# Dme Material

Topics: Elasticity, Spring, Force Pages: 14 (3767 words) Published: April 15, 2013
Design of Machine Elements (ME1302)
2 Marks Question with Answers UNIT I
1. Define: Factor of safety The ratio between maximum stresses to working stress is known as factor of safety. Maximum stress Factor of safety = Working stress 2. Define endurance limit. Endurance limit is the maximum value of completely reversed stress that the standard specimen can sustain an infinite number (106) of cycles without failure. 3. What is impact load? If the time of load application is less than one third of the lowest natural period of vibration of the part, it is called an impact load. 4. 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 5. What are the different types of loads that can act on machine components? a. Steady load. b. Variable load. c. Shock load d. Impact load. 6. What are the factors affecting endurance strength. Factors affecting endurance strength are i. Load ii. Surface finish iii. Size iv. Temperature v. Impact vi. Reliability 7. What are the types of variable stresses? a. Completely reversed or cyclic stresses b. Fluctuating stresses c. Repeated stresses

8. Differentiate between repeated stress and reversed stress. Repeated stress refers to a stress varying from zero to a maximum value of same nature. Reversed stress of cyclic stress varies from one value of tension to the same value of compression. 9. What are the types of fracture? a. Ductile fracture b. Brittle fracture 10. Distinguish between brittle fracture and ductile fracture. In brittle fracture, crack growth is up to a small depth of the material. In ductile fracture large amount of plastic deformation is present to a higher depth. 11. Define stress concentration and stress concentration factor. Stress concentration is the increase in local stresses at points of rapid change in cross section or discontinuities. Stress concentration factor is the ratio of maximum stress at critical section to the nominal stress 12. 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 13. Explain Griffith theory. (Or) State the condition for crack growth. A crack can propagate if the energy release rate of crack is greater than crack resistance. 14. What are the modes of fracture? a. Mode I (Opening mode) – Displacement is normal to crack surface. b. Mode II (Sliding mode) – Displacement is in the plane of the plate. c. Mode III (Tearing mode) – Out of plane shear. 15. What are the factors to be considered in the selection of materials for a machine element? i. Required material properties ii. Manufacturing ease iii. Material availability Cost iv. 16. What are various theories of failure? i. Maximum principal stress theory. Maximum shear stress theory. ii. iii. Maximum principal strain theory.

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List out the factors involved in arriving at factor of safety i. material properties ii. nature of loads iii. presence of localized stresses iv. mode of failures

18. Give some methods of reducing stress concentration. i. Avoiding sharp corners. ii. Providing fillets. iii. Use of multiple holes instead of single hole iv. Undercutting the shoulder parts. 19. Explain notch sensitivity. State the relation between stress concentration factor, fatigue stress concentration factor and notch sensitivity. Notch sensitivity (q) is the degree to which the theoretical effect of stress concentration is actually reached. The relation is, Kf = 1 + q (Kt-1) 20. What are the factors that effect notch sensitivity? i. Material ii. Notch radius iii. Size of component iv. Type of loading v. Grain Structure 21. What is the use of Goodman & Soderberg diagrams? They are used to solve the problems of variable stresses....