Testing Instruments By Standards
ASTM D785 is the quality test standard that is used for determining the Rockwell hardness number for plastics and insulation materials. The Rockwell Hardness Number is the amount of increase in the depth due to an indenter when it is applied on the test sample under specific loads. The following relation is applied while deriving the Rockwell Hardness tester.
Where HR is the Rockwell harness number and the ? is the depth of indentation after the load has been removed.