Design of Machine Elements - B.Tech 6th Semester Exam., 2018

2018•Semester 3•Civil-CA•End Semester
Bihar Engineering University, Patna
B.Tech 6th Semester Exam., 2018

Design of Machine Elements

Time: 3 hoursCode: 021615Full Marks: 70

Instructions:

  1. The marks are indicated in the right hand margin.
  2. There are NINE questions in this paper.
  3. Attempt FIVE questions in all.
  4. Question No. 1 is compulsory.
Q.1 Choose the correct option (any seven):[14]

  1. Steels used for automobile bodies and hoods are

    1. medium carbon steel
    2. mild steel
    3. high carbon steel
    4. alloy steel

  2. Material used for self-lubricated bearing is

    1. acetal
    2. polyurethane
    3. polytetrafluoroethylene (Teflon)
    4. Any one of the above

  3. In forged components

    1. fiber lines arranged in a predetermined way
    2. fiber lines of rolled stock are broken
    3. there are no fiber lines
    4. fiber lines are scattered

  4. When a circular shaft is subjected to torque, the torsional shear stress is

    1. maximum at the axis of rotation and zero at the outer surface
    2. uniform from axis of rotation to the outer surface
    3. zero at the axis of rotation and maximum at the outer surface
    4. zero at the axis of rotation and zero at the outer surface and maximum at the mean radius

  5. The thermal stresses are caused due to

    1. variation in temperature
    2. high temperature
    3. specific heat
    4. latent heat

  6. A stress that varies in sinusoidal manner with respect to time from tensile to compressive (or vice versa) and with zero mean is called

    1. reversed stress
    2. fluctuating stress
    3. repeated stress
    4. varying stress

  7. In order to find the endurance limit, the rotating beam specimen is subjected to

    1. repeated stresses
    2. reversed stresses
    3. fluctuating stresses
    4. maximum stress

  8. In design of screw jack from buckling considerations, the end conditions are assumed as

    1. both ends are hinged
    2. both ends are fixed
    3. one end fixed and other hinged
    4. one end fixed and other free

  9. In the running condition, the net force acting on the drum of centrifugal clutch is equal to

    1. the centrifugal force on shoe
    2. the centrifugal force on shoe minus spring force
    3. the centrifugal force on shoe plus spring force
    4. the spring force

  10. The maximum shear stress in spring wire is induced at

    1. inner surface of the coil
    2. outer surface of the coil
    3. central surface of the coil
    4. end coils
Q.2 Solve both questions:[14]

  1. What are the factors to be considered for selection of engineering materials for a machine component? Discuss the important manufacturing considerations in machine design.

  2. How will you select direction of fiber lines in forged components?

Q.3 Solve this question:[14]

  1. The force acting on a bolt consists of two components - an axial pull of \( 12 \text{ kN} \) and a transverse shear force of \( 6 \text{ kN} \). The bolt is made of steel having \( S_{yt}=310 \text{ N/mm}^2 \) and factor of safety is 2.5. Determine the diameter of the bolt using the maximum shear stress theory of failure.

Q.4 Solve this question:[14]

  1. A rotating bar made of steel having \( S_{ut}=620 \text{ N/mm}^2 \) is subjected to completely reversed bending stress. The corrected endurance limit of the bar is \( 310 \text{ N/mm}^2 \). Calculate the fatigue strength of the bar for a life of \( 1,00,000 \) cycles.

Q.5 Solve this question:[14]

  1. A forged steel bar of \( 55 \text{ mm} \) diameter is subjected to a reversed bending stress of \( 260 \text{ N/mm}^2 \). The bar is made of 40C8 steel \( (S_{ut}=610 \text{ N/mm}^2) \). Calculate the life of the bar for a reliability of 90%.

Q.6 Solve this question:[14]

  1. A transmission shaft carries a pulley midway between the two bearings. The bending moment at the pulley varies from \( 200 \text{ N-m} \) to \( 600 \text{ N-m} \), as the torsional moment in the shaft varies from \( 70 \text{ N-m} \) to \( 200 \text{ N-m} \). The frequencies of variation of bending and torsional moments of steel FeE 400 \( (S_{yt}=400 \text{ N/mm}^2 \) and \( S_{ut}=540 \text{ N/mm}^2) \). The corrected endurance limit of the shaft is \( 210 \text{ N/mm}^2 \). Determine the diameter of the shaft using a factor of safety of 2.5.

Q.7 Solve this question:[14]

  1. The layout of a wall crane and the pin-joint connecting the tie-rod to the crane post is shown. The tension in the tie rod is maximum, when the load is at a distance of \( 2 \text{ m} \) from the wall. The tie-rod and the pin are made of steel having \( S_{yt}=250 \text{ N/mm}^2 \) and factor of safety is 3.0. Determine the diameter of the tie rod and the pin.

    Question Diagram
Q.8 Solve this question:[14]

  1. A gearbox weighing \( 6 \text{ kN} \) is provided with a steel eyebolt for lifting and transporting on the shop floor. The eyebolt is made of 30C8 steel \( (S_{yt}=380 \text{ N/mm}^2) \) and factor of safety is 5. Determine the nominal diameter of the eyebolt having coarse threads if \( d_c=0.8d \) where \( d_c \) and \( d \) are the core and major diameters respectively.

Q.9 Solve this question:[14]

  1. A cylindrical pressure vessel with a \( 0.8 \text{ m} \) inner diameter is subjected to an internal steam pressure of \( 2 \text{ MPa} \). The permissible stresses for cylinder plate and rivets in tension, shear and compression are \( 80 \), \( 60 \) and \( 120 \text{ N/mm}^2 \) respectively. The efficiency of longitudinal joint can be taken as 80% for calculating the plate thickness. The corrosion allowance is \( 2 \text{ mm} \). The efficiency of circumferential lap joint should be at least 62%. Design the circumferential lap joint and calculate the thickness of plate, diameter of the rivets, number of rivets and pitch of rivets.