Design of Machine Elements UNIT –1

1. Define machine design.A machine is a combination of several machine elements arranged to work together as a whole to accomplish specific purposes. Machine design involves designing the elements and arranging them optimally to obtain some useful work.2: What is an adaptive design?Adaptive design is based on an existing design adapted for a new system or application, for example, design of a new model of passenger car.3: Suggest briefly the steps to be followed by a designer.Machine design requires a thorough knowledge of engineering science in its totality along with a clear decision making capability. Every designer follows his own methodology based on experience and analysis. However, the main steps to be followed in general are :• Define the problem.• Make preliminary design decisions.• Make design sketches.• Carry out design analysis and optimization.• Design the elements for strength and durability.• Prepare documentations to be followed for manufacture.4: Discuss ‘factor of safety ‘in view of the reliability in machine design.Reliability of a designed machine is concerned with the proper functioning of the elements and the machine as a whole so that the machine does not fail in use within its designed life. There is no single answer to this and an overall safe design approach at every stage of the design is needed. Use of factor of safety in designing the elements is to optimize the design to avoid overdesign for reliability.5: State atleast 5 important mechanical properties of materials to be considered in machine design.Some important properties of materials to be considered in design are:Elastic limit, yield and ultimate strength, hardness and toughness.6: Define resilience and discuss its implication in the choice of materials in machine design.Resilience is defined as the property of a material that enables it to resist shock and impact. The property is important in choosing materials for machine parts subjected to shock loading, such as, fasteners, springs etc.7. What is meant by tolerance? How many types of tolerance are there?

Tolerance is the difference between maximum and minimum dimensions of a component, ie, between upper limit and lower limit. Depending on the type of application, the permissible variation of dimension is set as per available standard grades. Tolerance is of two types, bilateral and unilateral. When tolerance is present on both sides of nominal size, it is termed as bilateral; unilateral has tolerance only on one side.

8. What are the types fit? Describe the differences.The nature of assembly of two mating parts is defined by three types of fit system, Clearance Fit, Transition Fit and Interference Fit.Clearance Fit: In this type of fit, the shaft of largest possible diameter can be fitted easily in the hole of smallest possible diameter.Interference Fit : In this type of fit, irrespective of tolerance grade there is always a overlapping of the matting parts.Transition Fit: In this case, a clearance is present between the minimum dimension of the shaft and the minimum dimension of the hole. However, the fit is tight, if the shaft dimension is maximum and the hole dimension is minimum. Hence, transition fit have both the characteristics of clearance fit and interference fit.

9. What are preferred numbers?A3. Preferred numbers are the numbers belonging to four categories of geometric progression series, called basic series, having common ratio of,

Preferred numbers of derived series are formed by multiplying or dividing the basic series by 10, 100 etc. These numbers are used to build-up or manufacture a product range. The range of operational speeds of a machine or the range of powers of a typical machine may be also as per a series of preferred numbers.1. What are the various phases of design process?

i. Recognition of need.ii. Definition of problemiii. Synthesisiv. Analysis and optimizationv. Evaluationvi. Presentation

2. Define: Factor of safetyThe ratio between maximum stresses to working stress is known as factor

of safety.Maximum stress

Factor of safety =Working stress.

3. What are the different types of loads that can act on machine components?a. Steady load.b. Variable load.c. Shock loadd. Impact load.

4. What are the types of variable stresses?a. Completely reversed or cyclic stressesb. Fluctuating stressesc. Repeated stressesd. Alternating stresses

5. Differentiate between repeated stress and reversed stress.Repeated stress refers to a stress varying from zero to a maximum value of

same nature. Reversed stress of cyclic stress varies from one value of tension to the

same value of compression.

6. What is impact load?If the time of load application is less than one third of the lowest natural

period of vibration of the part, it is called an impact load.

7. Define endurance limit. Endurance limit is the maximum value of completely reversed stress that

the standard specimen can sustain an infinite number (106) of cycles without failure.

8. What are the factors affecting endurance strength.Factors affecting endurance strength are

i. Load ii. Surface finishiii. Size iv. Temperaturev. Impact vi. Reliability

9. What are the types of fracture?a. Ductile fractureb. Brittle fracture

10. Distinguish between brittle fracture and ductile fracture.In brittle fracture, crack growth is up to a small depth of the material. In

ductile fracture large amount of plastic deformation is present to a higher depth.

11. What are the modes of fracture?a. Mode I (Opening mode) – Displacement is normal to crack surface. b. Mode II (Sliding mode) – Displacement is in the plane of the plate. c. Mode III (Tearing mode) – Out of plane shear.

