Using FEM (Finite Element Method) and other analytical approaches, a systematic methodology was developed to predict an engine valve's fatigue life. In this study, a steel (SAE 21-2N) exhaust valve on an engine with a type 2 valve train configuration was used as a test case. Temperature and stress/strain responses of each major event phase of the engine cycle were analytically simulated. CFD models were developed to simulate the exhaust gas flow to generate boundary conditions for a thermal model of the valve.
FEM simulations accounted for thermal loads, temperature dependent material properties, thermal stresses, closing impact stresses and combustion load stresses. An estimated fatigue life was calculated using Miner's rule of damage accumulation in conjunction with the Modified Goodman approach for fluctuating stresses.
Predicted life results correlated very well with empirical tests. In one scenario for an unstable valve train, early valve failure was predicted at 500 hours of engine testing that correlated to actual test failures from 460-500 hours. In other test scenarios, the methodology was able to accurately predict valve survivability to 600 hours of engine testing.