A new threaded insert reinforced joint to achieve ultra-high performance of CFRP bolted connections

This paper proposes a novel threaded insert reinforced joint, aiming to achieve ultra-high performance in CFRP bolted connections. Compared with the conventional through-hole and cylindrical insert reinforced joints, this innovative design significantly enhances load-bearing capacity and stiffness, with simulation results validating its structural optimization effect by accurately predicting stress distribution and failure trends. At the core of its performance lies a unique reinforcement mechanism: it transforms the original shear failure and tensile failure modes into extrusion failure, a critical shift that enables the joint to sustain additional tensile loads even when the material experiences damage. Experimental results confirm that the joint increases strength by 44.5 % and stiffness by 36.2 %. The threaded insert reinforced joint, as a key component of this joint, delivers multiple performance benefits; it significantly inhibits composite damage—micro-morphological observations of the hole wall show that the cylindrical insert reinforced joint and conventional through-hole joint suffer large-scale matrix cracking, expose numerous matrix fragments, and exhibit obvious fiber bending, while the threaded insert reinforced joint only has slight matrix destruction and limited fiber kinking or breakage—and it also effectively reduces hole circumferential strain and enhances joint strength, stiffness, and energy absorption capacity. Moreover, the joint excels in preload stability: its 24-h preload relaxation rate is 2.8 % and 168-h rate is 4.8 %, far lower than the through-hole joint's 10.9 % and 17.7 %, and even after preload relaxation, its strength decreases by only 2.6 %, much less than the 18.3 % reduction of the through-hole joint, demonstrating exceptional long-term performance stability.