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Ae 1253 -_mechanics_of_machines

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  • 1. NOORUL ISLAM COLLEGE OF ENGINEERING KUMARAKOIL DEPARTMENT OF AERONAUTICAL ENGINEERING AE 1253 - MECHANICS OF MACHINES 2 MARKS 1. Define a kinematics link UNIT - I Each parts of a machine, which moves relative to some other part is known as kinematics link or element. 2. What are the characteristic of a link? It should have relative motion. It must be a resistant body. 3. What are the types of links? Rigid link, Flexible link, Fluid link 4. Define a structure? It is an assemblage of a number of resistant known as member having no relative motion between them and meant for carrying loads having straining action. Example: Railway Bridge, truss. 5. What is higher pair? When the two element of a pair have a line or point contact when the relative motion takes place and the motion between the two elements is partly turning and partly sliding, then the pair is known as higher pair. 6. Define kinematic chain. When the kinematics pair is coupled in such a way that the last link is jointed to the first link to transmit definite motion it is called a kinematic chain. 7. Define kinematic pair. The two links or elements of a machine when in contact with each other are said to form a pair. If the relative motion between them is completely or successfully constrained the pair is known as kinematic pair. 1
  • 2. 8. Define mechanism. When the one of the links of a kinematic chain is fixed the chain is known as mechanism. 9. State Grubler’s criterion for plane mechanism? Grubler’s criterion applies to mechanism with only single degree of freedom joint where are overall mobility of the mechanism is unity. 3l-2j-4=0 10. Define inversion of the mechanism. The method of obtaining different mechanism by fixing different links in a kinematic chain is known as inversion of the mechanism. 11. What are the types of kinematic chain? Four bar chain or quadric cyclic chain, Single slider crank chain, Double slider crank chain 12. What is single cylinder crank chain? Single cylinder crank chain is a modification of the basic four bar chain. It consists of one sliding pair and three turning pairs. It is usually found in reciprocating steam engine. It converts rotary motion in to reciprocating motion and vice versa. 13. What are the following three inversion of double slider crank chain? Elliptical trammels, Scotch yoke mechanism, Oldham’s coupling 14. What are the methods for determining the velocity of a point on a link? Instantaneous centre method, Relative velocity method 15. State D-Alembert’s principle It start that the resultant force acting on a body together with the reversed effective force are in equilibrium. 16. State Grashof’s law for a four bar mechanism. According this law, the sum of the shortest and longest link length should not be greater than the sum of the remaining two link length if there is to be continuous relative motion between the two links. 2
  • 3. 17. Define Rubbing velocity at a pin joint? The links in amechanism are mostly connected by means of pin joints. The rubbing velocity is defined as the algebraic sum between the angular velocities of the two links which are connected by pin joints, multiplied by the radius of the pin. R= w.r. 18. Name any four types of kinematics part? Sliding pair Turning pair Rolling pair Screw pair Spherical pair 19. The Coriolis component of acceleration is taken in to account for …………… Quick return mechanism. 20. What is a rigid link? A rigid link is one which does not undergo any deformation while transmitting motion. 21. What is a belt? The belts or ropes are used to transmit power from one shaft to another by means of pulleys which rotates at the same speed or at different speeds. 22. What are the factors that have to be considered for the selection of a belt drive? Speed of the driving and driven shafts. Speed reduction ratio Power to be transmitted Shaft lay out Space available 23. What are the types of belt drives? Light drives Medium drives Heavy drives 24. What are the types of belt? Flat belt 3
  • 4. V-belt Circular belt or rope 25. Where is a flat belt used? It is mostly used in the factories and workshops where a moderate amount of power is to be transmitted from one pulley to another when two pulleys are not more than 8 m apart. 26. Where is a V belt used? The V belt is mostly used in the factories and workshops where a great amount of power is to be transmitted from one pulley to another when the two pulleys are very near to each other. 27. Define velocity ratio of a belt drive N1 d1 = N2 d2 When thickness of the belt is considered N 2 d1 + t = N1 d 2 + t 28. Define slip of the belt N1 d1 = N2 d2 S   1 − 100    29. What is the length of open belt drives?  (d1 − d 2 )2  π L= [d1 + d 2] + 2 x +     2 4x   30. What is the length of a crossed belt drives?  (d1 + d 2 )2  π L= [d1 + d 2] + 2 x +     2 4x   31. Define creep of the belt. Tension on the two pulleys is not equal. One side, the tension is greater than the other side due to the difference of two tensions, the belt continuously creeps over the pulleys. This movement of the belt is very small and is called creep of belt. 4
