The Practical Application of TDT Hardness Testing

The PC-based TDT system consists of a hand-held PC and the TDT probe. The interface between instrument and probe serves as power supply for the probe as well as connector for all control functions.

The interface also feeds the BAS signal from the CCD camera to the frame grabber. With special software the data can be evaluated, the diagonals measured and the hardness value calculated.

The live picture through the diamond can be displayed, enabling the diamond’s indentation process to be viewed, i.e. the growth of the indentation by applying the test load. It also allows an in situ quality characterization of the diamond and the diamond’s indentation, respectively.

Depending on the resolution and the test load, different hardness ranges can be analyzed. The standard TDT probe with a test load of 50 N allows a measurement range from about 100 HV5 to 900 HV5. For softer materials a lower test load has to be applied.

In principle, all kind of materials can be tested as long as the hardness value is in the range of the TDT probe used for the measurement.

Figure 4 shows some typical Vickers diamond indentations obtained by the TDT instrument on different materials under test. TDT – for example – allows to determine the hardness of bulk material

1. enables to measure the hardness on coils
2. and also opens up hardness testing to new applications like high-tech materials
3. ceramics
4. or rubber and plastics.

Summary

By viewing through the diamond under load the Through Diamond Technique opens up new applications for hardness testing. The portable instrument not only allows for on-site measurements but also enables hardness measurements on all kind of materials. The obtained hardness value corresponds to Vickers testing, with the exception that TDT measures under load, thus also enabling measurement of elastic materials where usual indentation hardness fails.

Conclusion

Mobile hardness testing instruments will not replace the conventional bench-top machines, but nevertheless, they became an indispensable addition for hardness testing units.

During the last decades several portable instruments based on different physical methods were developed. Today portable units are widespread and accepted tools for portable, on-site hardness testing applications.

Those instruments solve plenty of mobile hardness testing tasks, but however, each method is limited – more or less – to a specific application area and, therefore, the decision as to which method and instrument to use strongly depends on the testing application.