Hardness and impact tests

Abstract

This chapter explains hardness and impact tests and their results. The hardness of a material may be defined in the following ways: (1) the ability to scratch other materials, (2) the ability to resist scratching, (3) the ability to resist plastic spreading under indentation, (4) the ability to resist elastic deformation under indentation, and (5) the ability to resist deformation by rolling. Hardness tests are based on pressing a hard substance, such as a diamond or a steel sphere having known dimensions, into the material under test. The hardness can be determined from the size of indentation made for a known load. The three principal hardness tests are: (1) the Brinell test, (2) the Vickers test, and (3) the Rockwell test. To give an indication of the toughness of a material, that is, the energy needed to fracture it, impact tests are carried out. In an Izod test, a square test piece of side 10 mm and having a vee-notch of angle 45° machined along one side is clamped firmly in a vice in the base of the Izod test machine.