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B.E./B.Tech. DEGREE EXAMINATION,NOVEMBERIDECEMBER2008.Fifth Semester(Regulation 2004)

Mechanical EngineeringME 1302 - DESIGN OF MACHINE ELEMENTS

(Common to B.E. (Part-Time) Fourth Semester - Regulation 2005)Time: Three hours Maximum: 100marks

Answer ALL questions.

Use of approved design data book is permitted.

Assumptions and assumed data have to be stated clearly.

PARTA - (10 x 2 = 20marks)1. Mention some standard codes of specification ofsteels.2. What are the methods to reduce stress concentration?3. What is the significance of slenderness ratio in shaft design?4. Under what circumstances flexible couplings are used.5. Name the possible modes of failure of riveted joint.6. What is the minimum size for fillet weld? If the required weld size from

strength consideration is too mall how will you fulfill the condition ofminimumweld size?

7. Give some ofthe materials used for springs.

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8. Why are levers usually tapered? Why a brass sleeve is used in lever fulcrum?9. What is meant by life of anti-friction bearings?10. Define coefficientoffluctuation ofspeed and energy.

PARTB - (5x 16 = 80marks)11. (a) (i) A flat bar 32 mm wide and 12 mm thick is loaded by a steady

tensile load of 85 kN. The material is mild steel with yield pointstress of 315 Nzmm-. Find the factor of safety based on the yieldpoint. (8)

(ii) Aflat plate ofwidth 60mm has a central hole of 10mm diameter. Ifthe plate is subjected to an axial tensile load of 10 kN, determinethe thickness of plate. Assume yield point stress 300 MPa andfactor of safety as 2.5. (8)

Or(b) A hot rolled steel shaft of 40 mm diameter is subjected to a torsional

moment that varies from 330 Nm to - 110 Nm and an applied bendingmoment which rises from 440Nm to - 220 Nm. The material of the shafthas an ultimate strength of 550MN/m2and yield strength of 410MN/m2Find the approximate factor of safety using Soderberg equation allowingendurance limit to be half the ultimate strength and size factor andsurface finish factor to be 0.85 and 0.62respectively.

12. (a) Design a hollow shaft to transmit 25 hp at 300 rpm. The loading is suchthat the maximum bending moment is 1000Nm the maximum torsionalmoment is 500 Nm and axial thrust is 15 kN. The shaft is supported onrigid bearings 1500 mm apart. The inside diameter of the shaft is0.8 times the outside diameter. The load is cyclic in nature and appliedwith shocks. The values ofshock factors are 1.5 and m 1.6.

Or(b) Design a protective type of cast iron flange coupling for a steel shaft

transmitting 15 kW at 200 rpm and having an allowable shear stress of40 Nzmm-.The working stress in the bolt should not exceed 30 Nzmm-.Assume that the same material is used for shaft and key that thecrushing stress is twice the value of its shear stress. The maximumtorque is 25greater than the full load torque. The shear stress for castiron is 14Nzrnm-.

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13. (a) The structural connection shown in fig. 1 is subjected to an eccentricforce P of 10 kN with an eccentricity of 500 mm. The centre distancebetween bolts 1 and 2 is 200 mm and 1 and 3 is 150mm. All the bolts areidentical. Assume 80 Nzmm-for bolt material. Design the size of thebolts.

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Fig. 1

Or(b) A shaft of rectangular cross section is welded to a support by means of

fillet welds as shown in fig. 2. Determine the size of the weld, if thepermissible shear stress in the weld is limited to 75Nzrnm-.

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Fig. 2 .

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14. (a) Design a leaf spring for a truck to the followingspecifications:Maximum load on the spring 140kNNumber ofspring = 4Material Chromium vanadium steelPermissible tensile stress 600 Nzrnm-Maximum number ofleaves = 10Span ofspring = 1000mmPermissible deflection 80 mmYoung's modulus ofthe spring = 2 x 105 Nzmm''

Or(b) A hand lever is 1 m from centre of shaft to the point of application of

200 N calculate(i) Diameter of solid shaft allowable shear stress is 25 Nzmm-(ii) What is the twist of shaft per meter length?(iii) Determine the section of the lever near the boss, if the permissible

stress is limited to 75 Nzrnm''.(iv) Distance moved by the point of application of the load due to

elasticity of the shaft. Modulus of rigidity is 0.84 x 105 Nzmm.Take length of the shaft is 3 m.

15. (a) A full journal bearing of 50 mm diameter and 10mm long has a bearingpressure of 1.4Nzmm-.The speed of the journal is 900 rpm and the ratioof journal diameter to the diametral clearance is 1000. The bearing islubricated with oil whose absolute viscosity ofthe operating temperatureof 75C may be taken as O.Ollkg/msec. The room temperature is 35C.Find .(i) the amount ofartificial coolingrequired and(ii) the mass of lubricating oil required if the difference between the

outlet and inlet temperature of oil is 10C. Take specificheat of oilas 1850J/kg/C.

Or(b) A single cylinder double acting steam engine delivers 187.5 kW at

100 rpm. The maximum fluctuation of energy per revolution is 15.Thespeed variation is limited to 1either way from the mean. The meandiameter of the rim is 2.4 m. Design a cast iron flywheel for the engine.

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