Question

Following test is also known as microhardness test
1. Brinell hardness test
2. Vickers hardness test
3. Rockwell hardness test
4. Knoop hardness test

Answer 1

Correct Answer - Option 4 : Knoop hardness test

Explanation:

Brinell Hardness:

• In Brinell hardness tests, hard, hardened steel (or Tungsten carbide) spherical indenter is forced into the surface of a metal to be tested. This is a microhardness test.
• In the Brinell hardness test a hard spherical indenter of 10 mm diameter is used, and the load varies between 500 and 3000 kg. Harder materials require a greater applied load.

Rockwell hardness test:

• This test is also a microhardness test. In this test, a hardened steel ball indenter and a conical diamond (Brale) indenter, is used for the indentation of the material.
• Rockwell A scale, 60 kg with diamond indenter is used for steels and similar hard alloys.
• Rockwell B scale, 100 kg with 1/16 inch (1.6 mm) diameter sphere indenter are used for aluminum alloys.
• Rockwell C scale, 150 kg with the diamond pyramid indenter are used for steel and similar hard alloys.

Knoop Hardness Test

• The test is the micro indentation hardness test. For each test here, a small diamond indenter of pyramidal shape is forced into the specimen.
• For precise measurement, the sample must be polished properly. In the Knoop test, only the longer diagonal is measured, and the Knoop hardness is calculated based on the projected area of the indent. 

Vickers hardness test:

• In Vickers hardness test both diagonals of indentation are measured for calculation of Vickers hardness number (HV).