12. Explain Griffith theory. (Or) State the condition for crack growth. A crack can propagate if the energy release rate of crack is greater than

crack resistance.

13. Define stress concentration and stress concentration factor.Stress concentration is the increase in local stresses at points of rapid

change in cross section or discontinuities. Stress concentration factor is the ratio of maximum stress at critical

section to the nominal stress

14. Give some methods of reducing stress concentration.i. Avoiding sharp corners.ii. Providing fillets.iii. Use of multiple holes instead of single holeiv. Undercutting the shoulder parts.

15. What are the factors to be considered in the selection of materials for a machine element?i. Required material propertiesii. Manufacturing easeiii. Material availabilityiv. Cost

29. Write the bending equation. M/I = E/R = Fs/Y. M – Bending moment I - Moment of intertia E - Youngs modulus R - Radius of the shaft Fs – Shear stress Y - Distance from neutral axis 30. Write the torsion equation. T/J = CØ/L = Fs/R T – Torque J - Polar moment of intertia C- Rigidity modulus Ø – Angle of twist L – Length of the shaft Fs – Shear stress R - Radius of the shaft 25.Define fatigue When a material is subjected to repeated stress, it fails at stresses below the yield point stress; such type of failure of the material is called fatigue.

26. What is curved beam? In curved beam the neutral axis does not coincide with the centroidal axis.27. Give some example for curved beam. C frame, crane hook 16. Why are metals in pure form are unsuitable for industrial use?

In pure form, metals do not have required physical, chemical and mechanical properties. This makes them unsuitable for industrial use where severe service conditions exist.

17. What are various theories of failure?i. Maximum principal stress theory.ii. Maximum shear stress theory.iii. Maximum principal strain theory.iv. Maximum strain energy theory.

18. What is the use of Goodman & Soderberg diagrams?They are used to solve the problems of variable stresses.

19. Explain notch sensitivity. State the relation between stress concentration factor, fatigue stress concentration factor and notch sensitivity.

Notch sensitivity (q) is the degree to which the theoretical effect of stress concentration is actually reached. The relation is, Kf = 1 + q (Kt-1)

20. What are the factors that effect notch sensitivity?i. Materialii. Notch radiusiii. Size of componentiv. Type of loadingv. Grain Structure

21. Explain size factor in endurance strength.Size factor is used to consider the effect of the size on endurance strength.

A large size object will have more defects compared to a small one. So, endurance strength is reduced. If K is the size factor,

Actual endurance strength = Theoretical endurance limit x K

22. What is an S-N Curve?An S- N curve has fatigue stress on Y axis and number of loading cycles

in X axis. It is used to find the fatigue stress value corresponding to a given number of cycles.

23. Why normal stress theory is not suitable for ductile materials?Failure of ductile materials is mostly by shearing. But this theory

considers only tensile or compressive stresses. So, this is not suitable for ductile materials.

24. What are the methods used to improve fatigue strengthi. Cold working like shot peening, burnishing.ii. Heat treatments like induction hardening, case hardening, nitrating.iii. Pre – stressing (or) auto fretting.

25. Define strengthIt is the ability of material to resist the externally applied forces without

breaking or yielding .the internal resistance offered by a part to externally applied forces called stress.

26. Define stiffness It is the ability of the material to resist deformation under stress. The

modulus of elasticity is a measure of stiffness.

27. Define elasticityIt is the property of a material to regain its original shape after

deformation when external forces are removed. It is desirable for materials used in tools and machines.

28. Define plasticityIt is the property of the material, which retains the deformation produced

under load permanently. It is necessary for forging and in ornamental work.

29. Define DuctilityIt is the property of the material enabling it to be drawn into wire, with the

application of tensile force. It must be both strong and plastic. It is usually measured in terms of percentage elongation and reduction in area. (eg) Ni, Al, Cu

30. Define brittlenessIt is the property of the material opposite to ductility. It is the property of

breaking of a material with little permanent distortion. Brittle material when subjected to tensile loads snaps off without giving any sensible elongation.

(eg) cast iron

31. Define malleabilityIt is a special case of ductility, which permits material to be rolled or

hammered into thin sheets. The malleable material should be plastic but not essential to be so strong.

(eg) Lead, Cu, Al

32. Define toughnessIt is the property of the material to resist fracture due to high impact loads

like hammer blows. The toughness of material decreases when it is heated. It is desirable in parts subjected to shock and impact loads.

33. Define machinabilityIt is the property of the material, which refers to a relative case with which

a material can be cut. It is measured in a number of ways such as comparing the tool life for cutting different material.

