Design of Machine Elements

TWO MARK QUESTIONS & ANSWERS

UNIT- I
STEADY AND VARIABLE STRESSES

1. Define Design.
Creating a plan or drawing for a product using intellectual ability and scientific knowledge is called design. A product so designed should permit economical manufacture, and it should meet the specification requirements.

2. What are the classifications of machine design?
a) Adaptive design
b) Development design
c) New Design

3. What are the classifications of machine design based on methods?
a) Rational design
b) Empirical design
c) Industrial Design
d) Optimum design
e) System Design
f) Element design
g) Computer aided design

4. What are the general considerations to be considered in designing of a machinecomponent?
1. Type of load and stresses caused by the load
2. Motion of the parts or kinematics of machines
3. Selection of materials
4. Form and size of the parts
5. Frictional resistance and lubrication
6. Convenient and economical features
7. Use of standard parts
8. Safety of operation
9. Workshop facilities
10. Number of machines to be manufactures
11. Cost of construction
12. Assembling

5. Write down the general procedure in Machine Design.
a) Recognition of need
b) Specifications & Requirements – Design Synthesis
c) Feasibility Study
d) Creative Design Synthesis
e) Preliminary Design and Development

i. Analysis of forces
ii. Material Selection
f) Detailed Design of elements
g) Prototype Building, Testing and Modification
h) Detailed drawing and design for production

6. What are the factors to be considered during design?
a) Efficiency of machine
b) Absence of noise
c) Reliability
d) Life
e) Ease of control
f) Overload capacity
g) Maintenance
h) Space requirement
i) Weight
j) Size
k) Cost of manufacture
l) Ergonomics
m) Aesthetics
n) Safety

7. What are the ergonomic considerations in Design?
The ease with which the user of the designed equipment carries out various operations, like moving hand wheels and levers and seeing instrument dials fatigue of the operation, energy expenditure in hand and foot operations, environmental conditions (light, noise, and climate), human safety, etc. are the subject matter of ergonomics.

8. What are Preferred Numbers?
The preferred Numbers are the conventionally rounded off values derived from geometric series including the integral power of 10 and having as common ratio of the following factors: 510, 1010, 2010 and 4010. These ratios are approximately equal to 1.58, 1.26, 1.12 and 1.06. These series of preferred numbers are designated as R5, R10, R20 and R40 respectively. These four series are called basic series. The other series called derived series may be obtained by simply multiplying or diving the basic sizes by 10, 100, 1000 etc.

9. How do you classify materials for engineering use?
Engineering materials are classified as
1. Metals and their alloys such as iron, steel, copper, aluminium etc.
2. Non-metals, such as glass, rubber, plastic etc.
The metals may be further classified as Ferrous Metals and Non ferrous metals
10. What are the factors to be considered for the selection of materials for the design of machine elements?
a) Properties of materials
b) Manufacturing ease and cost
c) Quantity required
d) Availability of material
e) Space available
f) Cost

11. What are the different properties of materials and discuss?
a) Strength: It is the ability of a material to resist the externally applied forces without breaking or yielding. The internal resistance offered by a part to an externally applied force is called stress.

b) Stiffness: It is the ability of a material to resist deformation under stress. The modulus of elasticity is the measure of stiffness

c) Elasticity: It is the property of a material to regain its original shape after deformation when the external forces are removed. This property is desirable for materials used in tools and machines. It may be noted that steel is more elastic than rubber.

d) Plasticity: It is property of a material which retains the deformation produced under load permanently. This property of the material is necessary for forgings, in stamping images on coins and in ornamental work.

e) Ductility: It is the property of a material enabling it to be drawn into wire with the application of a tensile force. A ductile material must be both strong and plastic. Mild steel, copper, aluminium, nickel, zinc, tin and lead are the ductile materials

f) Brittleness: It is the property of a material opposite to ductility. It is the property of breaking of a material with little permanent distortion. Cast Iron is a brittle material.

g) Malleability: It is a special case of ductility which permits materials to be rolled or hammered into thin sheets. A malleable material should be plastic but it is not essential to be so strong. Lead, soft steel, wrought iron, copper and aluminium.

h) Toughness: It is the property of a material to resist fracture due to high impact loads like hammer blows. The toughness of the material decreases when it is heated. This property is desirable in parts subjected to shock and impact loads.

i) Machinability: It is the property of a material which refers to a relative case with which a material can be cut.

j) Resilience: It is the property of a material to absorb energy and to resist shock and impact loads. It is measured by the amount of energy absorbed per unit volume within elastic limit. This property is essential for spring materials.

k) Creep: When a part is subject to a constant stress at high temperature for a long period of time, it will undergo a slow and permanent deformation called creep. This property is considered in designing internal combustion engines, boilers and turbines.

l) Fatigue: When a material is subjected to repeated stresses, it fails at stresses below the yield point stresses. Such type of failure of a material is known as fatigue. The failure is caused by means of progressive crack formations which are usually fine and microscopic size. This property is considered in designing shafts, connecting rods, springs, gears etc.

m) Hardness: It is a very important property of the metals 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 a metal to cut another metal. The hardness is usually expressed in numbers which are dependent on the method of making the test.

12. What is impact strength?
Impact strength is a measure of the resistance of metals to impact loads. Also defined as the energy required bringing a specimen to rupture and calculated per unit area of its section.

13. What alloying element improves the Hardenability of steels?
Hardenability can be improved by using alloying elements like boron, vanadium, manganese, chromium and molybdenum.

14. What is strain hardening and damping capacity?
Strain Hardening: When drawing ductile materials like mild steel, copper, brass and aluminium through dies or when rolling them between rollers, plastic deformation takes place and this increases the yield point stress and ultimate strength. This is known as strain hardening.

Damping capacity: It is the ability of a material to damp vibration by absorbing the kinetic energy of vibration. CI has greater damping capacity than steel.

15. How does the carbon content affect the hardness and toughness properties of CI and steel? / How carbon content influences the properties of steel?
If the carbon content is going to be less than 0.83%, increase in carbon content increases the ultimate strength. If the carbon content is going to be more than 0.83%, the increase in carbon content reduces the strength. Hardness increases with carbon content but ductility and weldability decreases as carbon content increases.

