Identification of interface failure mechanisms of metallized glass fibre reinforced composites using acoustic emission analysis

In this work, interface failure mechanisms of metallized glass fibre reinforced epoxy composites were investigated using acoustic emission analysis. Sandblasting with Al2O3 was used to pre-treat the composite surface. The sandblasting time was varied from 2 s to 6 s. A two-step metallization process consisting of electroless and subsequent electroplating was used for depositing the copper coating on the pre-treated composite surface. A significant increase in adhesion strength was obtained due to the sandblasting pre-treatment. SEM and light microscopic investigations confirmed the results of the surface roughness and peel strength. The acoustic emission (AE) from the coating-substrate system was recorded during peel testing to characterize interfacial failure. AE-Signals were analyzed using pattern recognition and frequency analysis techniques. A correlation between the cumulative absolute AE-energy and the surface roughness/peel strength was successfully observed. It was shown that the absolute AE-energy is sensitive to changes in the surface topography and therefore peel strength, and the method is thus suitable for evaluating the peel strength of copper coated glass fibre reinforced composites. Furthermore, two different failure mechanisms could be correlated with the results from AE signal analysis, namely adhesive and cohesive failure. Differences in peak frequency, frequency distribution and the use of pattern recognition techniques allowed classifying the recorded signals. The classified failure mechanisms were confirmed by light microscopic images.