Coupling effect of braided structure and thermo-oxidative aging on torsional damages of 3-D braided composite tubes

The torsional behaviors of 3-D braided composite tubes are influenced by braided structure and environmental conditions. This paper reports the properties of aged and unaged 3-D braided carbon fiber/epoxy resin composite tubes with braided angle of 30°, 45° and 55°. The proposed multi-scale model aims to analyze the coupling effects of thermo-oxidative aging and braided structure, while supporting experimental measurements. Results show that the 45° specimens exhibit the highest torsional performances. Thermo-oxidative aging degrades failure torque, shear stress, strain and modulus of composite tubes. This effect weakens as the braided angle increases due to the tighter braided structure. The damage pattern extending along the braided angle is unaffected by aging, but earlier damage onset and more microcracks can be induced after aging. Designing tubes with larger braided angles helps maintain torsional performances under thermo-oxidative environment.