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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.

Typically, modern automotive engine designs include separate cylinder heads and cylinder blocks and utilize a multilayer steel head gasket to seal the resulting joint. Cylinder head bolts are used to hold the joint together and the non-linear properties of head gasket provide capability to seal the movement within the joint, which is essential for engine durability and performance. There are three major failure modes for head gasket joint: fluid or gas leakage due to low sealing pressure, head gasket bead cracking due to high gap alternation and scrubbing/fretting due to pressure and temperature fluctuations causing lateral movement in the joint. During engine operation, the head gasket design should be robust enough to prevent all three failure modes and the resulting design must consider all three major failure modes to provide acceptable performance.