This is how a hardness tester works
A Hardness Tester certainly, how resistant a material is to the penetration of a defined test objectIn industrial quality assurance, this test helps to... To evaluate materials, components or surfaces in a comparable manner and to determine their hardness.Depending on the testing method, either the size of a permanent indentation or the penetration depth is measured. Therefore, it is crucial to determine which method is suitable for the specific testing task and what requirements are placed on the equipment, sample, standard, and documentation.
the essentials in brief
- A hardness tester measures the resistance of a material to the penetration of a test object.
- Depending on the procedure, a Test impression or penetration depth evaluated.
- The most important procedures are Brinell, Rockwell, Vickers and Button.
- Meaningful results depend on the method, sample, test force, standard, and calibration.
- The appropriate level of automation depends on the testing volume, measurement task and documentation requirements.
What does a hardness tester measure?
A hardness tester measures the resistance that a material offers to the penetration of a test object. For this test, a defined test force is applied to a sphere, a diamond cone, or a diamond pyramid. The more the material resists the penetration, the higher the determined hardness value.
The result is always tied to a specific testing procedure. A hardness value therefore does not stand alone, but is evaluated together with the method used, the test force, and the test conditions. Only in this way can measurement results be reliably compared and documented.
How does a stress test work?
The procedure for a hardness test always follows a clearly defined testing process. The individual steps depend on the chosen method, but the basic principle remains the same: A sample is prepared, stressed, measured, and the result is documented.
- First, it is determined which testing method is suitable for the application, the material and the required standard.
- The sample is then prepared and securely positioned on the test table.
- Then the test specimen, test force and other test parameters are set.
- The hardness tester applies the specified force to the surface of the sample in a controlled manner.
- After the stress test, the resulting indentation or penetration depth is evaluated.
- Finally, the hardness value is calculated, tested, and documented in the test report.
Rockwell, Brinell, Vickers & Knoop: Why the process is crucial
Hardness tests follow the same basic principle, but differ significantly in test specimen, force range, and evaluation. Therefore, the Hardness testing method This is crucial in determining whether a hardness value is suitable for the test task and can be evaluated according to standards.
- Brinell is frequently used for materials with a coarse or uneven material structure, for example, cast materials.
- Rockwell enables a quick evaluation of the penetration depth and is therefore often used for testing large batch sizes.
- Vickers is universally applicable – for small components, thin layers, extremely hard (above Rockwell scale) or soft materials and hardness gradients.
- Knoop is particularly suitable for very thin, brittle, extremely hard layers because the diagonal is approximately 3 times longer (vs. HV).
The choice of method should always be based on the material, component geometry, testing standard and desired level of accuracy.
What factors are important for reliable measurement results?
Reliable hardness values are not achieved solely through the use of a hardness tester. The crucial factor is the interplay of a suitable testing method, a correctly prepared sample, appropriate test parameters, and regular verification of the device.
- The surface of the sample must be suitable for the chosen method and must not distort the measurement result.
- The test specimen and test force must be selected according to the standard and the material.
- The sample must lie stably and flat during the test.
- Distances to the edge of the sample or to adjacent test impressions must be maintained.
- The hardness testing device must be calibrated regularly and its functionality checked.
- The measurement results must be documented in a traceable manner so that they remain comparable internally and externally.
Manual, semi-automatic or fully automatic?
The appropriate level of automation depends on the frequency of testing, the number of measurement points required, and the comprehensiveness of the documentation. A different system is often sufficient for occasional individual tests than for serial testing, hardness profiles, or recurring testing procedures.
| Design | Suitable for | Typical characteristics |
|---|---|---|
| Manual hardness tester | Individual tests and low sample volume | Many steps are performed by the operator, such as positioning, measurement, or documentation. |
| Semi-automatic hardness tester | Regular testing tasks in laboratory and quality assurance | Individual steps such as force application, evaluation, or documentation are supported automatically. |
| Fully automatic hardness tester | Serial testing, hardness profiles and high sample numbers | Test procedures, measurement point sequences, evaluation and test reports can be carried out using software. |
These standards are important for the function of hardness testers.
Standards define how a hardness test is performed and evaluated. They specify, among other things, the test specimen, test force, test procedure, minimum distances, specimen requirements, and the documentation of the measurement results.
- DIN EN ISO 6508 This applies to the Rockwell hardness test.
- DIN EN ISO 6506 regulates the hardness test according to Brinell.
- DIN EN ISO 6507 describes the Vickers hardness test.
- DIN EN ISO 4545 This applies to the hardness test according to Knoop.
- DIN EN ISO 17025 This is relevant for testing and calibration laboratories that need to demonstrate their competence and traceability.
Everything else about the Standards for hardness testing You can find it in the linked article.
When which hardness testing device is useful
| Requirement | Sensible direction |
|---|---|
| Individual tests in the laboratory | Manual or semi-automatic device |
| Serial testing in QS | Semi-automatic or automatic device |
| Hardness profiles / weld seams | Automated Vickers system |
| Large or coarse components | Brinell or Rockwell, depending on the material |
| Several methods are in use | Universal hardness tester |
Frequently asked questions
How does a hardness tester work?
A hardness tester presses a defined test indenter into the surface of a sample with a specified force. Depending on the method, either the resulting indentation is then measured optically or the indentation depth is evaluated. The hardness value is derived from this.
What does the hardness value tell you about a material?
The hardness value describes a material's resistance to local indentation. It can provide information about wear behavior, strength, heat treatment, or material condition. It should always be evaluated in conjunction with the testing method, test force, and relevant standard.
Which hardness testing method is the right one?
The choice of hardness testing method depends on the material, microstructure, component geometry, and testing task. Brinell is suitable for coarse microstructures, Vickers for small components, thin layers, and hardness gradients, Knoop for very thin layers and minute indentations, and Rockwell for rapid serial testing with high sample throughput.
Why do the results differ depending on the method used?
The methods use different test specimens, test forces, and evaluation methods. Therefore, a hardness value according to Brinell, Vickers, Knoop, or Rockwell is not directly comparable. Conversions are only possible approximately, as there is no linear relationship between the hardness scales. Conversion tables may therefore only be used under certain conditions.
What role does rehearsal preparation play?
The sample surface significantly influences the measurement result. Uneven, contaminated, or unsuitable surfaces (Rockwell: underside of the sample) can lead to incorrect hardness values. Depending on the method, the sample must therefore be flat, clean, or metallographically prepared. When preparing samples for Vickers sections, unintentional hardening can be introduced – consult a metallographer.
