Code No: R Set No. 1

Transcription

1 Code No: R Set No. 1 III B.Tech I Semester Regular Examinations, November 2007 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 copper bar 50 mm in diameter is placed with a steel tube 75 mm external diameter and 50 mm internal diameter of exactly the same length. The two pieces are rigidly fixed together by two pins 18 mm in diameter, one at each end passing through the bar and tube. Calculate the stress induced in the copper bar, steel tube and pins if the temperature of the combination is raised by 50%. Take E s = 210GN/m 2 ; E c = 105GN/m 2 α s = / o C and α c = / o C. [16] 2. (a) Discuss the effects of the following factors on endurance limit. i. Load factor ii. Surface finish factor iii. size factor. (b) A circular bar of 500 m.m length is supported freely at it two ends. It is acted upon by a central concentrated cyclic load having a minimum value of 20 kn and a maximum value of 50 kn. Determine the diameter of the bar by taking a factor of safty of 1.5, size effect of 0.85, surface finish factor of 0.9. The material properties of bar are given by: ultimate strength of 650 Mpa, yield strength of 500 Mpa and endurance strength of 350 Mpa. [6+10] 3. (a) What are the advantages and disadvantages of welded joints over riveted joints. (b) A plate of 100mm wide and 10mm thick is to be welded with another plate by means of a transverse welds at the ends. If the plates are subjected to a load of 70 kn, find the size of the weld for static as well as fatigue load. The permissible tensile stress should not exceed 70 MPa. [6+10] 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) Explain the method of determining the size of the bolt when the bracket carries an eccentric load perpendicular to the axis of the bolt. [8+8] 5. (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) Design a cotter joint with two gibs to transmit an axial force of 130 kn. The permissible stresses are 165 MPa in tension; 100 M Pa in shear and 180 MPa in crushing. [8+8] 1 of 2

2 Code No: R Set No (a) What is the effect of keyway on: i. strength of shaft, ii. Torsional rigidity of Shaft. (b) Determine the inside and outside diameters of a hollow shaft, which will replace a solid shaft of diameter 50mm. Both the shafts are made of the same material. The hollow shaft should be equally strong in torsion, yet the weight should be half of the solid shaft. [6+10] 7. Design a bushed -pin type flexible couplings to transmit 25kW at 960rpm. Use the following stress values: Shear stress =50MPa(shaft and key) 30MPa(pin) Crushing stress =90MPa (key) Bearing pressure=0.45n/mm 2 (rubber bush). [16] 8. (a) Write short notes on leaf springs (b) A lift system is provided with cushion springs at the bottom of lift. The lift is free to fall. Springs are set in parallel. Specify the required number of springs if the lift has free fall of 1.5m from rest. Weight of lift = 30kN Allowable deflection per spring = 370 mm Number of active turns =15 Spring mean coil diameter =30 mm Spring wire diameter = 30mm Modulus of rigidity for spring =80Gpa. [6+10] 2 of 2

3 Code No: R Set No. 2 III B.Tech I Semester Regular Examinations, November 2007 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 load on a bolt consists of an axial pull of 10 k N together with a transver shear force of 5 kn. Find the diameter of bolt required according to (a) Maximum principal stress theory (b) Maximum shear stress theory (c) Max-principal strain theory (d) Maximum strain energy theory. Take permissible tensile stress at elastic limit=100 Mpa and Poisson s ratio=0.3. [16] 2. (a) Explain the Soderberg method for combination of stresses. (b) A steel rod is subjected to a reversed axial load of 180 kn. Find the diameter of the rod for a factor of safty of 2. Neglect column action. The material has an ultimate tensile strength of 1070 Mpa and yield strength of 910 Mpa. The endurance limit is reversed bending may be assumed to be one half of the ultimate tensile strength. The correction factors are as follows. Load factor =0.7; surface finish factor=0.8 Size factor =0.85; stress concentration factor = 1. [6+10] 3. (a) Classify the rivet heads according to Indian Standard Specification. (b) A double riveted lap joint is made between 15mm thick plates. The rivet diameter and pitch are 25mm and 75mm respectively. If the ultimate stresses are 400 MPa in tension and 320 MPa in shear and 640 MPa in crushing, find the minimum force per inch, which will rupture the joint. If the above joint is subjected to a load such that the factor of safety is 4, find out the actual stresses developed in the plates and the rivets. [6+10] 4. A bracket is bolted to a column by 6 bolts of equal size as shown in figure 4. It carries a load of 50 KN at a distance of 150 mm from the center of column. If the maximum stress in the bolts is to be limited to 150 MPa determine the diameter of bolt. [16] 1 of 2

4 Code No: R Set No. 2 Figure 4 5. (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) 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+10] 6. In axial flow rotary compressor, the shaft is subjected to a maximum twisting moment of 1500N-m and a maximum bending moment of 3000N-m. Neglecting the axial load on the shaft, determine the diameter of the shaft, if the allowable shear stress is 50N/mm 2. Assume K b = 1.5 and K t = 1.2. If the shaft is to be a hollow one with d i /d o =4, what will be the material saving in the hollow shaft. It is subjected to the same loading and of the same material as the solid shaft. Compare the torsional stiffness of the two shafts. [16] 7. Design a bushed-pin type flexible coupling for connecting a motor shaft to a pump shaft, with the following service conditions: Power to be transmitted=40kw Speed of the motor shaft=1000rpm Diameter of motor and pump shafts=45mm Bearing pressure on the rubber bush=0.7n/mm 2 Allowable stress in the pins=60mpa. [16] 8. A helical spring is to support a load of 1000N. The spring is guided by a rod of 50mm diameter. The spring undergoes a deflection of 40 mm under the load. Determine the diameter of the wire and the number of turns required, Use C-60 steel with a factor of safety 2. [16] 2 of 2

