JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year PRINCIPLES OF MACHINE DESIGN Previous Question Paper (November/December - 2018 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
Give the composition of 35 Mn 2 Mo 45 steel.
Answer
The composition of 35 Mn 2 Mo 45 steel is: Carbon (C) = 0.30% to 0.40% (average 0.35%), Manganese (Mn) = 1.30% to 1.80% (approx 2%), and Molybdenum (Mo) = 0.15% to 0.25%.
Write R20 series and R20/3 series for numbers between 10 and 100.
Answer
The R20 series (preferred numbers) between 10 and 100 are: 10, 11.2, 12.5, 14, 16, 18, 20, 22.4, 25, 28, 31.5, 35.5, 40, 45, 50, 56, 63, 71, 80, 90, 100. The R20/3 series (taking every third number) are: 10, 14, 20, 28, 40, 56, 80.
Draw schematic diagram of Gib-head key. List its uses.
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Show by neat sketches the various ways in which a riveted joint may fail.
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Differentiate between simplex and duplex chains.
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Enumerate the advantages and disadvantages of V-belt drive over flat belt drive.
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List the assumption made in Lewis equation to find the beam strength of gear teeth.
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Define formative or virtual number of teeth on a helical gear.
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What are the commonly used materials for sliding contact bearings?
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How do you express the life of a bearing? What is median life?
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Part B
Derive the relationship between the yield strength in shear and the yield strength in tensile using the Maximum shear stress theory.
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A mild steel shaft is to transmit 100 kW at 200 rpm. The allowable shear stress in the shaft is limited to 40 MPa and the angle of twist is not to exceed 1 degree in a length of 20 diameters. Calculate the suitable diameter for the shaft.
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Draw and explain S-N Curve. What is the difference between S-N Curve for ferrous and non-ferrous components?
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Calculate the fatigue strength for the specimen made of 30C8 steel with endurance strength 280 MPa and ultimate strength 600 MPa for a life of 200000 cycles of stress reversals. What would be the life of a specimen, if the fluctuating reversible stress is taken as 420 MPa?
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A bracket is riveted to a column by 6 rivets of equal size. It carries a load of 100 kN at a distance of 250 mm from the column. If the maximum shear stress in the rivet is limited to 60 MPa, find the diameter of the rivet.
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Design and draw a cotter joint to support a load varying from 30 kN in compression to 30 kN in tension. The material used is carbon steel for which the following allowable stresses may be used: Tensile stress = compressive stress = 50 MPa; Shear stress = 35 MPa and crushing stress = 90 MPa.
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A V-belt drive is required to transmit 10 kW of power to a compressor. The motor runs at 1440 rpm and the speed reduction is 3. Design the belt drive.
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The following data is given for a flat belt drive transmitting 6 kW of power at 1400 rpm. Speed of the driven pulley is 450 rpm and the maximum permissible peripheral speed is 16 m/s. Assume 3% of creep; load factor 1.2; density of the belt material = 980 kg/m3; modulus of elasticity for the belt = 100 MPa, ultimate strength = 25 MPa; centre distance = 2.8 m and endurance limit for the belt material is 4 MPa. Design for belt.
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A motor shaft rotating at 1440 rpm has to transmit 15 kW to a low speed shaft rotating at 500 rpm. The teeth are 20° involute with 25 teeth on the pinion. Both the pinion and gear are made of cast iron with a maximum safe stress of 56 MPa. A safe stress of 35 MPa may be taken for the shaft on which the gear is mounted. Design and sketch the spur gear drive to suit the above conditions. The starting torque may be assumed as 1.25 times the running torque.
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Explain the different causes of gear tooth failures and suggest possible remedies to avoid such failures.
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A pair of helical gears is to transmit 15 kW. The pinion runs at 10000 rpm and has 80 mm pitch diameter. The gear has 320 mm pitch diameter. Determine the tangential tooth load on the pinion and the gear. Also find the number of teeth and formative number of teeth on the pinion if the module is 2.5 mm and helix angle of 45°.
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What are the various non dimensional terms used in bearings analysis and design? Give their definitions in brief.
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Write a short note on materials used for bearing.
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Define the terms: static load capacity, dynamic load capacity and life of the bearing.
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Select a single row deep groove ball bearing for a radial load of 4000 N and an axial load of 5000 N, operating at a speed of 1600 rpm for an average life of 5 years at 10 hours per day. Assume uniform and steady load.
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