DESIGN OF MACHINE MEMBERS-I

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1 Code No: R31035 R10 Set No: 1 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec /Jan DESIGN OF MACHINE MEMBERS-I (Mechanical Engineering) Time: 3 Hours Max Marks: 75 Answer any FIVE Questions All Questions carry equal marks 1. a) Discuss strength versus rigidity in design. b) Discuss the materials of the following i) Rivets used in a boiler ii) Gears of a lathe c) Connecting rod of an IC engine iv) Safety valve. 2. A cold drawn steel rod of circular cross section is subjected to a variable bending moment of 500 Nm as the axial load varies from 4.5 kn to 13.5 kn. The maximum bending moment occurs at the same instant that the axial load is maximum. Find the diameter of rod neglecting stress concentration. Take Factor of safety as 2. Ultimate strength + 560MN/m 2, Yield strength = 476 MN/m 2 3. Two lengths of mild steel tie rods having width 200 mm and thickness 12.5 mm are to be connected by means of a butt joint with double cover plates. Design and draw the joint. Take allowable strength in tension as 120 N/mm 2, in shear as 80 N/mm 2, and in crushing as 240 N.mm 2 4. (a) Derive an expression for the maximum load in a bolt when a bracket with circular base is bolted to a wall by means of four bolts. (b) A pulley bracket is supported by 4 bolts as shown in fig. 1. The weight of the pulley and the bracket is 1kN and the load is 25kN. Determine the size of the fixing bolts taking allowable shear stress in bolts to be 45N/mm 2 All dimensions in mm Fig. 1 1 of 2

2 Code No: R31035 R10 Set No: 1 5. Design a gib and cotter joint to carry a tensile load of 40kN. The material of the gib, cotter and rods is the same for which the allowable safe stresses are: Tension=24MPa, compression=59mpa and, shear=19mpa 6. A hollow shaft of 0.5 m outside diameter and 0.3 m inside diameter is used to drive a propeller of a marine vessel. The shaft is mounted on bearings 6 metre apart and it transmits 5600 kw at 150 r.p.m. The maximum axial propeller thrust is 500 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. 7. Design and make a neat dimensioned sketch of a muff coupling which is used to connect two steel shafts transmitting 40 kw at 350 r.p.m. The material for the shafts and key is plain carbon steel for which allowable shear and crushing stresses may be taken as 40 MPa and 80 MPa respectively. The material for the muff is cast iron for which the allowable shear stress may be assumed as 15 MPa. 8. Write short note on (a) Leaf springs (b) Nature of failure of helical springs (c) Fracture toughness 2 of 2

3 Code No: R31035 R10 Set No: 2 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec /Jan DESIGN OF MACHINE MEMBERS-I (Mechanical Engineering) Time: 3 Hours Answer any FIVE Questions All Questions carry equal marks Max Marks: a) Discuss in detail about preferred numbers in design b) Give two typical applications of each of the following alloys i) Monel metal ii) Babbit metal iii) Copper-alluminium alloy iv) 70/30 Copper zinc alloy. 2. A pulley is keyed to a shaft midway between two bearings. The shaft is made of cold drawn steel for which ultimate strength is 550 MPa and the yield strength is 400 MPa. The bending moment at the pulley varies from (-150 Nm) to ( 400 Nm) and the torque on the shaft varies from (-50 Nm ) to (150 Nm). Determine the diameter of the shaft for an indefinite life. The stress concentration factor for the keyway at the pulley in bending and in torsion are 1.6 and 1.3 respectively. Take the following values : Factor of safety = 1.5, Load correction factors 1 in bending and 0.6 in torsion, size factor = 0.85, surface effect factor = Design a lap joint for a mild steel flat tie bar 200 mm x 10 mm using 24 mm diameter rivets. Take diameter of rivet hole as 25.5 mm. Design the joint for maximum efficiency. Take strength in tension as 120 N/mm 2, in shear as 80 N/mm 2, in crushing as 200 N/mm (a) Discuss on bolts of uniform strength. Give examples of practical applications of such bolts? (b) A shaft transmits 100kW at 240r.p.m to another shaft through a flange coupling. The bolts in the flange are arranged on a pitch circle of 200mm. Determine the number and size of bolts, if the permissible shear stress in the bolt material is 50MPa. 5. Two rods 40mm diameter are to be joined by a spigot and socket joint cotter joint to carry a load of 1MN in tension. Determine the dimensions of the spigot, socket, and cotter. The allowable stresses are: Tension = 300MPa, Crushing = 450MPa, Shear= 225MPa 6. A hollow steel shaft is to transmit 20 kw at 300 r.p.m. The loading is such that the maximum bending moment is 1000 N-m, the maximum torsional moment is 500 N-m and axial compressive load is 15 kn. The shaft is supported on rigid bearings 1.5 m apart. The maximum permissible shear stress on the shaft is 40 MPa. The inside diameter is 0.8 times the outside diameter. The load is cyclic in nature and applied with shocks. The values for the shock factors are Kt = 1.5 and Km = 1.6. Determine the diameters of the shaft. 1 OF 2

4 Code No: R31035 R10 Set No: 2 7. Design a cast iron protective type flange coupling to transmit 15 kw at 900 r.p.m. from an electric motor to a compressor. The service factor may be assumed as The following permissible stresses may be used : Shear stress for shaft, bolt and key material = 40 MPa Crushing stress for bolt and key = 80 MPa Shear stress for cast iron = 8 MPa Draw a neat sketch of the coupling 8. Write short notes on i. Stresses in helical springs ii. Coaxial springs iii. Different seals for bolted joints 2 of 2

