In Rockwell hardness testing method, the hardness of a material is measured by-

Explanation:

Hardness 

• It is the measure of materials localized plastic deformation.
• Hardness test are performed by forcing a small indentor into the surface of a material to be tested and under controlled conditions of load and rate of application.
• The size of the resulting indentation is related to hardness numbers.

Rockwell hardness test:

• Rockwell hardness testers use a number of indenters in combination with a variety of loads.
• It has 1/16, 1/8, 1/4, 1/2  inch diameter spherical steel indenter as well as conical diamond indenter which is used for the hardest material.
• Each of the indenters can be used with a major load of 60, 100, or 150 kg, and a minor load of 10 kg.
• The hardness number is the difference between the penetrations caused by major and minor load applications.
• Based on these load and indenters scales are developed,
  • 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 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.
  • Copper alloys are measured in k scales.
  • Polymers are measured in the Rockwell E and M scales. M scales are used for hard polymers.

Brinell hardness Scale:

• In 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 greater applied load.