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. The high cycle fatigue damage for any usage cycle can be calculated from the component stress history (output of transfer function) and used to assess the total damage, or expended life, of the cylinder head.
Due to the wide possibilities for the variation in inputs, model parameters and material properties, the high cycle fatigue damage range is first evaluated for a known engine dynamometer test cycle. With a known performance on engine dynamometer under controlled conditions, the wide range of inputs due to customer usage can then be evaluated for high cycle fatigue damage and used to determine the risk of failure in the field for any given customer duty cycle.