Design of machine elements

1. Unit - 3
KNUCKLE JOINT

2. • A knuckle joint is used to connect two rods
which are under the action of tensile loads.
• It consists of mainly three elements a fork
or double eye rod, a single eye rod and
knuckle pin.
• Its use may be found in the link of a cycle
chain, tie rod joint for roof truss

3. Knuckle joint Two or more rods subjected to tensile and
compressive forces are fastened together
Their axes are not in
alignments but meet in a point
The joint allows a small
angular moment of one
rod relative to another
It can be easily
connected and
disconnected
Applications: Elevator chains, valve rods, etc

8. Knuckle Joint

9. 1.Failure of solid rod in tension
Due to tensile load , the rods are subjected to tensile
stresses, and may fail if this stress exceeds the limit

10. 2.Failure of Knuckle Pin in Double
shear

11. The rod may tear along a plane passing through
the pin axis
3.Failure of the single eye or rod end
in tension

12. The rod end may be sheared off as shown in fig.
The resisting stress is
4.Failure of the single eye or rod end
in double shear

13. 5. Failure of single eye or rod end in
crushing
Due to tension load , the eye end may be crushed to failure. The area resisting
crushing is taken as the projected area and the corresponding stress is related to
the tensile load is

14. 6. Failure of forked end in Tension
The fork end may fail in tension across the pin hole

15. 7. Failure of forked ends in double shear
(as shear of eye)

16. 8. Failure of forked ends in Crushing
(as Crushing of eye)
The forked end is weak in crushing than in other modes,
it will result in crushing Failure

17. 9. Failure of Knuckle pin by Bending
• The loosely fitted knuckle pin experiences
bending.
• The load on pin uniformly varies over the pin area
in the fork.
• Maximum bending is at the mid of the pin.