III B.Tech I Semester Regular Examinations, November - 2017

DESIGN OF MACHINE MEMBERS-I

(Mechanical Engineering)

Time: 3 Hours Max. Marks: 70

Note: 1. Question Paper consists of two parts (Part-A and Part-B)

2. Answer ALL the question in Part-A

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3. Answer any THREE Questions from Part-B

PART-A

1. a) Define Principal stress and Principal plane. (2M)
   b) What are the factors to be considered while selecting the material for a machine element? (2M)
   c) Write about types of keys. (2M)
   d) What is the effect of keyway cut into the shaft? (2M)
   

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   e) Write the advantages of welded joints over threaded joints. (2M)
   f) What is self-locking of power screw? (2M)
   g) Explain about surge in springs. (2M)

PART-B

1. A mild steel bracket as shown in below figure is subjected to a pull of 20 KN acting at 45° to the vertical plane. Determine the tensile and shear stresses on the plane containing the bolt. (14M)
   
   

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2. A shaft is supported on bearings A and B, 800 mm between centers. A 20° straight tooth spur gear, 250 mm pitch diameter, is located 200 mm to the right of the left hand bearing A, and a 700 mm diameter pulley is mounted 250 mm to the left of bearing B. The gear is driven by a pinion with a downward tangential force while the pulley drives a horizontal belt having 180° wrap angle. The pulley also serves as a flywheel and weighs 2000 N. The maximum belt tension is 3000 N and the tension ratio is 3:1. Determine the maximum bending moment and the necessary shaft diameter if the allowable shear stress of the material is 40 MPa. (14M)
3. Design a muff coupling to connect two steel shafts transmitting 25 kW at 360 r.p.m. The material for the shafts and key is plain carbon steel for which allowable shear and crushing stresses may be taken as 44 MPa and 115 MPa respectively. The material for the muff is cast iron for which the allowable shear stress may be taken as 15 MPa. (14M)
4. A bracket, as shown in below figure, is fixed to a vertical steel column by means of five standard bolts. Determine:
   (i) The diameter of the fixing bolts;
   

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   (ii) The thickness of the bracket arm.
   Assume working stresses of 70 MPa in tension and 50 MPa in shear. (14M)
   
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5. Design a helical compression spring for a maximum load of 1000 N for a deflection of 25 mm. The spring index can be taken as 5. The ultimate tensile strength of the material of the spring is 1070 MPa and permissible shear stress is 50% of it. (14M)

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