The aim of this work is to study the effects of aging on the brittle-ductile transition temperature (T_b-d) and he yielding behavior of an unmodified PC. Fractures tests were performed over a range of aloading rates from 0.2mm/min to 2.5 m/s, using the single edge notched bending specimen (SENB). T_b-d. was determined from the observed fracture behavior as a function of loading rate and temperature. Their relationship is analysed by an activation energy approach, using te Arrhenius-type equation. The results show that ageing increases the temperature at brittle-ductile transition of the pollymer and this effect ismore important at high loading rates. The activation energy seems to change with temperature, suggesting that the time-temperature dependence of the brittle-ductile transition is not ocntrolled by a single molecular relaxation process. Plane strain compression tests were carrie out ovr a range of strain-rates from 0.001 to 0.5 s~-1, and a range of temperatures form -80 to 60 degC for samples energy activation energies of the primary and secondary molecular relaxation processes. and to analyse the correlation between strain rate and temperature. This model supplies and acceptable fit to the experiment data for analysing time-aging-temperature dependence of yielding.