What is the difference between Vickers and Knoop hardness test?

Differences Between Vickers and Knoop Hardness Tests

The Vickers and Knoop hardness tests are both methods used to measure the hardness of materials, but they have distinct differences in their application, indentation geometry, and suitability for different materials. Below are the key differences between these two tests:

Indentation Geometry

Vickers: Produces a diamond-shaped indentation with a square base. The Vickers test is known for its versatility and can be applied to all materials regardless of hardness.

Knoop: Results in an elongated diamond-shaped indentation. The Knoop test is particularly suited for brittle materials or thin layers where minimal damage is desired.

Load Application

Vickers: Uses a wide range of loads, making it adaptable to different materials and hardness levels. It can be applied from micro (10 grams) to macro (50 kilograms) loads.

Knoop: Generally employs lighter loads compared to Vickers, which makes it ideal for testing materials that are too thin or too brittle for standard Vickers testing.

Calculation of Hardness

Both tests calculate hardness by measuring the indentation's surface area, but due to their different geometries, the formulas used to calculate the hardness values differ.

Applications

Vickers: Because of its versatility, the Vickers test is used across a wide range of materials, including metals, ceramics, and composites.

Knoop: The Knoop test is preferred for materials that are susceptible to cracking under load, such as brittle ceramics or thin films.

Advantages and Limitations

Vickers: Offers a broad application range but requires careful preparation of the sample surface and is more sensitive to the operator's technique.

Knoop: Provides more accurate measurements for brittle materials but is limited in its application to softer materials and is more susceptible to measurement errors due to its elongated indentation shape.