  • 5. 32. Define angle of contact or lap. It is the angle subtended by the arc AB along which the belt touches the pulley at WKH FHQWUH ,W LV GHQRWHG E 32. What is the angle of contact for? (a) Open belt drive (b) Cross belt drive? 2SHQ EHOW GULYH º - 
  • 6. &URVV EHOW GULYH º + 2
  • 7. π rad 180 π rad 180 33. What is the ratio of driving tension for flat belts? T  2.3 log  1  = µθ  T2  34. Define centrifugal tension in a belt. Tc = mV2 = W 2 V g 35. What is the condition for the maximum power transmission? P = (T1 – T2) V For maximum power transmission T = 3Tc 36. What is the ratio of driving tension for V belt? T  2.3 log  1  = µθ cRVHF  T2  37. What is clutch? A clutch is a machine member used to connect a driving shaft to a driven shaft so that the driven shaft may be stared or stopped at with or with out stopping the driving shaft. It is used in automobile. 38. What are the types of clutches? Positive clutch Friction clutch 5
  • 8. 39. What are the types of friction clutch? Disc or plate clutch Cone clutch Centrifugal clutch 40. What is a single plate clutch? It is consist of the following parts Driving plate Driven plate Pressure plate 41. What are the functions of clutch? To engage or disengage the rest of transmission as required. To transmit the engine power to rear wheels when the rear wheels without shock. To enable the gear to get engaged when the vehicle is in motion. 42. What are the factors to be considered when designing a disc or plate clutch? When there is a uniform pressure When there is a uniform axial wear. 43. What is the formula for finding intensity of pressure? P= W 2 2 π (r1 ) − (r2 )    44. Define average pressure Pav? Pav = Total force on friction surface /Cross-sectional area of friction surface 45. What is the total frictional torque acting on the ring of the cone clutch?  (r )3 − (r )3   1 2 2  T = µWn   2  (r ) − (r )2   3 2  1    46. What is bearing? A bearing is a machine element which supports another moving machine element known as journal. It permits a relative motion between the contact surfaces of the member while carrying the load. 47. What are the types of bearing? Radial bearing 6
  • 9. Thrust bearing Sliding bearing Rolling contact bearing 48. Define journal bearing or sleeve bearing? The sliding bearing in which the sliding action is along the circumference of a circle or an arc of a circle and carrying radial loads are known as journal or sleeve bearings. 49. What is the thick film or hydrodynamic lubricated bearing? The thick film bearing are those in which the working surfaces are completely separated from each other by the lubricant. Such type of bearing are called hydrodynamic lubricated bearing 50. What is zero film bearing? The zero film bearing are those which operate with out any lubricant present 51. What is wedge film lubrication? The flow of a viscous fluid in a converging channel is known as wedge film lubrication. 52. What is squeeze film lubrication? The resistance of a viscous fluid to being squeezed out from between approaching surfaces known as squeeze film lubrication. 53. What are the types of rolling contact bearing? Ball bearing Roller bearing 54. What are types of friction clutch? Disc clutch Cone clutch Centrifugal clutch 55. Mention any two advantages of V belt drive over flat belt drive. It provides longer life 3 to 5 years It can be easily installed and removed High velocity ratio Drive is positive. 7
  • 10. 56. What is creep in belt? When the belt passes from the slack side to the tight side a certain portion of the belt extend and it contracts again when the belt passes from tight side to slack side. Due to these changes of length there is a relative motion between the belt and the pulley surfaces. This relative motion is termed as creep of belt. 57. Define Cam. A cam is a rotating machine element which gives reciprocating or oscillation motion to another element known as follower. 58. Where are cams used? The cams are widely used for operating the inlet and exhaust valves of IC engines automatic attachment of machineries paper cutting machines etc. 59. What are the types of follower? Knife edge follower Roller follower Mushroom follower Spherical face follower Reciprocating Oscillation follower Radial follower Offset follower 60. Define Radial follower When the motion of the follower is along an axis passing through the centre of the cam it is known as radial follower. 61. Define offset follower. When the motion of the follower is along as axis away from the cam centre it is called offset follower. 62. What are the types of cams? Radial or Disc cam Cylindrical cam 8
  • 11. 63. Define pressure angle It is the angle between the direction of the follower motion and a normal to the pitch curve. If the pressure angle is too large a reciprocating follower will jam in its bearing. 64. What are the motions of the follower? Uniform velocity Simple harmonic motion Uniform acceleration and retardation Cycloidal motion 65. What are dwell periods? The period during which the follower remains at rest are known as dwell periods. 66. Define angular velocity. It may be defined a ratio of change of angular displacement with respect to time. It is a vector quantity. 67. Define a gear. A gear is a wheel provided with teeth which mesh with the teeth on another wheel or on to rack so as to give positive transmission of motion from one component to another. 68. What are the types of gears? Spur gear Helical gear Bevel gear Worm gear Rack and pinion 69. Define pitch circle It is an imaginary circle which by pure rolling action would give the same motion as the actual gear. 70. Define pressure angle It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point. It is denoted by Ø The standard pressure angles are 141/2º and 20º 9
