07a50304 designofmachinemembers i

7/28/2019 07a50304 Designofmachinemembers i

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Code No: 07A50304 R07 Set No. 2

III B.Tech I Semester Supplementary Examinations,June 2010

DESIGN OF MACHINE MEMBERS - I

Common to Mechanical Engineering, Production Engineering

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

1. (a) Define the terms:

i. Stress area

ii. Pitch

iii. Major diameter related to screw fastenings:(b) The base of a pillar crane is fastened to the foundation by 12 bolts spaced

equally on a bolt circle of diameter 2 m. The diameter of the pillar base is 2.5m. Determine the size of bolts when the crane carries a load of 150 kN at adistance of 6 m from the centre of the base. The allowable stress for the boltmaterial is 170 N/mm2. [6+10]

2. (a) Classify the keys and state their applications.

(b) A gear is fastened by means of sunk key to the shaft subjected to the torsiononly.

i. Find the ratio of sectional areas of shaft and key, for equality of strengthof the key and shaft

ii. Find the length of the key of 20 mm width on 70 mm diameter shaft. Thepermissible shear stress for the key and the shaft materials is 50 and 60N/mm2 respectively. [6+10]

3. (a) Enumerate the common materials used in engineering design?

(b) Explain how can the properties of materials be improved for any two materials.[8+8]

4. (a) What is riveted joint? Explain the necessity of riveted joint in pressure vessels.

(b) A double riveted lap joint is made between 18 mm thick plates. The rivetdiameter and pitch are 30 mm and 80 mm respectively. If the ultimate stressesare 200 N/mm2 in tension, 160 N/mm2 in shear and 420 N/mm2 in crushing,find the minimum force per pitch which will rupture the joint. If the jointis subjected to a load such that the factor of safety is1.5, find out the actualstresses developed in the plates and the rivets. [6+10]

5. A rail carriage weighing 250 kN and running at 1.5 m/s is brought to rest by fourbuffer springs of close coiled helical type during connection with another carriagewhich is already at rest. The mean coil diameter is 6 times the wire diameter. The

deflection of each spring is 220mm, to bring the carriage to rest. Safe shear stressfor the spring material is 400N/mm2. Calculate the maximum load on the spring,diameter of wire and coil, number of turns and free length of spring. Assume theends of spring are squared and ground. Take G = 0.8104N/mm2. [16]

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6. (a) Define stress concentration factor? What are the different methods to reducethe stress concentration factor?

(b) A steel connecting rod is subjected to a completely reversed axial load of 10kN. Suggest suitable size of the rod using a factor of safety 2. The Ultimatestrength of the material is 11 kN/mm2 and yield strength is 9.3 kN/ mm2.The value of A, factor for correction for type of loading may be taken as 0.85and size factor as 0.85. Neglect the column action and the effect of stressconcentration. [6+10]

7. (a) What is the difference between a shaft and an axle? How the shafts areclassified?

(b) Determine the diameter of the hollow shaft having inside diameter 0.5 timesthe outside diameter. The permissible shear stress is limited to 250 N/mm2.The shaft carries a 800 mm diameter cast iron pulley. This pulley is drivenby another pulley mounted on the shaft placed below it. The belt ends areparallel and vertical. The ratio of tensions in the belt is 3. The pulley on thehollow shaft weighs 900 N and overhangs the nearest bearing by 250 mm. Thepulley is to transmit 35 kW power at 500 rpm. [6+10]

8. It is required to connect two co-axial shafts by a split muff coupling. The powertransmitted is 30 kW at 160 rpm. Assume that there are total of 12 clamping boltsdistributed equally on two sides of the muff and they can be stressed to a tensile

stress of 80 N/mm2

. The permissible shearing stress in the shaft and key is 35N/mm2. Determine the dimensions of the muff and diameter of clamping bolts.Assume coefficient of friction between muff and shaft is 0.26. [16]

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1. A steam engine of effective diameter 400 mm is subjected to a steam pressure of 2N/mm2. The cylinder cover is connected by means of 6 bolts having yield strengthof 450 N/mm2 and endurance limit of 275 N/mm2. The bolts are tightened with

an initial preload of 2.5 times that of steam force. A soft copper gasket is used tomake a leak proof joint. The stress concentration factor is 2.5 Determine the sizeof the bolts. [16]

2. Design a shaft coupling to transmit 100 kW at 1230 rpm. The permissible stressesfor the coupling and key are 75, 45 and 120 N/mm2 in tension, shear and com-pression respectively. Draw freehand sketch of the coupling showing importantdimensions. [16]

3. (a) Differentiate between a flat key and feather key.

