MECHANICAL ENGINEERING QUESTIONS -003

MECHANICAL ENGINEERING QUESTIONS -003

1. Why different types of sound are produced in different bikes, though they run on SI Engines?

 Engine specifications are different in different manufactures like as Bore Diameter (CC), Ignition timing. Also the exhaust passage takes more responsible for sound.

2. What are the factors that can affect the Factor of safety selection?

  The factor of safety is used in designing a machine component. Prior to selecting the correct factor of safety certain points must be taken into consideration such as:

·        the properties of the material used for the machine and the changes in its intrinsic properties over the time period of service.

·        The accuracy and authenticity of test results to the actual machine parts.

·        The applied load reliability.

·        The limit of stresses (localized).

·        The loss of property and life in case of failures.

·        The limit of initial stresses at the time period of manufacture.

·        The extent to which the assumptions can be simplified.

The factor of safety also depends on numerous other considerations such as the material, the method of manufacturing, the various types of stress, the part shapes etc.

3. What is heat treatment and why is it done?

 Heat treatment can be defined as a combination of processes or operations in which the heating and cooling of a metal or alloy is done in order to obtain desirable characteristics without changing the compositions. Some of the motives or purpose of heat treatment are as follows:

·        In order to improve the hardness of metals.

·        For the softening of the metal.

·        In order to improve the mach inability of the metal.

·        To change the grain size.

·        To provide better resistance to heat, corrosion, wear etc.

Heat treatment is generally performed in the following ways:

·        Normalizing

·        Annealing

·        Spheroidising

·        Hardening

·        Tempering

·        Surface or case hardening

4. What are the rules that must be kept in mind while designing castings?

Some of the points that must be kept in mind during the process of cast designing are as follows:

·        to avoid the concentration of stresses sharp corners and frequent use of fillets should be avoided.

·        Section thicknesses should be uniform as much as possible. For variations it must be done gradually.

·        Abrupt changes in the thickness should be avoided at all costs.

·        Simplicity is the key, the casting should be designed as simple as possible.

·        It is difficult to create true large spaces and henceforth large flat surfaces must be avoided.

·        Webs and ribs used for stiffening in castings should as minimal as possible.

·        Curved shapes can be used in order to improve the stress handling of the cast.

5. Which Mechanism is used in Automobile gearing system?

Differential mechanism

6. Explain the difference between pearlite and cementite?

 Pearlite is eutectoid mixture of ferrite and cementite. Cementite is chemical compound of iron and carbon.

7. Define buckling factor.

 It is the ratio of the equivalent length of column to the minimum radius of gyration.

8. What is endurance limit and what is its value for steel?

 Endurance limit is the maximum level of fluctuating stress which can be tolerated indefinitely. In most steels this stress is approximately 50% of the ultimate tensile strength and it is defined as the stress which can be endured for ten million reversals of stress.

9. Explain absolute viscosity?

 It is the ratio of shear stress and the gradient of velocity with distance between a fixed plate and moving plate (Its unit is Pa. s).

10. Explain difference between cohesion, adhesion and capillarity?

 Cohesion is the attraction of like molecules.

Adhesion is the attraction of unlike molecules for each other.

Capillarity is the elevation or depression of a liquid surface in contact with a solid.