Hardness testing
Hardness testing is essential for ensuring the quality and safety of components. Consider, for example, a bone implant: insufficient hardness could cause it to break under stress inside the body. This would lead to serious complications, which can be prevented through hardness testing procedures.
Table of contents
- What is hardness testing?
- How is hardness measured?
- What types of hardness testing methods are there?
- Reliable hardness testing in the laboratory
- Differentiating between various hardness testing methods
- What is measured during a hardness test?
- When is which hardness testing most appropriate?
- Applications of hardness testing
- The hardness testing process: From sample to measurement
- Comparison of micro- and macro-hardness testing
- In a summary: Hardness testing
Contact us –
expert support is just a conversation away.
Using state-of-the-art analytical methods, we assist you with quality issues, damage claims, and development challenges – providing precise, well-founded, and solution-oriented support.
What is hardness testing?
Hardness testing is a physical testing method used to determine the mechanical properties of a material and is a branch of metallography. It measures a material’s resistance to the penetration of a test indenter under a defined load. The values obtained provide information about a material’s strength, wear resistance, and load-bearing capacity. It is important to note that hardness can change under certain conditions, for example due to heat or the manner in which forces act on the material.
Purpose of the hardness test
Hardness testing is a crucial component of quality control and materials testing in industry. It serves to identify failures that are often invisible to the naked eye and enables systematic defect analysis. This is essential primarily for evaluating mechanical properties in research and development as well as in manufacturing. This is because hardness testing makes it possible to detect defects in material development at an early stage, thereby improving product quality.
How is hardness measured?
Hardness cannot be measured directly; therefore, it is determined indirectly using parameters such as penetration depth or indentation area, depending on the testing method used. To determine these parameters, a test force is applied to the surface of a material, and the resulting indentation on the surface is measured. The most common units of measurement for hardness are kilogram-force (kgf), Newton (N), Vickers hardness (HV), Knoop hardness (HK), Brinell hardness (HBW), and Rockwell hardness (HRA, HRB, HRC), which are specified depending on the hardness testing method.
What types of hardness testing methods are there?
There are various hardness testing methods, which are used depending on the material, application, and requirements. The most important methods are the standardized Vickers, Knoop, Brinell and Rockwell hardness testings. These standardized methods allow for the determination of internationally consistent and comparable measurement values.
Vickers hardness testing
The Vickers hardness test causes the least damage to the specimen. By using a diamond pyramid that strikes the test piece at a specific angle and with a defined load, the indenter leaves only a minimal impression. We perform Vickers hardness testing in accordance with the DIN ISO 6507 standard.
To calculate the Vickers hardness (HV), the diagonal length of the indentation in the test material is measured. This is a non-destructive method that, due to its precision, is suitable for a wide range of materials, from microhardness to macrohardness.
Knoop hardness testing
The Knoop hardness test is an alternative to the Vickers method that uses a low test force and is primarily used to test coatings and brittle materials such as ceramics. An elongated indenter is used. In the Knoop hardness test, the long diagonals of the indentation are measured. The Knoop hardness is designated as HK.
Brinell hardness testing
The Brinell hardness test is the method of choice for testing soft to medium-hard metals and workpieces that contain large, coarse, or non-uniform structural elements. The Brinell method is particularly gentle on the material. By using a carbide ball of known diameter as the indenter, an indentation is created under a specific load. Its diameter is then measured visually. The Brinell hardness is designated as HBW (Brinell Hardness with Tungsten Carbide Ball).
Rockwell hardness testing
The Rockwell hardness test is a static hardness testing method developed as a quick test for large, primarily metallic specimens with high hardness. Depending on the method, a diamond or metal ball is pressed into the specimen, and its penetration depth is measured. This method does not involve optical readout, and the specimen can be reused afterward. Rockwell hardness is denoted by HR (HRA, HRB, HRC).
Reliable Hardness testing in the laboratory
Quality Analysis checks your sample
We typically perform hardness testing using the Vickers method in accordance with DIN ISO 6507, but we also employ other hardness testing methods. This allows us to analyze samples of all hardness levels—from soft to hard—as well as metallic and non-metallic components. We also assess the hardness profile of a workpiece following heat treatment. The determination of surface hardness, case hardening depth, and nitriding hardening depth is performed in accordance with standards.
- Hardness testing according to Vickers, Brinell, and Knoop
- Determination of hardness profiles
- Testing of case hardening depth
- Determination of nitriding hardening depth
- Determination of induction hardening depth
- Microhardness testing
- Testing in accordance with all applicable standards
Differentiation of hardness testing methods
Hardness testing methods are generally classified into those involving static and dynamic loading. Dynamic hardness testing refers to tests in which the load is applied to the specimen abruptly or with rapid changes in load. In static hardness testing, on the other hand, the load remains constant or increases gradually.
