On the static and fatigue life of nano‐reinforced Al‐GFRP bonded joints under different dispersion treatments

Abstract As bonded components of engineering structures inevitably experience fatigue loading conditions during their service life, it is significant to find ways to enhance their endurance. Also, adding nanoparticles to the adhesive can be introduced as an approach to design more durable bonded joints. In this way, it is important to determine a nanoparticle dispersion method which can lead to the longest fatigue life. Accordingly, this paper aims to investigate the influence of various nanoparticle dispersion treatments on static and fatigue responses of aluminum‐to‐composite bonded joints under four‐point bending. For this purpose, four dispersion techniques of mechanical stirring, bath‐sonication, low‐power and high‐power probe‐sonication were used to disperse nanoparticles into the adhesive. Also, four specimen groups of neat (with no additive particles), graphene nano platelet (GNP)‐reinforced, nano silica‐reinforced, and hybrid‐reinforced (including GNP + nano silica) were prepared. Results indicated that, for the joints including GNPs, the longest fatigue life was achieved for the specimens prepared by low‐power sonication method, while for hybrid‐type reinforcements, using high‐power method led to the highest endurance. Moreover, for 0.5 and 1.0 wt.% of nano silica, the endurance of bath‐sonicated specimens was 12.77% and 9.28% longer than low and high‐power probe‐sonicated joints, respectively. Using the backface strain (BFS) measurement technique, the influence of dispersion methods was studied on extending the crack initiation life (CIL) of each joint group. It was revealed that, for 0.5 wt.% and 1.0 wt.% of nano silica, the CIL is independent of the dispersion method, while, for 1.5 wt.%, probe sonicated specimens had the longest CIL. The microstructural characterization of each dispersion method and major reinforcing mechanisms were interpreted by scanning electron microscopy (SEM). For future researches, using X‐ray tomography and health monitoring methods is recommended to detect size and location of damage for nanoparticle reinforced composite structures.