Abstract
The possibility of the application of mode I and mode II fracture mechanics to the characterization of the glass fibre/epoxy matrix interface has been studied here. The aim is to find out a method much more sensitive and reliable than the commonly used methods such as single filament tests which could allow a separate analysis of cracks initiation and potion phenomena that are involved in the damage of composite structures. One original contribution of this comparative analysis on materials differing only in their fibre sizing is the attempt to use the whole resistance curve of the materials including the propagation phase by assuming that some differences in the amplitude of the well known fibre bridging phenomenon are directly induced by differences in interface quality, which is the only parameter that is not kept constant. Both mode I and mode II tests have revealed a high sensitivity to the fibre/matrix interface quality: According to the property which is considered, variations are noted in a range of 150% to 300% for a modification of the interface by different sizing and in a range of 150% to 700% for an artificial modification of the interface by hydrothermal aging. Nevertheless mode II tests offered rather limited information (only about cracks initiation). On the other hand the interest of mode I fracture mechanics as fibre/matrix interface characterization method has appeared, in so far as this technique makes it possible to separate cracks initiation and then cracks extension phenomena, on which the fibre/matrix interface quality has a specific incidence, that is translated by variations of cracks initiation and propagation energies, of cracks growth rates and of acoustic emissions.
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