Standard Article

Hardness Testing

Mechanical Testing

  1. Janice Edwards

Published Online: 18 MAY 2012

DOI: 10.1002/0471266965.com025.pub2

Characterization of Materials

Characterization of Materials

How to Cite

Edwards, J. 2012. Hardness Testing. Characterization of Materials. 1–9.

Author Information

  1. JE Consulting, Round Lake, IL, USA

Publication History

  1. Published Online: 18 MAY 2012

Abstract

Indentation hardness tests such as Brinell, Rockwell, Vickers, Knoop, and instrumented indentation are frequently used methods for determining hardness. The basic concept utilized in all of these tests is that a set force is applied to an indenter in order to determine the resistance of the material to penetration. If the material is hard, a relatively small or shallow indentation will result, whereas if the material is soft, a fairly large or deep indentation will result.

These tests are often classified in one of the following two ways: by the extent of the test force applied or the measurement method used. A “macro” test refers to a test where a load >1 kg is applied; similarly “micro” refers to a test where a load of ≤1 kg of force is applied. Additionally, some instruments are capable of conducting tests with loads as light as 0.01 g and are commonly referred to as ultralight or nanoindentation testers. Rockwell and Brinell testers fall into the macro category, whereas Knoop testers are used for microindentation tests. Vickers and instrumented indentation testers can be employed for both macro- and microindentation tests. The measurement methods available include a visual observation of the indentation or a depth measurement of the indentation. Rockwell and instrumented indentation testers are capable of determining the depth of the indentation, whereas Brinell, Knoop, and Vickers testers require an indentation diameter measurement. These visual measurements can be automated, as will be discussed later in this article.

Hardness is not a fundamental property of a material, yet hardness testing is considered a useful quality-control tool. Many properties are predicted from hardness values when combined with additional information such as alloy composition. The following is a list of such properties: resistance to abrasives or wear, resistance to plastic deformation, modulus of elasticity, yield strength, ductility, and fracture toughness. Some of these properties, such as yield strength, have numerical relationships with hardness values, whereas others such as fracture toughness are based on observations of cracks surrounding the indentations. Data analysis and conversions will be discussed in greater detail later in this article.

Keywords:

  • hardness testing;
  • Brinell;
  • Rockwell;
  • Vickers;
  • Knoop;
  • Berkovich;
  • hardness value;
  • instrumented indentation