Temperature Effect in Exhaust System Fatigue Life Prediction

Automotive exhaust system experiences vibratory and thermal loads. Bogey test had been the major validation method until recent years when the strain-life approach was adopted to evaluate component's fatigue life. In practice, when using the strain-life model to evaluate a component subjected to elevated temperature, temperature effect on component fatigue life is considered by introducing a temperature scale factor K_C that is used to scale up the measured nominal strain, hence the mechanical load. This paper intends to propose a method to estimate K_C by designing component bench tests at room temperature and at elevated temperature, respectively. Two major failure modes in the exhaust system are investigated and different temperature effects on the base metal fatigue and on the weld or heat-affected zone are analyzed.