The development of storage systems for i.e. liquid hydrogen for future energy and cost efficient transport systems is becoming increasingly more important. The use of fibre-reinforced plastics for lightweight vessels are of special interest due to their high stiffness and strength to weight ratio. However, fiber reinforced plastics have very high permeability and leakage rates for hydrogen compared to metal. To meet these high leak-tightness requirements a copper coating can be used as a highly functional permeation barrier. But the use of copper coated fibre reinforced plastics for storage systems presents a specific challenge for a stable polymer metal composite regarding the interphase between the composite substrate and the coating. Failure of the interphase due to mechanical loadings strongly depends on the adhesion between the deposited copper and the substrate surface. Therefore, fundamental structure-property relationships between the surface structure of the composite substrate and the adhesion of the copper coating and secondly the micro-mechanical failure mechanisms of the coated substrate under mechanical loadings play a major role in this work. Thus, the goal of the work was to improve the adhesion between thermoset fibre-reinforced plastics and electroplated copper coatings by a specific surface treatment and to quantitatively investigate occurring failure mechanisms particularly within the interphase by means of acoustic emission analysis. For this purpose carbon and glass fibre-reinforced epoxy substrates were pre-treated with a mechanical, chemical or electrical pre-treatment method and coated by an electroless/electrolytical plating process. As a result the surface structure of the composite substrate significantly influences the resulting peel strength depending on the existing adhesion mechanism. The peel strength of 0,8 N/mm could be exceeded by chemical treatment of a polyester fleece modified GFRP-Substrate with acetic acid and hence an alternative more gentle pre-treatment method to chromic acid could be developed. Two different failure mechanisms within the interphase could be correlated with the results from acoustic emission signal analysis during peel testing, namely adhesive and cohesive failure. Futhermore, a quantification of the amount of each interphase failure mechanism was possible. During quasistatic tensile testing, differences in peak frequency, frequency distribution and the use of pattern recognition techniques allowed classifying the signal into three failure mechanisms for the uncoated samples and four failure mechanisms for the coated samples, namely matrix cracking, fibre-matrix interface failure, fibre breakage and substrate-coating interface failure.
|School:||Universitaet Bayreuth (Germany)|
|Source:||DAI-C 81/1(E), Dissertation Abstracts International|
|Subjects:||Materials science, Plastics|
|Keywords:||Fiber reinforced plastics|
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