R05321403-principles-of-machine-design

Set No. 1

Code No: R05321403

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Enumerate the most commonly used engineering materials and state at least one important property and application of each. [16] 2. (a) What are the principal causes of stress concentration? (b) A pulley is keyed to a shaft midway between two anti-friction bearings. The bending moment of the pulley varies from 150Nm to 450Nm as torsional moment of the shaft varies from 50Nm to 150Nm. The frequency of variation of the loads is the same as the shaft speed. The shaft is made of cold drawn steel having an ultimate strength of 550 MPa and yield strength of 310 MPa. Determine the required diameter for an indefinite life. The stress concentration factor for the key way in bending and torsion may be taken as 1.6 and 1.3 respectively. Use a design factor of 1.8, size factor 0.85 and surface correction factor 0.88. Use for torsion, size correction factor = 0.6 and The nominal design torsion stress = 0.6 Yield point in tension. [6+10] 3. A pillar crane having a circular base of 600 mm diameter is fixed to the foundation of concrete base by means of four bolts. The bolts are of size 30 mm and are equally spaced on a bolt circle diameter of 500 mm. The load lifted by the pillar crane is 60 KN and is at a distance of 1.5 m from the centre of the base. Find the maximum stress induced in the bolt material. [16] 4. (a) Differentiate between a cotter and a key. (b) Design a gib and cotter joint to connect square rods with a side of the square as 25mm.Consider σr =60MPa σ r = 90MPa and τ = 40MPa. The joint has to carry a load of 35kN.(t=8mm,B=55(30+25)mm and length of the tail of the rod is 12mm. [4+12] 5. (a) What is a spring and how they are classified? (b) Design a spring for spring loaded safely value for the following Conditions: Operating pressure 100N/cm2 . Diameter of valve seat 100mm. Design shear stress for the spring is 400 N/mm2 ,G=0.86×105 N/mm2 . The spring is to be kept in a casting of 120 mm inner diameter and 400 mm long. The spring should be at maximum lift of 6mm when the pressure is 107.5 N/cm2 . [4+12] 6. (a) What are the factors to be considered while selecting the material for plain Bearing?

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Set No. 1

Code No: R05321403

(b) The thrust of propeller shaft in a marine engine is taken up by number of collars integral with the shaft which is 300mm in diameter. The thrust on the shaft is 200kN and the speed is 75r.p.m. Taking coefficient of friction constant and equal to 0.05 and assuming the bearing pressure as uniform and equal to 0.3N/mm2 , find: i. Number of collars required, ii. Power lost in friction, and iii. Heat generated at the bearing in kJ/min.

[4+12]

7. (a) What is meant by creep of a belt and what is its effect? (b) A belt,100×10mm is transmitting power at 15m/s.The angle of contact on the driver (smaller ) pulley is 1560 . If the permissible stress for the belt material is 2N/mm2 ; determine the power that can be transmitted at this speed take the density of leather as 1000kg/m3 ,and coefficient of friction as 0.25. Calculate the maximum power that can be transmitted by this belt, and the speed at which this can be transmitted. [4+12] 8. (a) What is the herringbone gear? Where are they used. (b) A helical cast steel gear with 30o helix angle has to transmit 35kW at 2000 r.p.m. If the gear has 25 teeth, find the necessary module, pitch diameters and face width for 200 full-depth involute teeth. The static stress for cast steel may be taken as 100MPa. The face width may be taken as 3 times the normal pitch. The tooth form factor is given by expression y=0.154-0.912 / TE , where TE represents the equivalent number of teeth. The velocity factor is given by Cv = 6/ (6+V) where V is the peripheral speed of the gear in m/s. [4+12] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: R05321403

