# Hardness | Definition | Measuring Tests [Brief Explanation]

By | January 1, 2019

## What is hardness?

Hardness is the property of a material to resist surface indentation (and scratches).

Some materials are harder than other materials. For example, metals are harder than plastics, wood etc.

## Difference between hardness and toughness

Hardness is a property which is related to the surface of a material while toughness is a property which is related to whole material.

Toughness is the ability of a material to absorb energy until ultimate failure happens. It means more tough material will be fractured after less tough material.

## Hardness test

There are several tests to measure hardness of a material, some of them are.

1. Brinell Hardness Test
2. Rockwell Hardness Test
3. Knoop Hardness Test
4. Vickers Hardness Test

## Brinell Hardness Test

Brinell Hardness Test is most commonly used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested using another test method (for example parts made by castings and forging). Brinell testing often use a very high-test load (3000 kgf) and a 10mm diameter indenter so that the resulting indentation averages out most surface and sub-surface inconsistencies.

## Rockwell Hardness Test

Rockwell Hardness Test

Rockwell method measures the permanent depth of indentation produced by a force/load on an indenter. First, a preliminary test force (commonly referred to as preload or minor load) is applied to a sample using a diamond or ball indenter. This preload breaks through the surface to reduce the effects of surface finish. After holding the preliminary test force for a specified dwell time, the baseline depth of indentation is measured.

## Knoop Hardness Test

In Knoop hardness test a pyramidal diamond point is pressed into the polished surface of the test material with a known (often 100g) load, for a specified dwell time, and the resulting indentation is measured using a microscope.

## Vickers Hardness Test

Vickers Hardness Test

In Vickers Hardness Test a diamond pyramid is pressed against the solid with a certain normal load and the hardness is calculated based on the imprint left on the surface.

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References:

Brinell Hardness Test: https://www.hardnesstesters.com/test-types/brinell-hardness-testing

Rockwell Hardness Test: https://www.hardnesstesters.com/test-types/rockwell-hardness-testing

Knoop Hardness Test: https://en.wikipedia.org/wiki/Knoop_hardness_test

Vickers Hardness Test: http://www.tribonet.org/hardness-calculation-vickers-indenter/

Image source:

Rockwell hardness test: By Three-quarter-ten – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11461977

Vickers Hardness Test: Image attributions: By Freundchen – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=19350656

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