# Testing of Materials Questions and Answers – Microhardness Test

This set of Testing of Materials Question Bank focuses on “Microhardness Test”.

1. What is test load used in Micro hardness test?
a) 2-200 gmf
b) 5-1000 gmf
c) 60 gmf
d) 100 gmf

Explanation: In the case of micro hardness test, very small load is applied. Its range is 5 to 1000 gmf.

2. Which of the following is a Microhardness test?
a) Brinell
b) Knoop
c) Rockwell
d) Shore

Explanation: Brinell is a Macrohardness test. Knoop indenter is used in Micro hardness testing. Shore hardness is a dynamic hardness test.

3. What is the shape of indentation by knoop indenter?
a) Semi spherical
b) Square
c) Cone
d) Rhombohedral

Explanation: Knoop indenter is a diamond pyramid. It has one of the diagonals longer than the other. Shape of indentation is rhombohedral.

4. What is the diagonals’ ratio of Knoop indenter?
a) 1:1
b) 1:2
c) 7:1
d) 10:1

Explanation: Knoop indenter is a diamond pyramid. It has one diagonal longer than the other. Its ratio is 7:1.

5. Which test is more preferred for testing hardness of electroplated surface?
a) Dynamic hardness test
b) Scratch hardness test
c) Macrohardness test
d) Microhardness test

Explanation: Hardness of electroplated surface is tested by microhardness test. It may be chrome plating.

6. Which of the following is an angle between opposite faces in Knoop indenter?
a) 130°
b) 120°
c) 136°
d) 122°

Explanation: Knoop indenter is a diamond pyramid. The ratio of diagonals is 7:1. The angles between them are 130° and 172°.

7. What is the disadvantage of the Knoop hardness test?
a) Elastic recovery
b) Soft indenter
d) Cannot use thin specimen

Explanation: Knoop hardness test uses diamond indenter. Small load is used. This test gives a higher value of microhardness because of elastic recovery.

8. What is Knoop hardness of diamond?
a) 100 HK
b) 1000 HK
c) 7000 HK
d) 9000 HK

Explanation: Knoop hardness of diamond is 7000 HK. Brittle materials are tested by Knoop test. Vickers hardness of diamond is 10,000 HV.

9. What is Knoop hardness of gold foil?
a) 68 HK
b) 69 HK
c) 343 HK
d) 820 HK

Explanation: Gold foil has a hardness of 69 HK. Dentin has a hardness of 68 HK. Quartz has hardness 820 HK.

10. In microhardness test, Vickers test uses load less than 1 kgf.
a) True
b) False

Explanation: Vickers hardness test may be macro or microhardness test. In case of microhardness test, load is small. It is taken less than 1 kgf.

11. Microhardness test gives average hardness.
a) True
b) False

Explanation: Macrohardness tests give average hardness. Microhardness test gives hardness of individual grains or phase.

12. What is the formula for Knoop hardness number?
a) KHN = h – 500t
b) KHN = 1.854P/L2
c) KHN = P/ D2
d) KHN = P/L2C

Explanation: Knoop hardness number is given by formula KHN = P/L2C. Here L is longer diagonal length, P is load and C is constant.

Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.

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