Basic

As far as the mechanical designer and hardware manufacturer are concerned, the most immediate choice of units appears to be stress, elastic constants, and physical dimensions. The SI system differentiates rather strongly between the concepts of weight and mass. Weight is defmed as the force of gravity, and it is expressed in newtons. The newton, which is then a unit of force, is that magnitude. of a force which gives to a mass of 1 kilogram an acceleration of 1 meter per second per second (lm/sec2 ). On this basis, the stress, defmed as the force divided by the area, would be expressed as newtons divided by meters squared. In the SI system 1 pascal (pa) is equal to I newton per square meter, which is the formal SI unit for pressure, stress, material strength or elastic constants. The conventional acceleration of gravity, g, is now 9.8 m/sec2 •

For straightforward applications in fastener engineering the proposed unit "pascal" is not only too small for practical purposes, but it is also quite superfluous. It would appear much more reasonable to use newtons per area instead of pascals. This author prefers newtons per square millimeter and

there are several practical reasons why the use of N/mm2 should be promoted.