34. Define resilienceIt is the property of the material to absorb energy and to resist shock and

impact loads. It is measured by amount of energy absorbed / unit volume within the elastic limit. It is essential for spring materials.

35. Define creep When a part is subjected to a constant stress at high temperature for long time, it will undergo a slow, permanent deformation called creep.

36. Define fatigueWhen a material is subjected to repeated stress, it fails at stresses below

the yield point stress; such type of failure of the material is called fatigue.

37. Define hardnessIt is very important property of the material and has a wide variety of

meanings. It embraces many different properties such as resistance to wear, scratching, deformation and machinability etc. It also means the ability of the metal to cut another metal. It is usually expressed in numbers, which are dependent on method of making the test.

38. What is interchangeable manufacture?Manufacturing process in which the produced parts that go in to assembly

may be selected at random from a large number of parts.

39. Define: Tolerance Tolerance is the amount of variation permitted to a basic size. [Or]

Difference between maximum and minimum limits of size is called tolerance.

40. Define deviationDeviation is the difference between actual size and the basic size.

41. Define zero lineZero line is a line that represents basic size. Deviations are referred to this

line.

42. Explain hole basis system and shaft basis system.Hole basis system: - In this, the hole size is kept constant and shaft size is

varied to get required fit.Shaft basis system: In this, shaft size is kept constant and hole size is

varied to get the required fit.43. Why hole basis system is preferred?

Hole basis system is preferred because it requires less number of tools that results in less cost of manufacture.

44. Define fitFit is the degree of tightness or looseness between the two mating

surfaces.

45. What are the factors that influence the amount of tolerances to be given on a part?

i. Function of the product.ii. Manufacturing process available.iii. Cost of production.

47. Define ‘Lay’Lay is the principal direction of tool marks that make a pattern on the

machined surface.50. Define basic size

It is the size of a part to which all limits of variations are applied to get the final dimensioning of the mating parts.

51. Define actual size It is the actual measured dimension of the part. The difference between basic and actual size should not exceed a certain limit otherwise it will interfere with interchangeability of the mating parts.

52. Define limits of sizeThere are two extreme permissible sizes for the dimension of the part. The

largest permissible size of the part is called upper limit and the smallest size is called the lower or the minimum limit.

53. Define AllowanceIt is the difference between the basic dimensions of the mating parts. The

allowance may be positive or negative. when the shaft size is less than the hole size the allowance is positive and when the shaft size is greater than the hole size, then the allowance is negative.

55. Define unilateral toleranceWhen the tolerance is allowed on one side of the nominal size then it is

said to be unilateral tolerance.56. Define bilateral tolerance

When the tolerance is allowed on both sides of the nominal size then it is said to be bilateral tolerance.

UNIT-3

1. Define: Pitch, Lead.Pitch: Axial distance from a point on one thread to corresponding point on next thread.Lead: Distance the screw moves in one turn.

2. How is a bolt designated?i. A bolt is designated by a letter M followed by nominal diameter

and pitch in mm.

3. What factors influence the amount of initial tension?External loadMaterial usedBolt diameter

4. What is bolt of uniform strength?A bolt of uniform strength has equal strength at the thread and shank portion.

5. What are the ways to produce bolts of uniform strength?Reducing shank diameter equal to root diameter.Drilling axial hole

6. What stresses act on screw fastenings?Initial stresses due to screwing up

Stresses due to external forcesCombined stresses.

7. Define welding.i. Welding can be defined as a process of joining two similar or

dissimilar metals with or without application of pressure along with or without addition of filler material.

8. What are the types of welded joints?Butt jointLap jointT – jointCorner jointEdge joint.

9. Define butt and lap jointi. Butt joint: The joint is made by welding the ends or edges of two

plates.ii. Lap joint: The two plates are overlapping each other for a certain

distance. Then welded. Such welding is called fillet weld.

10. Define: Tee – joint and corner joint.i. T – joint: The two plates are arranged in ‘T’ shape, which means

the plates are located at right angles to each other. ii. Corner joint: Two plates are arranged at right angles such that it

forms an angle.

11. Define edge jointi. For plates of thickness less than 6mm, the ends of the overlapping

plates can be directly welded at the edges called edge weld.

12. When will the edge preparation need?i. If the two plates to be welded have more than 6mm thickness, the

edge preparation should be carried out.

13. What are the two types of fillet weld?Longitudinal or parallel fillet weldTransverse fillet weld.

14. When will the weld deposit be weaker?When the components are made of high carbon steel or alloy steel, the weld becomes weaker.