16. Why do we use alloy steels in some machine components?
In general, adding alloying elements to steel will improve the hardenability and steel may be heat treated to the desired hardness with less drastic quenching and therefore with less problem of distortion and cracking.

17. What are the effects of silicon and manganese on steel?
Silicon is added to steel as a deoxidizer to minimize the last traces of oxygen. As manganese content increases, ultimate strength and hardness increases and weldability decreases.

18. What are the effects of chromium, nickel and molybdenum on steel?
Chromium improves hardenability, corrosion resistance and increases wear resistance and hardness.

Nickel increases strength without decreasing ductility.

Molybdenum improves hardenability and creep strength, molybdenum is used in all creep resisting steel.

19. List a few alloys used for bearings.
a) Copper base alloys
b) Lead base alloys
c) Tin base alloys
d) Cadmium bas alloys
e) Gun metal
f) Phosphor bronze
g) Beryllium bronze
h) Monel metal
i) Tin babbit
j) Leadbabbit

20. What is duralumin?
Duralumin is an Al-Cu-Mg-Mn alloy and it has good corrosion resistance and strength. This alloy is available in the form of sheets, plates, tubes, rods, extruded section, bolts and rivets and is widely used in aircraft industry.

 

21. What are proof resilience and proof stress?
Greatest strain energy that can be stored in a member without permanent deformation is called the proof resilience and the corresponding stress is called the proof stress. The proof resilience per unit volume of a material is known as modulus of resilience.
22. What do you mean by factor of safety? / What is factor of safety?
Factor of safety is defined, as the ratio of the maximum stress to the working stress or ultimate stress to the working/design stress or yield stress to the working/design stress.
23. List the important factors that influence the magnitude of factor of safety?
1. Loading uncertainty
2. Type of loading
3. Material strength uncertainty
4. Size effect
5. Working in extreme environments
6. Effect of manufacturing process
7. Effect of stress concentration
8. Uncertainty due to the method of analysis.
9. Reliability requirements
10. Risk to life and property

24. What is design stress?
Permissible stress or design stress of a material is defined as the ratio between maximum stress (yield stress in case of brittle material / ultimate stress in case of ductile material) to the factor of safety.

25. Give the different failure theories and the type of materials for which these theories are applicable?
Failure theories relate a complex stress state to a single strength (yield point stress in tension) and from this relation design criteria for safety can be derived.

a) Maximum principle stress theory (Rankine theory): According to this theory, failure occurs whenever the maximum principle stress induced in the machine component becomes equal to the strength. Mathematically, for safety for ductile materials and for brittle materials and n = factor of safety. This theory is applicable to ductile materials.
b) Maximum shear stress theory (Guest’s or Coulomb’s theory): According to this theory, failure occurs whenever the maximum shear stress induced in the component becomes equal to the maximum shear stress in a tension test specimen when the specimen begins to yield. Mathematically for safety . This theory is best suited for ductile materials. Also according to this theory, for the case of pure shear and
c) Maximum strain theory (St. Venant’s theory): According to this theory, failure occurs whenever the maximum strain in the component becomes equal to the strain in the tension test specimen when yielding begins. Mathematically for safety where ν= Poisson’s ratio. This theory is not confirmed by experimental data.
d) Maximum strain energy theory (Haigh Theory): According to this theory failure will occur when the strain energy stored per unit volume of the stress element becomes equal to the strain energy stored per unit volume in the tension test specimen at the yield point. Mathematically, for safety . This theory is useful for ductile materials. According to this theory for the case of pure shear τy=0.62σy.

e) Distortion Energy theory / Shear energy theory / Von MisesHencky Theory / Octahedral Theory: According to this theory, failure will occur when the strain energy of distortion per unit volume of the component becomes equal to the strain energy of distortion per unit volume of the tension test specimen. Mathematically, for safety, . This theory is applicable to ductile materials. According to this theory, for the case of pure shear τy=0.577σy.

26. What is the importance of principle stresses?
Machine elements are subjected to several external loads of different nature, like bending and twisting. Therefore it becomes necessary to determine the equivalent single stress using the concept of principle stresses.

27. Sketch the bending stress distribution in a curved beam.
Refer data book page no. 6.2

28. Distinguish between endurance limit and endurance strength.
Endurance limit is the limiting value of alternating stress for which failure does not occur on the material for an infinite number of cycles.

Endurance (Fatigue) Strength is the alternating stress at which failure occurs for a particular finite value of life. Fatigue strength is always accompanied by a finite number of cycles.

29. What do you mean by S-N diagram?
The diagram, which is drawn using the alternating stress, is taken along the y-axis and the number of cycles for failure is taken along the x-axis. (Refer the figure in data book page no. 7.6)

30. Explain the following a)Stress concentration b)Size factor c)Surface finish factor d)Notch sensitivity
a) Stress Concentration: Stress concentration may occur due to abrupt changes of cross section of the member due to the presence of discontinuities like holes, notches, grooves or shoulders. It may also be due to the presence of internal cracks or air holes in the materials.

b) Surface finish factor: Nature of the surface has a great influence on the endurance strength of materials. Perfectly smooth, polished surfaces have the highest endurance strength. Grinding gives lesser strength and rough finish reduces further.

c) Notch Sensitivity: is defined as the degree to which the theoretical effect of stress concentration is actually reached.

31. What are factors affecting endurance (Fatigue) Strength / endurance limit?
a) Method of manufacture and heat treatment
b) Size
c) Surface conditions
d) Stress concentration
e) Type of stress involved (bending, axial, torsion)

32. What is meant by fatigue failure?
Many machine and structural members are subjected to loads that vary in magnitude. This induces cyclic or fatigue stresses in members and the members fail at a stress much less than the yield point stress. This is known as fatigue failure.

