INTERVIEW SHORT QUESTION ANSWERS-MACHINE DESIGN            Fatigue life-1          Torsion assignment           PTU SOM Paper Sol          Mech Properties-2


Definition of design

It is a process to create an object/machine to perform the required function satisfactorily over a reasonable period of time (life) with minimum cost.

Definition of design synthesis

It is a process to find various alternatives of a product/mechanism  to achieve the desired function satisfactorily over a reasonable period of time.

Definition of design analysis

It is a process of optimization to decide the best alternative to achieve the desired objective having reasonable life with minimum cost.

Q. What is meant by Adaptive Design?


In short, it is copying the existing design. It is used for the design of parts where the chances of further improvements are least. So it is said to adapt the existing design.

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


(i) Cast iron is highly brittle.

(ii) Cast iron is very weak in tension.

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

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


Bolted joints are very common in the construction of structures and machines. Bolts in the bolted  joints 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.

It can be achieved by the following steps.

  • Rolled bolt threads have longer fatigue life than normally cut threads.
  • Rolling of threads should be done after the HEAT treatment. 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 threads such as Spiralock threads 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.Explain the criterion for the SELECTION OF MATERIAL in design.


In engineering, there are two types of materials available. These are brittle and ductile materials. The selection depends upon the various desirable physical, chemical, mechanical and economic properties. These properties are well known and are easily available in literature.

Physical properties include boiling point, melting point, density, dielectric constant, specific heat, thermal conductivity, electrical conductivity, viscosity, magnetic permeability, refractive index, solubility etc.

Chemical properties include toxicity, corrosiveness, inflammability, inertness, stability etc.

Mechanical properties include tensile strength, compressive strength, bending strength, torsional strength, buckling strength, stiffness, ductility, brittleness, malleability etc.

Economical properties include initial cost and manufacturing cost, tendency to contaminate etc.

How do you classify machine design?


(i) Copied design

(ii) Improved design

(iii)Innovative design

Q.List the qualities of a good designer.


The  traits of a good designer are

(i) Good communication skill

(ii) good imagination

  • Good observation
  • Good listener
  • Great self confidence
  • Love art and nature
  • Creative mind
  • Flexible
  • Cooperative nature
  • Technically qualified
  • Good clarity about color and texture of materials
  • Great visionary
  • Problem solver
  • Logical thinking and reasoning
  • Thick skin to digest criticism

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



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


  • 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.