Design of machine elements university questions

This post covers the unit wise important questions asked by the Anna University, Chennai for the subject ME6503 Design of Machine Elements.  

Unit 1 Steady Stresses and Variable Stresses in Machine Members

Syllabus:

Introduction to the design process- Factors influencing machine design, selection of materials based  on mechanical properties-preferred numbers, fits and tolerances-Direct, bending and torsion stress equations-Impact and shock loading-Calculation of principle stresses for various load combinations, eccentric loading-curved beams-crane hook and C frames-factor of  safety-theories of failure-design based strength and stiffness-stress concentration-design for variable loading.

Unit 1 Steady Stresses and Variable Stresses in Machine Members

Part-A (2 Marks)

1.     What are the factors to be considered while design process?

2.     What are the factors influencing machine design?

3.     What are the mechanical properties were used while selecting the materials?

4.     What are preferred numbers?

5.     Define fits and tolerance with its types.

6.     Write the bending and torsion equations.

7.     Differentiate impact and shock loading.

8.     What do you meant by factor of safety?

9.     Define stress concentration factor.

10.   What are the theories of failure used in design process?

11.   Define stress concentration.

12.   What is meant by curved beams? Give its types.

13.   List the various steps involved in the design of a machine element?

14.   State difference between straight beams and curved beams?

          Part-B (16 Marks)

1. A hot rolled steel shaft is subjected to a torsion moment that varies from 330Nm clockwise to 110Nmcounter clockwise and an applied bending moment at a vertical section and no keyway is present at the critical section. Determine the required shaft diameter .the material has an ultimate strength of 550Mpa and yield strength of 410Mpa.take the endurance limit as half the ultimate strength, factor of safety of 2, size factor of 0.85 and a surface finish factor of 0.62

2. A bar of circular cross-section is subjected to alternating tensile forces varying from a  drawn diameter of the bar using safety factors of 3.5 related to ultimate tensile strength and 4 related to an durance limit and a stress concentration factor of 1.65 for fatigue load. Use Goodman  straight line as basis for design.

3. A hollow shaft of 40mm outer diameter and 25mm inner diameter is subjected to a twisting moment of 120 N-m, simultaneously; it is subjected to an axial thrust of 10Kn and a bending moment of 80N-m.calculate the maximum compressive and shear stresses.

4. A pulley is keyed to a shaft midway between two bearings. The shaft is made of cold drawn steel for which the ultimate strength is 550MPa and the yield strength is 400Mpa. The bending moment at the pulley varies from -150N-m to +400Mpa.as the torque on the shaft varies from -50Nm to +150Nm. obtain the diameter of the shaft for an indefinite life. The stress concentration factors for the keyway at the pulley in bending and in torsion are 1.6 and 1.3 respectively. Take the following values: factor of safety =1.5; load correction factors=1.0 in bending, and 0.6 in torsion; size effect factor=0.85; surface effect factor=0.88.

5. A hollow shaft is required to transmit 600kW at 110 r.p.m., the maximum torque being 20% greater than  the mean. The shear stress is not to exceed 63MPa and twist in a length of 3 meters not to exceed 1.4 degrees .find the external diameter of the shaft, if the internal diameter to the external diameter is 3/8. Take modulus of rigidity as 84GPa.

6. A Machine component is subjected to fluctuating stress that varies from 40 to 100N/mm2. The corrected endurance limit stress for the machine component is 70N/mm2. The ultimate tensile strength and yield strength of material are 600 and 450N/m2 respectively .find the factor of safety using: (a).Gerber theory; (b) Soderberg line; (c). Goodman line; and (d). Also, find factor of safety against static failure.

7. A Pulley is keyed to a shaft midway between two anti-friction bearings. The bending moment at the pulley varies from -170Nm to 510Nm as the torsional moment in the shaft varies from 55N m to 165Nm.The frequency of variation of the loads is the same as the shaft speed. The shaft is made of cold drawn steel having an ultimate strength of 538Mpa and yield strength of 400Mpa. Determine the required diameter for an infinite life. The stress concentration factor for the keyway in bending and torsion may be taken as 1.6 and 1.3 respectively. Use design factor N=1.5

8. A bolt is subjected to a tensile load of 25 KN and to a shear load of 10KN. suggest a suitable size of a bolt according to various theories of failure. Take allowable yield stress is 300N/mm2, Poisson’s ratio is 0.25

9. A 50 mm diameter shaft is made from carbon steel having ultimate tensile strength of 600Mpa. It is subjected to a torque which fluctuates between2000 N-m to -900N-m. Using soderberg method calculates the factor of safety.

10. (i) What are the factors influencing machine design? Explain it.

      (ii) Write short notes on the following:

       a. interchangeability       b. tolerance       c. allowance