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) What is meant by Yielding? How is Yield Strength defined for materials, which do not show a clear yield point? (b) Discuss briefly about different types of failures in machine parts. (c) What are the advantages of Plastics over the other materials? Give some examples. [4+6+6] 2. (a) Explain the following methods of reducing stress concentration. i. Removal of undesired material ii. Added grooves. (b) A steel connecting rod is subjected to a completely reversed axial load of 120 KN. Suggest the suitable size of the rod using a factor of safety 1.8. The ultimate strength of the material is 1000 MPa. Load correction factor 0.7 Size factor 0.85 Surface finish factor 0.8 [4+12] 3. The cylinder head of a 200 mm × 350 mm compressor is secured by means of 12 studs of rolled mild steel having yield point stress of 350 MPa and endurance limit of 240 MPa. The gas pressure is 1.5 MPa. The initial tension in the bolts, assumed to be equally loaded such that a cylinder pressure of 3 MPa is required for the joint to be on the point of opening. The joint is made leak-proof by using copper gasket, which renders the effect of external load to be half. Determine the size of bolts, if factor of safety is 2 and stress concentration factor is 2.8. [16] 4. (a) What is the effect of keyway on i. Strength of shaft ii. Torsional rigidity of Shaft. (b) Make a neat sketch showing two views of a cotter joint and write equations showing the strength of the joint for the most probable methods of failure. [6+10] 5. A truck spring has 10 leaves and is supported at a span length of 100cm, with central band of 80mm wide. A load of 6kN is applied at the center of spring whose permissible stress is 300N/mm2 . The spring has a ratio of total depth to width of about 2.5. Determine the width, thickness, deflection and length of all leaves. [16]

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Set No. 2

Code No: R05321403

6. (a) A 150mm diameter shaft supporting a load of 10kN has a speed of 1500 r.p.m. The shaft runs in a bearing whose length is 1.5 times the shaft diameter .If the diametral clearance of the bearing is 0.15 mm and the absolute viscosity of the oil at the operating temperature is 0.011 kg/m-s, find the power wasted in friction. (b) A 80mm long journal bearing supports a load of 2800N on a 50mm diameter shaft. The bearing has a radial clearance of 0.05mm and the viscosity of the oil is 0.021kg/m-s at the operating temperature. If the bearing is capable of dissipating 80J/s, determine the maximum safe speed. [8+8] 7. A V belt drive is used to transmit 80kW at a motor speed of 100 rpm, the driven pulley speed being 600 rpm. Approximate center distance is 1.110m, µ is 0.3, angle of groove is 40degree and Vmax =25m/sec. Neglecting the centrifugal tension, Calculate the size and number of belts. Also check the induced stress and find the induced stress and find the life of the belt assuming allowable endurance strength is 9MPa. [16] 8. A gear drive is required to transmit a maximum power of 22.5kW.The velocity ratio is 1:2 and pinion speed is 200 rpm. The approximate center distance between the shafts may be taken as 600mm.The teeth have 200 stub involute profiles. The static stress for the gear material (CI) is 60MPa and face width as 10 times the module. Find the module, Face width and number of teeth on each gear. Check the design for dynamic and loads. The deformation or dynamic factor in the Buckingham equation may be taken as 80 and combination factor for the wear as 1.4. [16] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: R05321403

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) How do you classify materials for engineering use? (b) A bolt is subjected to a direct tensile load of 18000 N and a shear load of 12000N. The yield stress of the bolt material in simple tension is 350 Mpa. Use a factor of safety of 3 and poison’s ratio of 0.25. Calculate the diameter of the bolt by : i. Maximum shear stress theory and ii. Maximum principal strain theory.

[4+12]

2. (a) Define stress concentration factor. (b) A hot rolled shaft is subjected to torsional load that varies from 320 Nm clockwise to 120Nm anti-clockwise and an applied bending moment at a critical section varies from 400Nm to 200Nm. The shaft is of uniform cross section. Determine the required shaft diameter. The material has an ultimate strength of 560MPa and yield strength of 420 MPa. Assume factor of safety to be 2. [6+10] 3. (a) Enumerate the different types of riveted joints. (b) Two plates 16 mm thick are joined by a double riveted lap joint. The pitch of each row of rivets is 90 mm. The rivets are 25 mm in diameter. The permissible stresses are 140 MPa in tension, 80 MPa in shear and 160 MPa in crushing. Find the efficiency of the joint. [8+8] 4. The shaft of an axial flow rotary compressor is subjected to maximum torque of 2000N-m and a maximum bending moment of 4000 N-m. The combined shock and fatigue factor in torsion is 1.5 and that in bending is 2. Design the diameter of the shaft ,if the shear stress in the shaft is 50MPa. Design a hollow shaft for the above compressor taking the ratio of outer diameter to the inner diameter as 2. What is the percentage saving in material? Also compare the stiffness. [16] 5. (a) With neat sketch Explain the difference between a close coiled and open coiled helical spring. (b) Design a coil spring for a spring-loaded governor to give a deflection of 1.25 mm under an axial load of 115N.The mean radius of the coil is 25mm and the wire diameter is 6mm.Take C= 0.8×105 N/mm2 . Check the spring for buckling. Give a neat sketch of the spring in the un-compressed state. [6+10] 6. (a) What is meant by square bearing? 1 of 2

