# Brinell Hardness Number

on . Posted in Classical Mechanics

The Brinell hardness number (HB or BHN) is a measurement of a material's hardness of metals and alloys, specifically its resistance to indentation.  It is determined using the Brinell hardness test, which involves pressing a spherical indenter (usually a hardened steel ball) into the surface of the material under a known load.  The diameter of the resulting indentation is measured, and the Brinell hardness number is calculated using a formula.

The Brinell hardness test is particularly suitable for materials that are too coarse or rough for other hardness testing methods.  It is commonly used for metals, especially softer metals, as well as certain non-metallic materials like plastics and composites.  The Brinell hardness number provides information about the material's ability to withstand localized deformation, wear, and abrasion.

It's important to note that the Brinell test results can be affected by factors like the size of the indenter, the load applied, and the properties of the material being tested.  Therefore, standard procedures and guidelines are followed to ensure accurate and consistent measurements.  Brinell hardness numbers are commonly used for quality control, material selection, and comparing the hardness of different materials.  Higher Brinell hardness numbers generally indicate greater hardness and resistance to indentation, while lower numbers indicate softer materials.

### Brinell Hardness Number formula

$$BHN = 2\;F_a \;/\; \pi \; D \; ( D - \sqrt{ D^2 - d^2}\; )$$
Symbol English Metric
$$BHN$$ = Brinell hardness number $$lbm\;/\;in^2$$   $$kg\;/\;mm^2$$
$$F_a$$ = applied load $$lbf$$ $$N$$
$$\pi$$ = Pi $$3.141 592 653 ...$$
$$D$$ = diameter of steel ball $$in$$ $$mm$$
$$d$$ = diameter of depression $$in$$ $$mm$$