| Resumo : |
Adhesive bonding technologies for thermosetting polymer composites have been applied in severa industrial sectors due to their excellent mechanical behavior (high strengthto-weight ratio, damage tolerance, and fatigue resistance). The great advantage of this technology compared to traditional mechanical fasteners is that in addition to giving a lower weight to the structure, the use of adhesive joints does not induce damage by delamination in the material during the joining process, as occurs when drilling holes for the assembly by rivets or bolts. The overall structural performance of the bonded joint depends on severa factors related to the joint manufacturing process, such as surface preparation procedure, type of adhesive and aging effects. For this reason, there is a clear need to better understand how the behavior of joints can be affected by these factors as well as the causes of eventual failures in arder to improve the design and performance. Ln this context, this work presents the application of Scanning Electron Microscopy (SEM) technique to perform the fractographic analysis in three different joint types, co-cured (CC), co-bonded (CB), and secondary bonded (SB), which were subjected to Mode 1 and Mode II interlaminar fracture toughness tests under both Roam Temperature Ambient (RTA) and Elevated Temperature Wet (ETW) conditions. The fracture surfaces of samples submitted to each loading condition were evaluated regarding their failure aspects, which were in turn associated with the mechanical behavior observed when submitted to the different loading modes and to the environmental conditioning. A detailed Fractographic characterization of the composite joints was carried out, correlating its specific behavior, type of processing and conditioning, thus validating the use of the material for conditions similar to those of real application. ln this work was observed that the CB composite joints present higher fracture toughness when subjected to environmental conditioning, due to the type of adhesion that occurs between the faces of the laminate during the manufacturing process. The CC joints showed a good result in Mode II ETW conditioning due to the thermoplastic particles tenacity. The SB joint presented the worst performance to conditioning in both loading conditions. ln conclusion, CB joints were considered the best configuration for bonded joints, followed by CC joints and finally SB joints. |