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An engine exhaust manifold undergoes repeated thermal expansion and contraction due to temperature variation. Thermomechanical fatigue (TMF) arises due to the boundary constraints on thermal expansion so that mechanical strain is introduced. Therefore, TMF evaluation is very important in engine design. In this work, the mechanical properties important for TMF assessment and modeling of a silicon (Si)- and molybdenum (Mo)-containing ductile cast iron used for exhaust manifold have been evaluated. Tensile, creep, isothermal low cycle fatigue (LCF), and TMF tests have been conducted. Parameters for material modeling, such as the viscoplastic constitutive model and the Neu-Sehitoglu TMF damage model, have been calibrated, validated, and used to evaluate the TMF life of the exhaust manifold.

Ford designed and built a midsize family sedan for the PNGV (Partnership for a New Generation of Vehicle). The side impact performance of the aluminum vehicle and the current CAE capability was studied. The vehicle was tested according to the specifications of FMVSS 214. The results show the vehicle meet the federal safety requirements. The impact performances of the front and rear dummies were comparable to those of the steel counterpart. CAE analysis was conducted to develop the body component design and to predict the structural and dummy responses. The results show that without modeling of the joint (rivet and weld) separation, the accuracy of the CAE crash analysis for this aluminum vehicle was inadequate. When empirical separation criteria were incorporated to model the joint, analysis results correlated with the test. Further development of robust modeling methods for joint separation is needed to improve the prediction of aluminum structure crash responses.

Cast austenitic stainless steels, such as 1.4837Nb, are widely used for turbo housing and exhaust manifolds which are subjected to elevated temperatures. Due to assembly constraints, geometry limitation, and particularly high temperatures, thermomechanical fatigue (TMF) issue is commonly seen in the service of those components. Therefore, it is critical to understand the TMF behavior of the cast steels. In the present study, a series of fatigue tests including isothermal low cycle fatigue tests at elevated temperatures up to 1100°C, in-phase and out-of-phase TMF tests in the temperature ranges 100-800°C and 100-1000°C have been conducted. Both creep and oxidation are active in these conditions, and their contributions to the damage of the steel are discussed.