33. What is fatigue strength reduction factor?
When components are subjected to fatigue loading, stress concentration is a serious problem for both ductile and brittle materials. For fatigue loading, fatigue stress concentration factor (fatigue strength reduction factor) Kf is used. Kf depends upon both the geometry and the material and processing of the part. Experimentally Kf is the ratio between endurance limit of notch free specimen and endurance limit of notched specimen.

34. What are the different failure modes of machine components?
a) Failure by yielding
b) Failure by fracture
c) Due to deflection
d) Due to wear
e) Due to buckling
f) Due to corrosion
g) Due to caustic embrittlement

35. What is Miner’s Rule and when is it used?
When missile and defense equipment parts are designed for finite life, Miner’s rule is used. If a component is subjected to a stress σ1, the life is N1 cycles, a stress σ2; the life is N2 cycles and so on. If the component is subjected to intermittent loads leading to stresses σ1, the life is n1 cycles (n1<N1), σ2, the life is n2 cycles (n2<N2), and so on, then according to Miner’s rule failure will occur if

36. Write the design equation for Finite Life.
The fatigue strength for finite life is calculated by using the equation , where σf = Fatigue strength for fatigue life, , and N = No. of cycles.

37. What is the relation between the stress due to gradually applied load and that due to suddenly applied load?
Suddenly applied loads – as produced by combustion in an engine or by an explosion.
Direct – impact loads, as produced by the dropping of a weight by a ram in a forging press, by a pile driver or by vehicle crash.

If the load W is dropped through height h, the equivalent gradually applied load P is given by . The instantaneous stress

If the weight W is applied instantaneously without any initial velocity, i.e., if h = 0, P = 2W and . The instantaneous stress is twice as that due to a gradually applied load.

38. Why Soderberg relation is called the most conservative design equation?
In the graph between alternating stress and mean stress, when there are no experimental data available σ-1 and σu are joined by a straight line known as Goodman line. If σ-1 and σy are joined by a straight line, we get Soderberg Line. The above lines and the parabola represent failure graphs; if the operating point is above the graphs, failure will occur. Thus we find Soderberg line as the most conservative. Refer fig in data book page no. 7.5

39. What is reliability factor?
In S-N curve is drawn through the middle points and the endurance limit is obtained. This endurance limit represents a survival rate of 50%. In other words, for the same life, 50% of the specimens could withstand higher stress amplitude and 50% of them could withstand lower stress amplitude. In order to make more than 50% of the parts survive, the stress amplitude should be less than the endurance limit given in the data book. Hence to modify the endurance limit, a reliability factor is used.

40. What is contact stress?
When two bodies having curved surfaces are pressed against each other, point or line contact becomes an area contact. The area is very small and hence high contact stress (surface stress or Hertz stress) develops. Contact stresses occur in the contact between a wheel and rail, between a cam and its follower, between a ball and its race or between a pair of mating gear teeth.

41. What is bearing stress?
Local compression occurs between two members held in contact, i.e., between the pin and the eye. The pressure distribution will not be uniform and it is difficult to determine accurately. Hence the average bearing pressure or bearing stress is obtained by dividing the load by the projected bearing area. Bearing stress or Bearing pressure , where l = Length of the pin in contact and d = diameter of the pin.

42. What are the different types of varying loads? Give one example for each.
Completely Reversed Loading – Shafts carrying pulleys
Repeated Loading – Gears, Chain
Fluctuating Loading – Vehicle springs, Engine valve springs
Alternating Loading – IC engine connecting rods

43. Differentiate between sudden and impact loads.
Suddenly applied loads – as produced by combustion in an engine or by an explosion
Direct – impact loads, as produced by the dropping of a weight by a ram in a forging press, by a pile driver or by vehicle crash.

44. In some situations, third principle stress being zero must be taken into calculation of maximum shear stress. Why?
In real bodies, three dimensional state of stress exists and hence it is best always to consider stresses as three dimensional. In uniaxial stress state (pure tension or compression), out of three principal stresses two of them are zero. In biaxial stress state one principal stress is zero. Forgetting about a zero principal stress will result in a serious error. Consider an element on the outer surface of a pressure vessel. On the outer surface load is zero and hence σ3 = 0. σ1and σ2 are both tensile and hence positive.

45. What is meant by eccentric loading and eccentricity?
An external load, whose line of action is parallel but does not coincide with the centroidal axis of the machine component, is known as an eccentric load. The distance between the centroidal axis of the machine component and the eccentric load is called eccentricity.

46. Define stress concentration factor.
Theoretical or form stress concentration factor is defined as the ratio of Maximum stress and Nominal stress.

47. What is ratio for factor of safety for fatigue loading?
The ratio between the endurance limit of a material to the working/design stress of the material is called as Factor of safety for fatigue loading.

48. Write Soderberg’s equation and state its application to different type of loadings.
For reversed axial loading . For reversed shear loading

49. Differentiate between design for finite life and design for infinite life.
Design for infinite life is based on the endurance limit of the material.
Design for finite life is based on the fatigue or endurance strength of the material.
50. Define- Allowance.
It is the difference between the basic dimensions of the mating parts.
51. Define- Tolerance
It is the difference between the upper limit and lower limit of a dimension.In other words, it is the maximum permissible variation in a dimension.

52. What are the types of tolerance?
Uni lateral and Bi-lateral tolerances.
53. Define- Fits
The degree of tightness or looseness between the two mating parts is known as a fit of the parts.
54. List out the types of fits.
i)Clearance fit ii) Interference fit iii) Transition fit.

 

DME –TWO MARK QUESTIONS & ANSWERS
UNIT- II - Design of Shafts and Couplings

1. Define shaft?
A shaft is a rotating machine element which is used to transmit power from one place to another. It is used for the transmission of torque and bending moment.
2. Differentiate between shaft and axle?
An axle though similar in shape to the shaft is a stationary machine element and is used for transmission of bending momentonly.it simply act as a support for some rotating body.
3. What is a spindle?
A spindle is a short shaft that imparts motion either to a cutting tool or to a work piece.
4. What are the materials used for shafts?
For ordinary shaft - mild steel
For high strength shafts - alloy steel such as nickel,
Ni-Cr steel and Cr-v steels

5. What are the types of shafts and give their importance?
a) Transmission shafts
These shafts transmit power between the source and the machine absorbing power. These shafts carry machine parts such as pulleys gears etc. They are subjected to bending in addition to twisting.
b) Machine shafts
These shafts form an integral part of the machine itself. The crankshaft is an example of machine shaft.

