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The Brinell scale characterises the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science.
Brinelling refers to surface fatigue caused by repeated impact or overloading. It is a common cause of roller bearing failures, and loss of preload in bolted joints when a hardened washer is not used. Engineers will use the Brinell hardness of materials in their calculations to avoid this mode of failure. Fretting corrosion can cause a similar-looking kind of damage and is called false brinelling even though the mechanism is different.
Proposed by a Swedish engineer Johann August Brinel (1849 - 1925) in 1900, it was the first widely used and standardised hardness test in engineering and metallurgy. The large size of indentation and possible damage to test-piece limits its usefulness.
The typical test uses a 10 mm diameter steel ball as an indenter with a 3,000 kgf load. For softer materials, a smaller load is used and for harder, a tungsten carbide ball. The indentation is measured and hardness calculated as:
- <math>\mbox{BHN}=\frac{P}{\pi D t}<math>
- where:
| P
| = applied load (kg)
|
| D
| = diameter of indenter (mm)
|
| t
| = depth of indentation (mm)
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Common values
When quoting a Brinell hardness number (HB), the conditions of the test used to obtain the number must be specified. The standard format for specifying tests can be seen in the example "HBW 10/3000". "HBW" means that a tungsten carbide ball indenter was used, as opposed to "HBS", which means a hardened steel ball. The "10" is the ball diameter in millimetres. The "3000" is the load in kilograms.
Brinell Hardness Numbers (standard test conditions unless otherwise stated)
| Material | Hardness
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| Soft wood (e.g. pine) | 1.6 BHS 10/100
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| Hard wood | 2.6 to 7.0 BHS 1.6 10/100
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| Aluminium | 15 BH
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| Copper | 35 BH
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| Mild steel | 120 BH
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| 18-8 (304) stainless steel | 250 BH
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| Glass | 550 BH
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| Hardened tool steel | 650 - 700 BH
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Standards
- International (ISO) and European (CEN) Standard
- EN ISO 6506-1 : Metallic materials - Brinell hardness test - Part 1 : test method.
- EN ISO 6506-2 : Metallic materials - Brinell hardness test - Part 2 : verification and calibration of testing machine.
- EN ISO 6506-3 : Metallic materials - Brinell hardness test - Part 3 : calibration of reference blocks)
- ASTM E10 : : Standard method for Brinell hardness of metallic materials.
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