Abstract: In this paper, the failure modes of the bonded-bolted lap joint of carbon-glass hybrid composite under bending loads were investigated through numerical simulations and experimental validation. The influence of the thickness ratio of the upper lap plate on the strength and stiffness of the hybrid joint was then examined, and the optimization design is presented based on the numerical and experimental results. The results show that the numerical and experimental load-displacement curves are in good agreement, with the initial damage occurring due to adhesive layer failure at the right end of the joint area, at which point the first peak load is achieved. With the increase of displacement, cracks continue to propagate until complete failure of the adhesive layer occurs, after which the bolt continues to bear load independently until the composite material undergoes compression failure, leading to the overall structural failure eventually. The optimization results indicate that increasing the thickness ratio of the upper lap plate can effectively enhance the ultimate load capacity of the joint. Specifically, the ultimate load capacity of the joint structure with a upper thickness of 65% of the total FRP skin is increased by 98.6% compared to the original design (with the upper thickness of 50% of the total). The final failure mode shifts from the compression at the right-side of the bolt hole in the upper lap plate to both the upper and lower plates with similar degrees of failure, and the optimal structural efficiency achieved.

Key words: composite material, bonded-bolted hybrid joint, failure mode, numerical simulation, optimization