6. What are the various types of stresses induced in the shafts?
The various types of stresses induced in the shafts are
a) Shear stress due to transmission of torque
c) bending stresses

d) stresses due to combined torsional and bending loads

7. What are the standard sizes of transmission shafts?
The standard size of transmission shafts are,
a) 25 mm to 60 mm with 5 mm steps
b) 60 mm to 110 mm with 10 mm steps
c) 110 mm to 140 mm with 15 mm steps
d) 140mm to 500 mm with 20 mm steps
Standard length-5 m, 6 m, and 7 m.
8. On what basis shafts are designed?
a) Based on rigidity and stiffness
b) Based on strength
c) Based on critical speed.

9. Differentiate the hollow shaft over a solid shaft?
The hollow shafts are used in marine work. These shafts are stronger per kg of material and they may be forged on a mandrel, thus making the material more homogeneous than a solid shaft.
10. Give examples fort shafts subjected to axial load in addition to torsion and bending loads.
The examples are
a) Propeller shaft of ships.
b) Shafts for driving worm gears
c) Main shafts of Kaplan turbine.

11. What are the desirable properties for the material for shaft and axles?
The desirable properties for the material for shaft and axles are
a) Sufficient high strength
b) A low sensitivity to stress concentration.
c) Ability to withstand heat and case hardening treatment.
d) Good machinability.

12. How the shafts are designed when it is subjected to twisting moment only?
When the shaft is subjected to torque only, then it is designed based on torsion equation.

13. Why rotating shafts are generally made with circular cross section? Stress distribution pattern will be uniform throughout the circular cross section

14. Write the formula for equivalent torque and bending moment when the shafts are subjected to fluctuating loads.

Equivalent torque Te= ((Km M)2+ (KtT)2)1/2

Equivalent bending moment Me = 1/2[ kmM + ( (Km M)2+ (ktT)2)1/2 ]
Where
km=combined shock and fatigue factor for bending
Kt=combined shock and fatigue factor for torsion

15.Define torsional stiffness of a shaft.
Torsional stiffness of shaft is defined as the resisting strength of a shaft to torsional load. Mathematically it can be calculated by the formula T/180=GJ/I
16. What are the ways of improving lateral rigidity of shafts?
The ways of improving lateral rigidity of shafts are,
a) Maintaining proper bearing clearances
b) Correct gear teeth alignment
17. Define critical speed of a shaft.
Rotating shaft tends to vibrate violently in transverse directions at certain speed is known as critical speed or whirling speed. When the natural frequency of vibration is equal to speed of shaft resonance will occur. Such a value of natural frequency is called critical speed or whirling speed.
18 State any two reasons for preferring hollow shafts over solid shafts.
The two reasons for preferring hollow shafts over solid shafts are
a) For same weight of shaft, hollow shaft can transmit 1.5 times the torque transmitted by solid shaft.
b) For a particular power transmission, hollow shaft requires minimumweight.

19. What is a key?
Key is an element which is used to connect two machine parts for preventing relative motion of rotation with respect to each other.
20. What is column factor?
If a long shaft is subjected to axial load in addition to torsion and bending, a factor must be introduced to take the column effect into account.
If L/K<115 If L/K>115
α = 1/ (1 - 0.0044(L/K)) α = σY(L/K)2/ C π2E

21. Name the stresses induced in a taper key.
The stresses induced in taper key are,
a) Shear stress
b) Crushing stresses

22. Give the specifications of a parallel key.
The specifications of a parallel key is given as,

L x b x h
Where,
L - Length of the key

b – Width of the key

h - Height of the key
23. Name the types of keys.
The types of keys are,
a) saddle key
b) tangent key
c) sunk key
d) round key and taper pin

24. How sunk keys are provided?
Sunk keys are provided half in the keyway of the shaft and half in the keyway of the hub or boss of the pulley.
25. List out the various types of sunk keys.
The various types of sunk keys are,
a) rectangular sunk key
b) square sunk key
c) parallel sunk key
d) gib head key
e) feather key
f) woodruff key

26. What is a keyway?
Keyway is a slot or recess in a shaft and hub of the pulley to accommodate a key.
27. Give the difference between square sunk key and rectangular sunk key.

Width

thickness Rectangular sunk key Square sunk key
d/4

d/6 d/4

d/4
28. What is a gib head key? What is its advantage?
A rectangular sunk key with a head at one end is known as gib head key.
It is usually provided to facilitate the removal of key.
29. What is a feather key?
A key attached to one member of a pair and which permits relative axial movements is known as feather key.
It is a special type of parallel key which transmit a turning moment and also permits axial movements.
30. What is a woodruff key?
Woodruff key is a piece from a cylindrical disc having segmental cross section. A woodruff key is capable of tilting in a recess milled out in the shaft by a cutter having the same curvature as the disc from which the key is made.
They are largely used in machine tools and automobile constructions.
31. What are the advantages and dis advantages of a woodruff key?
The advantages and dis advantages of a woodruff key are,
It accommodates itself to any taper in the hub or boss of the mating piece.
a) It is useful on tapering shaft end. Its extra depth in the shaft prevents any tendency to turn over in its keyway.

32. What are the two types of saddle keys?
The two types of saddle keys are,
a) Flat saddle key
b) Hollow saddle key

33. What are splines?
The keys are made integral with the shaft which fits in the keyways broached in the hub. Such shafts are known as splined shafts. These shafts usually have four, six, ten or sixteen splines. These splined shafts are relatively stronger than shaft having a single keyway.
34. What are round keys?
The round keys are circular in section and fit into holes drilled partly in the shaft and partly in the hub.
35. List the advantages of splines over keys?
The advantages of splines over keys are,
splines can be used when both axial movements as well as positive drive is to obtained.
a) It is used when the force is to be transmitted is large in proportion to the size of the shaft as in automobile transmission and sliding gear transmission.