15. What are the two types of stresses are induced in eccentric loading of loaded joint?

a. Direct shear stress.b. Bending or torsional shear stress.

16. State the two types of eccentric welded connections.Welded connections subjected to moment in a plane of the weld.Welded connections subjected to moment in a plane normal to the plane of the weld.

17. What is the significance of welding specification?a. To convey the designers idea to the welding operator by placing it to a

suitable place of the drawing.b. To specify the type of weld.

18. What are the main indications of complete weld symbol?A basic symbol is to specify the type of weld.An arrow and a reference line to indicate the location of the weld. Supplementary symbols to indicate special instructions. Dimensions of the weld in cross section and length.

19. What are the various parts of rivet?a. Shankb. Head

20. What are the materials used for making rivets?Mild steelWrought ironCopperAluminium

21. What are the applications of rivets?In structural connections.Pressure vessel work.General – purpose machines, turbines, brake bands etc.

22. What are the different working processes used for making riveting?Cold riveting.Hot riveting.

23. What are the types of riveted joints according to the type of joint?a. Lap jointb. Butt joint

24. What are the types of riveted butt joints according to the number of strap?a. Single strapb. Double strapc. Triple strapd. Quadruple strap.

25. What are the types of riveting?a. Chain riveting. 2.Zig – zag riveting.

26. Define Gauge line The line passing through the center of the rivets and parallel to the plate is called the gauge line. It is also known as pitch line.

27. Define the efficiency of a riveted joint.

The efficiency of a riveted joint is defined, as the ratio of strength of the joint at the weakest made of failure to the strength of unpunched plate in one pitch length of the joint.

Strength of the joint in the weakest mode = Strength of the unpunched plate

Least of Ft,, Fs and Fc

= p x t x t

28. Define longitudinal jointThe ends of the plate are joined to get the required diameter of a boiler.

29. Define circumferential joint.The ends of the plates are joined to the required length of the shell and to close its ends.

30. What does a rivet mean?A rivet is a short cylindrical bar with a head integral to it. The cylindrical portion of the rivet is called shank or body and the lower portion of shank is known as tail.

31. What are the two types of fastenings?The two types of fastenings are

Permanent fasteningsTemporary or detachable fastenings

32. What is a permanent fastening? Give example?The permanent fastenings are those fastenings, which cannot be disassembled without destroying the connecting components. E.g. riveted joints

33. What is a temporary fastening? Give example.The temporary or detachable fastenings are those fastenings, which can be disassembled with out destroying the connecting components. E.g. screws, keys, pins.

34. What are the methods of riveting? The two types of riveting are

Cold riveting b. Hot riveting35. What does cold riveting mean?

The plates to be riveted are drilled together and a rivet is introduced into the plates and the point is then formed. When a cold rivet is used, the process is known as cold riveting.

36. What is meant by hot riveting?The plates to be riveted are drilled together and a rivet is introduced into the plates and the point is then formed. When a red hot rivet is used, the process is known as cold riveting.

37. What are the applications of cold and hot riveting?The cold riveting is used for making structural joints. The hot riveting is used for making leak proof joints.

38. What are the types of riveted joints depending upon the way in which the plates are connected?

The two types riveted joints areLap jointButt joint

39. What is meant by a lap joint?A lap joint is a type of joint in which one plate overlaps the other and the two plates are then riveted together.

40. What is meant by a butt joint?A butt joint is a type of joint in which the main plates are kept in alignment butting each other and a cover plate placed either on one side or on both sides of the main plates. The cover plate is then riveted with the main plates.

41. What are the types of butt joint?The two types of butt joints are

Single strap butt jointDouble strap butt joint

42. What are the types of riveted joints depending upon the number of rows of rivets?The types of riveted joints depending upon the number of rows of rivets are

Single riveted jointDouble riveted jointTriple riveted jointQuadruple riveted joint

43. What is meant by pitch in a riveted joint?Pitch (p) in a riveted joint is the distance from the Centre of one rivet to the Centre of the next rivet measured parallel to the seam.

44. What is meant by back pitch in a riveted joint? Back pitch (pb) is the perpendicular distance between the centre lines of successive rows of rivets.

45. What is meant by diagonal pitch in a riveted joint?Diagonal pitch is the distance between the centres of the rivets in adjacent rows of zig-zag riveted joints.

46. What is meant by margin or marginal pitch in a riveted joint?Marginal pitch is the distance between the centres of rivet hole to the nearest edge of the plate.

