Mechanical Question/Answer

Q  Explain the effect of the alloying element chromium and nickel in stainless steel?

Addition of nickel and chromium the tensile strength and increase in resistance to corrosion takes place.

Q Mention two type of dislocations?

Dislocation to a break in the continuity of the lattice, in the continuity of the lattice, one place of atom   gets squeezed out. In screw dislocation the lattice atom move from their regular ideal position.

Q What are the principle constituent of the brass?

Principle constituent of the brass is copper and zinc.

Q What is the Curie point?

Curie point is a temperature at which ferromagnetic materials can no longer be magnetised by outside forces.

Q specific strength of materials is very high when they are in fibre but lower when they are in bar from?

Crystal structure has ordered, repeating arrangement of atoms. Fibres are liable to maintain this and thus have high specific strength. As size increases, the condition of ordered and repeating arrangements can`t be guaranteed because of several types of defects and dislocations and thus the specific strength gets lower.

1. Cast iron has 2.5% carbon.
2. Chromium increases the corrosion strength when it added in steel.
3. Individual materials retain their property in composite material.
4. When an elastomer has grater then 100% elongation then it is a polymer.
5. When % elongation is more than 200% then it is classified as rubber.
6. Ductility is the defined as the property of material by virtue of which it can be drawn into wire without rapture.
7. Pitch distance between two rivet is minimum 2.5d, where d is the rivet diameter.
8. Bernoulli theorem states that the sum of pressure head velocity head and monometric head at a point is constant during pipe flow.
9. When carbon % increase in steel brittleness of the steel is increased.
10.  When oxygen content is removed from steel. This type of steel is known as the killed steel.
11.  In the turning of the plane gyroscopic principle is used.
12. Gas turbine works on the brayton or Atkinson cycle.  
13.  In the water tube boiler water flow inside the water tube and gases around it. While fire tube boiler hot gases flow inside the tube and water its surrounding.
14. Ash has the same percentage of content in ultimate and proximate analysis.
15. The crown of the fire box is made hemispherical in order to resist instance heat in fire box.
16. India biggest thermal power station is 500mw.
17.  Humidification involves an increase in specific humidity.
18. Due to lower weight of machine per ton of refrigeration air refrigeration cycle is used in the aeroplanes.
19.  During sensible cooling process relative humidity is increase.
20.  Joule is the unit of the energy.
21. First law of motion is provides the definition of the force.
22. Heavy body have greater momentum if two bodies one light and anther heavy body have equal kinetic energy. In case of simple pendulum of oscillation is given by
23. 
    
24. Hooks law holds good up to limit of proportionality.
25. Young`s modules is defined as the ratio of the longitudinal stress to longitudinal strain.
26.  Snap type rivet head is used in the boiler plate riveting.
27.  Perpendicular distance between two rivets in chain riveting is 2d+6mm, where d is diameter of the rivet.
28. The edge of the boiler plate is bevelled at 80o
29. According to I.B.R. lap joint is preferred for the circumferential joint.
30.  Shape of  the woodruff key is like semicircle .
31.  Ionic reaction generally occurs in solution in polar solvent.
32.  Polyethylene has an ortho rhombic structure.
33.  The degree of freedom of monoatomic gas is 3.
34.  White phosphorus is used as the passion.
35. Hydrofluoric acid is used for the etching of the glass.
36.  Rubber is visco-elastic material.
37. Specific gravity has a dimension less quantity.
38. Cadmium rod is used for slow down the neutron in the reactor.
39.  for NPN transistor negative voltage required at collector.
40. If the spring is cut into parts spring constant does not change.
41. Copper has a common element between brass and bronze.
42. FG250 indicates that the grey cast iron having tensile strength 250 MPa.
43.  Entropy is the extensive property.
44. Throttling process has no work during process.
45.  With the increase of the temperature the ratio of Cp/Cv is decrease.
46.  If the cut off ratio of the diesel cycle increase efficiency of the cycle is decrease.
47.  Straight sided splines, triangular splines, and involute splines is used in the machine element.
48.  The ratio of the fatigue limit to the tensile strength is known as the endurance ratio.
49. GFRP is standing for the glass fibre reinforced plastic.
50. The value of the passion ratio for non-dilatent material is 0.5.
51. Sand graded in foundry according to clay content and grain size.
52.  Shape factor of the casting is the ratio of the sum of the maximum length and maximum width to the maximum thickness.
53. Due to insufficient fluidity of the molten metal causes misran defect in the casting.
54.  Copper is used for the soldering iron bit.
55.  Flux is used in the soldering to prevent oxidation of welded surface.
56. Hurdy cross method is commonly used for computer program for a pipe network.
57. If shear stress is less than half of tensile strength then tensile member is fail in shear.
58. By increasing coefficient of friction and decreasing helix angle a power screw can be made self-locking.
59.  Ackerman steering formed a lower pair.
60.  Copper tool is used in the EDM process.
61. Momentum is defined as mass × velocity.
62.  In hydrostatic lubrication system starting friction is low. 
63. Intensity of radiation at a surface in perpendicular direction is equal to (1/π)×emissive power.
64. Prandtl  number is the ratio of kinematic viscosity and thermal diffusivity.