36. What are the various forces acting on sunk key?
The various forces acting on sunk key are,
a) Force due to fit of the key in its keyway
b) Forces due to torque transmitted by the shaft
37. List the various purposes of shaft coupling?
The various purposes of shaft coupling are,To provide for the connection of shafts of units that are manufactured separately and to provide for disconnection for repairs or alternations.
a) To provide misalignments of shafts or to introduce mechanical flexibility.
b) To introduce protection against overloads.
c) To reduce the transmission of shock loads from one shaft to another.

38. List out the requirements of a shaft coupling?
The requirements of a shaft coupling are,
a) it should be easy to connect or disconnect
b) it should transmit the full power of the shaft
c) it should hold the shaft in perfect alignment
d) it should have no projecting parts
39. What is rigid coupling? What are its types?
Rigid coupling is used to connect two shafts which are perfectly aligned. The types are a) Sleeve or muff coupling
b) Clamp or split muff or compression coupling
c) Flange coupling

40. What is flexible coupling? What are its types?
Flexible coupling is a type of coupling used to connect two shafts having both lateral and angular misalignments. The types are
a) Bushed pin type coupling
b) Universal coupling
c) Oldham’s coupling
41. What is a flange coupling?
Flange coupling is a coupling having two separate cast iron flanges. Each flange is mounted on the shaft end and keyed to it. The faces are turned up at right angles to the axis of shaft. One of the flanges has a projected portion and other face has a corresponding recess. This helps to bring the shaft into line and maintain alignment.
42. What are the different types of flange coupling?
The different types of flange coupling are,
a) Unprotected type flange coupling
b) Protected type flange coupling
c) Marine type flange coupling
43. What is the difference between rigid and flexible coupling?

Rigid coupling Flexible coupling
It is used to connect two shafts which are perfectly aligned It is used to connect two shafts having both lateral and angular misalignment.

44. Write the equations for failure modes of a key?
a) shearing of a key
Torque = f x d/2
=l x w x τ x d/2
b) crushing of a key
Torque = f x d/2
= l x t/2 x σcx d/2
Where,
L- Length of the key
W- Width of the key
t- Thickness of the key
d- Diameter of the shaft
τ- Shear stress & σc- crushing stress

45. Write the formula for the shaft subjected to constant torque and bending moment?
Equivalent torque Te= (M2+ τ2)1/2
Equivalent bending moment
Me = 1/2[ M+ (M2+T2)1/2 ]
46. List any two methods used for manufacturing of shaft?
The two methods used for manufacturing of shaft are,
a) cold rolling
b) hot rolling
c) turning or grinding from rough bars

47. What is the effect of keyway cut into shaft?
The keyway cut into the shaft reduces the load carrying capacity of the shaft. This is due to the stress concentration near the corners of the keyway and reduction in cross sectional area of the shaft. In other words the torsional strength of the shaft is reduced.

48. What is the difference between coupling and a clutch?
A coupling is a device used to make permanent or semi-permanent connections whereas a clutch permits rapid connection or disconnection at the will of the operator.

49. What is the mode of failure of the bolts in a flange coupling?
Direct shear stress failure due to torque transmission is the mode of failure of the bolts in the flange coupling.

50. Indicate what type of coupling is used under following conditions?
a) With shaft’s having collinear axis b) shafts having intersect axis c) shafts having a parallel axis with a small distance apart?
a) Rigid or flexible coupling
b) Universal coupling
c) Double slider crank principle mechanism
51. When a solid flange coupling is preferred?
For a very large shafts or when large torsional moments and forces to be transmitted such as those used for propeller shafts, solid flange coupling are preferred.
52. How coupling are specified?
Couplings are specified as follows.
a) diameter of shaft
b) Diameter of sleeve or muff
c) Length of sleeve or muff
d) Outer diameter of hub
e) Nominal diameter of bolt
f) PCD of bold circle
53. Differentiate between a cotter joint and a knuckle joint?
Cotter joint is used to connect two rigid rods for transmitting motion without rotation. This joint is subjected to axial forces.
Knuckle joint is used for connecting two rods and transmitting axial force. This joint permits a small amount of flexibility.
54. Which type of key is used for mounting shifting gears in gear boxes?
Spline type of key is used for mounting shifting gears in gear boxes.
55. What is knuckle joint?
Knuckle joint is used to connect two rods which are under the action of tensile loads.
56. What are the various methods of failure of knuckle joint?
The various methods of failure of knuckle joint are,
a) Failure of solid rod in tension
b) Failure of knuckle pin in shear
c) Failure of single eye or rod end in shear
d) Failure of single eye or rod end in tension
d) Failure of forked end in shear
e) Failure of single eye or rod end in crushing
f) Failure of forked end in tension
g) Failure of forked end in crushing

57. Identify the weakest component while designing shaft and hub assembly?
Key is the weakest component is designing shaft and hub assembly.
58. The taper of the rectangular sunk key is 1 in 100
59. The sleeve or muff coupling is designed as a hollow shaft.
60. In a steam engine, the valve rod is connected to an eccentric means of a knuckle joint

DME –TWO MARK QUESTIONS & ANSWERS
UNIT- III --- DESIGN OF FASTENERS AND WELDED JOINTS

1. Define pitch and lead of a thread?

Axial distance from a point on one thread to corresponding point to next thread is called pitch.Lead is the distance the screw moves in one turn
2. What are stresses that act on screw fastening?
Stresses that act on screw fastening are,
a) initial stresses due to screwing up
b) stresses due to external forces.
c) Combined stresses

3. Give some examples for temporary joints and permanent joints?
Some examples for temporary joints and permanent joints are,
Permanent joints – Riveted joints, Welded joints, bonded joints.
Temporary joints – Threaded joints, cotter joints, knuckle joints

4. List the advantages of screwed joints
The advantages of screwed joints are,
Highly reliable
a) Convenient to assemble and disassemble
b) Relatively cheap to produce due to standardization and highly efficient manufacturing processes.

