33 - Hardness and impact tests

Abstract

This chapter describes the hardness and impact tests conducted on materials. The hardness of a material can be defined as the ability to scratch other materials, the ability to resist scratching, the ability to resist plastic spreading under indentation, the ability to resist elastic deformation under indentation, and 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. There are three main hardness tests, namely, the Brinell test, the Vickers test, and the Rockwell test. Impact tests are conducted to determine the toughness of a material, that is, the energy needed to fracture it. Izod test, principally used in the Great Britain and the Charpy test, which is widely used on the continent of Europe, are two popular impacts tests.