Structural behavior of secondary-bonded composite joints subjected to Mode II fatigue induced delamination

• Published in: IOP conference series. Materials Science and Engineering 2018-07, Vol.388 (1), p.12009
• Main Authors: Garpelli, F P, Ramírez, F M G, Resende, H B, Donadon, M V
• Format: Article
• Language: English
• Subjects: Adhesives; Bending fatigue; Bonded joints; Carbon fibers; Crack propagation; Delamination; Displacement; Fatigue life; Fatigue tests; Flexing; Fracture surfaces; Laminates; Strain energy release rate; Structural behavior
• ISSN: 1757-8981; 1757-899X
• DOI: 10.1088/1757-899X/388/1/012009

This paper analyses the Mode II fatigue delamination growth onset for secondary bonded joints compared to co-cured joints. The materials used were composed by two carbon fiber reinforced sub-laminates joined by the secondary bonded and co-cured (without adhesive) methods. Mode II fatigue tests were performed using three-point bending End Notched Flexure test setup. The tests were performed under displacement control and a sinusoidal displacement applied at a frequency of 5 Hz with a Rd = 0.1, that mean, δmin = 0.1 δmax. The main objective of this study was to obtain the strain energy release rate (SEER) versus number of cycles (Nf) in order to evaluate the effect of the adhesive on fatigue life of bonded joints. A Closed form solution for 3-ENF setup was used in order to define the displacement amplitudes that were applied in the fatigue test. The results show that the use of adhesive causes a reduction on Mode II fatigue delamination growth onset SERR (Gth) for secondary-bonded compared to co-cured joints. Finally, a scanning electron microscopy (SEM) was used to analyze the fracture surfaces of the Mode II secondary bonded specimens. The fractography images show no crack growth for the specimens tested below or at Gth loading levels, which indicated that the value corresponds to the threshold.