Hardness testing is essential to ensure the quality and safety of components. Think of a bone implant, for example: insufficient hardness can cause it to break during physical loading. This would lead to serious complications that are prevented by hardness testing procedures.
TABLE OF CONTENTS
- Why is hardness testing necessary?
- Quality Analysis checks the hardness of your sample
- Hardness testing methods and what exactly is meant by them
- The areas of application of hardness testing
- How hardness testing is carried out
Why is hardness testing necessary
Hardness testing methods are a crucial part of quality control and material testing in industry. They are used to identify defects that are often invisible to the naked eye and enable systematic damage analyses. This is particularly essential for the evaluation of mechanical properties in research and development work as well as production. After all, hardness testing makes it possible to detect defects in material development at an early stage and thus improve product quality.
Quality Analysis tests the hardness of your sample
When testing hardness, the sample is permanently deformed by the penetration of a test specimen into it. Measuring the indentation provides information about the hardness of the material. The hardness can in turn be used as a measure of the strength and the expected wear. We usually carry out hardness testing according to Vickers in accordance with the DIN ISO 6507 standard, but other hardness testing methods are also used. In this way, we can analyze samples of all degrees of hardness – from soft to hard – as well as metallic and non-metallic components. We also check the hardness progression of a workpiece after heat treatment. The determination of surface hardness, case hardening depth and nitriding hardness depth is carried out in accordance with standards.
fast and reliable
- Hardness testing according to Vickers, Brinell, Knoop
- Determination of hardness progression curves
- Testing the case hardening depth
- Determination of the nitriding hardness depth
- Determination of the melt hardness depth
- Microhardness testing
- Standard-compliant testing in accordance with all current standards
hardness testing method and what exactly is meant by it
Hardness testing is a physical analysis method for determining the strength of components and is a branch of metallography. This deals with the examination of the internal structure of metallic materials. Put simply, hardness testing answers the question: How hard is the material?
Hardness is the resistance that a material offers to the mechanical penetration of another body. This resistance can provide information about the strength, wear resistance and other mechanical properties of a material.
However, the hardness of materials can change under certain conditions, for example due to heat or the way in which forces act on them, i.e. whether a lot of force is exerted at once or by slowly increasing it.
Furthermore, hardness cannot be measured directly, but is derived from the measured variables that result from the hardness testing. These are, for example, indentation depth or indentation area – depending on which hardness test method is used. To determine these key figures, a test force is applied to the surface of a material and the resulting indentation on the surface is measured.
Depending on the respective hardness testing method, a different unit of measurement is specified. The most common units of measurement for hardness are kilogram force (kgf), Newton (N), Vickers hardness (HV), Brinell hardness (HBW), Knoop hardness (HK) and Rockwell hardness (HRA, HRB, HRC), depending on the method and the specific scales within the Rockwell method.
the different types of hardness testing methods
A distinction is made between different types of hardness testing methods. Dynamic hardness testing refers to tests in which the load is applied to the specimen abruptly or with rapid load changes. In static hardness testing, on the other hand, the load remains constant or increases gradually.
A distinction is also made between destructive and non-destructive hardness testings. Destructive tests lead to permanent deformation and damage to the material, while non-destructive tests only lead to slight deformation and do not impair the function of the test piece.
brinell hardness testing
Brinell hardness testing is the method of choice for testing soft to medium-hard metals and workpieces that have large, coarse or inhomogeneous structural elements. The Brinell method is particularly gentle on the material. By using a ball with a known diameter, an indentation is generated under a certain load. Its diameter is then measured optically.
vickers hardness testing
This method causes the least damage to the sample. By using a pyramid that hits the test piece at a specific angle and a defined load, the indenter leaves only a minimal impression. We carry out the 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 sample material is measured. This is a non-destructive method that is suitable for a wide range of materials, from microhardness to macrohardness, thanks to its precision.
knoop hardness testing
The Knoop hardness testing is an alternative to the Vickers method with low test force and is mainly used for testing thin layers. A pyramid-shaped diamond is used as the indenter. In the Knoop hardness measurement, the long diagonals of the indentation are determined.
rockwell hardness testing
This static hardness testing method was developed as a quick test for large, mainly metallic test pieces with high hardness. Depending on the method, a diamond or metal ball is pressed into the sample and its indentation depth is measured. No optical readout is used for this and the test piece can be reused afterwards.
When is which hardness testing method the best?
The choice of the right hardness testing method depends on various factors, such as the material, the sample size and the surface condition. Generally speaking, the Vickers hardness testing is the most versatile method, as the indenter has little effect on the specimen, making it suitable for measurements from micro to macro hardness. It is therefore also ideal for measuring the hardness of weld seams and thin materials. In addition, all hardness curves, such as a case hardness depth or a nitriding hardness depth, are measured in Vickers in accordance with the standard.
While the Rockwell hardness testing is best suited for large and coarse specimens, the Brinell hardness test is ideal for soft to medium-hard metals and the Knoop measurement is ideal for coatings.
the application areas of hardness testing
Hardness tests are used in many areas of industry and research. At Quality Analysis, hardness tests are carried out for the following industries, for example:
The demands placed on components and component groups in the automotive industry are high. E-mobility in particular demands ever lighter (and therefore thinner-walled) components that nevertheless have to withstand the same loads as conventional components. A Vickers or Brinell hardness testing gives you the certainty that your customer's requirements will be met.
Doctors need to be able to rely on the reliable functioning of their instruments in their work. The requirements for implants are even higher: Once in the body, they must perform their task reliably for years. By testing the hardness of weld seams and soldered joints, we ensure that the instruments and implants you manufacture meet all requirements.
In the aerospace industry, particularly high demands are placed on the strength and resilience of components. After all, a lot depends on the smooth functioning of each component – not least the health of the crew and passengers. A Brinell or Vickers hardness testings gives you the certainty that your components can withstand the extreme loads that regularly occur during use in these industries.
how a hardness testing is carried out
testing process – from the sample to the hardness measurement
The hardness testing process includes the preparation of the sample and the actual test. The process differs depending on the method, but the general procedure consists of the following steps.
The sample is prepared to a specific surface roughness. Sometimes it is necessary to clean the sample or grind it flat. The correct indenter is then attached to the tester and the correct test force is set – this depends on the method and the material. The sample is then subjected to the load and the measurement basis is created. How long the load lasts depends entirely on the method.
Depending on the method, diagonal lengths, indentation diameters or depths are measured using a measuring microscope or laser microscope. The measured indentation depth or indentation diameter is used to calculate the hardness of the material. The values must then be calculated and analyzed using the appropriate formula for the respective method. Alternatively, a hardness tester can be used.
Hardness testing is essential to ensure the quality and safety of components in various industries. These procedures enable the early detection of defects that are often invisible to the naked eye and are used for systematic damage analysis. In many industries, they are crucial for ensuring that components and materials can withstand the high demands placed on strength, toughness and wear resistance.