Question Set 87

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

Ans: If a material exhibits same mechanical properties regardless of loading direction, it is isotropic, e.g., homogeneous cast materials. Materials lacking this property are anisotropic.

2.What are orthotropic materials ?

Ans: It is a special class of anisotropic materials which can be described by giving their properties in three perpendicular directions e.g. wood; composites.

3.What is view factor ?

Ans: View factor is dependent upon geometry of the two surfaces exchanging radiation.

4.What properties need to be considered for applications calling for following requirements : (i) rigidity(ii) strength for no plastic deformation under static load(iii) strength to withstand overload without fracture.(iv) wear resistance(v) reliability and safety.

Ans: (i) Rigidity—Elastic modulus and yield strength

(ii) Strength (for no plastic deformation under static loading)—yield point

(iii) Strength (overload)—Toughness and impact resistance

(iv) Wear resistance—Hardness

(v) Reliability and safety—Endurance limit and yield point.

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

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

6.Mention two types of dislocations.

Ans: Dislocation refers to a break in the continuity of the lattice. In edge dislocation, one plane of atoms gets squeezed out. In screw dislocation the lattice atoms move fom their regular ideal positions.

7.What are the principal constituents of brass?

Ans: Principal constituents of brass are copper and zinc.

8.What is Curie point ?

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

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

Ans: 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.

10.What is the percentage of carbon in cast iron ?

Ans: 2.5%.