  • 12. 71. Define Dimeteral pitch. It is the ratio of number of teeth to the pitch circle diameter in mm 72. Define module. It is the ratio of the pitch circle diameter in mm to the number of teeth. 73. Define arc of contact It is the path traced by a point on the pitch circle from the beginning to the end of engagement of a given pair of teeth. 74. State law of gearing. The common normal at the point of contact between a pair of teeth must always pass through the pitch point. 75. Define interference The phenomenon when the tip of a tooth under cuts the root of its mating gear is known as interference. 76. Define gear train The combination of gear wheels by mean of which motion is transmitted from one shaft to another shaft is called a gear train. 77. What are the types of gear train? Simple gear train Component gear train Epicyclic gear train 78. What is simple gear train? A simple gear train is one in which each shaft carries one wheel only. Simple gear trains are employed where a small velocity ratio is required. 79. Define train value It is the reciprocal of velocity ratio = Speed of the driven No. of teeth on driver = Speed of the driver No. of teeth on driven 80. What is a compound train? A compound gear train is one in which each shaft carries two wheels one of which acts as a follower and other acts as a driver to the shaft. It is used for high velocity ratio. 10
  • 13. 81. What are the uses of epicyclic gear train? Transmitting high velocity ratio, with gears of moderate size in a comparatively lesser space. 82. What are the types of vibration? Free vibration Force vibration Damped vibration 83. What are the free vibrations? Longitudinal vibration Transverse vibration Tensional vibration 84. What is degree of freedom? The minimum number of independent coordinates required to specify the motion of a system at any instant is known as degree of freedom of the system. 85. What is simple harmonic motion? The motion of a body, to and fro a about a fixed point is called simple harmonic motion. 86. What is critical or whirling or whipping speed? It is the speed at which the shaft tends to vibrate violently in the transverse direction. The critical speed of the shaft in rps is equal to the natural frequency of transverse vibration in HZ. 87. What is force vibration? When the body vibrates under the influence of external force then the body is said to be under force vibration. 88. What is magnification factor? The ratio of maximum displacement of the forced vibration to the static deflection under static force is known as magnification factor. 89. What is frequency response curve? A curve between magnification factor and frequency ratio ids known as is frequency response curve. 11
  • 14. 90. What is transmissibility? It is defined as the ratio of the force transmitted to the force applied on the system. 91. What is torsionally equivalent shaft? It is the shaft which has the same torsional stiffness as that of the stepped shaft so that it twists to the same extent under a given torque as the stepped shaft would. 92. What is single rotor system? A shaft fixed at one end carrying a rotor at the free end, is known as single rotor system. 93. What is node? The point is section at which the amplitude of vibration is zero, is known as node. 94. What is two node frequencies? One set of values given by the quadratic equation gives the position of two node and the frequency thus obtained is known as two node frequency. 95. What is balancing? Balancing is the process of designing or modifying machinery so that the unbalance is reduced to an acceptable level and if possible is eliminated entirely. 96. What is mass moment? The product of B.b or m.r is called as the mass moment. 97. What is reference plane? Transfer the centrifugal force acting in each plane to a single parallel plane which is termed as reference plane. 98. What is static balance? A system is rotating masses is said to be in static balance if the combined mass centre of the system lied on the axis of rotation. 99. What are conditions for complete balancing? The resultant centrifugal forces must be zero The resultant couple must be zero. 100. What is dynamic balance? A system of rotating masses is in dynamic balance when there does not exist any resultant centrifugal force as well as resultant couple. 12
  • 15. 101. What are the types of locomotive? Coupled locomotive Uncoupled locomotive. 102. Define tractive force The resultant unbalance force due to the two cylinders along the line of stroke is known as tractive force. 103. What is swaying couple? The unbalance forces acting at a distance between the line of stroke of the two cylinders constitute a couple in the horizontal direction. This couple is known as swaying couple. 104. Define hammer blow The maximum magnitude of the unbalance forces along the perpendicular to the line of stroke is known as hammer blow. 13