| Composite structures are subjected to multi-axial fatigue loads while in service. The objective of this thesis is to study the effect of load path (sequence of application of load) on biaxial fatigue behavior of multidirectional composites. The fatigue behavior of thin walled [+/-45]2 s graphite fiber composite tube was experimentally studied under uniaxial and biaxial loading. The sequence of application of, and the phase difference between the tensile and torsional loads was varied. While an in-phase torque, superposed on to the tensile load, extended the fatigue life, an out-of-phase torque, superposed onto the tensile load, reduced the fatigue life, with respect to uniaxial fatigue life. An out-of-phase torque applied prior to the tensile load had the most impact on the fatigue life, when compared to the torque applied after the tensile load. These results establish the effect of load path on the fatigue life of composites under biaxial loading. |
