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In a separate SAE paper (Cylinder Head Design Process to Improve High Cycle Fatigue Performance), cylinder head high cycle fatigue (HCF) analysis approach and damage calculation method were developed and presented. In this paper, the HCF damage calculation method is used for risk assessment related to customer drive cycles. Cylinder head HCF damage is generated by repeated stress alternation under different engine operation conditions. The cylinder head high cycle fatigue CAE process can be used as a transfer function to translate engine operating conditions to cylinder head damage/life. There are many inputs, noises, and design parameters that contribute to the cylinder head HCF damage CAE transfer function such as cylinder pressure, component temperature, valve seat press fit, and cylinder head manufacturing method. Material properties and the variation in material properties are also important considerations in the CAE transfer function.

For aluminum automotive cylinder head designs, one of the concerning failure mechanisms is thermo-mechanical fatigue from changes in engine operating conditions. After an engine is assembled, it goes through many different operating conditions such as cold start, through warm up, peak power, and intermediate cycles. Strain alternation from the variation in engine operation conditions change may cause thermo-mechanical fatigue (TMF) failure in combustion chamber and exhaust port. Cylinder heads having an integrated exhaust manifold are especially exposed to this failure mode due to the length and complexity of the exhaust gas passage. First a thermo-mechanical fatigue model is developed to simulate a known dynamometer/bench thermal cycle and the corresponding thermo-mechanical fatigue damage is quantified. Additionally, strain state of the cylinder head and its relation to thermo-mechanical fatigue are discussed. The bench test was used to verify the TMF analysis approach.