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Behaviour of Polymers under the Influence of Changing Evironmental Humidity and Temperature

In this work the influence of short term changes in environmental conditions and the long term behaviour off glass reinforced unsaturated polyester resins as well as non-reinforced and reinforced PC and PA 6 are described.

After storing the UP-resin laminates and the thermoplastics in water, clear differences with regard to the damage behaviour were seen. The UP-resin laminates become opaque indicating damage to the resin/fiber interface. This damage can be traced back to an osmotic process. A Small amount of sizing of the glass fibers is dissolved in the water. Using a computer estimation it is shown that the osmotic pressure generated in the voids can be extremely high and thus contribute to initial laminate damage. In contrast non-reinforced and reinforced thermoplastics materials exhibit no damage after storage in water.

Temperature cycling between 23°C and -20°C involving unidirectionally reinforced standard UP-resin laminates with surface glass matting stored in water until saturation led to the formation of bubbles (delamination beneath the matting layer).

Water collects and freezes here because of the smaller diffusion coefficient of the unidirectional layer. Because of the phase change of the water (water-ice) and the 8% increase in volume associated with it, the individual layers are forced apart by the resulting pressure.

Non reinforced and reinforced PC and PA 6 withstand temperature changes during storage in water without damage.

The internal stresses in the polymer caused by swelling and thermal strains resulting from water uptake and humidity and temperature cycling can become so large that they can lead to a shift in the effective maximum loading capability. The larger the influence of moisture on the decreasing Young’s modulus, the smaller is the damaging influence of Diffusion.

A method is shown that enables calculation of the diffusion and temperature change dependent stresses in reinforced UP-resins. These residual stresses must be superimposed with mechanical loadings on the laminate.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Karin Lutterbeck

Karin Lutterbeck
Institut für Kunststoffverarbeitung
Rheinisch-Westfälische Technische Hochschule Aachen

Information

Free keywords: GFRP-UP, PC, PA 6, changes in humidity, changes in temperature, sorption, diffusion, osmosis, internal stresses
Institute / chair: Fakultät für Maschinenwesen der Rheinisch-Westfälischen Technischen Hochschule
Language: German
Technical consultant for expert services: Prof. Dr.-Ing. G. Menges (Betreuer), Prof. Dr.-Ing. G. W. Ehrenstein
Publication year: 1984
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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