Q: We’re told from partners to use N/mm² to show compressive strength. But there’s only N is displayed on force gauge, N and N/mm² are the same?
A: No, N（newton）and N/mm２（newton per square mm）are different unit. But it’s not so difficult to convert from N to N/mm2.
The biggest difference between N and N/mm2 is to consider the size of the compressed surface area or not. N shows force value applied to whole contact area. N/mm2 shows value per mm2. N/mm2 can be calculated with N dividing by the size of the compressed surface area (mm2). Compressive force applying per unit area, as in N/mm2, is called pressure and is considered distinct from simple compressive force.
In case that compression force (N) is same but contact area is different, the pressure (N/mm2) that applied to objects is different. In other words, the wider the contact area gets, the less the value of pressure will be since the compression force will be distributed. Thus higher compression force will be required to break or deform objects with larger contact area. *1
When evaluating material characteristics (compressive strength), generally a unit of pressure is used: the unit without consideration to the size of the test sample.
On the other hand, when managing the strength of products, such as in quality control of finished products or parts, the unit of compressive force (N) is often used.
*1 Assume the sample is homogeneous and has a uniform thickness (rectangular prism, cylinder, etc.) In the case of inhomogeneous samples or complex shape, the strength varies depending on the indentation position, it may differ from above.
| Unit | Convert with N/mm2 |
|---|---|
| N/m | 1 N/m2 = 1000000 N/mm2 |
| MPa | 1 MPa = 1 N/mm2 |
| kgf/cm2 | 1 kgf/cm2 = 0.0981 N/mm2 |
Some of IMADA’s force gauges can install the automatic unit conversion function for measurement results into pressure units by presetting the contact area.
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