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Lakkonavar, Virupakshappa
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General Motors LLC-Peggy Jones, Margarita Thompson, Yew Sum Leong, Paul Crepeau
General Motors Technical Center India-Virupakshappa Lakkonavar, Swaroop Kavi
  • Technical Paper
  • 2020-01-1072
To be published on 2020-04-14 by SAE International in United States
The market for electric vehicles and hybrid electric vehicles is expected to grow in the coming years, which is increasing interest in design optimization of electric motors for automotive applications. Under demanding duty cycles, the moving part within a motor, the rotor, may experience varying stresses induced by centrifugal force, a necessary condition for fatigue. Rotors contain hundreds of electrical steel laminations produced by stamping, which creates a characteristic edge structure comprising rollover, shear and tear zones, plus a burr. Fatigue properties are commonly reported with specimens having polished edges. Since surface condition is known to affect fatigue strength, an experiment was conducted to determine the effect of sample preparation in stamped specimens. Tensile properties were unaffected by polishing. In contrast, polishing was shown to increase fatigue strength by approximately 10-20% in the range of 105-107 cycles to failure.
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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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