Considerations for Selecting a Hardness Tester

Choose the correct test method based on the application.
Plan to use the highest test force and largest

Answer these key questions:
1.  Does your test prescribe a specific hardness scale to be used?
2.  What is the material to be tested, and is this material suitable to the type of test method you are considering?
3.  How large is the part, component or specimen to be tested?
4.  Is the test point difficult to reach?
5.  What is the volume of testing that will be done?
6.  How accurate does your test result need to be?
7.  What is your budget?
8.  What is the required return on investment and do you have ways to measure reductions in costs- yields, throughput, operator efficiency?
9.  What testing problems have you experienced in your current method?
10. How knowledgeable are the users of the tester?

Verify the test results meet your requirements for accuracy and repeatability.
Consider performing a Gage R&R to gather quantifiable data on how much error is attributed to the operator and the measurement system employed.

There are significant differences between levels of performance within each classification of tester. A difficult job on one tester could be very simple and fast on another. So, although hardness testers within a test method and classification look alike, there are many features that can significantly affect productivity and accuracy. A good example of features affecting performance is demonstrated in bench Rockwell hardness testing systems. All can handle moderately long parts using larger anvils or jack rests, however the

 

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Test Type

Test Method

Test Force Range

Indenter Type

ASTM Reference

Measure Method

Rockwell

Regular

60, 100, 150 kgf

Conical Diamond & Small Ball

E 18

Depth

Rockwell

Superficial

15, 30, 45 kgf

Conical Diamond & Small Ball

E 18

Depth

Rockwell

Light Load

3, 5, 7 kgf

Truncated Cone Diamond

Informal

Depth

Rockwell

Micro

500, gf

Small Truncated Cone Diamond

Informal

Depth

Rockwell

Macro

500 to kgf

5, 10mm Ball

E103

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Depth

Microhardness

Vickers

5 to gf

136° Pyramid Diamond

E 384

Area

Microhardness

Knoop

5 to gf

130° x 172° Diamond

E 384

Area

Microhardness

Rockwell

500 gf to 30 kgf

Truncated Cone Diamond

Informal

Depth

Brinell

Optical

62.5 to kgf

5, 10mm Ball

E 10

Area

Brinell

Depth

500 to kgf

5, 10mm Ball

E103

Depth

When selecting a hardness tester for your application, it is important for you to consider the following:Plan to use the highest test force and largest indenter possible. Consider the effects of the shape and dimensions of your test sample.1. Does your test prescribe a specific hardness scale to be used?2. What is the material to be tested, and is this material suitable to the type of test method you are considering?3. How large is the part, component or specimen to be tested?4. Is the test point difficult to reach?5. What is the volume of testing that will be done?6. How accurate does your test result need to be?7. What is your budget?8. What is the required return on investment and do you have ways to measure reductions in costs- yields, throughput, operator efficiency?9. What testing problems have you experienced in your current method?10. How knowledgeable are the users of the tester?Consider performing a Gage R&R to gather quantifiable data on how much error is attributed to the operator and the measurement system employed.There are significant differences between levels of performance within each classification of tester. A difficult job on one tester could be very simple and fast on another. So, although hardness testers within a test method and classification look alike, there are many features that can significantly affect productivity and accuracy. A good example of features affecting performance is demonstrated in bench Rockwell hardness testing systems. All can handle moderately long parts using larger anvils or jack rests, however the Versitron Series can usually test large parts more quickly and accurately, when compared to other bench testers, which require external support stands or fixtures. The Indentron Series , on the other hand, is much easier to use on small, awkward parts.

The Knoop hardness test is a variation of the Vickers hardness test, designed for very thin or brittle materials, or for measuring the hardness of specific features or regions. It involves applying a low load to a material using a diamond rhombic indenter, and measuring the long diagonal length of the indentation. The hardness value is calculated from the ratio of the load to the surface area of the indentation, and is expressed as a number followed by HK or GPa. The Knoop hardness test can be used for metals, ceramics, glass, minerals, and biological materials, and it has some advantages, such as the low load and indenter size, the minimal damage or deformation to the sample, and the ability to perform microhardness testing. However, it also has some limitations, such as the need for high magnification and precision of the measurement, the asymmetry and non-uniformity of the indentation, and the dependence of the results on the orientation and anisotropy of the material.