Code No: RR Set No. 1

Transcription

1 Code No: RR Set No. 1 III B.Tech I Semester Supplementary Examinations, March 2006 DESIGN OF MACHINE MEMBERS-I ( Common to Mechanical Engineering and Production Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) State advantages and drawbacks of cast iron as an engineering material? (b) Discuss in detail the factors which govern the selection of material for a machine component? [6+10] 2. (a) Explain the salient features of the maximum principal stress theory and indicate under what conditions such a theory is useful? (b) A shaft is designed based on maximum distortion energy theory with a factor of safety of 2.0. The material used is 30C8 steel with a yield stress of 310 MPa. It is subjected to an axial load of 40 kn. Determine the maximum torque capacity. Diameter of the shaft is 20 mm. [6+10] 3. (a) Explain the effect of the following factors on the type of fatigue failure i. Range of imposed stress ii. Surface treatement (b) A stepped shaft transmits a torque varying from 800 N m to 1200 N m. The ratio of diameter is 1.5 and the stress concentration factor is 1.2. Determine the diameter of the shaft for an infinite life for a design factor of safety 1.8. The ultimate tensile strength of the material of the shaft is 600 MPa. Yield stress of the material is 450 MPa. Consider the size effect and surface finish effect. [6+10] 4. (a) What do you understand by the term riveted joint? Explain the necessity of such a joint. (b) A double riveted lap joint is made between 15-mm thick plates. The rivet diameter and pitch are 25 mm and 75 mm respectively. If the ultimate stresses are 400 MPa in tension, 320 MPa in shear and 640 MPa in crushing, find the minimum force per pitch which will rupture the joint. If the above joint is subjected to a load such that the factor of safety is two, find out the actual stresses developed in the plates and the rivets. [6+10] 5. A bracket carrying a load of 15 KN is to be welded as shown in Figure1. Find the size of weld required if the allowable shear stress is not to exceed 80 MPa. [16] 6. (a) Describe the purpose of gib in cotter joint? What are the applications of cotter joints? (b) Design a knuckle joint to transmit 140 kn, with permissible stresses in tension; shear and compression are 75 Mpa ; 60 Mpa and 150 Mpa respectively.[6+10] 1 of 2

2 Code No: RR Set No. 1 Figure 1: 7. A solid shaft transmitting 15kW at 250 rpm is supported on two bearings 1m apart and has two gears keyed to it. The pinion having 30 teeth of 5mm module is located. 0.12m to the left of the right hand bearing and drives power horizontally to the right. The gear having 100 teeth of 5mm module is located 0.18m to the right of the left hand bearing and receives power in a vertical direction from below. Using an allowable stress of 58 N/mm 2 in shear. Determine the diameter of the shaft. [16] 8. (a) Write a short note on universal coupling. (b) Design a solid muff coupling made of cast iron to connect two shafts transmitting 35KW at 150rpm with a capability of 25% maximum torque greater than the mean torque. The shaft and key are made of mild steel for which permissible shear and crushing stress are 30MN/m 2 and 80MN/m 2 respectively. Permissible shear stress in CI is 15MN/m 2. [6+10] 2 of 2

3 Code No: RR Set No. 2 III B.Tech I Semester Supplementary Examinations, March 2006 DESIGN OF MACHINE MEMBERS-I ( Common to Mechanical Engineering and Production Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) Write a brief note on different phases of design. (b) Discuss various general considerations that are taken into account while designing a machine element. [8+8] 2. (a) Explain about the Maximum Normal Stress, Maximum Shear Stress and Maximum Distortion Energy Theories (b) A 50mm diameter steel shaft is supported on bearings 1.5m apart and carries a fly wheel weighing W. The allowable bending stress for the shaft material and the maximum deflection are limited to 100MPa and 2 mm respectively. The young s modulus for the shaft material is 210GPa. Determine the Maximum permissible weight of the flywheel. [8+8] 3. (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 (a) Enumerate the different types of riveted joints. [6+10] (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. [6+10] 5. The head of an air compressor cylinder is attached by eight bolts. The cylinder bore diameter is 80 mm and the maximum working pressure is limited to 3 MPa. Determine the diameter of bolt, when a copper-asbestos is used between the head and the cylinder and an initial compressive load of 5 KN is required on the gasket for a leak proof joint. Ultimate tensile strength, Yield strength and endurance limit for material are 400 MPa, 340 MPa and 200 MPa respectively. A factor of safety of three is desired and the stress-concentration factor of 2.84 may be assumed.[16] 1 of 2

4 Code No: RR Set No (a) Discuss the effect of keys and key ways on the strength of the shaft. (b) Design and draw a sleeve and cotter joint to connect two rods to transmit maximum tensile load of 82 kn. Assume sleeve cotter and rods are made of same material and design stresses in the material are 65 Mpa in tension; 130 in crushing and 50 Mpa in shear. [6+10] 7. A hollow shaft of 0.5m outside diameter and 0.3m inside diameter is used to drive a propeller of a marine vessel. The shaft is mounted on bearings 6 meter apart and it transmits 5600 KW at 150 rpm. The maximum axial propeller thrust is 500 kn and the shaft weighs 70 kn determine the maximum shear stress developed in the shaft and the angular twist between the bearings. [16] 8. (a) Write a short note on universal coupling. (b) Design a solid muff coupling made of cast iron to connect two shafts transmitting 35KW at 150rpm with a capability of 25% maximum torque greater than the mean torque. The shaft and key are made of mild steel for which permissible shear and crushing stress are 30MN/m 2 and 80MN/m 2 respectively. Permissible shear stress in CI is 15MN/m 2. [6+10] 2 of 2

