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Thermoelastic stress analysis on short-fibre reinforced thermoplastics

In thermoelastic stress analysis (TSA) small temperature changes in solid bodies caused by cyclic loading are measured. The thermoelastic temperature change is proportional to the change of the sum of the principal stresses. At constant absolute temperatures TSA-measurement systems measure a thermoelastic signal which is proportional to the thermoelastic temperature change. If the absolute temperature is changing, the thermoelastic signal changes non-linearly with the temperature, as the sensitivity of the infrared sensors used in TSA is related non-linearly with the absolute temperature. In this work a methodology is presented, how the influence of the absolute temperature on the thermoelastic signal can be corrected by a direct calibration of the thermal signal. The corrected thermoelastic signal is proportional to the thermoelastic temperature change.

To evaluate the mechanical stress from a measured thermoelastic signal, the TSA-signal has to be calibrated. The injection moulded short-fibre reinforced thermoplastics investigated in this work have inhomogeneous mechanical and thermoelastic properties along their cross-section, due to the manufacturing process. It is shown, that if the layer-wise changing mechanical and thermoelastic properties are taken into account, a strain oriented approach of the thermoelastic effect is much more effective to calibrate the thermoelastic signal than the common stress oriented approach. If the strain oriented approach is used, the measured thermoelastic signal can be directly related to the sum of the principal strains evaluated with a reference measuring system.

The temperature of short-fibre reinforced thermoplastics is increasing at high loading frequencies, due to the viscoelastic properties of the matrix material. It is shown in this work, that the increase in absolute temperature correlates very well with the mechanical loss-energy, which is an indicator for the degradation of the material. In a load-increase test, the thermoelastic signal increases at a certain load disproportionately high compared with the applied load, dependent on the fibre orientation in the material. The change of the thermoelastic response is indicating the beginning disruption of the material. Single-load fatigue measurements are presented which indicate, that the maximum applicable load under cyclic loading conditions can be determined from the thermoelastic signal.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Andreas Klavzar

Andreas Klavzar
Lehrstuhl für Ressourcengerechte Produktentwicklung
Technische Universität Kaiserslautern

Information

Free keywords: Thermoelastic stress analysis, optical strain measurement, short-fibre reinforced thermoplastics, PA6 GF30, calibration, temperature measurement, fatigue
Institute / chair: Fachbereich für Maschinenbau und Verfahrenstechnik der Technischen Universität Kaiserslautern
Language: German
Technical consultant for expert services: Prof. Dr.-Ing. Rainer Renz (Betreuer), Prof. Dr.-Ing. Martin Maier, Prof. Dr.-Ing. Jörg Seewig
Publication year: 2009
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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