47. What are the types of failures in riveted joints?The types of failures in riveted joints are

Tearing of the plate at an edge

Tearing of the plate across a row of rivetsShearing of the rivetsCrushing of the plate or rivets.

48. What are the advantages of welded joints over riveted joints?The advantages of welded joints over riveted joints are

a. The welded joints are relatively lighter than riveted structures.

b. The welded joints provide maximum efficiency, which is not possible in riveted joints

c. Welding provides very rigid jointsd. It is possible to weld any part of a structure at any point. But

riveting requires enough clearance.

49. What are the disadvantages of welded joints?The disadvantages of welded joins are

a. There is uneven heating and cooling during fabrication, therefore additional stress may develop

b. Highly skilled labour are requiredc. Since no provisions is kept for expansion and contraction in the frame,

there is a possibility of cracks developing in it.d. The inspection of welding work is more difficult.

50. How are welding processes classified?The welding process may be broadly classified into two groups. They are

i. Welding process that use heat alone.ii. Welding process that use both heat and pressure

51. What are the different methods of fusion welding?The different methods of fusion welding are

Thermit weldingGas weldingElectric arc welding52. What are the different types of welded joints?

The different types of welded joints areLap or fillet jointButt joints

53. What are the different types of butt joints?The different types of butt joints are

Square butt jointSingle V-butt jointSingle U-butt jointDouble V-butt jointDouble U-butt joint

54. What are the main considerations involved in selection of weld type?The main considerations involved in selection of weld type areThe shape of the welded components required.The thickness of the plate to be weldedThe direction of the forces applied.

55. What are the different applications of screwed fasteners?The different applications of screwed fasteners are

For readily connecting & disconnecting machine parts with out damage The parts can be rigidly connectedUsed for transmitting power

56. What are the advantages of screwed fasteners?The advantages of screwed fasteners are

They are highly reliable in operationThey are convenient to assemble & disassembleA wide range of screws can be used for various operating conditionsThey are relatively cheap to produce.

57. What is the disadvantage of screwed fasteners?The disadvantage of screwed fasteners is the stress concentration in the thread portions, which are vulnerable points under loaded condition.

58. Define major diameter of screwed fastenersMajor diameter is defined as the largest diameter of an external or internal screw thread. It is also known as outside or nominal diameter.

59. Define minor diameter.Minor diameter is defined as the smallest diameter of an external or internal screw thread. It is also known as core or root diameter.

60. Define pitch diameter.Pitch diameter is defined as the diameter of an imaginary cylinder on a screw thread, the surface of which passes through the thread at such points as to make the width and space equal between threads. It is also called as effective diameter.

61. Define pitch.Pitch is defined as the distance from appoint on one thread to the corresponding on the adjacent thread in the same axis plane.

62. Define lead.Lead is defined as the distance, which a screw thread advances axially in one rotation of the nut.

63. Define the terms 1) crest 2) roota. Crest is defined as the top most surface of the thread b. Root is defined as the bottom surface created by the two adjacent flanks of

the thread

64. Define the terms 1) depth of thread 2) flankDepth of the thread is the perpendicular distance between the crest and the root.Flank is defined as the surface joining the flanks and the root

65. Define angle of thread of screw fastenersAngle of thread is defined as the angle included by the two flanks of the thread.

66. Define slope of a screw of a screw thread.Slope of the screw thread is defined as the half of the pitch of the thread.

67. What are the various forms of screw threads?The various forms of screw threads are

British standard whitworth thread (BSW)British association thread (BA)American national standard threadUnified standard threadSquare threadAcme threadKnuckle threadButtress threadMetric thread68. What are the common types of screw fastening?

The common types of screw fastening areThrough holesTap boltsStudsCap screwsMachine screwsSet screws69. Why do we go for locking devices in screwed fasteners?

Ordinary thread fastenings remain tight under static loads, but many of these become loose under variable loads or vibrations. The loosening of screw is very dangerous so devices called locking device are used for tightening the fasteners.

70. What are the different types of locking devices?The different types of locking devices used in screwed fasteners areJam nut or lock nutCastle nut Sawn nutPenn, ring or grooved nutLocking with pin Locking with plate Spring lock washer71. What does a bolt M24 *2 mean?

The nominal diameter is 24 mm and the pitch is given as 2 mm.72. What are the stresses induced in screw fastening due to static loading?

Under static loading screwed fasteners are subjected toInternal stress due to screwing up forcesStresses due to external forcesStress due to combination of both73. What are the stresses induced in a bolt when it is screwed up tightly?

