Experimental study on the mechanical properties of three-dimensional braided composite circular tubes with preembedded licker-in

This study investigates the tensile and compression properties of three-dimensional five-direction (3D5D) braided composite circular tubes with preembedded titanium alloy licker-ins. The influence of the braided angle, braided thickness, and braided configuration on the bearing capacity is analyzed, and the microdamage morphology and failure mechanism of the tube structure are examined using scanning electron microscopy. Results show that the 3D5D braided tube has a larger tensile failure load than the 3D full five-direction braided tube of the same outer diameter. In circular tubes of the same braided configuration and outer diameter, the compression failure load increases with the wall thickness, and the C-o30t3 circular tube achieves the maximum compression failure load. The damage morphology is characterized by the pulling-off failure of the licker-in joint. The T-o30t2.5 and T-o25t3 circular tubes achieve a large failure load, with an average tensile load of over 120 kN. The failure morphology is characterized by the cracking of the fiber at the end of the tube after the licker-in joint has been pulled off. The average tensile failure load of the T-o30t3 circular tubes is over 105 kN, and the failure morphology reveals a broken licker-in joint, indicating design deficiencies that require further optimization. The findings of this paper can provide an important scientific basis for the lightweight and high-strength connection design for 3D braided composites in near-space aerostats and their flight applications.