# Units of vickers,brinell and rockwell . . .

1. Nov 4, 2009

### kafri09

hello everyone.

a little question...(or mybe two...)...

why does vickers and brinell hardness test have the units of stress ?

and why does rockwell test has no units at all ?

thanks to all !

2. Nov 4, 2009

### Mapes

Hi kafri09, welcome to PF. Hardness is a measure of resistance to yield (plastic deformation), and the yield strength $\sigma_y$ has units of stress. Thus, the Vickers and Brinell hardness measurements, which are related to $\sigma_y$, do too. The Rockwell hardness is measured on a calibrated scale, where the calibration points correspond to well-defined tests on well-defined materials (similar to the temperature scale, which is calibrated by certain equilibrium phase change reactions). Does this answer your question?

3. Nov 4, 2009

### kafri09

yes it does.

thank u Mapes!