The various stresses induced are Tensile stress due to stretching of bolt

Torsional shear stress caused by the frictional resistance of the threadsShear stress Compression or crushing stress on threadsBending stress74. What are the stresses induced in a bolt when it is subjected to external forces

or loads? The stresses induced due to external loads or forces areTensile stress

Shear stressCombined tension and shear stress

UNIT-2

1. Define the term critical speed.The speed, at which the shaft runs so that the additional deflection of the

shaft from the axis of rotation becomes infinite, is known as critical or whirling speed.

2. Write down the dunker ley’s equation for the critical speed of the shaft. When a shaft carries n pulleys or gears, the critical speed of the shaft may

be found by Dunker ley’s equation.

1 1 1 1= + + ………+

22 1

2 22 n

2

Where 1, 2, 3, ……….. n are the critical speeds of the shaft when each mass is considered.

3. What is key?A key is device, which is used for connecting two machine parts for

preventing relative motion of rotation with respect to each other.

4. What are the types of keys?i. Saddle keyii. Tangent keyiii. Sunk keyiv. Round key and taper pins

5. What is the main use of woodruff keys?A woodruff key is used to transmit small value of torque in automotive

and machine tool industries. The keyway in the shaft is milled in a curved shape whereas the key way in the hub is usually straight.

6.List the various failures occurred in sunk keys.1. Shear failure2. Crushing failure

7.What is the function of a coupling between two shafts?Couplings are used to connect sections of long transmission shafts and to

connect the shaft of a driving machine to the shaft of a driven machine.

8. Under what circumstances flexible couplings are used?They are used to join the abutting ends of shafts when they are not in exact

alignment. They are used to permit an axial misalignment of the shafts without under absorption of the power, which the shafts are transmitting.

9. What are the purposes in machinery for which couplings are used?i. To provide the connection of shafts of units those are manufactured separately

such as motor and generator and to provide for disconnection for repairs or alterations.

ii. To provide misalignment of the shafts or to introduce mechanical flexibility. iii. To reduce the transmission of shock from one shaft to another. iv. To introduce protection against over load.

UNIT -V1. What is bearing?

Bearing is a stationery machine element which supports a rotating shafts or axles and confines its motion.

2. Classify the types of bearings.i. Depending upon the type of load coming upon the shaft:

a. Radial bearingb. Thrust bearings.

ii. Depending upon the nature of contact:a. Sliding contactb. Rolling contact bearings or Antifriction bearings.

3. What are the required properties of bearing materials?Bearing material should have the following properties.

i. High compressive strengthii. Low coefficient of frictioniii. High thermal conductivityiv. High resistance to corrosionv. Sufficient fatigue strengthvi. It should be soft with a low modulus of elasticityvii. Bearing materials should not get weld easily to the journal material.

4. What is a journal bearing? A journal bearing is a sliding contact bearing which gives lateral support

to the rotating shaft.

5. What are the types of journal bearings depending upon the nature of contact?2. Full journal bearing3. Partial bearing4. Fitted bearing.

6. What are the types of journal bearing depending upon the nature of lubrication? 1. Thick film type2. Thin film type3. Hydrostatic bearings4. Hydrodynamic bearing.

7. What is known as self – acting bearing?The pressure is created within the system due to rotation of the shaft, this

type of bearing is known as self – acting bearing.

8. Define Kinematic viscosity.

The Kinematic viscosity is defined as the ratio of absolute viscosity to the density of oil. It is denoted by ‘’.

9. What is connecting rod?Connecting rod is a machine member, which used to transmit power from

a reciprocating member to rotary one or vice versa.

10. What is the function of piston?The function of piston is to transfer the gas forces and inertia forces to the

connecting rod and crank shaft.

11. What is the use of ribs in piston?Ribs make the piston rigid and prevent distortion due to gas load and

connecting rod thrust.

12. What is the use of piston rings?Piston rings impact necessary radial pressure to maintain the seal between

the piston & cylinder bore.

13. What are the materials used for piston rings?The material of piston rings is cast iron or alloy cast iron. This has good

wear resisting qualities.

14. When the thrust is maximum on the piston? Thrust on the piston is maximum, when the crankshaft is perpendicular to

connecting rod.

15. Define antifriction bearings.In antifriction bearings the contact between the bearing elements is rolling

and this type has very small friction. Hence the name antifriction bearings.

16. What are the types of rolling contact bearings?Depending upon the type of rolling element.

a. Ball bearing and Roller bearingDepending upon the load to be carried Radial Angular contact and Thrust bearing.17. State the components of rolling contact bearings.

i. Outer race ii. Inner race iii) Rolling element andiv. Retaining race or separator.