Set No. 3

Code No: R05321403

(b) Specify a suitable deep groove ball bearing for a radial load of 2.5kN and a thrust load of 0.9kN.The operating speed is 3000 r.p.m. Assume steady load, and life of 15000 hours at 95% reliability. Recommend the bearing with the maximum possible bore size. [2+14] 7. (a) How are the chain drives classified? (b) Design a chain drive to actuate a compressor from 15kW electric motor running at 1000 rpm. The compressor speed being 350 rpm. The minimum center distance is 500mm. The compressor operates 16 hrs/day. The chain tension is adjusted by shifting the motor on slides. [4+12] 8. (a) What is the herringbone gear? Where are they used. (b) A helical cast steel gear with 30o helix angle has to transmit 35kW at 2000 r.p.m. If the gear has 25 teeth, find the necessary module, pitch diameters and face width for 200 full-depth involute teeth. The static stress for cast steel may be taken as 100MPa. The face width may be taken as 3 times the normal pitch. The tooth form factor is given by expression y=0.154-0.912 / TE , where TE represents the equivalent number of teeth. The velocity factor is given by Cv = 6/ (6+V) where V is the peripheral speed of the gear in m/s. [4+12] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: R05321403

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Explain how cast iron is obtained. (b) Classify and explain different types of cast irons.

[8+8]

2. (a) Explain the effect of the following factors on the type of fatigue failure i. ii. iii. iv.

Stress distribution Manner of loading Strain rate Type of material

(b) Determine the diameter of a circular rod made of ductile material with fatigue strength (complete stress reversal) Endurance limit = 280 MPa and a tensile yield strength of 350 MPa. The member is subjected to a varying axial load from 700 kN to 300 kN. Assume Fatigue stress concentration factor = 1.8 and Factor of Safety = 2. [8+8] 3. (a) What is the difference between caulking and fullering? Explain with the help of neat sketches. (b) A double riveted double cover butt joint in plates 20-mm thick is made with 25 mm diameter rivets at 100 mm pitch. The permissible stresses are 120 MPa in tension, 100 MPa in shear and 150 MPa in crushing. Find the efficiency of joint, taking the strength of the rivet in double shear as twice than that of single shear. [8+8] 4. (a) What are the uses of knuckle joint? (b) Design a sleeve and double cotter joint to be designed for connecting two steel rods. An axial tensile load of 30000N acts on the rods. Permissible stresses. σ t = 55 MPa , σ c = 70MPa and τ = 40MPa. [4+12] 5. (a) Define the following terms i. ii. iii. iv. v.

Spring index Solid length Spring stiffness Free length pitch.

(b) A close coiled helical compression spring of 16 active coils has a spring stiffness of 10 N/mm. It is cut in to two springs having 7 and 9 turns .Determine the spring stiffness of resulting springs. [8+8] 1 of 2

Set No. 4

Code No: R05321403 6. (a) Define the following terms: i. journal ii. Eccentricity ratio.

(b) A bearing, supporting a power transmitting shaft, is subjected to 3000N radial load and 45000N axial thrust. The shaft rotates at 400r.p.m and the expected life of the bearing is 10,000hours. Select a suitable bearing, if the diameter of the shaft is 40mm. [2+14] 7. (a) What are the advantages and disadvantages of V- belt drive? (b) A fly wheel having four arms is brought to rest from an angular velocity of 36 rad/s in three revolutions, by the application of a brake. The mass of the rim is 250kg and the radius of gyration of the rim is 0.75m. Determine the size of the cross section of the rims; assuming it to be elliptic with minor axis equal to 0.6 times the major axis, and permissible bending stress for the flywheel material as 30MPa. [4+12] 8. (a) Write the expression for static strength, limiting wear load and dynamic load for helical gears and explain the various terms used. (b) Two precision cut forged helical gears have 200 full depth involute teeth. The angle of helix is 230 . Permissible static bending stress 100MPa,module 3mm, face width 500mm. The speed of rotation of pinion 900rpm gear ratio 5:1, surface endurance strength 630MPa. Find the transmitted and wear load and state whether the design is safe. [8+8] ⋆⋆⋆⋆⋆

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