Tensile Behavior of Pre-Embedded Titanium-Alloy Joints in Filament-Wound Carbon-Fiber Composite Tubes After Low-Temperature Conditioning

Pre-embedded metal inserts provide a direct load-introduction path for filament-wound composite tubes without cutting the load-carrying fibers. This study evaluates the room-temperature axial tensile response of T700 carbon-fiber/TDE86 epoxy tubes containing grooved, internally threaded TC4 titanium-alloy inserts after one programmed low-temperature conditioning cycle and separately examines a small ambient end-enlarged configuration. Twenty-one destructive test records were analyzed: nine ambient constant-section (“equal-section”) specimens, nine independent equal-section specimens after a 25 → −70 → 25 °C chamber-setpoint cycle followed by 24 h at room temperature, and three ambient end-enlarged specimens. At 1 mm/min, the three cohorts had mean peak loads of 81.39, 81.31, and 88.26 kN and coefficients of variation of 14.04%, 8.70%, and 7.85%, respectively. The −0.07 kN difference between the two independent equal-section cohort means does not establish equivalence or absence of a conditioning effect, and the three-specimen end-enlarged comparison does not isolate a causal geometry effect. Macroscopic failure was dominated by insert pull-out accompanied by visible adhesive/interfacial separation, laminate-layer damage, attached fragments, and local splitting. Because local slip, bond-line deformation, and system compliance were not measured, equilibrium and competing limit states are used only as a qualitative framework. The results concern post-conditioning room-temperature response, not in situ performance at −70 °C.