Difference Between Rockwell, Brinell, Vickers and Knoop Hardness Test

https://pursuitengineering.blogspot.com/2016/12/difference-between-rockwellbrinellvicke.html

Introduction

Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting

The usual method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of a specific shape, with a specific force applied for a specific time

Hardness Tests

Rockwell Hardness Test No specimen preparation required

Hardness value directly readable, no optical evaluation required

Quick & cost-effective process

Non-destructive testing

Not always the most accurate hardness testing method

The test location must be completely free of all contamination (e.g.

scale, foreign bodies or oil

The indenter has unknown effects on the test results

With increasing hardness, it becomes increasingly difficult to

distinguish between materials

Rockwell Hardness Test

Brinell Hardness Test The specimen surface can be rough

Good illumination of the test indent is important for ensuring correct evaluation

of the test indent (e.g. with the aid of a ring light).

The process is slow (by comparison with the Rockwell method). The test cycle

takes somewhere between 30 and 60 seconds

Limitation in applying the method on thin specimens of very hard materials

High risk of deforming the material to be tested when testing in the macro

range with high test loads

The surface quality of the specimen must be good, because the indent is

measured optically

Relatively large test indents that are easier to measure the rather small

Vickers indentations

Can be used for testing non-homogeneous materials (e.g. castings)

Brinell Hardness Test

Vickers Hardness Test Specimens need to be prepared

Due to the need to conduct optical indent evaluation,

Vickers hardness testers must be equipped with an optical system

The process is rather slow. The test cycle takes somewhere between 30

and 60 seconds

Non-destructive testing is possible

More expensive to purchase than Rockwell testers due to optical system

The surface quality of the specimen must be good (ground and polished)

Only one type of indenter

The Vickers method can be used with any and all materials and test

specimens

Vickers Hardness Test

Knoop Hardness Test Specimen should be polished

Evaluation is more precise than the Vickers method,

Must be equipped with an optical system

The process is rather slow (compared with the Rockwell method). The test cycle takes

somewhere between 30 and 60 seconds

The test is non-destructive

More expensive to purchase than Rockwell testers

The surface quality of the specimen must be good, because the indent is measured

optically

There is only one type of indenter

It is particularly suitable for testing small, longish components and very thin layers as

well as brittle materials (glass and ceramics) for which no other method is appropriate.

 

Knoop Hardness Test