Indentation hardness

Indentation hardness is a measure of a material's resistance to permanent deformation due to a constant load from a sharp object. The concept is essential in materials science, engineering, and quality control because it provides insight into the material's mechanical properties, such as its strength, ductility, and wear resistance. Various tests and scales have been developed to quantify indentation hardness, each suitable for specific materials and applications.

Principles of Indentation Hardness

Indentation hardness tests involve pressing a hard indenter into the surface of a test material under a specific load for a defined period. The test measures either the depth or the size of the indentation left by the indenter. The basic principle is that a harder material will produce a smaller indentation. The most common parameters affecting indentation hardness are the applied force, the indenter's material and geometry, and the test duration.

Common Indentation Hardness Tests

Several tests are widely used to measure indentation hardness, each with its specific indenter shape, load range, and hardness scale.

Brinell Hardness Test

The Brinell Hardness Test uses a spherical indenter, typically made of hardened steel or carbide, pressed into the material under a specific load. The Brinell hardness number (BHN) is calculated from the diameter of the indentation.

Vickers Hardness Test

The Vickers Hardness Test employs a diamond pyramid-shaped indenter. The Vickers hardness number (VHN) is derived from the diagonal length of the square indentation, allowing for a wide range of materials to be tested.

Rockwell Hardness Test

The Rockwell Hardness Test is another widely used method, utilizing either a diamond cone or a hard steel ball as the indenter. The Rockwell hardness number (RHN) is determined based on the depth of penetration under a major load compared to the depth under a preliminary minor load.

Knoop Hardness Test

The Knoop Hardness Test is particularly useful for brittle materials or thin layers. It uses a diamond indenter with an elongated pyramid shape, producing an indentation that is measured for its longest diagonal.

Applications and Limitations

Indentation hardness testing is crucial in material selection, quality control, and predicting material behavior under stress. However, it is important to note that indentation hardness is not a fundamental material property but rather a composite property that may be influenced by other factors such as material microstructure, temperature, and test conditions. Therefore, while indentation hardness can provide valuable comparative data, it should be considered alongside other material properties for comprehensive material characterization.

See Also

• Materials Science
• Mechanical Engineering
• Wear Resistance
• Ductility

References

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