Viscoelastic behaviour of composites with epoxy matrix filled by cork powder

摘要

Due to the viscoelastic properties of cork and polymeric matrices, stress relaxation and creep behaviour of multiphase composites incorporating cork are important properties that should be considered at the design stage. For this purpose, composites with the same lay-up but with different fibres were manufactured with neat epoxy resin and epoxy resin filled with cork powder. It was concluded that higher values of relaxation and creep displacement occur when Kevlar fibres are used in place of carbon fibres and, for both, when cork powder was introduced into the resin. Considering the strain correspondent to 150 MPa for Kevlar composites, the difference observed between the initial and final bending stress is around 19.1 MPa for laminates with neat resin and 13.5% higher for laminates with matrix filled by cork powder. In terms of creep and comparatively to the neat resin, the displacement increases 24.6% when the resin incorporates cork powder. Regardless of whether the resin was pure or filled with cork powder, the same trend was observed for carbon composites, but with less expressive values for the same comparisons previously established. Finally, the maximum error obtained between the theoretical and experimental results of 0.6% for all conditions tested shows that the Kohlrausch-Williams-Watts (KWW) function can be used to accurately predict the relaxation stress response. In terms of creep response, this function was compared with the Findley model and, regardless of the success obtained with both, the best predictions are reached with the KWW model.