INTERVIEW SHORT QUESTION ANSWERS-JOINTS

INTERVIEW SHORT QUESTION ANSWERS -JOINTS

Q. List the assumptions used in the design of riveted joints.

A.

Assumptions

  • Load is equally distributed in all the rivets.
  • Rivets are in shear only.
  • There is no bending of rivets.
  • Tensile force is equally distributed in the plate section between the
  • Analysis is done for 1 largest pitch of the rived joint.
  • The rivet fills the hole completely after it has been driven ( the other head is made).

 

Q.What are the methods to increase the fatigue strength of bolted joints?

A.

Bolted joints are very common in the construction of structures and machines. Mostly Bolts are under fluctuating tension which causes fatigue. But there fatigue strength is less. Therefore chances of crack initiation and propagation are bright. Thus fatigue strength needs to be increased.

Steps to increase fatigue strength

  • Rolled bolt threads have longer fatigue life than normally cut threads.
  •  HEAT treatment is necessary for threads. This heat treatment induces compressive stresses in the roots of the threads which increases the fatigue life.
  • On the larger size of bolts, initial compressive stresses can be easily achieved by shot peeing because it is more costly by rolling on larger size of bolts.
  • Nuts should have two or more than two thread pitches distance from threads run out region to increase fatigue life. It normally doubles the fatigue life.
  • By increasing the minimum root radius to 0.15 p instead of normal 0.125 p increases the fatigue life.
  • Mounting of bolts straight increases fatigue life. Even a small angle of tilt in mounting reduces the fatigue life significantly.
  • Asymmetric thread profile in the nut  increases the fatigue life by 20 %.
  • Use of different material of nut with higher Young’s modulus increases the fatigue life.
  • Tighten the bolt very firmly to increase fatigue life.

Q.What are the advantages and disadvantages of cotter joints?

A.

ADVANTAGES

  •  Easy to design and manufacture.
  •  Assembling and dissembling is easy.
  • Tightening force is very high due to wedge action. It prevents the loosening of parts.

DISADVANTAGES OF COTTER JOINTS

  • It cannot connect two shafts having rotary motion.
  • Rods of rectangular sections cannot be connected by a cotter joint.
  • It does not allow any angular alignment between the two rods being connected.

Q. List the assumptions used in the design of riveted joints.

A.

Assumptions

Load is equally distributed in all the rivets.

  • Rivets are in shear only.
  • There is no bending of rivets.
  • Tensile force is equally distributed in the plate section between the
  • Analysis is done for 1 largest pitch of the rived joint.
  • The rivet fills the hole completely after it has been driven ( the other head is made).

Q.State the differences between Caulking and Fullering.

A.

Table Differences between Caulking and Fullering

Sr. No. Caulking Fullering
1.  makes the riveted joint leak proof Used to make the riveted joint leak proof
2. Thickness of Caulking tool is much less than the thickness of the plates. Thickness is roughly 5 mm. Thickness of Fullering tool is equal to the thickness of the plates.
3. Caulking tool is a blunt tool. Fullering tool is not a blunt tool.
4. It is for low pressure vessels.  Used for making joint leak proof joint in high pressure vessels.
5 It can harm the plates There is no harm to the plates being connected.
6. Less surface finish is obtained. More surface finish is obtained.

Q. What are the disadvantages of cast iron from design considerations?

A.

Cast iron is

(i) highly brittle.

(ii)  very weak in tension.

(iii)  has almost zero deform-ability or zero elongation.Thus it is difficult to give the desired shape to cast iron by cold or hot working (by forging).