Browse Publications Technical Papers 2019-01-0534
2019-04-09

Constitutive Modeling and Thermomechanical Fatigue Life Predictions of A356-T6 Aluminum Cylinder Heads Considering Ageing Effects 2019-01-0534

Cast aluminum alloys are frequently used as materials for cylinder head applications in gasoline and diesel internal combustion engines. These components must withstand severe cyclic mechanical and thermal loads throughout their lifetime. Reliable computational methods allow for accurate estimation of stresses, strains, and temperature fields and lead to more realistic Thermomechanical Fatigue (TMF) lifetime predictions. With accurate numerical methods, the components could be optimized via computer simulations and the number of required bench tests could be reduced significantly. These types of alloys are normally optimized for peak hardness from a quenched state that maximizes the strength of the material. However due to high temperature exposure, in service or under test conditions, the material would experience an over-ageing effect that leads to a significant reduction in the strength of the material. To numerically account for ageing effects, the Shercliff & Ashby ageing model is combined with a Chaboche-type unified constitutive model and is implemented into a User Material Model (UMAT) in the general finite element analysis code Abaqus. The Chaboche model with ageing is correlated with uniaxial cyclic isothermal tests in the T6 state and the overaged state as well as thermomechanical tests. On the other hand, the mechanism-based TMF damage model (DTMF) is calibrated for both T6 and over-aged state. Both the constitutive and the damage model are applied to a cylinder head component sub-model simulating an engine dynamometer test. The impact of including ageing effects for both models are shown.

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