1Shaft DesignChapter 12Material taken from Mott, 2003, Machine Elements in Mechanical DesignShaft Design• A shaft is the component of a mechanical device that transmits rotational motion and power.• It is integral to any mechanical system in which power is transmitted from a prime mover, such as an electric motor or an engine, to other rotating parts of the system.Shaft Design Procedure• Because of the simultaneous occurrence of torsional shear and normal stresses due to bending, the stress analysis of a shaft virtually always involves the use of a combined stress approach.•The recommended approach for shaft design and analysis is the distortion energy theory of failure.
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2Shaft Design Procedure• Vertical shear stresses and direct normal stresses due to axial loads may also occur.• On very short shafts or on portions of shafts where no bending or torsion occurs, such stresses may be dominant. Procedure1.Determine the rotational speed of the shaft.2.Determine the power or the torque to be transmitted by the shaft.3.Determine the design of the power-transmitting components or other devices that will be mounted on the shaft, and specify the required location of each device.Procedure con’t4.Specify the location of bearings to support the shaft. Normally only two bearings are used to support a shaft. The reactions on bearings supporting radial loads are assumed to act at the midpoint of the bearings.•Bearings should be placed on either side of the power-transmitting elements if possible to provide stable support for the shaft and to produce reasonably well-balanced loading of the bearings.