Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech III Year PRINCIPLES OF MACHINE DESIGN Previous Question Paper (February - 2022 - R13)
Answer any FIVE Questions. All Questions carry Equal Marks.
Main
The principal stresses induced at a point in a machine component made of steel 50C4 (Syt = 460 N/mm2) are as follows: Maximum principal stress = 200 N/mm2 and Minimum principal stress = 150 N/mm2. Calculate the factor of safety by:
Maximum shear stress theory
Answer
According to the Maximum Shear Stress Theory (Guest's Theory), the factor of safety (FOS) is calculated by equating the maximum shear stress in the component to the shear yield strength of the material. For a two-dimensional stress state where the principal stresses are σ1 = 200 N/mm2 and σ2 = 150 N/mm2, the maximum shear stress is given by τmax = (σ1 - σ2) / 2 = (200 - 150) / 2 = 25 N/mm2. The shear yield strength is τy = Syt / (2 * FOS). Alternatively, the condition is σ1 - σ2 = Syt / FOS. Substituting the values: 200 - 150 = 460 / FOS. Therefore, FOS = 460 / 50 = 9.2.
Distortion energy theory
Answer
According to the Distortion Energy Theory (von Mises-Hencky Theory), the factor of safety is determined by the von Mises stress (σ') which must be less than or equal to the yield strength divided by the factor of safety. The formula for von Mises stress in a 2D state is σ' = sqrt(σ12 - σ1σ2 + σ22). Substituting the given values: σ' = sqrt(2002 - (200 * 150) + 1502) = sqrt(40000 - 30000 + 22500) = sqrt(32500) ≈ 180.28 N/mm2. The factor of safety is FOS = Syt / σ' = 460 / 180.28 ≈ 2.55.
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Explain Goodman and Soderberg’s methods for combination of stresses.
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Explain the design of welded joints subjected to axial load.
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Two plates 16 mm thick are joined by a double U butt weld and a single U butt weld. Determine the strength of the welded joint in tension in each case. Effective length of weld is 150 mm. Allowable stress in butt weld in tension is 142 N/mm2.
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Explain the design procedure for sleeve and cotter joint.
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What are the types of Keys? Explain them.
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What are the advantages and disadvantages of V-belt drive over flat belt drives?
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A pulley of 0.9m diameter revolving at 200 rpm is to transmit 7.5 kW find the width of a leather belt if the maximum tension is not to exceed 145 N in 10mm width. The tension in the tight side is twice that in the slack side. Determine the diameter of the shaft and the dimensions of the various parts of the pulley, assuming it to have six arms. Maximum shear stress is not to exceed 63 MPa.
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Select a wire rope for a vertical mine hoist to lift a load of 55kN from a depth 300 metres. A rope speed of 500 metres/min is to be attained in 10 seconds.
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Design a spur gear for transmitting 8kW power pinion speed = 764 rpm; speed ratio = 2; the gears are made up of C45 steel; life = 10000 hrs.
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Explain radial ball bearing in brief.
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A radial ball bearing has a basic load rating of 50 kN. If the desired rating life of the bearing is 6000 hrs. What equivalent radial load can the bearing carry at 500 rev/min.
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