Rockwell, Brinell, Vickers Hardness Test & More
Hardness testing measures a material’s strength by determining resistance to penetration. Laboratory Testing Inc. near Philadelphia, PA (USA) performs microhardness and various hardness test methods and offers the following:
- Tests for metals, plastics and elastomers
- Testing performed to ASTM and other required specifications for the type of material and application
- Test specimens
The hardness test is extremely useful in material selection because it provides a hardness value which indicates how easily a material can be machined and how well the material will wear. Hardness testing is also valuable in making decisions about treatments and coatings.
Array of Hardness Test Methods
- The Rockwell Hardness Test and Superficial Rockwell are performed on castings, forgings and other relatively large metal products and samples because the tests produce a large visible indentation.
- The Brinell Hardness Test can be applied to almost any metallic material and is the method most commonly used to test castings and forgings that have a grain structure too coarse for other hardness testing methods.
- Microhardness testing by Knoop and Vickers Hardness Test methods measure small samples or small regions in a sample. They are often used to measure surface or coating hardness on carburized or case-hardened parts, as well as surface conditions such as grinding burns or decarburization. (Vickers is also available on the macro scale to 50 kg.)
- The Shore Durometer Test measures the hardness of polymeric materials.
Conversion Charts comparing scales are available on LTI’s website.
- Rockwell – ASTM E18; NASM-1312-6
- Superficial Rockwell – ASTM E18; NASM-1312-6
- Brinell – ASTM E10
- Microhardness – ASTM E384; NASM-1312-6
- Vickers – ASTM E384, ASTM E92
- Shore – ASTM E2240
Hardness testing is usually performed using test machines equipped with an indenter that is forced into the test material over a certain amount of time. The shape of the indentor varies by type of hardness test and includes cone, ball and pyramid shapes. Each test machine also uses a different force or load application system and records an indentation hardness value in kilograms-force according to their individual hardness scales.
The Test Processes
Brinell Hardness Test
The Brinell Hardness Test can be applied to almost any metallic material and is the method most commonly used to test castings and forgings that have a grain structure too coarse for other hardness testing methods. During the test, a carbide ball indenter is pressed into the sample with accurately controlled force for a specific amount of time. When removed, the material has a round indent that is measured to calculate material hardness according to a formula.
Rockwell Hardness Test
In addition to a Rockwell Hardness Test, there is a Superficial Rockwell. For each test, a minor load is applied to either a diamond cone or a steel ball indenter positioned on the test material’s surface to establish a zero reference position. Next, a major load is applied for a specified amount of time, leaving the minor load applied upon release. The Rockwell hardness number will be the difference in depth between the zero reference position and the indent due to the major load.
The choice of indenter is dependent upon the characteristics of the test material. The Rockwell Hardness Test applies larger minor and major load values than the Superficial Rockwell, yet both tests offer three different major load options. More than thirty different scales are used between Rockwell and Superficial Rockwell hardness testing due to the various choices and combinations of tests, indenters and major loads.
Knoop Hardness Test
This microhardness test is used on very small parts and material features that are unable to be tested by the other methods and employs a test load of 1000 grams or less. The Knoop Test is performed like Brinell hardness by applying controlled force for a specific amount of time to an indenter in a rhombus-shape. The impression is measured microscopically and is used along with the test load to calculate the hardness value on the Knoop scale.
Vickers Hardness Test
A Vickers Hardness Test can be performed on both the micro and macro scales (some Vickers testers have a maximum test load of up to 50 kilograms). This type of hardness test is also performed by applying controlled force for a specific amount of time to an indenter, which in this case is a square-based diamond pyramid. The impression measurement and test load are used in the appropriate formula to calculate the Vickers hardness value. Like Brinell and Knoop, this method has one scale that covers its entire hardness range.
Shore Durometer Test
Hardness testing of polymeric materials, including plastics and rubbers, is performed by the Shore Durometer Test according to ASTM D2240. Like the hardness tests for metal, this method determines a material’s hardness value or resistance to indentation by penetration of an indenter into the test sample. Because the flexibility of polymers varies, LTI is equipped with various indenters for use in testing different types of materials from elastomers to rigid plastics.
- Materials Tested – metals, elastomers and plastic
- Test Methods
- Rockwell and Superficial Rockwell – used to assist in determining the grade of metal
- Brinell – typically used with castings, forgings and thicker samples
- Microhardness – Vickers (load weights up to 50 kg) and Knoop (load weights up to 1000 gm)
- Shore Durometer – testing of elastomers and plastics
Test Specimens – all hardness test specimens can be prepared at LTI