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Brinell hardness test
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 Brinell (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 (29 kN) force. For softer materials, a smaller force is used and for harder, a tungsten carbide ball. The indentation is measured and hardness calculated as:
- where:
| P | = applied force (kgf) |
| D | = diameter of indenter (mm) |
| t | = depth of indentation (mm) |
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 force in kilograms force.
| Material | Hardness |
|---|---|
| Soft wood (e.g. pine) | 1.6 HBS 10/100 |
| Hard wood | 2.6 to 7.0 HBS 1.6 10/100 |
| Aluminium | 15 HB |
| Copper | 35 HB |
| Mild steel | 120 HB |
| 18-8 (304) stainless steel | 250 HB |
| Glass | 550 HB |
| Hardened tool steel | 650 - 700 HB |
Standards
- 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
- US standard (ASTM International)
- ASTM E10 : : Standard method for Brinell hardness of metallic materials.
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