Effects of temperature and stress ratio on fatigue life of injection molded short carbon fiber-reinforced polyamide composite

The effects of temperature and stress ratio on fatigue life of short carbon fiber-reinforced polyamide-6 composite have been examined. Static tension and compression tests are carried out at room temperature (RT), 50 °C and 70 °C, respectively. For each of these temperatures, constant amplitude fatigue tests are performed at different stress ratios. Experimental results show that the temperature dependence of static strength can be described by a single equation of the Arrhenius type in the range higher than room temperature for each of tension and compression. The tensile strength turns to be smaller than the compressive strength at high temperature. The effect of temperature on fatigue life can approximately be removed by normalization of fatigue stress with respect to static strength, regardless of stress ratio. The asymmetry and nonlinearity in constant fatigue life diagram turns to be more significant with increasing temperature, and they can adequately be modeled by means of the anisomorphic constant fatigue life diagram. The temperature-dependent anisomorphic constant fatigue life diagram approach is also tested. It is demonstrated that this method allows adequately predicting the S-N curves for any stress ratios as well as the constant fatigue life curves for the whole range of mean stress at any temperature in a range that includes the test temperatures.