5 Code No: R Set No. 3 III B.Tech I Semester Regular Examinations, November 2007 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) Classify the various types Machine Design. (b) What is the procedure adopted in the design of Machine elements. [6+10] 2. A cold drawn steel rod of circular cross-section is subjected to a variable bending moment of 565 N-m to 1130 N-m as the axial load varies from 4500 N to 13500N. The maximum bending moment occurs at the same instant that the axial load is maximum. Determine the required diameter of the rod for a factor of safty 2. Neglect any stress concentration and column effect. Assuming ultimate strength = 550 Mpa, yield strength =470Mpa, size factor=0.85, surface finish factor = Correlation factors = 0.1 for bending and 0.7 for axial load. The endurance limit is reversed bending may be taken as one half the ultimate strength. [16] 3. A low carbon steel plate of 0.7m width welded to a structure of similar material by means of two parallel fillet welds of m length (each) is subjected to an eccentric loa of 4000N, the line of action of which has a distance of 1.5m from the center of gravity of the weld group. Design the required thickness of the plate when the allowable stress of the weld metal is 60 Mpa and that of the plate is 40 Mpa. [16] 4. (a) Define the following terms with necessary sketch. i. Major diameter ii. Minor diameter iii. Pitch iv. Lead. (b) Derive an expression for the maxim load in a bolt. When a bracket with a circular base is bolted to a wall by means of four bolts. [8+8] 5. (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 M Pa; 60 M Pa and 150 M Pa respectively. [6+10] 6. Design a line shaft transmitting power to two machine tools. The power received by the shaft is 30kW at 300 rpm. The power absorbed by pulley P 1 is 12 kw and the remaining power is absorbed by pulley P 2. The diameter of pulley P 1 is 300mm and its mass is 40Kg. the diameter and mass of pulley P 2 are 600mm and 1 of 2

6 Code No: R Set No. 3 75Kg respectively. Assume the belt tension ratio of 2 for both pulleys and the shaft material as 30C8 steel with K m = 2 and K t = 1.5. Draw the B.M and torque diagram s. Assuming maximum shear stress theory. [16] 7. (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 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] 2 of 2

7 Code No: R Set No. 4 III B.Tech I Semester Regular Examinations, November 2007 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 short notes on free cutting steel and stainless steel. (b) State the alloying elements added to steel and the effects they produce in steel. [8+8] 2. A hot rolled steel shaft is subjected to a torsional moment that varies from 330Nm clockwise to 110 N-m counter clock wise and an applied bending moment at a critical section varies from 440 N-m to -220 N-m. The shaft is of uniform crosssection and no key is present at the critical section. Determine the required shaft diameter. The material has an ultimate strength of 550 M N/m 2 and a yield strength of 410MN/m 2. Take the endurance limit as half the ultimate strength, factor of safty of 2, size factor of 0.85 and surface finish factor of [16] 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 is made in 12mm thick plates with 18mm diameter rivets. Find the efficiency of the joint for a pitch of 80mm, if σ t = 115MPa; τ= 80MPa; and σ c = 160Mpa. [6+10] 4. Determine the size of the bolts and the thickness of the arm for the bracket as shown in the figure 4, if it carries a load of 40 KN at an anlge of 60 0 to the vertical. The material of the bracket and the bolt is same for which the safe stresses can be assumed as 70,50 and 105 MPa in tension, shear and compression respectively. [16] 1 of 2 Figure 4

8 Code No: R Set No (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) Design a cotter joint with two gibs to transmit an axial force of 130 kn. The permissible stresses are 165 MPa in tension; 100 M Pa in shear and 180 MPa in crushing. [8+8] 6. Design a line shaft transmitting power to two machine tools. The power received by the shaft is 30kW at 300 rpm. The power absorbed by pulley P 1 is 12 kw and the remaining power is absorbed by pulley P 2. The diameter of pulley P 1 is 300mm and its mass is 40Kg. the diameter and mass of pulley P 2 are 600mm and 75Kg respectively. Assume the belt tension ratio of 2 for both pulleys and the shaft material as 30C8 steel with K m = 2 and K t = 1.5. Draw the B.M and torque diagram s. Assuming maximum shear stress theory. [16] 7. Design a cast iron protective type flange coupling to connect two shafts in order to transmit 7.5kW at 720rpm. The following permissible stresses may be used: Permissible shear stress for shaft, bolt and key material=33mpa Permissible crushing stress for shaft, bolt and key material=60mpa Permissible shear stress for the cast iron=15mpa. [16] 8. (a) List out the functions of springs. (b) A spring for spring balance is to elongate 100mm, when subjected to a load of 200N. Assume that the mean diameter of the coil is to be 6 times the diameter of the wire and the maximum stress to be induced is limited to 400N/mm 2. Determine the diameter for the wire, for the coil and the number of coils required and length of spring. Modulus of rigidity G= N/mm 2. [4+12] 2 of 2