1. Enumerate the most commonly used engineering materials and state some important properties and their engineering applications.

Transcription

1 Code No: R Set No. 1 III B.Tech I Semester Regular Examinations, November 2008 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. Enumerate the most commonly used engineering materials and state some important properties and their engineering applications. [16] 2. (a) Explain the effect of the following factors on the type of fatigue failure. i. Type of material ii. Stress distribution (b) A shaft made of steel having ultimate tensile strength of 700 MPa and yield point 420 MPa is subjected to a torque of 2000 N m clockwise to 600 N m anti-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.[4+12] 3. A bracket is riveted to a column by 6 rivets (A,B,C,D,E and F) of equal size as shown in Figure 3. The centres of rivets A,B,C are on the same vertical line and the centres of E, F are on the another vertical line. The centres of B, D are on the same horizontal line. The centres of A, E are on one horizontal line and the centres of C,F are on another horizontal line. The vertical distance between A,B and B,C are 75 mm and 75 mm respectively. The horizontal distance between B,D and C,F are 75 mm and 150 mm respectively. It carries a load of 100 KN at a horizontal distance of 250 mm from the central line of rivet D. If the maximum shear stress in the rivet is limited to 63 MPa, find the diameter of the rivet. [16] Figure 3 4. (a) Sketch various types of threads giving their applications. 1 of 2

2 Code No: R Set No. 1 (b) A lever loaded safty valve has a diameter of 100 m.m and the blow off pressure is 1.6N/m.m 2. The fulcrum of the lever is screwed into the cast iron body of the cover. Find the diameter of the threaded part of the fulcrum, if the permissible tensile stress is limited to 50 MPa and the lever ratio is 8. [8+8] 5. (a) Explain the bending failure of cotter and knuckle pin? (b) Two steel rods are to be connected by means of a sleeve, and two steel cotters. The rods are subjected to a tensile load of 40kN. Design the joint, using the permissible stress in tension as 60MPa, in shear as 50MPa, and in crushing as 120MPa. [6+10] 6. A shaft of 30kW 710 rpm motor is 40mm in diameter and is supported in Bearings 500 mm apart. Calculate, (a) stress due to bending if the armature weighing 10,000 N concentrated at the centre acting vertically (b) Stress due to torsion (c) Equivalent shear stress and tensile stress due to bending moment and torque. [16] 7. A sleeve coupling is used to connect two 75mm shafts whose shearing stress is 70 N/mm 2. (a) What torque is transmitted by the shafting? (b) To what torsional moment is the coupling subjected? (c) Find the diameter and the length of the coupling. (d) What will be the induced stress in the sleeve if the diameter of the part (c) is used. (e) If cast iron sleeve with ultimate shearing stress of 140 N/mm 2 is used. What is the numerical value of the factor of safety? [16] 8. A diesel engine weighs 800kN and is mounted on 16 springs in order to protect the building from vibrations. The section of the spring wire is rectangular with side ratio1.8. One spring has four effective coils and the spring index is 6. Determine: (a) Section of the spring so that long side is parallel to the axis of the spring (b) Deflection under load when engine is stationary (c) Maximum coil diameter (d) Shear stress induced if shorter side is parallel to the spring axis. Permissible shear stress in spring wire material is 300N/mm 2 and modulus of rigidity is N/mm 2. [16] 2 of 2

3 Code No: R Set No. 2 III B.Tech I Semester Regular Examinations, November 2008 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 is an Engineering design. (b) Explain the stages in the design of machine members. [4+12] 2. (a) Explain the effect of the following factors on the type of fatigue failure. i. Range of imposed stress ii. strain rate (b) A rotating shaft carries a 18 KN pulley at the center of a 0.75 m simply supported span. The average torque is 230 N m. Assume the torque range to be 10 % of the average torque. The material has yield point of 770 MPa and the endurance limit of 450MPa.Determine the required diameter of the shaft based on i. Maximum stress theory and ii. distortion energy theory. Stress concentration factor may be taken as 1.5 and a factor of safety 2. [4+12] 3. (a) What do you understand by the term welded joint? How it differs from the riveted joint? (b) A plate 75 mm wide and 12.5 mm thick is joined with another plate by a single transverse weld and a double parallel fillet weld as shown in Figure3b. The maximum tensile and shear stresses are 70 MPa and 56 MPa respectively. Find the length of each parallel fillet weld, if the joint is subjected to both static and fatigue loading. Assume a length of 12.5 mm for starting and stopping of weld run. Take stress concentration factor for transverse weld as 1.5 and for parallel fillet welds as 2.5. [4+12] 1 of 3