5. What are the various forms of screw threads?

The various forms of screw threads are,
a) British standard Whitworth (BSW) thread
b) British association thread
c) Unified standard thread
d) American national standard thread
e) Square method
f) Acme thread
g) Metric thread

6. Define pitch diameter of a screw thread
Pitch diameter of a screw thread is the diameter of an imaginary cylinder on which screw thread surface would pass through the thread at such points make equal width of thread and equal width of spaces between threads.
7. How screw threads are formed?
A screw thread is formed by cutting a continuous helical groove on a cylindrical surface.
8. What is the difference between a stud and a bolt?
Stud is a round bar threaded at both ends
Bolt is a cylindrical bar with threads for nut at one end and head at the
other end.
9. What do you mean by single start threads?
When a nut is turned on a bolt having a single continuous thread cut on it by one full turn, it advances axially through a distance equal to pitch. Hence in a single continuous thread, called single start thread, the lead is equal to pitch.

10. Explain why a soft material is for the nut in power screws.
Soft bearing material used for nut wears fast. To reduce cost of replacement nut of small size is replaced.
11. List one of the locking devices.
Some of the locking devices are,
a) lock nut
b) catle nut
c) sawn nut
d) grooved nut

12. What is designation of screw thread?

a) Size designation

M_X_

b) Tolerance designation
A letter followed by a number
Letters used are,

H – Unit thread
D – Bolt thread with alloance
H –bolt thread without allowances
Numbers used are,
7 - For fine grade
8 - for normal or medium grade
9 – carse grade

13. what are the essential stresses induced due to screwing up forces?

The initial stresses induced due to screwing up forces are,
a) Tensile stresses dye to stretching of bolt
b) Torsional shear stress caused by frictional resistance of threads during its tightening
c) Shear stress across threads
d) Compression or crushing stress on threads

14. what is bolt of uniform strength?
A bolt of uniform strength has equal strength st the thread and shank position

15. What are the ways to produce bolts of uniform strength?
a) Reducing shank diameter equal to root diameter
b) Drilling axial holes

16. what are advantages of pre loading?
a) stops leakages
b) improve fatigue strength

17. By what materials threaded fasteners are made?
Steel is the material of which most of the fasteners are made. For improving their properties alloy steels like, nickel steel, Ni-Cr steel and Cr-V steel are performed.

18. What is a turn buckle and where it is used?
A turn buckle is a type of connecting element for connecting two tie rods. In this type of joint, one of tie rods is having right hand threads and the other is having left hand threads. These rods are screwd into the threaded hole of the turn buckle. It is also called as couple nut.

19.In what way coarse thread is different from fine thread?
Fine and coarse threads are having same major and minor diameters except their pitch values. Fine threads having smaller pitches than coarse threads.
20. State the relationship between pitch and lead for single start and double start threads.

L = n * p

Where L – Lead
N – Number of starts
P - Pitch

For single start thread , Lead = Pitch
For double start thread , Lead = 2*pitch

21. what are the various methods of preventing thread loosening?

a) Providing locking devices
b) Selecting screw having large numbers of threads per unit length

22. Enumerate the demerits of screw joints
a) stress concentration is available in threaded positions and hence lessening their life
b) self loosening properties and hence air tight joints can not be maintained unless providing some locking devices.

 

23. Define self locking in power screws

If the friction angle is greater than the helix angle of the power screw, the torque required to lower the load will be positive, indicating that an effort is applied to lower the load.
24. What are the main indications of complete weld symbol?
a) Reference line
b) Arrow
c) Basic weld symbol
d) Dimensions
e) Tail
f) Supplementary symbol
g) Finish symbol
h) Specification process

25. what are the main types of welding?
a) Forge welding
b) Fusion welding
c) Electric resistance

UNIT- IV - DESIGN OF SPRINGS AND LEVERS

1. What is spring and where it is employed?
A spring is an elastic body, which distorts when loading and recover its original shape when the load is removed. It finds application in many places such as automobiles, railway wagons, brakes, clutches, watches and so on.

2. By what materials the springs can be made?
Springs are made of oil tempered carbon steel containing 0.6 to 0.7% carbon and 0.6 to 1% manganese. Phosper bronze, monel metal, beryllium copper are used for special purpose.
3. What type of spring is used in rams bottom safety valve?
Helical tension spring is used in rams bottom safety valve.
4. What are the functions of spring?
The functions of the spring are,
To mearure forces in spring balance, meters and engine indicators.
To store energy
5. What is spring and where it is employed?
A spring is an elastic body, which distorts when loading and recover its original shape when the load is removed. It finds application in many places such as automobiles, railway wagons, brakes, clutches, watches and so on.
6. By what materials the springs can be made?
Springs are made of oil tempered carbon steel containing 0.6 to 0.7% carbon and 0.6 to 1% manganese. Phosper bronze, monel metal, beryllium copper are used for special purpose.
7. What type of spring is used in rams bottom safety valve?
Helical tension spring is used in rams bottom safety valve.
8. What are the functions of spring?
The functions of the spring are,
To mearure forces in spring balance, meters and engine indicators.
To store energy.
9. Name the various type of springs?
Helical springs, spiral springs, leaf springs and disc or Belleville springs are the various type of springs.
10. What is spring index?
Spring index is the ratio of mean pitch diameter to the diameter of the wire
11.What are active and inactive coils?
The coils which are free to deflect under load is called active coils and the coils which do not take part in deflection of a spring is called inactive coils.
12.Define the term spring rate?
Spring rate is defined as the load required per unit deflection. It is also called as stiffness of the spring.
13.Define surging of springs?
The spring material is subjected to higher stresses, which may cause earlier fatigue failure of springs. This effect is called as surging of springs.

14.How will you find weather the given helical spring is a compression spring or tension spring?
The ends of compression springs are flat whereas for tension springs, hooks will be provided at the ends.
Coils will be slightly open for compression springs to facilitates compression whereas in tension springs the coils are very close.

