Power transmission shafts such as drive shafts or automotive propeller shafts should transmit static and dynamic torques without whirling vibration. Hybrid shafts composed of unidirectional fiber-reinforced composite and metal have high fundamental bending natural frequency as well as high torque transmission capability: composite increases the fundamental bending natural frequency due to its high specific stiffness, while metal such as aluminum or steel transmits the required torque However, fabrication-induced thermal residual stresses are developed during manufacturing hybrid shafts due to the coefficient difference of thermal expansion of the composite and the metal so that the high residual stresses reduce fatigue resistance of the hybrid shafts, especially at low operating temperatures.
In this thesis, the torsional fatigue characteristics of the aluminum/composite co-cure joined hybrid shafts were investigated with respect to axial preload. To change the thermal residual stresses, an axial compressive preload was given to the aluminum tube by a compressive jig during the co-cure bonding operation. In order to determine the thermal residual stresses with respect to the preload and temperature difference, the stress analyses of the hybrid shaft were performed by simple equations from mechanics of materials and finite element method. Then the static torque capacities and fatigue strengths of the hybrid shafts from the static and fatigue torsional tests were correlated with the calculated thermal residual stresses. From the investigation, it was found that the fatigue strength of the hybrid shaft was much improved by the axial compressive preload, exceeding that of a pure aluminum shaft. Also, the degradation of the fatigue resistance of the hybrid shaft at subzero operating temperature could be overcome by the axial compressive preload.
