Effect of moisture on pure mode I and II fracture behaviour of composite bonded joints

The effect of moisture on the fracture properties of composite bonded joints under pure mode I and pure mode II was analysed in this work. The double cantilever beam and end notched flexure tests were used for mode I and mode II fracture characterisation, respectively. Three different moisture conditions (55% and 75% of relative humidity (RH) and immersion in distilled water (IW)) were tested to assess its influence on the fracture behaviour under both pure loading modes. It was verified that fracture energy is drastically affected for the immersion in water in both loading modes. A cohesive zone model was also used to estimate the influence of RH on the cohesive parameters defining the law that mimics accurately the fracture process for each case. It was concluded that alterations on the cohesive laws reflect an increase of material brittle behaviour with the increase of the moisture uptake.