Your complete guide to Rockwell Hardness Testing

Rockwell hardness testing is a useful and efficient way to determine the hardness of a material. It measures the depth of penetration of an indenter on the material being tested, making it possible to calculate its relative hardness and durability. It offers direct readings without the need for secondary calculations and measurements, making it a straightforward and reliable part of the QA process. 

See a Rockwell hardness testing solution in action

Check out this short video guide to the True Blue II, a Rockwell Hardness testing machine from Universal Testing. 

What is Rockwell hardness testing?

The Rockwell Hardness Test is generally a non-destructive test performed on samples when it’s necessary to determine how hard a material is. It’s generally considered easier to perform compared to other methods, like Vickers or Brinell hardness testing. Another advantage is the small area of indentation needed to carry out the test, reducing wastage during the testing process. 

What is Rockwell Hardness Testing used for?

It’s used to determine the relative hardness of a material. 

When did Rockwell Hardness Testing become popular?

Rockwell hardness testing has a long history. The idea was first conceived by Viennese professor Paul Ludwik in 1908, but it wasn’t until Connecticut’s Hugh M. and Stanley P. Rockwell co-invented the first tester that the method took off. They expanded on the concept of utilizing a conical diamond indentation test based on displacement, and a patent was granted in 1919. 

Rockwell hardness testing and ASTM E18 standards

Hardness is defined as a material’s resistance to permanent indentation. Current Rockwell hardness test methods are specified in ASTM E-18 and anyone wishing to perform a Rockwell Hardness test should become familiar with this test standard. The most common industry standards adhered to when using the Rockwell method are: 

• ASTM E18 for metals 

• ISO 6508 for metals 

• ASTM D785 for plastics 

• ISO 2039 for plastics 

How Rockwell Hardness Testing is carried out

The Rockwell Hardness Test uses a diamond cone or hardened steel ball to indent the material being tested. Each time a test is performed, two loads are applied to the sample. 

First, the indenter is forced into the test material under a preliminary minor load. This depth is recorded. Then, with the minor load still applied, an additional load is introduced. This is known as the major load, and it increases the depth of penetration on the sample. The Major load is then removed, and the force on the sample is returned to the minor load.

The increase in the depth of penetration that results from applying and removing the major load is used to calculate the Rockwell Hardness value.