Effect of fiber architecture on tension–tension fatigue behavior of bolted basalt composite joints

The effect of fiber architecture, i.e., unidirectional (UD) vs. multi-directional (MD), on the tension–tension fatigue behavior of bolted double-lap basalt composite joints was experimentally investigated. The fatigue load-life (F-N) curves of MD and UD bolted joints were established and fatigue degradation was characterized by cyclic displacement, cyclic energy dissipation, cyclic stiffness, and self-generated heat. The failure mechanisms and fatigue life of MD and UD bolted joints during fatigue were discussed and further compared to similar adhesively bonded joints. The results showed that the MD bolted joints exhibited much longer fatigue life than UD bolted joints, however, the rapid damage initiation and propagation in the former led to a slightly steeper slope of the F-N curve. The fatigue life of the MD bolted joints was much shorter than that of the bonded joints mainly due to the lower static resistance of the former. However, the slope of the F-N curve of the MD bolted joints, resulting from fiber-dominated fatigue damage, was much flatter than that of the bonded joints caused by polymer-dominated creep-fatigue interaction.