Instrumented Hardness Measurement with Tempering
Instrumentierte Härtemessung mit Temperierung | A service provided by |
|---|
|
| Polymer Service GmbH Merseburg |
| Tel.: +49 3461 30889-50 E-Mail: info@psm-merseburg.de Web: https://www.psm-merseburg.de |
| Our further education offers: https://www.psm-merseburg.de/weiterbildung |
| PSM on Wikipedia: https://de.wikipedia.org/wiki/Polymer Service Merseburg |
Instrumented hardness measurement with tempering
General information
Instrumented macro hardness testing with test specimen temperature control is an extension of recording hardness testing, which is normally carried out at room temperature. Since the hardness of polymer materials, in analogy to other mechanical properties, is strongly influenced by the test temperature, this new development can be used to investigate the dependence of hardness on test temperature as well as the creep and relaxation behaviour of plastics and composite materials with different indenter geometries. Another area of application for this prototype device is indentation fracture mechanics, which is not applicable at room temperature due to the mostly ductile behaviour of plastics, but is of interest at low temperatures, especially from the point of view of small specimen quantities, e.g. in electronics or microsystem technology, for the fracture mechanical characterisation of toughness.
Measurement system with tempering
The basic design of the measuring system with connected temperature chamber in the range from 20 °C to -100 °C is shown in Fig. 1 below. For investigations in the temperature range from 20 °C to +100 °C, the chamber can be converted with a heating table system.
| Fig. 1: | Schematic Arrangement of Instrumented Macrohardness with Temperature Chamber |
Due to the adapted temperature control, an extended contact foot and indenter must be used, in contrast to instrumented hardness measurement without temperature control. Since the measuring system works with a relative indentation depth measurement between the contact ring and indenter, no temperature compensation of the measurement result is required for this test method. The working distance is determined by a reference measurement, which must be carried out when changing specimens and temperatures.
The temperature chamber has a pair of plates for heating or cooling, with temperature regulation achieved via a modified Eurotherm controller with two thermal sensors. The thermal sensors are integrated in the centre of the lower and upper plates. The cascade regulation is designed so that the upper thermal sensor acts as the master, controlling the set temperature value. The lower temperature sensor controls the slave control loop, which means that the lower plate has a difference of approx. 10 K to the upper plate, ensuring only slight overshoot and rapid attainment of the set-point. The regulation behaviour of the system can be controlled via the connected computer.
Adapting hardness measurement to a universal testing machine offers the advantage of being able to select different control systems and test types. This makes it possible to control the test via the load, the indentation depth or the traverse path, which also enables creep and stress relaxation tests to be performed depending on the test temperature. Furthermore, various indenters such as Vickers, Knoop or Berkovich diamonds, or hardened steel balls and carbide balls of various diameters can be used
Specimen positioning in the temperature chamber
The specimen size is limited by the temperature chamber and should not exceed 50 x 50 mm² in base area and a minimum height of ten times the expected indentation depth. Furthermore, the specimens must be plane-parallel and smooth, although roughness is not as important here as it is in microhardness testing. The specimen is positioned in the temperature chamber using a micrometer screw with a positioning plate (Fig. 2).
| Fig. 2: | Specimen positioning in the open temperature chamber |
| Fig. 3: | View of specimen positioning in the temperature chamber |
See also
- Instrumented hardness test – method & material parameters
- Instrumented hardness test – creep
- Instrumented hardness measurement – relaxation
- Instrumented hardness measurement, Indentation depth measurement with modified contact foot
- Hardness
References
- Bierögel, C., Schöne, J., Lach, R., Grellmann, W.: Bewertung des temperatur- und zeitabhängigen Verhaltens von Thermoplasten und Elastomeren mittels der instrumentierten Makroeindringprüfung. In: Grellmann, W. (Ed.): Neue Entwicklungen in der Werkstoffprüfung – Herausforderung an die Kennwertermittlung. "Werkstoffprüfung 2011", December 1 and 2, 2011, Berlin, Proceedings pp. 285–292 (ISSN 1861–8154; ISBN 978-3-9814516-1-0; see AMK-Library under A 13)
- Lach, R., Schöne, J., Bierögel, C., Grellmann, W.: Instrumented Macroindentation Techniques for Polymers and Composites – Mechanical Properties, Fracture Toughness and Time-Dependent Behaviour as a Function of the Temperature. Macromolecular Symposia 315 (2012) 125–131; https://doi.org/10.1016/j.polymertesting.2013.09.016
- Schöne, J.: Mehrparametrige Bewertung des temperaturabhängigen Eindruckverhaltens an Kunststofen mittels eines messtechnisch erweiterten, restrierenden Makrohärteprüfsystems. Martin-Luther-Universität Halle-Wittenberg, Promotion 2019, Shaker Publishing 2020 (ISBN 978-3-8440-7183-2, see AMK-Library under B 1-30)