Dry cast iron exhaust manifolds experience thermo-mechanical fatigue (TMF) during engine operation. This is one of the critical failure modes. It is difficult to accurately predict TMF life of exhaust manifold in FEA due to dependency on multiple factors such as non-linear material behavior, temperature dependent material behavior, oxidation effects, creep effects, accuracy in prediction of metal temperatures and joint friction coefficients. Typically, non-linear material models, creep effects and oxidation effects are accounted by advanced fatigue processing software. Also, non-linear material models account for material and temperature dependent non-linearity. However, the material model and fatigue parameters are often developed using uniaxial specimen level testing which doesn’t account for all the complexity and manufacturing defects and actual component level loading. FEA processes for exhaust manifolds are seldom calibrated with on-engine measurements due to the complexity of obtaining these measurements in an environment that has severe temperatures and vibrations. Hence, an attempt was made as part of this work to acquire on-engine measurements to identify how closely current FEA models replicate actual on-engine manifold behaviorExhaust manifold is mounted on cylinder head, with gasketed joints. In current work, thermal expansion of exhaust manifold was measured between two extreme ports of an inline 6-cylinder engine. Expansion measurement was done using guided LVDTs (Linear Variable Differential Transducer). Mounting LVDTs on an engine during a live test was a challenge and so a setup was designed to isolate the LVDTs from both thermal and vibration perspective. To reduce un-certainty with other inputs like thermal BCs and bolt loads, skin temperatures at various points on manifold and preload information was also recorded.&nbsp; All the relevant data was collected for 50 thermal cycles. FEA models were calibrated and correlated with the test dataCorrelation study highlighted that the manifold was excessively clamped in FEA raising questions on the gasket coefficient of friction and working preloads. Using reduced friction and non-linear material properties for manifold capscrews helped to achieve better correlation. Replacing material properties of manifold capscrews with non-linear data provided capability to simulate localized yielding of capscrews and hence the corresponding load loss. Using these new settings for few other case studies also showed improvement in correlation. Outcome of this work was a refined FEA approach which showed better FEA to Test correlation for exhaust manifold TMF life predictionKeywords: Exhaust Manifold, LVDT measurement, Gasket Friction, Thermo-mechanical Fatigue (TMF), Exhaust Manifold Capscrews

On-Engine Expansion Measurement of Exhaust Manifold for Calibrating Thermo-Mechanical Fatigue FEA Model

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2021/volume/85512

ASME 2021 Internal Combustion Engine Division Fall Technical Conference (ICEF2021)

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