Formula Sheet: Cotter and Knuckle Joint | Design of Machine Elements - Mechanical Engineering PDF Download

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Cotter and Knuckle Joint Formula Sheet
1. Cotter Joint (for axial tensile or compressive load)
Used to connect two coaxial rods.
(a) Failure Modes of Rod and Cotter
• Tensile failure of rod: P =
p 4
d
2
s t
• Shear failure of cotter: P = 2btt
• Crushing failure of cotter: P = 2bts
c
(b) Failure of Spigot End
• Tearing across slot: P =

p 4
D
2
- d
1
t
2


s t
• Shearing of spigot collar: P =pd
1
tt
• Crushing of spigot collar: P =pd
1
ts
c
(c) Failure of Socket End
• Tearing across slot: P =

p 4
(d
2
2
- d
2
)- d
1
t

s t
• Shearing of socket collar: P =pd
2
tt
• Crushing of socket collar: P =pd
2
ts
c
Design Symbols:
• d = rod diameter, d
1
= diameter at slot, d
2
= outer socket dia
• t = thickness of cotter, b = width of cotter
• s t
= allowable tensile stress
• t = allowable shear stress
• s c
= allowable crushing stress
2. Knuckle Joint (for tensile load only)
Used to connect two rods under tensile load with angular motion allowed.
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Page 2


Cotter and Knuckle Joint Formula Sheet
1. Cotter Joint (for axial tensile or compressive load)
Used to connect two coaxial rods.
(a) Failure Modes of Rod and Cotter
• Tensile failure of rod: P =
p 4
d
2
s t
• Shear failure of cotter: P = 2btt
• Crushing failure of cotter: P = 2bts
c
(b) Failure of Spigot End
• Tearing across slot: P =

p 4
D
2
- d
1
t
2


s t
• Shearing of spigot collar: P =pd
1
tt
• Crushing of spigot collar: P =pd
1
ts
c
(c) Failure of Socket End
• Tearing across slot: P =

p 4
(d
2
2
- d
2
)- d
1
t

s t
• Shearing of socket collar: P =pd
2
tt
• Crushing of socket collar: P =pd
2
ts
c
Design Symbols:
• d = rod diameter, d
1
= diameter at slot, d
2
= outer socket dia
• t = thickness of cotter, b = width of cotter
• s t
= allowable tensile stress
• t = allowable shear stress
• s c
= allowable crushing stress
2. Knuckle Joint (for tensile load only)
Used to connect two rods under tensile load with angular motion allowed.
1
Cotter & Knuckle Joints
(a) Failure Modes
• Tensile failure of rod: P =
p 4
d
2
s t
• Shear of pin: P =
p 4
d
2
p
t • Crushing of pin: P =d
p
× t
1
× s c
• Tearing of eye: P = (d
e
- d
p
)· t· s t
• Shearing of eye: P = 2· d
p
· t· t • Tearing of fork: P = 2(d
f
- d
p
)· t· s t
• Shearing of fork: P = 2· d
p
· t· t Design Symbols:
• d = rod diameter, d
p
= pin diameter
• t = thickness of eye/fork arm, t
1
= eye thickness
• d
e
= outer diameter of eye, d
f
= outer diameter of fork
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