Shaft Design - Shaft Design Chapter 12 Material taken from...

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1 Shaft Design Chapter 12 Material taken from Mott, 2003, Machine Elements in Mechanical Design Shaft 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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2 Shaft 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. Procedure 1. 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’t 4. 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.
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3 Procedure con’t 5. Propose the general form of the geometry for the shaft, considering how each element on the shaft will be held in position axially and how power transmission from each element to the shaft is to take place. Intermediate Shaft Mott, 2003, Machine Elements in Mechanical Design Procedure con’t 6. Determine the magnitude of torque that the shaft sees at all points. • It is recommended that a torque diagram be prepared. 7. Determine the forces that are exerted on the shaft, both radially and axially.
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4 Procedure con’t 8. Resolve the radial forces into components in perpendicular directions, usually vertically and horizontally. 9. Solve for the reactions on all support bearings in each plane. 10. Produce the complete shearing force and bending moment diagrams to determine the distribution of bending moments in the shaft. Procedure con’t 11. Select the material from which the shaft will be made, and specify its condition: cold-drawn, heat-treated, etc Plain carbon or alloy steels with medium carbon content are typical, such as AISI 1040, 4140, 4340, 4660, 5150, 6150, and 8650. Good ductility with percent elongation
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Shaft Design - Shaft Design Chapter 12 Material taken from...

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