The mechanical performance of composite components repaired with bonded patches depends on the moisture content of the adherents. There is a need to define drying procedures which guarantee the quality of the bonded joint. An experimental investigation has been carried out on the effect of pre-bond moisture on the fracture toughness (GIC) and failure behavior of repair joints bonded with adhesive films. Substrates were conditioned by immersion in distilled water at 70 C for 336 h and subsequently dried for 1 h or 24 h to achieve different moisture contents before bonding. Specimens of bonded joints were tested under mode I loading at room temperature. The fracture toughness (GIC) decreased with increasing pre-bond moisture level in the substrates. Fractographic inspection revealed an enhancement of the cohesive mode of failure as the pre-bond moisture decreased. Extending the duration of the drying operation of the substrate with pre-bond moisture, caused an improvement in the fracture toughness of the joint, although not a full recovery of the reference values obtained in absence of pre-bond moisture
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