4 Code No: R Set No. 2 Figure 3b 4. (a) An eye bolt is to be used for lifting a load of 60 KN. Find the nominal diameter of the bolt, if the tensile stress is not to exceed 100 MPa. Assume coarse threads. (b) Two shafts are connected by means of a flange coupling to transmit torque of 25 N-m. The flanges of the coupling are fastened by four bolts of the same material at a radius of 30 m.m. Find the size of the bolts if the allowable shear stress for the bolt material is 30 MPa. [8+8] 5. (a) A belt pulley is fastened to a 70mm dia shaft running at 200 r.p.m by means of a key, 20mm wide and 120mm long. Permissible stresses for the shaft and key materials are 50 and 90MPa respectively Determine the power that can be transmitted at 240 r.p.m also determine the thickness of the key. (b) Design and sketch a cotter joint for fastening the piston rod to the cross head of the engine having cylinder diameter 250mm and steam pressure 1.05N/mm 2. The thickness of the cotter is to be 0.3 times piston rod diameter at the point where cotter is located. Allowable stresses in tension, shear and compression are 50 N/mm 2, 40N/mm 2 and 84 N/mm 2 respectively. [6+10] 6. (a) What are the causes of failure of shaft? (b) A hollow shaft 0.5m outside diameter and 0.3m inside diameter is supported by two bearings 6m apart, the shaft is driven by a flexible coupling at one shaft end and drives a ship s propeller at 10.5 rad/sec. The maximum thrust on the propeller is 540kN when the shaft is transmitting 5885kW. The shaft weight is 67.5kN. Determine the maximum shear stress in the shaft considering the weight of the shaft and the column effect. Assume K b = 1.5 and K s =1.0. [4+12] 7. Design a clamp coupling completely for a shaft diameter of 50mm. The torsional moment to be transmitted by this coupling taking in to account overloading is 140Nm. The number of bolts used is 4 and the allowable stress in the material of the bolt is limited to 70 N/mm 2. The coefficient of friction between the shaft and muff material is 0.3. Draw sectional elevation of the designed clamp coupling. [16] 2 of 3

5 Code No: R Set No A semi elliptical laminted spring is to carry of load of 5000N and consists 8 leaves 46 mm wide, two of the leaves being of full length. The spring is to be made 1000mm between the eyes and is held at the center by a 60mm wide band. Assume that the spring is initially stressed so as to induce an equal stress of 500N/mm 2 when fully loaded. Design the spring (a) Thickness of leaves (b) Eye diameter (c) Length of leaves (d) Maximum deflection and camber. Assume E = N/mm 2. [4 4=16] 3 of 3

6 Code No: R Set No. 3 III B.Tech I Semester Regular Examinations, November 2008 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 is conceptual design. (b) Explain the manufacturing consideration in the design. [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) Sketch and discuss the various types of welded joints used in pressure vessels. (b) A mm angle is joined to a frame by two parallel fillet welds along the edge of 200 mm length. If the angle is subjected to a static load of 200 KN, find the length of weld at the top and bottom. The allowable shear stress for static loading may be taken as 75 MPa. [6+10] 4. (a) Write a short note on bolts of uniform strength. (b) The cylinder head of a steam engine is subjected to a steam pressure of 0.7N/mm 2. It is held in position by means of 12 bolts. A soft copper gasket is used to make the joint leak-proof. The effective diameter of cylinder is 300mm. Find the size of the bolt so that the stress in the bolts is not to exceed 100 MPa. [6+10] 5. (a) Differentiate between a cotter and a key. (b) Design a gib and cotter joint to resist safely a tensile load of 40kN. The material of the gib, cotter and rods is same for which the allowable safe stresses are: σ c =60 N/mm 2, σ t =25 N/mm 2 and τ s =20 N/mm 2. [4+12] 6. A shaft is supported on two bearings 1800mm apart and rotates at 800 rpm. Two pulleys B and C are located on the shaft at distance of 600mm and 1350 mm respectively to the right of the left bearing. The distance of the pulleys B and C are 750 mm and 600 mm respectively. 50kW power is supplied to the shaft through pulley B and output is through pulley C. The drive to pulley B is vertically downward while from C the drive is downward at an angle of 60 0 to the horizontal. In both cases the tension ratio is 2 and the angle of lap is The combined fatigue and shock factors for tensions and bending may be taken. Working stresses to be 40N/mm 2 in shear and 80N/mm 2 in tension. [16] 1 of 2