18. Define the term bearing life. The life of a radial ball bearing is the number of revolutions or hours at a

given constant speed that the bearing runs before the first evidence of fatigue develops in the material of either ring or in a ball.

19. What is load rating?The load carrying capacity of a rolling element bearing is called its load

rating.

20. What is basic static load rating?It is defined as load acting on a non-rotating bearing under which

permanent deformation of 0.0001 times the ball or roller diameter.

21. Define the term dynamic load rating.The dynamic load rating is defined as the radial load in radial bearings (or

thrust load in thrust bearings) that can be carried for a minimum life of one million revolutions.

UNIT-4

1. What is a spring?A spring is an elastic member, which deflects, or distorts under the action of load and regains its original shape after the load is removed.

2. State any two functions of springs. To measure forces in spring balance, meters and engine indicators. To store energy.

3. What are the various types of springs?Helical springsSpiral springsLeaf springsDisc spring or Belleville springs

4. Classify the helical springs.a. Close – coiled or tension helical spring.b. Open –coiled or compression helical spring.

5. Define : Leaf springsA leaf spring consists of flat bars of varying lengths clamped together and supported at both ends, thus acting as a simply supported beam.

6. Define : Belleville SpringsThey are made in the form of a cone disc to carry a high compressive force. In order to improve their load carrying capacity, they may be stacked up together. The major stresses are tensile and compressive.

7. What is pitch?The axial distance between adjacent coils in uncompressed state.

8. What is solid length? The length of a spring under the maximum compression is called its solid length. It is the product of total number of coils and the diameter of wire.

Ls = nt x dWhere, nt = total number of coils.

9. What are the requirements of spring while designing?Spring must carry the service load without the stress exceeding the safe value. The spring rate must be satisfactory for the given application.

10. What are the end conditions of spring?i. Plain end.

ii. Plain and ground endiii. Squared endiv. Squared and ground end.

11. What is buckling of springs?The helical compression spring behaves like a column and buckles at a comparative small load when the length of the spring is more than 4 times the mean coil diameter.

12. What is surge in springs?The material is subjected to higher stresses, which may cause early fatigue failure. This effect is called as spring surge.

13. What is a laminated leaf spring?In order to increase, the load carrying capacity, number of flat plates are placed and below the other.

14. What semi – elliptical leaf springs?The spring consists of number of leaves, which are held together by U- clips. The long leaf fastened to the supported is called master leaf. Remaining leaves are called as graduated leaves.

15. What is nipping of laminated leaf spring? Prestressing of leaf springs is obtained by a difference of radii of curvature known as nipping.

16. What are the various application of springs?The springs are used in various applications, they are Used to absorb energy or shocks (e.g. shock absorbers, buffers, e.t.c.) To apply forces as in brakes clutches, spring-loaded valves, e.t.c.To measure forces as in spring balances and engine indicatorsTo store energy in watches.

17. Define free length.Free length of the spring is the length of the spring when it is free or unloaded condition. It is equal to the solid length plus the maximum deflection or compression plus clash allowance.

Lf = solid length + Ymax + 0.15 Ymax

18. Define spring index.Spring index (C) is defined as the ratio of the mean diameter of the coil to the diameter of the wire. C =D/d

19. Define spring rate (stiffness).The spring stiffness or spring constant is defined as the load required per unit deflection of the spring.

K= W/y Where W-load y-deflection

20. Define pitch.Pitch of the spring is defined as the axial distance between the adjacent coils in uncompressed state. Mathematically

Pitch=free lengthn-1

21. What are the points to be taken into consideration while selecting the pitch of the spring?

The points taken into consideration of selecting the pitch of the springs are

The pitch of the coil should be such that if the spring is accidentally compressed the stress does not increase the yield point stress in torsion.The spring should not be close up before the maximum service load is reached.

22. Define active turns.Active turns of the spring are defined as the number of turns, which impart spring action while loaded. As load increases the no of active coils decreases.

23. Define inactive turns.Inactive turns of the spring are defined as the number of turns which does not Contribute to the spring action while loaded. As load increases number of inactive coils increases from 0.5 to 1 turn.

24. What are the different kinds of end connections for compression helical springs?The different kinds of end connection for compression helical springs are

Plain endsGround endsSquared endsGround & square ends

25. Write about the eccentric loading of springs?If the load acting on the spring does not coincide with the axis of the spring, then spring is said to be have eccentric load. In eccentric loading the safe load of the spring decreases and the stiffness of the spring is also affected.