5 Code No: R31035 R10 Set No: 3 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec /Jan DESIGN OF MACHINE MEMBERS-I (Mechanical Engineering) Time: 3 Hours Max Marks: 75 Answer any FIVE Questions All Questions carry equal marks 1. a) Discuss materials for the following i) Shaving blade ii) Nib of a pen iii) Drawing board pins iv) pressure cooker b) Discuss the following i) Basic hole system of dimensioning ii) Need for tolerances in manufacture iii) Types of fits 2. A simply supported beam has a concentrated load at the center which fluctuates from a value of P to 4P. The span of beam is 50cm and its cross section is circular with a diameter of 60 mm. Take loading factor in bending as unity. Size factor = 0.9. surface finish factor = fatigue stress concentration factor = 1. Reliability factor = 1. Yield stress=390 MPa, ultimate strength=520 MPa. Calculate maximum permissible value of P for a factor of safety of Determine the main dimensions of the longitudinal and circumferential joints of a boiler whose inner diameter is 1.7m and the pressure of steam is 40 N/mm 2. The tensile strength of the plate material is 400 N/mm (a) Define the following terms with necessary sketch. (i) Major diameter (ii) Minor diameter (iii) Pitch (iv) Lead. (b)the cylinders head of a steam engine is subjected to a steam pressure of 0.7 N/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 the cylinder is 300mm. Find the size of the bolt so that the stress in the bolt is not exceed 100N/mm (a) What is the difference between a cotter and key? Why a single taper is provide in cotter and not on both sides? Discuss the advantages and limitations of cotter joint. (b) Two mild steel rods of 36mm diameter are to be connected by means of a cotter joint. The ends of the rod to be suitably enlarged by forging. The thickness of the cotter is 12mm. Calculate the dimensions of the joint, if the permissible stresses are 60MPa in tension, 45MPa in shear, and 90MPa in compression 6. A steel spindle transmits 4 kw at 800 r.p.m. The angular deflection should not exceed 0.25 per metre of the spindle. If the modulus of rigidity for the material of the spindle is 84GPa, find the diameter of the spindle and the shear stress induced in the spindle. 1 of 2

6 Code No: R31035 R10 Set No: 3 7. Design a bushed-pin type of flexible coupling to connect a pump shaft to a motor shaft transmitting 32 kw at 960 r.p.m. The overall torque is 20 percent more than mean torque. The material properties are as follows : (a) The allowable shear and crushing stress for shaft and key material is 40 MPa and 80 MPa respectively. (b) The allowable shear stress for cast iron is 15 MPa. (c) The allowable bearing pressure for rubber bush is 0.8 N/mm 2. (d) The material of the pin is same as that of shaft and key. Draw neat sketch of the coupling. 8. Wrote short note on 1. Energy storage capacity of springs. 2. springs in series and parallel. 3. Knuckle joints 2 of 2

7 Code No: R31035 R10 Set No: 4 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec /Jan DESIGN OF MACHINE MEMBERS-I (Mechanical Engineering) Time: 3 Hours Max Marks: 75 Answer any FIVE Questions All Questions carry equal marks 1. a) Discuss the BIS codes of steels. b) Discuss the theories of failure. 2. A 50mm diameter shaft is made from cold drawn low carbon steel. It is subjected to a fluctuating torque 2000 Nm to (-800 Nm). Calculate the factor of safety if the size factor is 0.9 and surface finish factor is Neglect the stress concentration factor. 3. Design a butt joint for two mild steel tie bars 250mm x 10mm. Take allowable stresses in tension as 120N/mm 2, in shear as 85 N/mm 2, in crushing as 240 N/mm (a) Explain the method of determining the size of the bolt when the bracket carries an eccentric load perpendicular to the axis of the bolt. (b) For supporting the travelling crane in a workshop, the brackets are fixed on steel columns as shown in fig. 1. The maximum load that comes on the bracket is 12kN acting vertically at a distance of 400mm from the face of the column. The vertical face of the bracket is secured to a column by four bolts, in two rows (two in each row) at a distance of 50mm from the lower edge of the bracket. Determine the size of the bolts if the permissible value of the tensile stress for the bolt material is 84MPa. Also find the crosssection of the arm of the bracket which is rectangular Fig (a) What is the difference between a knuckle and a cotter joint? Where is the use of knuckle joint is best suited, give some examples of its use. (b) Design a cotter joint with two gibs to transmit an axial force of 115kN. The permissible stresses are 165MPa in tension; 100 M Pa in shear and 180MPa in crushing. 1 of 2

8 Code No: R31035 R10 Set No: 4 6. Compare the weight, strength and stiffness of a hollow shaft of the same external diameter as that of solid shaft. The inside diameter of the hollow shaft being half the external diameter. Both the shafts have the same material and length. 7. Design a bushed-pin type flexible coupling for connecting a motor shaft to a pump shaft for the following service conditions : Power to be transmitted = 40 kw ; speed of the motor shaft = 1000 r.p.m. ; diameter of the motor shaft= 50 mm ; diameter of the pump shaft = 45 mm. The bearing pressure in the rubber bush and allowable stress in the pins are to be limited to0.45 N/mm 2 and 25 MPa respectively. 8. Write short note on a. Springs for fatigue loading b. Helical torsion springs c. Split muff coupling 2 of 2