In addition, another distinction can be made: between destructive and non-destructive hardness testing. Destructive methods result in permanent deformation or damage to the workpiece, whereas non-destructive testing methods cause only slight deformation without impairing the material’s functionality.
What is measured during a hardness test?
Hardness testing is typically performed using static methods in which a test force is applied to the material. There are two different approaches: measuring the depth of penetration or measuring the size of the indentation left by the test specimen in the material.
Depending on the procedure, a distinction is made between the following testing methods:
Depth measurement methods
This test determines how deeply the indenter penetrates the material. The best-known and standardized depth measurement method is the Rockwell hardness test (ISO 6508, ASTM E18). However, there are also non-standardized Brinell and Vickers depth hardness testing (HBT, HVT).
Optical measurement methods
This method determines the size of the permanent indentation in the material. Well-known optical testing methods include the Brinell hardness testing (ISO 6506, ASTM E10), the Knoop hardness testing (ISO 4545, ASTM E92, ASTM E384), and the Vickers hardness testing (ISO 6507, ASTM E92, ASTM E384).
In addition to static testing methods, there are also methods that use dynamic force, such as the Leeb hardness testing (ISO 16589, ASTM A965). In this method, a ball is fired at the material with a specific amount of energy, and the rebound height is measured. This provides information about the hardness of the material.
When is which hardness testing most appropriate?
The choice of the appropriate hardness testing method depends on various factors, such as the material, the sample size, and the surface roughness.
Generally speaking, the Vickers hardness testing is the most versatile method, as the indenter has minimal impact on the test specimen, making it suitable for measurements ranging from micro- to macro-hardness. This also makes it ideal for measuring the hardness of welds seams and thin materials. In addition, all hardness profiles, such as case hardening depth or nitriding hardening depth, are measured in Vickers according to the standard.
While the Rockwell hardness test is best suited for large and coarse test specimens, the Brinell hardness test is ideal for soft to medium-hard metals, and the Knoop hardness test is ideal for coatings.
Applications of Hardness Testing
Hardness testing is used in many areas of industry and research. At Quality Analysis, for example, we perform hardness testing for the following industries:
Automotive
The automotive industry places high demands on components and component assemblies. E-mobility, in particular, calls for increasingly lighter (and thus thinner-walled) components that must nevertheless withstand the same stresses as conventional components. A Vickers or Brinell hardness test provides the assurance that your customer’s requirements are being met.
Medical technology
Doctors must be able to rely on the reliable performance of their instruments in their work. The standards for implants are even higher: once inside the body, they must perform their function reliably for years. By testing the hardness of weld seams and solder joints, we ensure that the instruments and implants you manufacture meet all requirements.
Aerospace industry
In the aerospace industry, components are subject to particularly stringent requirements regarding strength and durability; after all, a great deal depends on the smooth operation of every component—not least the safety of the crew and passengers. A Brinell or Vickers hardness testing gives you the warranty that your components can withstand the extreme stresses that regularly occur during operation in these industries.
Anwendung 4
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum.
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum.
Anwendung 5
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum.
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum.
The hardness testing process: From sample to measurement
The hardness testing process involves preparing the specimen and conducting the actual test. While the process varies depending on the method used, the general procedure consists of the following steps:
1.
Sample preparation
The specimen is prepared to have a specific surface roughness. Sometimes it is necessary to clean the specimen or grind it flat. Next, the appropriate indenter is mounted on the testing machine and the correct test force is set—these depend on the method and the material.
2.
Testing
The specimen is then subjected to the load, and the measurement data is obtained. The duration of the load depends entirely on the method used. Depending on the method, diagonal lengths, indentation diameters, or indentation depths are measured using a measuring microscope or a laser microscope. The measured indentation depth or indentation diameter is used to calculate the hardness of the material.
3.
Analysis
The values must then be calculated and analyzed using the formula appropriate for the specific method. With modern hardness testers, this step is usually performed automatically: The device records the measurement data, calculates the hardness value on its own, and displays the results immediately. This speeds up the evaluation process and reduces measurement errors.
Comparison of micro- and macro-hardness testing
Hardness testing can be divided into three categories based on the test force applied. Macro hardness testing uses higher test forces starting at 5 kgf, which leaves larger indentations in the material. This method is well-suited for larger workpieces and is often performed using methods such as Brinell, Vickers, or Rockwell.
Microhardness testing, on the other hand, uses very low test forces of less than 0.2 kgf, resulting in only very small indentations. This method is ideal for measuring thin layers or small structures within the material. Test forces falling between these two ranges are referred to as low-load hardness testing.
In short: Hardness testing
Hardness testing methods are a central component of materials testing and play a key role in quality assurance. Choosing the right method is crucial for obtaining reliable and comparable measurement results. By applying the appropriate testing methods, companies can ensure that their components meet the industry’s high standards and deliver optimal performance over the long term.