(b) A square key is to be used to key a gear to a 50 mm diameter shaft. The

length of the hub of the gear is 80 mm. Both shaft and key are made ofsame material, having an allowable shear stress of 65 N/mm2. What are theminimum dimensions of the key if 300 N-m of torque is to be transmitted.

[6+10]

4. A Power is transmitted to a shaft supported on bearings, 1000mm apart, by a beltdrive, running on a 550 mm pulley, which overhangs the right bearing by 300 mm.Power is transmitted from the shaft through a belt drive, running on a 350 mmpulley, located mid-way between the bearings .The belt drives are at right angle toeach other, and the ratio of belt tensions is 3.5 with the maximum tension in boththe belts being limited to 4 kN. Determine the diameter of the shaft, assumingpermissible stress as 65 N/mm2. Indicate the assumptions made, if any. Draw theBM & S.F diagrams. [16]

5. (a) Why the compression springs are predominantly used compared to the exten-sion springs?

(b) A spring for spring balance is to elongate 100 mm, when subjected to a loadof 200 N. Assume that the mean diameter of the coil is to be 5 times thediameter of the wire and the maximum stress to be induced is limited to 400N/mm2. Determine the diameter for the wire, for the coil and the numberof coils required and length of spring. Modulus of rigidity (G) is 0.8105

N/mm2. [6+10]

6. (a) Explain the terms

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i. Caulking

ii. Fullering(b) Two plates of 6 mm thick are connected to a triple riveted lap joint of zig-zag

pattern. Calculate the rivet diameter, rivet pitch and distance between rowsof rivets for the joint. Also state the mode of failure of the joint. The safeworking stresses are as follows. t = 100 N/mm2; = 80 N/mm2; c =150N/mm2. [6+10]

7. (a) Write the significance of stresses and stress concentration considerations inmanufacturing design.

(b) What is meant by preferred numbers and explain their use in engineering

design? [8+8]8. (a) Discuss the influence of various factors in the design of machine members

subjected to variable load.

(b) A leaf spring an automobile is subjected to cyclic stresses. The average stressis 250 N/mm2, Variable stress is 525 N/mm2, ultimate stress is 590 N/mm2,yield point stress is 450 N/mm2 , and endurance limit is 250 N/mm2. Estimate,under what factor of safety the spring is working, by Goodmans and Soderbergformulae. [8+8]

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1. (a) Define factor of safety under static and fluctuating loads.

(b) A steel connecting rod is subjected to a completely reversed axial load of 16kN. Suggest the suitable diameter of the rod using a factor of safety 2. The

ultimate tensile strength of the material is 11000 N/mm2

, and yield strength9300 N/mm2. Neglect column action and the effect of stress concentration.[6+10]

2. (a) A punching press is required to punch a maximum hole size of 30 mm diameterin a material having ultimate shear strength of 350 N/mm2. If the thicknessof the sheet is 6 mm, design the screw and the nut.

(b) An eye bolt is to be used for lifting a load of 100 kN. Find the nominal diameterof the bolt, if the tensile stress is not to exceed 130 N/mm2. [8+8]

3. (a) Describe various types of keys.

(b) Design and draw a sleeve and cotter joint to connect two rods to transmitmaximum tensile load of 100 kN. Assume sleeve, cotter and rods are made ofsame material and design stresses in the material are 75 N/mm2 in tension,150 in crushing and 45 N/mm2 in shear. [6+10]

4. (a) Under what circumstances concentric springs are preferred?

(b) A load of 2 kN is dropped axially on a close coiled helical compression springfrom a height of 260 mm. The spring has 16 active coils. Take wire diameteras 20 mm, spring index as 8. Determine the deflection and stress induced inthe spring. Take G= 0.84 105 N/mm2. [6+10]

5. (a) Classify different types of riveted joints and rivets.

(b) A low carbon steel plate of 75 mm width welded to a structure of similar ma-terial by means of two parallel fillet welds of 120 mm length each is subjectedto an eccentric load of 50 kN, the line of action of which has a distance of 110mm from the center of gravity of the weld group. Design the required thick-ness of the plate when the allowable stress of the weld metal is 70 N/mm2 andthat of the plate is 50 N/mm2. [6+10]

6. (a) State the advantages and drawbacks of cast iron as an engineering material.

