Anna University,Chennai Nov/Dec 2012 Examinations
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ME2303– DESIGN OF MACHINE ELEMENTS
1. Explain with mathematical expressions. Maximum principal stress theory and Von-Mises-Henky theory
2. A transmission of shaft made C45 steel subjected to a fluctuating torque varying from -100N-m to +500N-m.Also a fluctuating bending moment acts on the shaft which varies from +500N-m to -500Nm. Let the stress concentration factor be 2. The shaft is machined for a factor of safety 1.5.Determine the required diameter of the shaft
3. A circular bar is simply supported with a span of 0.5mand is subjected to a concentrated cyclic load at its midspan. The load varies from a minimum value of20KN to maximum value of 45 KN. The load 3 direction is transverse to the shaft axis. Decide upon the diameter of the bar taking a factor of safety of 1.5 and factor of 0.85 and 0.89 respectively for size effect and surface finish. Take often following values for material properties. Ultimate strength = 650N/mm2, Yield strength = 450N/mm2 Endurance strength =350N/mm2
4. A steel member is subjected to a 3-D stress system and resulting principal stress are 120N/mm2 tension, 80N/mm2and 40N/mm2 co.mpression. If the proportional limit of the material in simple tension is 280N/mm2 and its poison's ratio is O.3.Determine the factor of safety according to (a) Maximum principal stress theory (b) Maximum principal strain theory (c) Maximum shear stress theory.
5. An electric generator rotates at 200rpm and receives 300KW from the driving engine. The armature of the generator is 60cm long and located between bearing 120cm center to center. Owing to the combined weight of armature and magnetic pull, the shaft is subjected to 9000kg acting at right angles to the shaft. The ultimate stress for the shaft is 4480kg/cm2 and shear stress is 3920kg/cm2.Find the diameter of the shaft for a factor of safety of 6
6. Design a cast iron protective type flange coupling to transmit 15KW at 900rpm from an electric motor to a compressor. The service factor may be assumed as 1.35. The following permissible stress may be used: Shear stress for the shaft, bolt and key material=40MPa Crushing stress for bolt and key=80Mpa Shear stress for cast iron=8Mpa
7. Design and sketch protective type C.I flange coupling to transmit 10KW at 250rpm. The permissible shear stress for key, shaft, and bolt as 50N/mm2.Take crushing stress of key as 90N/mm2 and shear stress for C.I as 14N/mm2.Assume maximum torque is 30% higher than mean torque.
8. A line shaft rotating at 200rpm is to transmit 20KW power. the allowable shear stress for the shaft material is 42N/mm2.If the shaft carries a central load of 900N and is simply supported between bearing 3meters apart determine the diameter of the shaft. The maximum tensile or compressive stress is not to exceed 56N/mm2
9. A steam of effective diameter 300mm is subjected to a steam pressure of 1.5N/mm2.The cylinder head is connected by 8 bolts having yield point 330MPa and endurance limit at 240MPa.The bolts are tightened with an initial per load 1.5 times the steam load. A soft copper gasket is used to make the joint leak proof. Assuming a factor of safety 2, find engine size of bolt required. The stiffness factor for copper gasket may be taken as 0.5.
10.A plate 75mm wide and 10mm thick is jointed with another plate by a single transverse weld and double parallel fillet as shown in fig. The joint is subjected to a maximum tensile force of 55KN. The permissible tensile and shear stress are 70MPa and 50MPa respectively. Find the length of each parallel fillet weld
11. A plate 100m wide and 12.5mm thick is to be welded to another plate by means of two parallel fillet welds. The plates are subjected to a load of 50KN.Find the length of the weld so that the maximum stress does not exceed 56N/mm2. (Do the calculations under static loading).
12. A gas engine valve spring is to have a mean diameter 37.5mm.The maximum load will have to sustain is 450N with a corresponding deflection of 12.5mm.The spring is to be subjected to repeated loading and fatigue must be considered a low working stress of 300N/mm2 will be used. Find the sizefor the wire and number of coil used. Take rigidity of modulus as 0.8XI05 N/mm2
13. A closely coil helical spring is made of 10mm diameter steel wire, the coil consisting of 10 complete turns with a mean diameter of 120mm.The springs carries an axial pull of 200N.Determine also deflection in the spring, its stiffness and strain energy stored by it if the modulus of rigidity of the material is 80KN/mm2
14.A semi-elliptical leaf spring of 1m long and is required to resist a load of 50KN.The spring has 15 leaves of which three are full length leaves. The width of central band is 100mm. All the leaves are to be stressed to 420MPa.The ratio of total depth to width is 3.Take, =2.1Xl05MPa.Determine, (i) The thickness and width of the leaves. (ii)The initial gap that should be provided between the full lengths and graduated leaves before assembly. (iii)The load exerted on the band for the assembly
15. Design of leaf spring for a truck to the following specifications: Maximum load on the spring = 140KN No of spring = 4 Material for spring chromium vanadium steel Permissible tensile stress = 600N/mm2 Maximum number of leaves =10 Span of spring = 1000mm Permissible deflection = 80mm Young's modulus of the spring = 200N/mm2
16.Design a journal bearing for a centrifugal pump from the following data: Load on the journal=20000N, Speed of the journal=900rpm, Type of oil is SAElO, for which the absolute viscosity at 55°C=0.017kg/m-s, Ambient temperature of oil = 15.50C, Maximum bearing pressure for the pump=1.5N/mm2.Calculate also mass of the lubricating oil required for artificial cooling, If the rise of temperature, if the rise of temperature of oil be limited to lOoC heat dissipation coefficient=1232W/m2/oC
17. A 150mm diameter shaft supporting a load of 10KN has a speed of 1500rpm.The shaft run in whose bearing length is 1.5 times the shaft diameter. If the diametric clearance of bearing is 0.15mm and the absolute viscosity of the oil at the operating temperature is 0.011 Kg/m-s. Find the power wasted in friction
18.A full journal bearing of 50mm diameter and 100mm long has a bearing pressure of l.4N/mm2• The speed of the journal is 900rpm and the ratio of journal diameter to the diametric clearance is 1000. The bearing is lubricated with oil, whose absolute viscosity at the operating temperature of 75°C may be taken as 0.011 kg/m-s. The room temperature is 350C.Find, (1) The amount of artificial cooling required. (2)The mass of lubricating oil required, if the difference between the outlet and inlet temperature of the oil is 10°C. Take specific heat of oil as 1850J/Kg/0C.
19.The turning moment diagram of a multi-cylinder engine is drawn with a scale of (1 mm = 1°) on the abscissa and (1 mm = 250 Nm)on the ordinate. The intercepted between the torque developed by the engine and the mean resisting torque of the machine, taken in order from one are -350,+800,- 600,+900, 11-550,+450,-650 mm2.The engine is running at a mean speed fluctuations is limited to 0.02.A rimmed flywheel made of grey cast iron FG 200 (Density=7100Kg/m3) is provided. The spokes, shaft and hub are assumed to contribute 10% of the required moment of inertia. The rim has rectangular cross section and the ratio of width to thickness is 1.5.Determine the dimensions of the rim.