26. Explain about surge in springs?When one end of the spring is resting on a rigid support and the other end is loaded suddenly, all the coils of spring does not deflect equally, because some time is required for the propagation of stress along the wire. Thus a wave of compression propagates to the fixed end from where it is reflected back to the deflected end this wave passes through the spring indefinitely. If the time interval between the load application and that of the wave to propagate are equal, then resonance will occur. This will result in very high stresses and cause failure. This phenomenon is called surge.

27. What are the methods used for eliminating surge in springs?The methods used for eliminating surge are By using dampers on the center coil so that the wave propagation dies out By using springs having high natural frequency. By using springs having different pitch of coils near the end different than at the center to have different natural frequency.

28. What are the disadvantages of using helical spring of non-circular wires?The quality of the spring is not good the shape of the wire does not remain constant while forming the helix. It reduces the energy absorbing capacity of the spring.The stress distribution is not favorable as in circular wires. But this effect is negligible where loading is of static nature.

29. Derive the expression for the equivalent stiffness of the spring in series?Let us consider q1 and q2 be the stiffness for the two springs 1 & 2 respectively. Then the equivalent stiffness of the springs is given by

1/qe =1/q1

+1/q2

30. What is the equivalent stiffness of the spring in parallel?Let us consider q1 and q2 be the stiffness for the two springs 1 & 2 respectively. Then the equivalent stiffness of the springs is given by

q1 q2

p

31. Why concentric springs are used?To get greater spring force with in a given spaceTo insure the operation of a mechanism in the event of failure of one of the spring

32. What is the advantage of leaf spring over helical spring?The advantage of leaf spring over helical spring is that the end of the spring may be guided along a definite path as it deflects to act a structural member in addition to energy absorbing device.

33. Write notes on the master leaf & graduated leaf?The longest leaf of the spring is known as main leaf or master leaf has its ends in the form of an eye through which bolts are passed to secure the spring.The leaf of the spring other than master leaf is called the graduated leaves.

34. What is meant by nip in leaf springs?By giving greater radius of curvature to the full length leaves than the graduated leaves, before the leaves are assembled to form a spring thus a gap or clearance will be left between the leaves. This initial gap is called nip.

35. What is the application of leaf spring?The leaf springs are used in automobiles as shock absorbers for giving suspension to the automobile and it gives support to the structure.

36. Define flat spiral spring.A flat spiral spring is a long thin strip of elastic material wound like a spiral. These springs are frequently used in watch springs, gramophones, e.t.c

37. What are the differences between helical torsion spring and tension helical springs?

Helical torsion springs are wound similar to that of tension springs but the ends are shaped to transmit torque. The primary stress in helical torsion spring is bending stress whereas in tension springs the stresses are torsional shear stresses.

38. Define helical springs. The helical springs are made up of a wire coiled in the form of a helix and are primarily intended for compressive or tensile load.

39. What are the differences between closed coil & open coil helical springs?

qe = q1 +q2

40. What are conical or volute springs?

Conical or volute springs are made either partially or completely telescoping. They have constant pitch and lead angles. They are used in places where spring rate gradually increases with the load is desired.

41. What is flywheel?Flywheel is a machine elements used to minimize the fluctuation of speed in a engine.

42. What is the function of flywheel?A flywheel used in machine serves as a reservoir which stores energy during the period when the supply of energy is more than the requirement and releases it dulling the period when the requirement of energy is more than the supply.

43. Define the term ‘fluctuation of speed’ and ‘fluctuation of energy’.The ratio of maximum fluctuation of speed to the mean speed is called co efficient of fluctuation of speed. The ratio of fluctuation of energy to the mean energy is called coefficient of fluctuation of energy.

44. State the type of stresses induced in a rim flywheel? Tensile stress due to centrifugal force Tensile bending stress caused by the

restraint of the arms and The shrinkage stresses due to unequal rate of cooling of casting.

45. What are the stresses induced in flywheel arms?Tensile stress due to centrifugal force. Bending stress due to torque.Stress due to belt tension.

46. How does the function of flywheel differ from that of governor?A governor regulates the mean speed of an engine when there are variations in the mean loads. It automatically controls the supply of working fluid to engine with the varying load condition & keeps the mean speed with contain limits. It does not control the speed variation caused by the varying load. A flywheel does not maintain const speed.

Closed coil helical spring Open coil helical spring

The spring wires are coiled very closely, each turn is nearly at right angles to the axis of helix

The wires are coiled such that there is a gap between the two consecutive turns.

Helix angle is less than 10o Helix angle is large (>10o)