Effects of injection molding weld on fatigue crack resistance of CPVC at different temperatures

This study addresses the effects of injection molding weld line on the fatigue crack resistance of commercial CPVC in the temperature range of −10 to 70 °C. Fatigue crack growth (FCG) tests were conducted on SEN specimens prepared from 100 mm. injection molded pipe-fittings with and without weld line. Crack growth behavior was studied using LEFM concepts where the stress intensity factor was modified to include the plastic zone effect. The weld line is found to drastically reduce the fatigue propagation life of the specimens at temperatures ranging from 23 and 70 °C. Weld line effect on FCG rate is observed to be insignificant at −10 and 0 °C. The crack growth resistance was found to decrease with temperature increase for both weld and non-weld specimens. Fractographic examination showed that for both types of specimens, crazing was the dominant fatigue mechanism at high temperature, while shear yielding was the dominant mechanism under sub-room temperature conditions. The variation of FCG rate was plotted versus 1/T. These results showed that the transition from shear yielding to crazing occurred around the room temperature.