 

15.what material is used for leaf spring?
Plain carbon steel having 0.9 to 1% carbon in annealed condition is normally used for leaf springs. chrome vanadium and silica manganese steels are used for the better grade springs.
16.What is nipping of laminated leaf spring? Discuss its role in spring design?
Pre stressing of leaf springs is obtained by a difference of radii of curvature known as nipping.
The initial gap can be adjusted so that under maximum load conditions the stress in all the leaves will be same or, if desired the stress in the full length leaves may be less.
17.What are the functions of a rebound clip and a U-clip in a leaf spring?
A rebound and are used for holding the leaves of the spring together.
18.what are the end conditions of springs?
The end conditions of springs are,
a)plain end.
b)plain and ground end.
c)squared end.
d)squared and ground end.
whywhals factor is to be considered in the design of helical compression spring?
When wire wound in the form of helix, compressive stress is induced in the inner side of the spring and tensile stress is induced in the outer side of the spring. Due to this stress concentration is produced in the outer side of the spring .so whales factor is to be considered in the design of helical compression spring.
17.what is buckling of springs?
The helical compression springs behave like a column and buckles at a comparative small load when the length of the spring is more than four times the mean coil diameter.
18.why leaf springs are made in layers instead of a single plate?
Leaf springs are made in layer only for distributing the shear forces and bending moment evenly.

19. Define solid length of helical spring.
When compression spring is compressed until the coils come in contact with each other , then the spring is said to be solid and resulting length is called solid length.
20.Define free length of a helical spring.
It is the length of the spring in free on unloading condition.
21.why the clearance is provided between adjacent of the helical spring ?
To prevent closing of the coils during service with maximum working load.
22.Define the term spring stiffness or spring rate?
Spring stiffeness or spring rate is defined as the load required per unit deflection of the spring.
23. Define pitch of the spring coil?
It is defined as the axial distance between adjacent coils in uncompressed state.
24.What are the points to be considered in choosing the pitch of spring coils?
a)It should be such that if the spring is accidently carelessly compressed, the stress does not increase the yield stress in torsion.
b)spring should not close up before maximum service load is reached.
25.What are the methods used for elimination of surges in springs?
a) By using friction dampers on the centre coils so that the waves propagation dies out. b)By using springs of high natural frequency.
c)By using springs having pitch of coils near the ends different at the centre to have different natural frequencies.
26.How to avoid buckling of springs?
In order to avoid buckling of spring, it is either mounted on a central rod or located on a tube
27.What are the disadvantages in helical springs of non-circular wire?
a)The quality of material used for springs is not so good.
b)The shape of the wire doesnot remain square or rectangular while forming helix resulting in trapezoidal cross sections.It reduces the energy absorbing capacity of the spring.
c)The stress distribution is not favourable as for circular wires.
28.How equalized stress in leaf spring leaves is achieved?
a)By making the full length of leaves of smaller thickness than the graduated leaves.
b) By giving greater radius of curvature to the full length leaves than graduated leaves.
29. What is meant by initial tension in helical torsion springs?
In tension helical springs it is necessary to apply from 20 to 30% of the maximum load before the coils begin to separate during close coil windings.
30.Name few applications of helical springs.
a)Door hinge springs.b)springs for starters in automobiles.c)springs for brush holders in electric motors.
31.What are the purpose of composite springs?
a)To obtain greater spring force within a given space.
b)To ensure the operation of a mechanism in the event of failure of one of the springs.
31.What are torsion springs?
Torsion springs may be of helical or spiral type.The helical type may be used only in applications where the load tends to wind-up the spring and are used in various electrical mechanisms. The spiral type is also used where the load tends to increase the number of coils and when made of flat strips are used in watches and clocks.
32.How the stiffness of the spring can be increased?
The stiffness of the spring can be increased by decreasing the number of turns.
33.What types of stresses are induced in the wires of helical compression spring and torsional spring?
Compressive or tensile stresses in helical compression spring and both tensile and compressive stresses in case of torsional spring are due to bending.
34.What are the advantages of leaf springs over helical springs?
Leaf springs are made out of flat plates.The advantages of leaf spring over the helical spring is that the end of the spring may be guided along a defined path as it deflects to act as a structural member in addition to energy absorbing device.
35.How concentric springs are obtained?
Two or more springs are joined to form a nest and thus concentric springs are obtained.

36.Define chamber?
It is the vertical distance between the centre of the eye to the maximum deflection in main or master leaf in the leaf spring.

37.Name the springs used in gramophones?
Flat, spiral spring is used in gramophones.
38.Why full length leaves are used in automobiles?
This is desirable in automobile springs in which full length leaves are designed for lower stress because full length leaves carry additional load caused by swaying and twisting.
39.What factors are considered for design of spring?
Deflection criteria, material strength properties, service environment, desired life, manufacturing cost ,etc.
40.How the load is made to act concentric with spring axis in helical spring?
By making the two ends of spring as squared and ground ends, the load can be made to act concentric with spring axis.
41.Define lever?
It is a rigid rod or bar capable of turning about a fixed point called fulcrum. It is used as a machine to lift a load by the application of a small effort.
43.Name the types of lever?
First type, second type and third type.
44.Give examples of lever?
First type-Bell crank lever,Rocker arm in IC engines,Foot lever.
Second type-Lever of load safety valves.
Third type-Treadle of sewing machine.
45.What are the forces acting on lever?
Load(W),Effort(P),Reaction at the fulcrum(Rf).
46.List the basis on which the design of pin or rocker arm of an IC engine is made?
The pin or rocker arm of an IC engine is made on the basis of bearing, shearing and bending failure.

