| Resumo : |
In this work, the structural behavior of three composite joint technologies, named as co-cure, co-bonding and secondary bonding, under Mode I and Mode II fatigue loading was evaluated, in terms of the minimum strain energy release rate associated with fatigue induced delamination growth onset (Gth), in order to obtain the G-Nf curves and evaluate the best fatigue performance. Samples were submitted to Mode I fatigue tests using the Double Cantilever Beam and Mode II were performed with three-point bending End Notched Flexure. The results show that the adhesive improves the threshold energy release rate value (Gth) for Mode I fatigue test, consequently the fatigue life behavior for the different joints respected the following order: similar G-Nf behavior was found for co-bonded and secondary bonded joints with G values slightly higher than co-cured joints. For specimens submitted to Mode II, the results show a reduction on Gth for secondary-bonded and co-bonded composite joints, when compared to co-cured joints, where no adhesive is used. Fractographic analyses were also performed in order to identify the main failure mechanisms related to each joining technology under Mode I and Mode II fatigue induced delamination. |