Why have different types of hardness tests been developed Ho

Why have different types of hardness tests been developed? How would you measure the hardness of a very large object such as a steel shaft? Which hardness tests and scales would you use for very thin strips of material, such as aluminum foil?

Solution

Actually, finding the hardness of any of the material for any given application demands several factors including the type of material, its geometry, surface conditions, exposure to the heat treatmnt process used, and production requirements. Therefore,we need some different types of hardness tests to find different hardness values for the same test specimen. Selecting the kind of hardness test we need to do is often influenced by end-customer requirements, because hardness measurements are commonly accounted values on specification sheets coming with the delivery of manufactured goods.

To measure the hardness of a very large object such as a steel shaft, we can use portable hardness testers. An LVDT (linear variable differential transform) may be used. It can record the shaft position, thereby measuring the indentation depth and the spring force that is applied at one time.

The micro hardness tests example Knop or Vickers would be suitable for thin aluminium strips.