This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Volume Imperfections”.
1. Which one of the following, is not volume defect?
d) Blow hole
Explanation: Pore, void and blow hole are three dimensional defects (volume defects). Vacancy is an empty atomic site. So vacancy is categorised as zero dimensional defect.
2. Continuous precipitation is observed in the system ________
Explanation: In aluminium-copper system, CuAl2 particles precipitate continuously throughout the matrix. That’s why it is also known as continuous precipitation. Fe-C, Pb-Sn and Al-Mg systems exhibit discontinuous precipitation.
3. Cellular precipitation is also known as ______
d) Semi coherent
Explanation: Cellular precipitation is known as discontinuous precipitation. Because a sudden change of composition takes place in cellular precipitation. Non cellular precipitation is known as continuous precipitation.
4. Precipitation hardening deteriorates ______ of material.
a) Tensile strength
b) High temperature properties
Explanation: Precipitate particles hinder the motion of dislocations so ductility of materials decreases. Simultaneously, precipitation hardening increases hardness and tensile strength. Precipitation hardened alloys exhibit good high temperature properties.
5. What is the dimension of voids?
a) 106 – 108 nm
b) 10 – 107 nm
c) 10 – 105 nm
d) 10 – 102 nm
Explanation: Voids generally have size range of 106 – 108 nm. 10 – 107 nm is size range for grains. 10 – 105 nm is size range for precipitate and 10 – 102 nm is for dislocations.
6. Which one of the following factor does not favour void formation?
a) Slow quenching rates
b) Low ageing temperature
c) High ageing temperature
d) Presence of gas
Explanation: Slow quenching rates favour formation of voids. Presence of gas atoms is required to nucleate void. High ageing temperature favors atom diffusion, which leads to void formation.
7. Hydrogen induced cracks are generally intergranular.
Explanation: Cracks, due to hydrogen, are generally trans granular. These cracks develop across the boundary between grains. Intergranular cracks are also observed in some alloys but only in special cases.
8. Voids formed due to shrinkage of material, during its solidification, are known as _______
d) Blow hole
Explanation: Voids formed due to shrinkage of material, during solidification, are referred as cavitation. While void formed due to entrapment of air in material, during solidification, is porosity. Inclusions are metallic impurities.
9. What causes blow holes in casting?
a) Soft ramming
c) Insufficient permeability
d) Risering system
Explanation: Insufficient permeability causes blow holes in metal casting. It may be due to fine sand grains or hard ramming. Venting, controlled ramming and risering system reduce chances of forming blow holes in casting.
10. If Young’s modulus of tungsten carbide is 450 GPa, what will be Young’s modulus for 4% porous tungsten carbide?
a) 450 GPa
b) 415.8 GPa
c) 410.4 GPa
d) 425.8 GPa
Explanation: E = E0 (1 – 1.9p)
Here, P = porosity fraction, E0 = Young’s modulus for uncracked material, E = Young’s modulus
E = 450 (1 – 1.9×0.04)
= 415.8 GPa.
11. With increase in porosity Young’s modulus ________
c) Remains constant
d) First increases and then decreases
Explanation: Relation for Young’s modulus and porosity can be understood by MacKenzie’s equation. E = E0 (1 – 1.9p). Here, P = porosity fraction, E0 = Young’s modulus for uncracked material, E = Young’s modulus. Presence of porosity decreases Young’s modulus.
12. Ceramics are sensitive for defects like inclusion and void.
Explanation: Inclusions act as preferable sites for fracture initiation. Ceramics are generally produced by powder metallurgical methods so these are prone to contain inclusions and porosity. That’s why inclusions and pores are undesirable.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.