Name the various type of springs?
Helical springs, spiral springs, leaf springs and disc or Belleville springs are the various type of springs.
1. What is spring index?
Spring index is the ratio of mean pitch diameter to the diameter of the wire.
1. What are active and inactive coils?
The coils which are free to deflect under load is called active coils and the coils which do not take part in deflection of a spring is called inactive coils.
2. Define the term spring rate?
Spring rate is defined as the load required per unit deflection. It is also called as stiffness of the spring.
1. Define surging of springs?
The spring material is subjected to higher stresses, which may cause earlier fatigue failure of springs. This effect is called as surging of springs.
2. How will you find weather the given helical spring is a compression spring or tension spring?
The ends of compression springs are flat whereas for tension springs, hooks will be provided at the ends.
Coils will be slightly open for compression springs to facilitates compression whereas in tension springs the coils are very close.
11.what material is used for leaf spring?
Plain carbon steel having 0.9 to 1% carbon in annealed condition is normally used for leaf springs. chrome vanadium and silica manganese steels are used for the better grade springs.
12.What is nipping of laminated leaf spring? Discuss its role in spring design?
Pre stressing of leaf springs is obtained by a difference of radii of curvature known as nipping.
The initial gap can be adjusted so that under maximum load conditions the stress in all the leaves will be same or, if desired the stress in the full length leaves may be less.
13.What are the functions of a rebound clip and a U-clip in a leaf spring?
A rebound and are used for holding the leaves of the spring together.

14.what are the end conditions of springs?
The end conditions of springs are,
a)plain end.
b)plain and ground end.
c)squared end.
d)squared and ground end.
16. whywhals factor is to be considered in the design of helical compression spring?
When wire wound in the form of helix, compressive stress is induced in the inner side of the spring and tensile stress is induced in the outer side of the spring. Due to this stress concentration is produced in the outer side of the spring .so whales factor is to be considered in the design of helical compression spring.
17.what is buckling of springs?
The helical compression springs behave like a column and buckles at a comparative small load when the length of the spring is more than four times the mean coil diameter.
18.why leaf springs are made in layers instead of a single plate?
Leaf springs are made in layer only for distributing the shear forces and bending moment evenly.
19. Define solid length of helical spring.
When compression spring is compressed until the coils come in contact with each other , then the spring is said to be solid and resulting length is called solid length.
20.Define free length of a helical spring.
It is the length of the spring in free on unloading condition.

21.why the clearance is provided between adjacent of the helical spring ?
To prevent closing of the coils during service with maximum working load.
22.Define the term spring stiffness or spring rate?
Spring stiffeness or spring rate is defined as the load required per unit deflection of the spring.
23. Define pitch of the spring coil?
It is defined as the axial distance between adjacent coils in uncompressed state.
24.What are the points to be considered in choosing the pitch of spring coils?
a)It should be such that if the spring is accidently carelessly compressed, the stress does not increase the yield stress in torsion.
b)spring should not close up before maximum service load is reached.
25.What are the methods used for elimination of surges in springs?
a) By using friction dampers on the centre coils so that the waves propagation dies out. b)By using springs of high natural frequency.
c)By using springs having pitch of coils near the ends different at the centre to have different natural frequencies.
26.How to avoid buckling of springs?
In order to avoid buckling of spring, it is either mounted on a central rod or located on a tube
27.What are the disadvantages in helical springs of non-circular wire?
a)The quality of material used for springs is not so good.
b)The shape of the wire doesnot remain square or rectangular while forming helix resulting in trapezoidal cross sections.It reduces the energy absorbing capacity of the spring.
c)The stress distribution is not favourable as for circular wires.
28.How equalized stress in leaf spring leaves is achieved?
a)By making the full length of leaves of smaller thickness than the graduated leaves.
b) By giving greater radius of curvature to the full length leaves than graduated leaves.
29. What is meant by initial tension in helical torsion springs?
In tension helical springs it is necessary to apply from 20 to 30% of the maximum load before the coils begin to separate during close coil windings.

30.Name few applications of helical springs.
a)Door hinge springs.b)springs for starters in automobiles.c)springs for brush holders in electric motors.
31.What are the purpose of composite springs?
a)To obtain greater spring force within a given space.
b)To ensure the operation of a mechanism in the event of failure of one of the springs.
31.What are torsion springs?
Torsion springs may be of helical or spiral type.The helical type may be used only in applications where the load tends to wind-up the spring and are used in various electrical mechanisms. The spiral type is also used where the load tends to increase the number of coils and when made of flat strips are used in watches and clocks.
32.How the stiffness of the spring can be increased?
The stiffness of the spring can be increased by decreasing the number of turns.
33.What types of stresses are induced in the wires of helical compression spring and torsional spring?
Compressive or tensile stresses in helical compression spring and both tensile and compressive stresses in case of torsional spring are due to bending.
34.What are the advantages of leaf springs over helical springs?
Leaf springs are made out of flat plates.The advantages of leaf spring over the helical spring is that the end of the spring may be guided along a defined path as it deflects to act as a structural member in addition to energy absorbing device.
35.How concentric springs are obtained?
Two or more springs are joined to form a nest and thus concentric springs are obtained.
36.Define chamber?
It is the vertical distance between the centre of the eye to the maximum deflection in main or master leaf in the leaf spring.

37.Name the springs used in gramophones?
Flat, spiral spring is used in gramophones.
38.Why full length leaves are used in automobiles?
This is desirable in automobile springs in which full length leaves are designed for lower stress because full length leaves carry additional load caused by swaying and twisting.
39.What factors are considered for design of spring?
Deflection criteria, material strength properties, service environment, desired life, manufacturing cost ,etc.
40.How the load is made to act concentric with spring axis in helical spring?
By making the two ends of spring as squared and ground ends, the load can be made to act concentric with spring axis.
41.Define lever?
It is a rigid rod or bar capable of turning about a fixed point called fulcrum. It is used as a machine to lift a load by the application of a small effort.
43.Name the types of lever?
First type, second type and third type.
44.Give examples of lever?
First type-Bell crank lever,Rocker arm in IC engines,Foot lever.
Second type-Lever of load safety valves.
Third type-Treadle of sewing machine.
45.What are the forces acting on lever?
Load(W),Effort(P),Reaction at the fulcrum(Rf).
46.List the basis on which the design of pin or rocker arm of an IC engine is made?
The pin or rocker arm of an IC engine is made on the basis of bearing, shearing and bending failure.