Nanoindentation of dry and aged pultruded composites containing fillers and low profile additives
Résumé
In this article, the distribution through the thickness of both the matrix's modulus and the interfacial shear strength (IFSS) in dry and aged pultruded polyester/glass fiber composites containing fillers and low profile additives are experimentally evaluated, using the nanoindentation test. The obtained results indicate that for the dry composite, both the matrix's modulus and the IFSS are constant across the thickness of that material. As a consequence of the immersion in distilled water at high temperature (65°C), the IFSS was found to exhibit a parabolic trend through the thickness of the aged specimen, with the lowest value at the external surfaces. Such minimum was reached after a short time of immersion. At the saturation time, the IFSS at all layers of the aged specimen reaches lowest value. This was not the case for the matrix's modulus, since the later was found to be not affected by the amount of the absorbed humidity. Similar results were obtained after immersion in sea water at the same temperature. However, the only difference noted was at the external surface of the aged specimen where additional degradation had taken place in the matrix and at the fiber/matrix interface. This was attributed to the accumulation of a large amount of salt molecules at the external surface of the aged specimen during the exposure process. Additional mechanical tests show that after 120 days immersion in hot water the interlaminar shear strength of the material as measured according to the ASTM standard D2344, is reduced by 35%.