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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 1 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I 8-1 Thread Standards and Definitions 8-2The Mechanics of Power Screws 8-3Strength Constraints 8-4Joints-Fasteners Stiffness 8-5Joints-Member Stiffness 8-6Bolt Strength 8-7Tension Joints-The External Load 8-8Relating Bolt Torque to Bolt Tension 8-9Statically Loaded Tension Joint with Preload 8-10Gasketed Joints 8-11Fatigue Loading of Tension Joints 8-12Shear Joints 8-13Setscrews 8-14Keys and Pins 8-15Stochastic Considerations 8-1 Thread Standards and Definitions 8-2The Mechanics of Power Screws 8-3Strength Constraints 8-4Joints-Fasteners Stiffness 8-5Joints-Member Stiffness 8-6Bolt Strength 8-7Tension Joints-The External Load 8-8Relating Bolt Torque to Bolt Tension 8-9Statically Loaded Tension Joint with Preload 8-10Gasketed Joints 8-11Fatigue Loading of Tension Joints 8-12Shear Joints 8-13Setscrews 8-14Keys and Pins 8-15Stochastic Considerations CH-8 LEC 39 Slide 2 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I 8-12Shear Joints 8-13Setscrews 8-14Keys and Pins 8-12Shear Joints 8-13Setscrews 8-14Keys and Pins CH-8 LEC 39 Slide 3 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I 8-12 Shear Joints Joints should be loaded in shear so that the fasteners see no additional stress beyond the tightening. Shear loading is resisted in two ways: The shear load is carried by friction between the members and ensured by the clamping action of the bolts or cap screws. The shear load is carried by dowel pins in reamed holes, placed in both parts while clamped together to ensure alignment. The dowels will carry the shear load. CH-8 LEC 39 Slide 4 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 5 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Bolt loaded in double shear.

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 6 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Failure modes due to shear loading of riveted fasteners. (a) Bending of member; (b) shear of rivet; (c) tensile failure of member; (d) bearing of rivet on member or bearing of member on rivet.

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 7 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Integral to the analysis of a shear joint is locating the center of relative motion between two members. In Fig. 8-23 let A 1 to A 5 be the respective cross-sectional areas of a group of 5 points, or hot driven members. Under this assumption the rotational pivot point lies in the centroid of the cross-sectional area pattern of the pins, rivets or bolts. The centroid G is located by and, where and are the distances to the ith area center Figure 8-23 Centroid of pins, rivets, or bolts. Centroid of pins, rivets or bolts

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 8 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Centroid of pins, rivets or bolts (8-49)

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 9 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints An example an eccentric loading of fasteners is shown in Figure 8-24.

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 10 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 11 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 12 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 13 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints If bolts are not same size only bolts with maximum load should be considered

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 14 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints See Example 8-6 and 8-7(Textbook)

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 15 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Example 8-6 (Textbook)

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 16 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 17 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 18 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 19 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Example 8-7 (Textbook)

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 20 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 21 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 22 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I Used to prevent relative motion between the two parts. Unlike bolts and screws, which depend on tension to develop a clamping force, the setscrew depends on compression to develop the clamping force. A set screw is screwed through a threaded hole in one part so that its point presses against the other part. CH-8 LEC 39 Slide 23 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints 8-13 Setscrews A set screw is screwed through a threaded hole in one part so that its point presses against the other part.

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ME 307 Machine Design I ME 307 Machine Design I Setscrews depend on compression to develop a clamping force The resistance to axial motion of the collar or hub relative to the shaft is called holding power. This holding power, is a force resistance due to frictional resistance of the contacting portions of the collar and shaft as well as any slight penetration of the setscrew into the shaft. CH-8 LEC 39 Slide 24 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints 8-13 Setscrews

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 25 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Table 8-18 lists values of the seating torque and the corresponding holding power for inch-series setscrews. The values listed apply to both axial holding power and resisting torsion. Typical factors of safety are 1.5 and 2.0 for static loads and 4 to 8 for various dynamic loads. Setscrews should have a length of about half of the shaft diameter. This practice also provides a rough rule for the radial thickness of a hub or collar. Table 8-18

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 26 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints 8-13 Keys and Pins Keys and pins are used on shafts to secure rotating elements, such as gears, pulleys, or other wheels. Keys are used to enable the transmission of torque from the shaft to the shaft- supported elements.

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 27 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I Pins are used for axial positioning and for the transfer of torque or thrust or both. Pins are useful when the principal loading is shear and when both torsion and thrust are present. Taper pins are sized according to the diameter at the large end. Some of the most useful sizes of these are listed in Table 8-19. The diameter of the small end is where d = diameter at small end, in D = diameter at large end, in L = length, in CH-8 LEC 39 Slide 28 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints 8-13 Keys and Pins (8-51)

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 29 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Square Keys The standard sizes of square and rectangular keys, together with the range of applicable shaft diameters are listed in Table 8-20. The length of key is based on the hub length and the torsional load to be transferred.

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 30 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Gib-Head Key It is tapered. When firmly driven, it acts to prevent relative axial motion. This also gives the advantage that the hub position can be adjusted for the axial location. Head makes removal possible without access to the other end, but the projection may be hazardous.

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 31 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Woodruff Key It is useful when a wheel is to be positioned against a shaft shoulder. It also yields better concentricity after assembly of the wheel and shaft.

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ME 307 Machine Design I ME 307 Machine Design I D imensions for some standard Woodruff key sizes can be found in Table 8- 21, and Table 8-22 gives shaft diameters for which the different keyseat widths are suitable. Stress-concentration factors for keyways depend for their values upon the fillet radius at the bottom and ends of the keyway. For fillet cut by standard milling-machine cutters, Peterson charts give K t = 2.4 for bending and K ts = 2.62 for torsion. CH-8 LEC 39 Slide 32 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 33 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Retaining Ring A retaining ring is frequently used instead of a shaft shoulder or a sleeve to axially position a component on a shaft or in a housing bore. A groove is cut in the shaft or bore to receive the spring retainer.

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 34 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints Example 8-8 (Textbook)

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ME 307 Machine Design I ME 307 Machine Design I CH-8 LEC 39 Slide 35 Dr. A. Aziz Bazoune Chapter 8: Screws, Fasteners and the Design of Nonpermanent Joints

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