# Machine Design Basic | Interview Question and Answers

### Machine Design Basic – Interview ,viva , Objective Question and Answers

1. Define design.

Design is a process of activities to gather all the information necessary to realize the designer’s idea as real product.

2. What are the various phases of design process?

(i) Recognition of need
(ii) Definition of problem
(iii) Synthesis
(iv) Analysis and optimization
(v) Evaluation
(vi) Presentation

3. List some factors that influence machine design.

(i) Strength and stiffness
(ii) Surface finish and tolerance
(iii) Manufacturability
(iv) Economic and aesthetics
(v) Working atmosphere
(vi) Safety and reliability cost

4. Define optimization?

Optimization is the process of maximizing a desired quantity or minimizing the unwanted one.

5. What are the various optimization methods available?

(i) Optimization by evaluation
(ii) Optimization by intuition
(iii) Optimization by trial& error
(iv) Optimization by numerical algorithm

6. Describe material properties hardness, stiffness and resilience.

• Hardness is the ability of material to resist scratching and indentation Stiffness is the ability of material to resist deformation under loading.
• Resilience is the ability of material to resist absorb energy and to resist shock and impact load.

7. What is an impact load? Give examples.

If the time load application is less than one third of the lowest national period of vibration of the part, the load is called an impact load. Example: Punching presses, hammers, loads exerted on cams during the motion due to eccentricity, loads imposed on gear teeth due to irregular tooth profile.

8. Define principal plane and principal stresses?

A plane where only normal stresses act, with no shear stress acting is called principal plane. The (normal) stress acting on this plane is called principal stresses.

9. Define factor of safety?

The ratio between maximum stresses to working stress is known as factor of safety.
Factor of safety= Maximum stress/ working stress

10. What are the factors to be considered in the selection of material for a machine element?

a. Required material properties
b. Manufacturing ease
c. Material availability
d. Cost

11. Why normal stress theory is not suitable for ductile materials?

Ductile materials mostly fail by shearing. But this theory considers only tensile or compressive stresses. So this is not suitable for ductile materials.

12. State the various methods of finding stresses concentration factors?

a. Photo elasticity method
b. Grid method
c. Brittle coating method
d. Strain gauge method
e. Finite element techniques

13. Give some methods of reducing stress concentration?

a. Avoiding sharp corners
b. Providing fillets
c. Use of multiple holes instead of single holes.

14. What are the factors that affect notch sensitivity?

a. Materials
c. Size of component
e. Grain Structure

15. What are the types of variable stresses?

a. Completely reverse or cyclic stresses
b. Fluctuating stresses
c. Repeated stresses
d. Alternating stresses

16. What are the various theories of failure?

a. Maximum principal stress theory
b. Maximum shear stress theory
c. Maximum principal strain theory
d. Maximum strain energy theory

17. Explain size factor in endurance strength?

Size factor is used to consider the effect of the size on endurance strength. A large size object will have more defects compared to a small one. So endurance strength is reduced.

If K is the size factor,
Actual endurance strength = theoretical endurance limit x K

18. What are the methods used to improve fatigue strength?

(i) Cold working like short peening, burnishing
(ii) Heat treatments like induction hardening
(iii) Pre stressing

19. What is an S-N curve?

An S-N curve has fatigue stress on Y- axis and number of loading cycles in X- axis. It is used to find the fatigue stress value corresponding to a given number of cycles.

20 What is low and high cycle fatigue?

Fatigue within 10 ^3  cycles is known as low cycle fatigue. Fatigue at high number cycles is called high cycle fatigue.