This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Hardness”.
1. ______ is the resistance of a material to plastic deformation by indentation.
a) Toughness
b) Resilience
c) Hardness
d) Stiffness
View Answer
Explanation: Hardness is the property of a material to resist indentation. Stiffness is the resistance of a material to elastic deflection. The toughness of a material is resistance against fracture.
2. What is SI unit of hardness?
a) kg/m3
b) kg/m2
c) g/m2
d) N/m
View Answer
Explanation: The hardness number is determined by the load over the surface area of the indentation. Thus unit is kg/m2. CGS unit is g/cm2.
3. The hardness of martensite ______ with an increase in carbon content.
a) Increases
b) Decreases
c) Remains constant
d) First increases and then decreases
View Answer
Explanation: Hardness of martensite increases with an increase in carbon content. It is due to an increase in lattice distortion. This also increases brittleness, which is undesirable.
4. _____ is the strongest bond.
a) Van der Waals bond
b) Metallic bond
c) Covalent bond
d) Hydrogen bond
View Answer
Explanation: Covalent bond is the strongest bond. This is formed by the sharing of a pair of electrons. That’s why the diamond has the highest hardness.
5. ______ improve hardness.
a) Strain hardening
b) Plasticizers
c) Over aging
d) Tempering
View Answer
Explanation: Strain hardening increases the hardness of a material. Plasticizers reduce hardness when added to plastics. Over aging and tempering reduces the hardness of a material.
6. What is the hardness of silicon carbides?
a) 5-10 HV
b) 10-14 HV
c) 15-20 HV
d) 20-30 HV
View Answer
Explanation: Silicon carbide has a very high hardness of 20-30 HV. Glasses have hardness 5-10 HV. Aluminium nitride and alumina have hardness 10-14 and 15-20 HV respectively.
7. When hardness is measured under dynamic loading conditions, it is known as _____ hardness.
a) Brinell
b) Rebound
c) Knoop
d) Rockwell
View Answer
Explanation: Hardness is both a static and a dynamic property. When hardness is measured by dynamic loading, it is known as rebound hardness. It is related to the height of the rebound.
8. With an increase in temperature, hardness of material _____ and ductility ______
a) Increases, increases
b) Increases, decreases
c) Decreases, increases
d) Decreases, decreases
View Answer
Explanation: With an increase in temperature, material becomes softer. So hardness of material decreases. As a result, ductility increases.
9. Which process increases the hardness of the material?
a) Tempering
b) Annealing
c) Quenching
d) Over aging
View Answer
Explanation: Quenching of Steel gives martensite structure. It makes Steel harder by a factor of about four. Temperature, annealing and over aging decrease hardness of steel.
10. Which statement is false?
a) Alloying increases hardness of the pure metal
b) Dual phase alloys are harder than single phase alloys
c) Interstitial solid solutions are harder than substitutional solid solutions
d) Heat treatment always decreases the hardness of a material
View Answer
Explanation: Heat treatment can increase or decrease the hardness of a material. Quenching improves the hardness of a material by generating internal stress. Some other heat treatments soften the material as annealing or normalizing.
11. Which scale is not used to measure indentation hardness?
a) Rockwell
b) Bennett
c) Shore
d) Brinell
View Answer
Explanation: Bennett hardness scale is used to measure rebound hardness. Rockwell, shore and brinell are indentation hardness scales.
12. Cooling rate _____ with distance from the quenched end, and the hardness _____
a) Increases, increases
b) Increases, decreases
c) Decreases, increases
d) Decreases, decreases
View Answer
Explanation: As the distance increases, the heat flow rate decreases and cooling rate decreases. Hardness is a function of cooling rate. Thus, areas with low cooling rate remain less hard.
13. Stamping operation increases hardness.
a) True
b) False
View Answer
Explanation: Stamping (pressing) is a sheet metal forming process. It causes strain hardening in metals or alloys. As a result, hardness increases in Stamping.
14. Which microconstituent of Steel is hardest?
a) Spheroidite
b) Pearlite
c) Bainite
d) Martensite
View Answer
Explanation: Martensite is the hardest microconstituent in steel. It is due to high lattice distortion. Other microconstituents are softer than it.
15. Coarse pearlite is harder than fine perlite for the same composition of Steel.
a) True
b) False
View Answer
Explanation: Fine pearlite is harder than coarse pearlite. With a decrease in distance between cementite platelets, hardness increases. It is due to higher resistance to plastic deformation by cementite platelets.
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.
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