Optimal tubular adhesive-bonded lap joint of the carbon fiber epoxy composite shaft

Abstract

The effects of adhesive thickness and adherend surface roughness on the fatigue strength of the tubular adhesive-bonded single lap joint were experimentally investigated using small fatigue test specimens (φ21 mm) whose adherends were made of S45C carbon steel. From the fatigue experiments, it was found that the optimal arithmetic surface roughness of the adherends was about 2 μm and the optimal adhesive thickness was about 0·15 mm. Also, the manufacturing method of the adhesive-bonded tubular single lap joint was discussed for the reliable and optimal joint quality. Using the optimal adhesive thickness and the optimal adherend roughness, the prototype torsional adhesive joints for the power transmission shafts (φ66 mm) of an automotive or a small helicopter were manufactured and statically tested under torque. The tests were performed on the single lap joint, the single lap joint with scarf, the double lap joint, and the double lap joint with scarf. The one part of the adherend of the joint was made of high strength carbon fiber epoxy composite material and the other part of the adherend was made of S45C carbon steel. The stresses of joints were analyzed by the finite element method. In applying the finite element method to the composite adherends, the smeared laminate properties were used. From the experiments, it was found that the double lap joint was the best among the joints in terms of torque capacity as well as manufacturing cost.