Tension-tension fatigue behavior of basalt composite hybrid joints

The tension–tension fatigue behavior of pseudo-ductile hybrid bonded-bolted double lap basalt composite joints, composed of pseudo-ductile adhesives and adherends with multi-directional fiber architecture, was experimentally investigated. The fatigue damage initiation and propagation of the hybrid joints were characterized by cyclic energy dissipation, cyclic displacement, cyclic stiffness and self-generated heat and further compared to similar bonded and bolted joints. The results showed that the slope of load-fatigue life (F-N) curve of the hybrid joints was similar to that of the bonded joints, however, much higher than that of the bolted joints, since it depended on materials and locations where damage occurred. The fatigue degradation of the hybrid joints was mainly driven by fatigue damage, while that of the bonded joints was dominated by creep at low load levels and by fatigue damage at high load levels. Due to almost full stretching of the adhesive's molecular chains, hybrid and bonded joints failed at almost the same failure displacement, independent of loading conditions. Hybrid joints exhibited a much longer fatigue life than both bonded and bolted joints because the cyclic creep displacement of the adhesive was delayed by the bolt and more cycles were sustained to reach the failure displacement.