DESIGN OF KNUCKLE JOINT(BASICS)

KNUCKLE JOINT

·         Knuckle join is used to connect two rods whose axes are either coincide or intersect and lie in one plane.

·         The construction of this joint permits limited relative angular movement between rods in this plane about the axis of the pin.

·         The rods connected by knuckle joint are subjected to tensile force.

APPLICATION

·         Joint between the links of suspension bridge.

·         Joint in valve mechanism of reciprocating engine.

·         Fulcrum for levers.

·         Joint between tie bars in roof stress.

Knuckle joint is unsuitable to connect two rotating shaft which transmit torque.

ADVANTAGES

·         The joint is simple to design and manufacture.

·         The assembly or dismantling of parts of knuckle joint is quick and simple.

For the purpose of stress analysis of knuckle joint following assumptions are made:

i)          The rods are subjected to axial tensile force.

ii)         The effect of stress concentration due to holes is neglected.

iii)        The force is uniformly distributed in various parts

1.          Tensile Failure of Rods

             Each rod is subjected to tensile force P.  The tensile stress in rod is given by.

            

             The enlarged diameter D₁ of the rod near the joint is determined by

             D₁ = 1. 1 D

2.          Shear failure a pin:

             The pin is subjected to double shear.  The area of each of the two planes that resists shear failure is .

            

            

3.          The crushing of pin in Eye:

             When a cylindrical surface such as pin is subjected to force along its periphery, its projected area is taken into consideration, to find out the stress.  The projected area of the cylindrical surface is (l × d).

            

4.          Crushing Failure of pin in Fork:

             The total projected area of the pin in the fort is (2 ad) and compressive stress between the pin and fork is given by

            

5.          Bending Failure of pin:

            

6.          Tensile Failure of Eye

            

7.          Shear failure of eye

             The eye is subjected to double shear.  The area of each of the two planes resulting shear failure is

            

            

8.          Tensile Failure of Fork:

            

9.          Shear failure of Fork:

            

             a = 0.75 n

             b = 1.25 D

             d₁ = 1.5 d

             x = 10 mm

REFERENCES

1. Mechanical Engg. Design                               –          Joseph Shigley
2. Machine Design                                              –          Mubeen
3. Machine Design                                              –          Black
4. Machine Design                                              –          R. K. Jain
5. Machine Design an integral approach             –          Norton, Pearson
6. Machine Design data hand book                                –          Lingayah Vol I.
7. Elements of Machine Design                         –          Pandya & Shah