Mechanical Interview questions- Material and Metallurgy

1. What is the difference between isotropic and anisotropic materials?

If a material exhibit same mechanical properties regardless of loading direction, it is isotropic ie .homogeneous cast materials . Materials lacking this property are anisotropic.

2.what are orthotropic materials?.

It is a special class of anisotropic materials which can be described by giving their properties in three perpendicular directions.

3. Explain the effects of alloying chromium and  nickel in stainless steel?

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

4.What are the principal constituents of brass?

Principal constituents of brass are copper and zinc.

5.What is curie point?

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

6.Specific strength of materials is very high when they are in fibre size but lower when they are in bar form~Why?

Crystal structure has ordered by repeating arrangement of atoms. Fibers are liable to maintain this band 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.

7.If percentage elongation of a material is more than 200 percentage it is classified as ?

Rubber

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

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

9.Why fatigue strength decrease as size of a part increases beyond around 10 mm?

Perfection of material conditions is possible at lower sizes as size increases it is not possible to attain uniform structure of the material.

10.While normal carburizing and nitriding surface treatments increase fstigue strength, excessive treatments  May decrease the fatigue strength. Why?

Normal carburizing/ Nitriding treatments increase volume due to phase transformation at surface and introduce residual compressive surface stress and thus increase the fatigue strength. By excessive treatment the high compressive stresses are introduced but these are balanced by high internal tensile stresses of equal and the subsurface fatigue cracks may develop in the regions of high tensile stress and lead to early fatigue failure.

11.Which theories of failure are used for ductile materials and brittle materials?

For ductile materials theories of failure used are maximum shear stress theory and maximum energy of distortion theory, while for brittle materials theory of maximum principal stress and maximum strain are used.

12.What is the common element between brass and bronze?

Copper.

13.Define ceramics?

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

14.How oxygen can be removed easily from molten steel. What harm hydrogen has on property on steel?.

 Oxygen can be removed by adding elements such as manganese, silicone or aluminum 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.

15.what is the difference between alpha iron, Delta iron, and gamma iron?

The bcc form of iron exists between room temperature and 910degree Celsius and between 1400 degree Celsius and the melting point at 1539 degree Celsius. 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 degree Celsius and 1400 degree Celsius to as gamma iron.

16.What is the difference between isotropic material and homogeneous materials?

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

17. What is mass transfer and state fick s law?

Transfer of one constituent from a region of higher concentration to that of lower concentration is known as mass transfer.

Mass transfer by molecular diffusion is analogous to conduction of heats in solids and is stated by Ficks law according to which  rate of mass flux of the diffusing component in mole/sec/unit area is equal to diffusivity and the local concentration gradient of the diffusing component.