Experimental Investigation of Thermal Effects on the Natural Frequencies of GFRP Single-Lap composite Joints Bonded with Al

This study is focused on the thermal and vibration characteristics of glass-fibre reinforced polymer (GFRP) structural laminated joints (SLJs) that use epoxies modified through the addition of alumina nanoparticles. Use of adhesive bonded SLJs for lightweight structures is more beneficial than using mechanical fasteners such as bolts or rivets due to advantages related to better distribution of load and lower stress concentration, as well as a lighter overall structural weight. Unfortunately, due to their nature, adhesive bonded joints can fail under simultaneous application of thermal and vibration forces. Therefore, to limit this problem, alumina nanoparticles were added to an epoxy adhesive in various fractions ranging from 0 to 1 wt%. This modified epoxy was then cured along with the bidirectionally woven E-glass/epoxy adherend materials. The modal analysis was conducted using an impact hammer and a frequency response function based vibrational testing apparatus at three different temperatures of 40°C, 50°C, and 60°C. The results demonstrate that the use of nanoparticles significantly increases the stiffness and modal properties of the laminated joint (SLJ). Of the modified epoxies tested, the composition with the addition of 0.50 wt% had the highest thermal stability (i.e., 98.9%) and exhibited the best retention of natural frequency across all temperature ranges. At higher loadings (≥0.75 wt%), thermal stability and frequency retention decreased due to particle agglomeration and micro-void formation. This work gives insight into optimizing nanoparticle concentration for enhancing stability and durability in composite joints loaded thermally. The results provide the basis for the development of high-performance nanocomposite adhesive systems for aerospace, automotive, and marine applications.