5 Code No: RR Set No. 3 III B.Tech I Semester Supplementary Examinations, March 2006 DESIGN OF MACHINE MEMBERS-I ( Common to Mechanical Engineering and Production Engineering) 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) Write a note on important non-metallic materials of construction in engineering practice? [6+10] 2. (a) State and explain any two theories of failure (b) The principal stresses induced at a point in a machine component made of steel 50C4(S yt = 460 N/mm 2 ) are as follows: Maximum principal stress = 200 N/mm 2 and Minimum principal stress = 150 N/mm 2. Calculate the factor of safety by i. maximum shear stress theory and ii. distortion energy theory. [6+10] 3. (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 150 N m to 450 N m as torsional moment of the shaft varies from 50 N m to 150 N m. 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 Use for torsion, Size correction factor = 0.6 and The nominal design torsion stress = 0.6 Yield point in tension. [6+10] 4. (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. [6+10] 5. A bracket carrying a load of 15 KN is to be welded as shown in Figure1. Find the size of weld required if the allowable shear stress is not to exceed 80 MPa. [16] 1 of 2

6 Code No: RR Set No. 3 Figure 1: 6. (a) A feather key is 12mm wide and is to transmit 700N-m torque from a 400mm diameter shaft. The steel key has an allowable stress in tension and compression of 120Mpa and an allowable shear stress of 575Mpa. Determine the required length of key. If the key dimensions are reversed as 9mm wide and 12mm deep, what would have been the required length of key for same load and material. (b) Design a cotter joint to withstand an axial load varying from 45kN in tension to 45 kn in compression. The allowable for the steel used in the joint are 60Mpa in tension; 70 Mpa in crushing; 45 Mpa in shear. [6+10] 7. A hollow shaft carries a 90cm diameter CI pulley which is driven by another pulley mounted on a shaft placed below it through belt drive. The belt ends are parallel and vertical. The ratio of tensions in the belt in 3HP. Hp transmitted is 50 at 400rpm. The pulley mounted on the hollow shaft weighs 800N and overhangs the nearest bearing by 25cm. Calculate the diameter of the hollow shaft when the ratio of inside diameter to outside diameter is 0.5 when permissible shear stress for the shaft material is limited to 200N/mm 2. [16] 8. Design and draw a muff coupling to transmit 50Hp at 120 rpm. The shaft and key are made of the same material having allowable shear stress of 30N/mm 2 and compressor stress of 80N/mm 2. The flange is made, as cast Iron with allowable shear stress is 15N/mm 2. [12+4] 2 of 2

7 Code No: RR Set No. 4 III B.Tech I Semester Supplementary Examinations, March 2006 DESIGN OF MACHINE MEMBERS-I ( Common to Mechanical Engineering and Production Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) What are the steps to be followed while designing a machine element? [8] (b) Define the following properties of a material: i. Ductility ii. Toughness iii. Hardness and iv. Creep. [4+4] 2. (a) What is factor of safety? List the important factors that influence the magnitude of factor of safety? (b) A cast iron pulley transmits 15 kw at 350 rpm. The diameter of the pulley is 520mm and it has four straight arms of elliptical cross section in which the major axis is twice the minor axis. Find the dimensions of the arm, if the allowable bending stress is 25 MPa. [6+10] 3. (a) Explain the following methods of reducing stress concentration i. Drilled holes ii. Using large fillet radius iii. Added grooves (b) A shaft is made of steel [ultimate tensile strength 700 MPa and yield point 420 MPa is subjected to a torque varying from 200N m] anti-clockwise to 600 N m clockwise. Calculate the diameter of the shaft if the factor of safety is 2 and it is based on the yield point and the endurance strength in shear.[6+10] 4. (a) What do you understand by the term riveted joint? Explain the necessity of such a joint. (b) A double riveted lap joint is made between 15-mm thick plates. The rivet diameter and pitch are 25 mm and 75 mm respectively. If the ultimate stresses are 400 MPa in tension, 320 MPa in shear and 640 MPa in crushing, find the minimum force per pitch which will rupture the joint. If the above joint is subjected to a load such that the factor of safety is two, find out the actual stresses developed in the plates and the rivets. [6+10] 5. A bracket carrying a load of 15 KN is to be welded as shown in Figure1. Find the size of weld required if the allowable shear stress is not to exceed 80 MPa. [16] 1 of 2

8 Code No: RR Set No. 4 Figure 1: 6. (a) It is required to design a square key for fixing a gear on a shaft of 60 mm diameter; to transmit 5 kw power at 480 RPM. The key is made of 50 C4 steel with f yt =460 Mpa and FOS=3.The yield strength and compressive strength of key material is assumed to be equal. Design the key. (b) Design a knuckle joint to withstand a tensile load of 75 kn using steel with the permissible stresses in tension 63 Mpa; in crushing 75 Mpa; in shear 50 Mpa. [6+10] 7. (a) Derive the equation for torque acting upon a hollow shaft from the torsion equation. (b) Find the diameter of a solid shaft to transmit 25 kw at 300 rpm. Take the maximum allowable shear stress as 50 N/mm 2. If a hollow shaft is to be used in place of the solid shaft, find the inside and outside diameter when the ratio of inside to outside diameter is 0.6. [6+10] 8. Design and draw a bush type flexible flange coupling to transmit 15Hp at 960 rpm allowable shear stress for the shaft and key may be taken as 53.5N/mm 2. the shear stress in the bolts should not exceed 35N/mm 2. the bearing pressure between the bush and coupling should be 2N/mm 2. [12+4] 2 of 2