7 Code No: R Set No (a) The bolt in the flange coupling should be made weaker than the other components of coupling, Why? (b) In a flange shaft coupling having 37.5mm bore it is desired that torsional stress in the shaft will not exceed 25 N/mm 2. The outside diameter of the coupling limited by space is 200mm. There are three 15mm bolts on a bolt circle diameter of 140mm. The radial flange thickness is 18mm. Determine the following: i. The power that may be transmitted at 600 rev/min. ii. The shearing stress in the bolts. iii. The bearing pressure on the bolts. [4+12] 8. A semi-elliptical laminated spring is made of no.10.b.w.g. steel 50mm wide. The length between the supports is 66.25cm and the band is 63 mm wide. The spring has two full length and five graduated leaves. A central load if 158 kg is carried. (a) Determine the maximum stress in each set of leaves for an initial condition of no stress in the leaves. (b) Draw to half or quarter full size the elevation and plan of the spring (c) Determine the maximum stress if the initial stress is provided to cause equal stresses when loaded. (d) Determine the deflection in parts (a)and (b) respectively. [16] 2 of 2

8 Code No: R Set No. 4 III B.Tech I Semester Regular Examinations, November 2008 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) Explain the concept of philosophy of engineering design. (b) Explain the following terms: i. Conceptual design ii. Innovative design. [8+8] 2. (a) Explain the effect of the following factors on the type of fatigue failure. i. Stress distribution ii. Surface treatment (b) Determine the maximum load for a simply supported beam of 0.4m length if the load at the mid-span varies cyclically from 2P to 4P. The size of the beam is 0.05m diameter. The endurance limit for reversed bending is 350 MPa and the yield point in tension is 520 MPa. Take Size correction factor = 0.85 and Surface correction factor = 0.9. Design factor of safety may be taken as 1.9. [4+12] 3. (a) What are the relative advantages and disadvantages of welded joints over riveted joints. (b) A mm angle is joined to a frame by two parallel fillet welds along the edge of 125 mm length. If the angle is subjected to a static load of 180 kn, find the length of weld at the top and bottom. The allowable static load per mm weld length is 430N. [8+8] 4. (a) List out the advantages and disadvantages of screw joints. (b) A mild steel cover plate is to be designed for an inspection hole in the shell of a pressure vessel. The hole is 120 m.m in diameter and the pressure inside the vessel is 6N/mm 2. Design the cover plate along with the bolts. Assume the allowable tensile stress for mild steel on 60 MPa and for bolt material as 40 MPa. [6+10] 5. (a) What is a key? Where it is used? In what basis it is selected? (b) Design a gib and cotter joint to connect square rods with a side of the square as 25mm. Consider σ t = 60MPa σ c = 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. [6+10] 6. (a) Explain the reasons for preferring hollow shafts over solid shafts. 1 of 2

9 Code No: R Set No. 4 (b) A shaft, 2m long between bearings, carries a 900N pulley at its mid-point. Through a belt drive, the shaft receives 25kW at 180 r.p.m. The belt drive is horizontal, and the sum of the belt tensions is 7kN. Determine the shaft diameter and angle of twist, the shaft undergoes. Take G= 80GN/m 2. [4+12] 7. A plane flange coupling for a 75mm shaft has the following dimensions: bore of flange =75mm, hub diameter =135mm, hub length=100mm, flange diameter =250mm, flange thickness=28mm, bolt circle diameter=200mm, bolt diameter=19mm, number of bolts=6, and the key size is 18mm square. All the parts are made of carbon steel having a shearing strength of 400N/mm 2 and a tensile strength of 650N/mm 2. This coupling is rated at 37.3kW power at 100rev/min. (a) Determine the shearing,bearing and tensile stresses in all parts of the coupling. (b) What F.O.S does this coupling have? (c) Is there a possibility of the flange shearing off at the hub? Assume perfect shaft alignment. [16] 8. (a) Why the circular cross section is most commonly used for spring and not others? Under what circumstances the non- circular section would be recommended (b) Design a helical spring for a spring loaded safety valve from the following data: Valve diameter = 65mm Maximum pressure when the valve blows off freely = 0.75 N/mm 2 Valve lift when pressure rises from 0.7 to 0.75 N/mm =3mm Maximum permissible stress in the material of the spring =500 N/mm 2 Spring index = 6 Modulus of rigidity of the spring material = N/mm 2. [6+10] 2 of 2