An automotive driveshaft or propeller shaft transmits power from the engine to the differential gear box of rear wheel-drive vehicle. The torque transmission capability of the driveshaft for passenger cars, small trucks and vans should be larger than 3,500 Nm and the fundamental bending natural frequency should be higher than 6,500 rpm to avoid whirling vibration. The whirling of the driveshaft which is a resonance vibration occurs when the rotational speed is equal to the fundamental bending natural frequency which is inversely proportional to the square of the length of shaft and proportional to the square root of specific stiffness. Since the fundamental bending natural frequency of one-piece drive shafts made of steel or aluminum cannot be higher than 6,500 rpm when the length of the drive shaft is longer than 1.0 m, the steel drive shaft is usually manufactured in two-piece. The fundamental bending natural frequency of the driveshaft made of the composite can be twice higher than that made of steel or aluminum because the carbon/epoxy composite material has more than 4 times higher specific stiffness than steel or aluminum. It is possible to manufacture the composite driveshaft for passenger cars in one-piece.
In this paper, the composite-aluminum driveshafts were designed and manufactured to co-cure the carbon/epoxy composite to aluminum tube, in which the carbon/epoxy composite increases the fundamental bending natural frequency and the aluminum tube sustains the transmitted torsional load. A compressive preloading method was developed to reduce the residual thermal stresses produced by the difference of the coefficients of thermal expansion. The load bearing capability of the hybrid structure with the co-cured joint i.e. the composite-aluminum driveshaft was calculated by finite element analysis. It was found that the finite element analysis considering the influence of the residual thermal stresses and the thermal degradation of the composite must be used in order to calculate the stress distributions of the co-cured joint at elevated environmental temperatures. Also, it was found that the accurate failure index might be calculated with considering the thermal degradation of the composite. The thermal degradation was represented by the retention ratio, which was the degrading tendency of the matrix-dominated properties with respect to temperature.
