1. Part II Design of Fasteners and Joints

2. What is a fastener?
a fastener is any device used to connect two or more components.
there are two types:
1)permanent fastener: rivet, welding, adhesive
2)separable fastener: bolts, screws, studs, keys

3. Chapter 5 Design of Threaded Fasteners and Joints
Key Terms:
Threaded fastener
Power screw
Bolt
Nut
Stud
Washer
Preload

4. 5.1 Basic Concepts

6. Left-handed thread or right-handed thread
External thread or internal thread

7. Rolled Thread

8. Cut Thread

9. 5.2 Thread Standards and Definition
1、Terminology
major diameter : d
minor diameter : d1
mean diameter : d2
pitch : p
lead : S=np
thread angle : 
Thread height ：h
lead angle: 
Starts ：

10. Screw Terminology
Thread Designation: M241.5

11. Lead Angle

12. 2、Types of Screw Thread 1) Classification according to profile
2) Classification according to purpose
a. fastening threads
b. fastening and sealing threads
c. power threads

13. Screw Jack

14. 5.3 Screw Fasteners
Bolts
Studs　
Cap Screws　
Setscrews　

15. Bolts Precision Screw

16. Studs

17. Cap Screws

18. Setscrews

19. Screw Fasteners
1、bolts
2、studs
3、screws

20. Heads of Cap Screws

21. 4、nuts
standard nut
thin nut
thick nut
round nut
castellated nut

22. Locknuts
Castellated Nut

23. 5、washers
Plain washer
spring washer
lugged washer

24. Spring washer
lugged washer

25. 5.4 Screw-up Torque, Efficiency and Self-locking Condition

26. The condition of self-locking:
<v

27. Screw-up torque: T=T1+T2
T1——torque in the thread;
T2——torque at the bearing surface, collar friction ;

28. 5.5 Bolt Tightening and Initial Tension

29. F'——initial tension, preload
T——tightening torque
F'——initial tension, preload
d——major diameter
Torque-wrenches

30. 5.6 Preventing Unintentional Unscrewing of Screw Joints
1) By Supplementary Friction
jam nut

31. 2) By Special Locking Devices
split cotter pin

32. Arrangement of the Bolts Group

35. 5.7 Screw and Thread Element Design for Steady Loads
1) Failure Modes: rupture, crushing

36. 2) Design for screws loaded without initial preload
Crane

38. Check Equation:
Design Equation:

39. Example 1 Solution Obtained From the Design Manual:
A crane hook is shown below, assuming F=25KN, use the number 35 steel, the allowable stress []=60Mpa, find the major diameter of the thread.
Solution
Obtained From the Design Manual:
M27 is suitable, d1=23.752mm

40. 3) Design for screws loaded with initial preload
Tensile stress caused by Initial tension F':
Shear stress caused by Torque in the thread T1:

41. Equivalent stress by The Fourth Strength Theory:So

42. 5.8 Design of Screw Joints Subject to Loads in the Plane of the Joints
1.Joints subject to shearing force

43. 1) Common screw joints
The holding power condition: R

44. The strength condition
R——external shear force
m——number of joint plane
——coefficient of friction
K——safety factor
z——number of screws
The strength condition

45. Load Relieving Devices

46. 2) Precision screw jointsFs Fs

47. Example 2
As shown below, two steel plates are connected by two bolts, which made of Q235 steel having the strength class of 5.8; Assuming the applied tensile load is 6400N, the coefficient of friction is 0.2, let S=2, K=1.2; Determine the diameter of the bolt.

48. 2. Joints subject to shearing moment
1) Common screw joints
The holding power condition:

49. T——external applied moment
F'——initial tension
——coefficient of friction
K——safety factor
z——number of screws
r1,r2,…rz——radii about the centroid of the joint

50. 2) Precision screw joints
Equilibrium condition:

51. Example 3
A flange coupling, which rated torque T=1.5kN.m is transmitted, is connected by four M16 bolts made of Q235 steel. The coupling is made of HT Given: the diameter of distribution circle D0=155mm, height of flange h=23mm, coefficient of friction =0.15, safety factor K=1.2 .
Check the strength of the bolts respectively in two cases: common screw joints or precision screw joints.

52. Example 5.1 P T

54. Homework 1 Textbook P93，5.5 Textbook P93，5.6
A screw joint as shown below, given: F=56kN, the screw is made of Q235, 4.6 strength class, determine the nominal diameter of the screw.

55. 4) A bolt joint as shown below, assuming the moment exerted on the handle M=4.5104N.mm，diameter of the clamped element d=30mm, coefficient of friction =0.15, yield strength of bolt s=480MPa, let S=2.5, K=1.5, determine the minor diameter of the bolts.

56. 5.10 Bolt Tension with External Joint-separating Force

57. F1——the resultant load on bolt
F——the external load
F''——the clamping force
Reference:
Common case: F''=(0.2~0.6)F
Sealing case: F''=(1.5~1.8)F

58. Plot of the Force-deflection

60. ——relative stiffness of the bolt
F1—— resultant load on bolt
F—— external load
F'—— preload
K1——stiffness of the bolt
K2 ——stiffness of the connected members
——relative stiffness of the bolt

63. Example 4
As shown below, a bearing cap is attached to the housing by four screws, which made of 235 steel having the yield strength of 135Mpa, assuming the safety factor S=4, F''=0.4F, the external applied load F=20kN, Find the minor diameter of the screw.

64. Example 5
The cover of a pressurised cylinder is attached by 12 identical bolts. The fluid pressure is 0~1.2 Mpa,the relative stiffness of bolts is 0.8, let D=500mm,F''=1.5F, Find the maximum and minimum load on each bolt.

65. Example 6
A tightened bolt connecting is subject to varying axial load F=0~4000N，given preload F'=4000N，the stiffness of bolt and the clamped members is the same, Find:
1) The maximum and minimum load on bolt;
2) The maximum and minimum compression on the clamped members.

66. 5.9 Design of Screw Joints Subject to the Overturning Moment

67. Equilibrium condition:

69. Check the Extrusion Strength:
Check the Separating:

70. Example 6

71. Design for Fatigue Strength
Applied Force:
Forces felt by the bolt:
Amplitude of stress:
Factor of safety:

72. 5.13 Power Screws A power screw is a drive device which
used to convert rotary motion into linear motion.

73. Different Motion Types for Power Screws
a) screw rotating,
nut moving.
b) nut rotating,
screw moving.

74. c) screw rotating and
moving, nut is fixed.
d) nut rotating and
moving, screw is fixed.

75. Ball-bearing Screw

76. Design of Power Screws
1. Materials
2. Wear Criterion

77. 3. Self-lock Checking
4. Strength Criterion for Screw

78. 5. Strength Criterion for Nut

79. 6. Stability Condition

80. Design Project Title: Design a Screw Jack Request:
a assembly drawing（3#）
a design record

85. Force
Force
Deflection
Time
Time
Deflection

86. Vee thread
Pipe thread

87. Square thread
Trapezoidal thread
Buttress thread

88. Metric Thread Dimensions

89. single thread screw
double threads screw
triple threads screw

92. The end Thanks!