Mechanical Basic Interview Question and Answers Part 5

Basic of Mechanical Engineering Interview, viva ,Oral Question and Answers Part 5

Mechanical Engineering Interview Technical questions and answers with explanation for Job interview, competitive examinations and entrance tests.

121. What does thermal diffusivity of metals signify.

Thermal diffusivity is associated with the speed of propagation of heat into solids during changes in temperature with time.

122. For conduction of heat, the instantaneous rate of heat flow is product of three factors. What are these ?

Area of the section of the heat flow path, perpendicular to the direction of heat flow. temperature gradient, i.e. change of temperature w.r.t. length of path. Thermal conductivity of material.

123. How convective heat transfer is effected and on what factors it depends ?

Convective heat transfer is effected between a solid and fluid by a combination of molecular conduction within the fluid in combination with energy transport resulting from the motion of fluid particles. It depends on boundary layer configuration, fluid properties and temperature difference.

124. Which is the common element between brass and bronze ?

Copper.

125. What does following alloy designation indicate FG 250 ?

Grey cast iron with tensile strength of 250 MPa.

126. How is ceramic defined ?

It is a solid formed by combination of metallic and non-metallic elements.

127. Give one example of metal classified as per structure as BCC, FCC, HCP and CCP.

BCC (body centred cubic) structure—Molybdenum
FCC (face centred cubic) structure—Aluminium
HCP (hexagonal closed packed) structure—Zinc
CCP (cubic dosed packed) structure-Copper.

128. What is the name of solid solution of carbon in alpha iron and delta iron ?

Ferrite and austenite respectively.

129. Explain the difference between pearlite and cementile ?

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

130. Give one example each of the following proportion of materials dimensional, physical, technological and mechanical.

Roughness, enthalpy, toughness, and hardness respectively.

131. For which parts the Wahl factor and Lewis form factor used ?

For springs and gears respectively.

132. How oxygen can be removed from steel during melting? What are fully killed steels ?

Oxygen can be removed by adding elements such as manganese, silicon or aluminium which, because of their high affinity for oxygen, react with it to form non-metallic oxides which rise into the slag. Steels which have had most of their dissolved oxygen removed are called “fully killed steels”.

133. Hydrogen cannot be removed easily from molten steel. What harm hydrogen has on property of steel ?

Execessive hydrogen results in the formation of small fissures often described as hairline cracks or flakes in the steel. Large forgings in alloy steel are particularly sensitive to this phenomenon.

134. What is allotrope ? In what forms of cubic pattern, iron exists ?

Some elements exist in more than one crystalline form. Each form is known as “allotrope”. Iron exists in two forms of cubic pattern, namely body centered cubic (bcc) and face-centered cubic (fee).

135. What is the difference between alpha iron, delta iron and gamma iron ?

The bcc form of iron exists between room temperature and 910°C, and between 1400°C and the melting point at 1539°C.
The lower temperature form is known as “alpha”-iron and the higher temperature form as “delta”-iron. The face-centered cubic form existing between 910°C and 1400°C is referred to as “gamma-iron”.

137. What is the difference between isotropic material and homogeneous material ?

In homogeneous material the composition is same throughout and in isotropic material the elastic constants are same in all directions.

138. Explain the difference between the points of inflexion and contraflexure.

At points of inflexion in a loaded beam the bending moment is zero and at points of contraflexure in loaded beam the bending moment changes sign from increasing to decreasing.

139. What is the difference between proof resilience and modulus of resilience ?

Proof resilience is the maximum strain energy that can be stored in a material without permanent deformation. Modulus of resilience is the maximum strain energy stored in a material per unit volume.

140. What is the difference between column and strut ?

Both column and strut carry compressive load. Column is always vertical but strut as member of structure could carry axial compressive load in any direction.

141. Explain the difference between ferrite, austenite and graphite ?

Ferrite is the solid solution of carbon and other constituents in alpha-iron. It is soft, ductile and relatively weak.
Austenite is the solid solution of carbon and other constituents in gamma-iron. It exists in ordinary steels at elevated temperatures, but it is also found at ordinary temperatures in some stainless steels.
Graphite has a hexagonal layer lattice.

142. Explain the terms solid solution, eutectic, eutectoid and peritectic.

Solid Solution. When a homogeneous mixture of two (or more) atomic forms exists in solid state, it is known as solid solution.
Eutectic. A mixture of two (or more) phases which solidify simultaneously from the liquid al¬loy is called an eutectic. Alloys in which the components solidify simultaneously at a constant tem¬perature the lowest for the given system, are called eutectic alloys.
Eutectoid. Eutectoid alloys are the alloys for which two solid phases which are completely soluble become completely insoluble on cooling before a certain temperature called eutectoid tem¬perature.
Peritectic. A peritectic transformation involves a reaction between a solid and liquid that form a different and new solid phase.
This three phase transformation occurs at a point called peritectic point.

143. What do you understand by critical points in iron, iron-carbide diagram ?

The temperatures at which the phase changes occur are called critical points (or tem¬peratures).

145. Why PERT is preferred over CPM for evaluation of project ?

PERT is based on the approach of multiple time estimates for each activity.

146. What is the percentage of chromium in 18 : 4 : 1 IISS ?

4%.

147. What is stellite ?

It is a non-ferrous cast alloy containing cobalt, chromium and tungsten.

148. Which rays are produced by cobalt-60 in industrial radiography ?

Gamma rays.

149. What are killed steels and what for these are used ?

Killed steels are deoxidised in the ladle with silicon and aluminium. On solidification no gas evolution occurs in these steels because they are free from oxygen.

150. What is critical temperature in metals ?

It is the temperature at which the phase change occurs in metals.