Unit 3---knuckle joint--

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

4. Knuckle Joint

5. 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

6. 2.Failure of Knuckle Pin in Double shear

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

8. 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

9. 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

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

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

12. 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

13. 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.