What Is a Hardness Test?
A hardness test is an assessment conducted to measure a material’s hardness. This test is critical in industrial applications as it allows for the inference of various mechanical properties from the obtained hardness value.
Characterized by a range of methods and relative simplicity, it is crucial to choose the right test, as definitions and values of hardness can vary significantly depending on the technique used.
Uses of Hardness Tests
Hardness tests are primarily used to estimate mechanical properties such as strength, tensile strength, and wear resistance, based on the hardness value. These tests are advantageous for their speed and simplicity compared to other material tests.
However, for materials with high impurities or complexities, where hardness values alone may be insufficient, additional tests like tensile or impact tests, and metallographic analysis may be necessary.
Principles of Hardness Testing
There are two main principles used in hardness testing:
1. Principle of Indentation Testing
This method involves pressing objects of various shapes into the specimen and determining hardness from the resulting indentation. It’s the most widely used principle for hardness testing.
2. Principle of Dynamic Testing
This method involves striking a sphere against the specimen and determining hardness based on the sphere’s rebound parameters. It’s less accurate than indentation testing but does not damage the specimen.
Types of Hardness Tests
Several common methods are used in hardness testing:
- Rockwell Hardness Test: Used for heat-treated steel components, measuring hardness based on the depth of an indentation made by a diamond cone or a steel ball.
- Vickers Hardness Test: Suitable for a wide range of materials, using a diamond pyramid to create an indentation and measuring based on its surface area.
- Knoop Hardness Test: Similar to the Vickers test but uses a differently angled diamond pyramid, ideal for thin and brittle materials.
- Brinell Hardness Test: Measures hardness over a broad range, using a steel ball to create an indentation, frequently used for metals like cast iron.
- Shore Hardness Test: Measures hardness based on the rebound height of a diamond-made sphere, ideal for finished items where surface preservation is essential.
- Durometer Hardness Test: Used for plastics and rubbers, measuring hardness based on the depth of an indentation made by a needle-shaped cone.
- Barcol Hardness Test: Used for metals, plastics, and FRP, measuring hardness based on the depth of an indentation made by a needle-shaped cone.