Design of Machine Elements - B.Tech 6th Semester Exam., 2022 (New Course)
Design of Machine Elements
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
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18/8 steel contains
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The parts of circular cross-section which are symmetrical about the axis of rotation are made by
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The ratio of linear stress to linear strain is called
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Two shafts will have equal strength, if
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A line joining the centres of rivets and parallel to the edge of the plate is known as
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In transverse fillet welded joint, the size of weld is equal to
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A spring used to absorb shocks and vibrations is
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The material used for lining of friction surfaces of a clutch should have ________ coefficient of friction.
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A brake commonly used in motorcars is
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The number of starts on the worm for a velocity ratio of 40 should be
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State the advantages and disadvantages of hot working of metals. Discuss any two hot working processes.
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A steel rod of \( 20 \text{ mm} \) diameter passes centrally through a copper tube of external diameter \( 40 \text{ mm} \) and internal diameter \( 20 \text{ mm} \). The tube is closed at each end with the help of rigid washers (of negligible thickness) which are screwed by the nuts. The nuts are tightened until the compressive load on the copper tube is \( 50 \text{ kN} \). Determine the stresses in the rod and the tube, when the temperature of whole assembly falls by \( 50^\circ\text{C} \). Take \( E_s = 200 \text{ GPa} \); \( E_c = 100 \text{ GPa} \); \( \alpha_s = 12 \times 10^{-6}/^\circ\text{C} \) and \( \alpha_c = 18 \times 10^{-6}/^\circ\text{C} \).
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How is the shaft designed when it is subjected to twisting moment only?
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A mild steel shaft transmits \( 20 \text{ kW} \) at \( 200 \text{ r.p.m.} \). It carries a central load of \( 900 \text{ N} \) and is simply supported between the bearings \( 2.5 \text{ meters} \) apart. Determine the size of the shaft, if the allowable shear stress is \( 42 \text{ MPa} \) and the maximum tensile or compressive stress is not to exceed \( 56 \text{ MPa} \). What size of the shaft will be required, if it is subjected to gradually applied loads?
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Classify the rivet heads according to Indian Standard specifications.
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Find the efficiency of the following riveted joints:
(i) Single riveted lap joint of \( 6 \text{ mm} \) plates with \( 20 \text{ mm} \) diameter rivets having a pitch of \( 50 \text{ mm} \).
(ii) Double riveted lap joint of \( 6 \text{ mm} \) plates with \( 20 \text{ mm} \) diameter rivets having a pitch of \( 65 \text{ mm} \).
Assume permissible tensile stress in plate \( = 120 \text{ MPa} \), permissible shearing stress in rivets \( = 90 \text{ MPa} \), permissible crushing stress in rivets \( = 180 \text{ MPa} \).
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A bracket, carries a load of \( 10 \text{ kN} \). Find the size of the weld if the allowable shear stress is not to exceed \( 80 \text{ MPa} \).
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A \( 125 \times 95 \times 10 \text{ mm} \) angle is joined to a frame by two parallel fillet welds along the edges of \( 150 \text{ mm} \) leg. The angle is subjected to a tensile load of \( 180 \text{ kN} \). Find the lengths of weld if the permissible static load per mm weld length is \( 430 \text{ N} \).
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With the help of neat sketches, differentiate between single and multi-plate clutches.
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A multiple disc clutch, steel on bronze, is to transmit \( 4.5 \text{ kW} \) at \( 750 \text{ r.p.m.} \). The inner radius of the contact is \( 40 \text{ mm} \) and outer radius of the contact is \( 70 \text{ mm} \). The clutch operates in oil with an expected coefficient of \( 0.1 \). The average allowable pressure is \( 0.35 \text{ N/mm}^2 \). Find:
(i) the total number of steel and bronze discs;
(ii) the actual axial force required;
(iii) the actual average pressure;
(iv) the actual maximum pressure.
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Discuss the different types of brakes giving at least one practical application for each.
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A double-shoe brake is capable of absorbing a torque of \( 1400 \text{ N-m} \). The diameter of the brake drum is \( 350 \text{ mm} \) and the angle of contact for each shoe is \( 100^\circ \). If the coefficient of friction between the brake drum and lining is \( 0.4 \); find:
(i) the spring force necessary to set the brake;
(ii) the width of the brake shoes, if the bearing pressure on the lining material is not to exceed \( 0.3 \text{ N/mm}^2 \).
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A \( 15 \text{ kW} \) and \( 1200 \text{ r.p.m.} \) motor drives a compressor at \( 300 \text{ r.p.m.} \) through a pair of spur gears having \( 20^\circ \) stub teeth. The centre-to-centre distance between the shafts is \( 400 \text{ mm} \). The motor pinion is made of forged steel having an allowable static stress as \( 210 \text{ MPa} \) while the gear is made of cast steel having an allowable static stress as \( 140 \text{ MPa} \). Assuming that the drive operates 8 to 10 hours per day under light shock conditions, find from the standpoint of strength:
(a) Module;
(b) Face width and
(c) Number of teeth and pitch circle diameter of each gear.
Check the gears thus designed from the consideration of wear. The surface endurance limit may be taken as \( 700 \text{ MPa} \).
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What are springs? Differentiate between helical springs, conical springs and laminated springs with neat sketches. [Image comparing helical, conical, and leaf springs]
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Design a close-coiled helical compression spring for a service load ranging from \( 2250 \text{ N} \) to \( 2750 \text{ N} \). The axial deflection of the spring for the load range is \( 6 \text{ mm} \). Assume a spring index of \( 5 \). The permissible shear stress intensity is \( 420 \text{ MPa} \) and modulus of rigidity \( G = 84 \text{ kN/mm}^2 \). Neglect the effect of stress concentration. Draw a fully dimensioned sketch of the spring, showing details of the finish of the end coils.