Difference between, Brinell,Rockwell and Vickers Hardness Test
What is Hardness?
Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting.
Measurement of Hardness:
Hardness is not an intrinsic material property dictated by precise definitions in terms of fundamental units of mass, length and time. A hardness property value is the result of a defined measurement procedure. Hardness of materials has probably long been assessed by resistance to scratching or cutting. An example would be material B scratches material C, but not material A. Alternatively, material A scratches material B slightly and scratches material C heavily. Relative hardness of minerals can be assessed by reference to the Moh’s Scale that ranks the ability of materials to resist scratching by another material. Similar methods of relative hardness assessment are still commonly used today. An example is the file test where a file tempered to a desired hardness is rubbed on the test material surface. If the file slides without biting or marking the surface, the test material would be considered harder than the file. If the file bites or marks the surface, the test material would be considered softer than the file. The above relative hardness tests are limited in practical use and do not provide accurate numeric data or scales particularly for modern day metals and materials. The usual method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of a specific shape, with a specific force applied for a specific time. There are three principal standard test methods for expressing the relationship between hardness and the size of the impression, these being Brinell, Vickers, and Rockwell. For practical and calibration reasons, each of these methods is divided into a range of scales, defined by a combination of applied load and indenter geometry.
No specimen preparation required
The specimen surface can be rough
Specimens need to be prepared
Hardness value directly readable, no optical evaluation required
Good illumination of the test indent is important for ensuring correct evaluation
of the test indent (e.g. with the aid of a ring light).
Due to the need to conduct optical indent evaluation, Vickers hardness testers
must be equipped with an optical system
Quick and cost-effective process
The process is slow (by comparison with the Rockwell method). The test cycle
takes somewhere between 30 and 60 seconds
The process is rather slow. The test cycle takes somewhere between 30 and 60
Limitation in applying the method on thin specimens of very hard materials
Non-destructive testing is possible
Not always the most accurate hardness testing method
High risk of deforming the material to be tested when testing in the macro range
with high test loads
More expensive to purchase than Rockwell testers due to optical system
The test location must be completely free of all contamination (e.g. scale,
foreign bodies or oil)
The surface quality of the specimen must be good, because the indent is measured
The surface quality of the specimen must be good (ground and polished)
The indenter has unknown effects on the test results
Relatively large test indents that are easier to measure the rather small Vickers
Only one type of indenter
With increasing hardness, it becomes increasingly difficult to distinguish between materials
Can be used for testing non-homogeneous materials (e.g. castings)
The Vickers method can be used with any and all materials and test specimens
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