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Random Vibration Fatigue Life Assessment of Transmission Control Module (TCM) Bracket Considering the Mean Stress Effect due to Preload

General Motors LLC-Neeraj Carpenter, Sudeep Yesudas, Michael D. Nienhuis
  • Technical Paper
  • 2020-01-0194
To be published on 2020-04-14 by SAE International in United States
Transmission Control Module (TCM) bracket is mounted on the vehicle chassis and is subjected to the random load excitation due to the uneven surface of the road. Assembly of the TCM bracket on the vehicle chassis induces some constant stress on it due to bolt preload, which acts as a mean stress along with the varying random loads. It is important for a design engineer and CAE analyst to understand the effect of all sources of loads on vehicle mount brackets while designing them. The objective of this study is to consider the effect of mean stress in the random vibration fatigue assessment of TCM bracket. The random vibration fatigue analyses are performed for all the three directions without and with consideration of mean loads and results are compared to show the significance of mean stresses in random vibration fatigue life. It was found from this study that mean stress affects the vibration fatigue life and it can increase or decrease the fatigue damage depending upon the nature of the mean stress.
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Fatigue Tests of Un-Notched and Notched Specimens and Life Prediction Using a Variable Critical Distance Method

General Motors-Neeraj Carpenter, Pankaj Jha, Sudipto Ray, Michael D. Nienhuis
Published 2019-04-02 by SAE International in United States
Fatigue is one of the most common failure mechanism in engineering structures. The statistical nature of fatigue life and the stress gradient are the two challenges among many while designing any component or structure for fatigue. Fatigue lives of the identical components exhibit the considerable variation under the same loading and operating conditions due to the difference in the material micro-structures and other uncontrolled parameters. Stress concentration at the notch causes stress gradient and therefore, applying the plane specimen results for actual engineering components with notches does not give quantitatively reliable results if the stress gradient effects are not considered. The objective of the work presented here was to carry out the fatigue tests of un-notched, U and V-notch specimens which were die cast using aluminum alloy (A380) and to obtain fatigue life using a variable critical distance method which considers the stress gradient due to the notch geometry. Specimens were prepared in the foundry shop in a way to minimize the microstructural variations and a radiography study was carried out to ensure that cast…
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Prediction of Secondary Dendrite Arm Spacing in Directional Solidification of Aluminum Alloy by Casting Simulation and Micro-Structural Inspection

General Motors Global Propulsion System-Pankaj Jha, Michael Nienhuis
General Motors Technical Center India-Nilankan Karmakar, Sudipto Ray, Neeraj Carpenter, Akshay A., Virupakshappa Lakkonavar
Published 2019-01-09 by SAE International in United States
In automotive industry, many of the powertrain components (for e.g. engine head and cylinder block) are generally manufactured by a casting procedure. Secondary Dendrite Arm Spacing (SDAS) is one of the most important microstructural features in dendritic solidification of alloys (for e.g. Al-Si alloys) during the casting process. SDAS has a significant influence on the mechanical behavior of the cast aluminum components. A lower value of SDAS is desired in order to achieve better fatigue strength of the cast components which can be controlled by governing several casting parameters. For directional solidification, SDAS is dependent on various casting parameters i.e. chemical composition of the alloy, cooling rate and liquid melt treatment. During industrial casting of an alloy with predefined chemical composition, cooling rate during the mushy zone becomes the dominant parameter for controlling SDAS. The objective of this study was to predict the SDAS of die cast Al-Si alloy samples subjected to different cooling rates by varying the mold temperature. The SDAS was predicted by a casting simulation and utilizing the empirical relationship between solidification…
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