(b) A cast iron pulley transmits 16 kW at 1440 rpm. The diameter of the pulleyis 1.5 m and it has four straight arms of elliptical cross section, in which themajor axis is three times the minor axis. Determine the dimensions of thearm, if the allowable bending stress is 20N/mm2. [6+10]

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7. (a) Define the terms,

i. equivalent bending moment, andii. equivalent twisting moment.

(b) A hollow shaft of 0.6 m outside diameter and 0.3minside diameter is used todrive a propeller of a marine vessel. The shaft is mounted on bearings 8 mapart and it transmits 6 MW at 250 rpm. The maximum axial propeller thrustis 600 kN and the shaft weighs 70 kN. Determine:

i. The maximum shear stress developed in the shaft and

ii. The angular twist between the bearings. [6+10]

8. Design a bush pin flexible coupling for connecting a motor shaft to a pump shaft

for the service conditions: Power to be transmitted is 70 kW, speed of the motorshaft is 1440 rpm, diameter of the motor shaft is 60 mm, diameter of the pumpshaft is 45 mm. The bearing pressure in the rubber bush and allowable stress in thepins are to be limited to 0.5 N/mm2 and 35 N/mm2. [16]

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1. (a) Explain the situation where the flexible couplings are selected?

(b) Design a protective type flange coupling for the following requirements. Powerto be transmitted is 15 kW at 1440 rpm. Flange material is Cast Iron. Shafts

and keys are made of medium steel. Assuming appropriate factors, calculatethe dimensions of coupling. [6+10]

2. (a) Explain the details of shaft design based on:

i. Torsional rigidity

ii. Lateral rigidity.

(b) A centrifugal circulating pump for a steam turbine condenser is to be con-nected to a motor through a short shaft and a pair of flexible couplings. Thepump delivers 36000 liters/minute at 1000 rpm against a dynamic head of 10m. The pump efficiency is 75%. Assuming a permissible shear stress of 65

N/mm2, determine the diameter of the shaft required. [6+10]

3. (a) Explain various factors effecting endurance limit in the case of a ductile ma-terial.

(b) Determine the diameter of a circular rod made of ductile material with afatigue strength (completely stress reversal) e = 280 N/mm

2 and a tensileyield strength of 550 N/mm2. The member is subjected to a varying axialload from 1050 kN to - 450 kN. Assume Kt=1.7 and F.S=1.25. [6+10]

4. (a) Classify the rivet heads according to Indian Standard Specification.

(b) A double riveted double cover butt joint in plates 20 mm thick is made with25 mm diameter rivets at 100 mm pitch. The permissible stresses are Pt =120 N/mm2, Ps = 100 N/mm

2, and Pc = 150 N/mm2. Find the efficiency of

the joint, taking the strength of the rivet in double shear as twice than thatof single shear. [6+10]

5. (a) Explain the classification of engineering materials based on their propertiesand applications.

(b) Differentiate between High speed steel and spring steel. [8+8]

6. (a) Derive an expression for the maximum load in a bolt when a bracket withcircular base is bolted to a wall by means of 8 bolts.

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(b) A steam engine cylinder of size 350 350 mm operates at 3 N/mm2 pressure.The cylinder head is connected by means of 12 bolts having yield stress of 450N/mm2 and the endurance limit of 365 n/mm2 by using gasket, which rendersthe effect of external load to be half. Determine the size of bolts, if factor ofsafety is 2.5 and stress concentration factor is 0.5. [6+10]

7. (a) What is the function of key and what types of stresses are induced in a key?

(b) A 75 mm diameter shaft has a key 20 20 mm. The shaft material has yieldstrength of 350 N/mm2. Assume shear stress as half of the tensile strengthand factor of safety as 2. The shaft fits in to a cast iron hub for which theworking stress in compression is 175 N/mm2. Determine the length of the keyin the hub to carry the torque of the solid shaft. [6+10]

8. A concentric spring for an air craft engine valve is to exert a maximum force of 8kN under an axial deflection of 50 mm. Both the springs have same free length,same solid length and are subjected to equal maximum shear stress of 560 N/mm2.If the spring index for both the springs is 5, find

(a) The load shared by each spring,

(b) The main dimensions of both the springs and

(c) The number of active coils of each spring. Assume G = 0.8 105 N/mm2 anddiametral clearance to be equal to the difference between the wire diameters.

[16]

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07a50304 designofmachinemembers i

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