 Q Why is it that the maximum value at which the residual stress can reach is the elastic limit of the material?

A stress in elastic limit, with no external force to oppose it, will relive itself by plastic deformation until it reaches the value of yield stress.

 

Q Distinguished between creep and fatigue?

Creep is low and progressive deformation of the material with time under a constant stress at high temperature applications. While fatigue is the reduced tendency of material to offer resistance to applied stress under repeated are fluctuating loading condition.  

THERMODYNAMICS

1. Temperature pressure volume and atomic mass control the physical property of a perfect gas. 
2. Boyle’s law, Charles law Gay-Lussac law and joule’s law is applicable for the behaviour of the perfect gas.
3. Kelvin is the S.I unit of the temperature.
4. S.I unit of the mass is kilogram.
5. The S.I unit of the length is meters.
6. S.I unit of the energy is joule.
7. According to Charles law for a perfect gas T2/T1 = V2/V1, if P is kept constant.
8. According to Gay-Lussac law for a perfect gas the absolute pressure is given mass varies directly as absolute temperature, if volume is kept constant.
9. An ideal gas as compared to real gas occupied more volume.
10. General gas equation is PV = mRT.
11.  The S.I unit of the time is Second.
12. Gas law is applicable to gases alone not to vapours.
13.  According to Dalton’s law the total pressure of a mixture of gases is equal to sum of the partial pressure of all gases.
14. O2, H2, N2 and air can be regarded as gas. So the gas laws could be applicable, within the commonly encountered temperature limit.
15. Pascal is the S.I unit of the pressure.
16. In a polytrophic process, the perfect gas equation P1V1/T1 = P2V2/T2 can be used only to determine one property at one of the states, provided all other properties is known.
17. A closed system is one in which mass does not cross the boundaries of the system, through energy may do so.
18. Temperature of a gas is produced due to kinetics energy of molecules.
19.   According to the kinetic theory of gases, the absolute zero temperature is attained when kinetic energy of the molecule is zero.
20. Kinetic theory of gases assumes that the collision between the molecules are perfectly elastic.
21. The pressure of gas in terms of its mean kinetic energy per unit volume E is equal to 2E/3.
22.   Kinetic energy of gases in term of the molecules in term of absolute temperature T is proportional to T.
23. Superheated vapour behaves approximate as a gas

ENGINEERING MATERIAL

1. Ductility of the material can be defined as ability to undergo large deformation in tension.
2. Malleability of a material is defined as ability to undergo large permanent deformation in compression.
3. Stress relaxation is the phenomenon in which deformation tend to loosen the joint and produces a stress reduction.
4. Wrought iron is highly resistance to corrosion.
5. In malleable iron carbon is present in the form of nodular aggregates of graphite.
6. In compression a prism of brittle material will break by shearing along oblique plane.
7.  The elastic stress strain behavior of rubber is non-linear.
8. In nodular iron graphite is in the spheroids.
9. Isotropic material is those which have the same elastic properties in all direction.
10. The metallic structure of mild steel is body centered cubic.
11. The ability of material to resist softening at high temperature is known as hot hardness.
12.  In grey cast iron carbon is present in the form of flacks.
13.   The crystal of alpha iron is body centered cubic.
14. Re-crystallization temperature is one at which new spherical crystals first begin to form from the old deformed one a strained metal is heated.
15. Mild steel is belonging to low carbon steel category.
16. The crystal structure of gamma iron is face centered cubic.
17. Cast iron is characterized by minimum of 2% of carbon.
18. Point of arrest for iron corresponding to stage at which allotropic forms change.
19. The ultimate tensile strength of low carbon steel by working at a high strain rate will increase.
20. Face centered cubic lattice type of material are usually most ductile.
21.  The unique property of cast iron is its high damping characteristics .
22. Delta iron occurs at the temperature of b/w 14000c and 15390c.
23. Slow plastic deformation of metals under a constant stress is known as creep.
24. Pure iron is the structure of ferrite.
25. Pig iron is the name given to product of blast furnace made by reduction of iron ore.
26.  The molecules in solid moves back and forth like tiny pendulums.
27. A material is known as allotropic or polymorphic if it exist in several crystal forms at different temperatures.
28. The ultimate tensile strength and yield strength of most of the metals when temperature falls from o to -1500c will increase.
29. The percentage of carbon in grey cast iron usually varies b/w 2.5 to 4.5%.
30. A reversible change in the atomic structure of steel with corresponding change in the properties is known as allotropic  change.
31. For the allotropic forms of iron, the point of arrest is the point of discontinuity.
32. Alpha iron gamma iron and delta iron represents the allotropic forms of carbon.
33. Super conduction by metals is observed in the temperature range of below 100k.
34. The number of in 1 cm3 of metals would be of order of 1022.
35. The temperature at which ferromagnetic alpha iron transform to paramagnetic alpha iron is 7700c.
36. Paramagnetic alpha iron changes to gamma iron at 9100c.
37. The percentage of carbon in pig iron varies from 4 to 4.5%.
38. Ferromagnetic alpha iron exists in temperature range of below 7230c.
39. Ferrite constituents of steel are softest and least strong.
40. Gamma iron exists at the temperature b/w 9100c to 14000c.
41. Piezometer is used to measure very low pressure.