Hardness Testing is used to determine a materials resistance to indentation, the point where plastic deformation occur on the material.
Hardness Measurement Methods
There are different types of hardness tests used across industries, and determine the materials resistance to penetration when a indenter with a cone or ball at the end is pressed against the material with a given force and over a given time. The hardness is defined based on how far the indenter sinks into the material tested.
Some of the most common methods is listed and described below.
Brinell Hardness Testing
During this test a indenter with a ball shape at the end is pressed into the sample with a given force over a given amount of time. The hardness is defined based on the size of the round indentation after the test.
Rockwell Hardness Test
For this test either a diamond cone or ball end indenter can be used depending on the material. Initially a minor load is applied and reference zero is determined, followed by adding a major load for a given amount of time, and leaving the minor load upon releasing the major load.
The hardness is then determined based on the difference in depth between when the minor load and major load is applied.
Vickers Hardness Test
The Vickers hardness test is often used for measuring materials extremely hard surfaces. The test is done by pressing a diamond shaped indenter into the test sample, and the hardness is defined based on the measurement of the diagonal dimension of the indentation.
Knoop Hardness Test
The knop hardness test is often used on small parts and material that can’t be tested with methods using high loads. The test uses a load of maximum 1 kg.
Shore Hardness Test
The Shore Durometer test is used on polymers including rubber and plastic, and the hardness is defined by the penetration value of the indenter. Due to the type of material, several types of indenters are used.
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