Study on glue‐bonding and shear automated addition and reduction yarn technology for variable cross‐section three‐dimensional braided composites

Abstract Based on the principle of automated addition and reduction of yarn in three‐dimensional variable cross‐section braiding with an active yarn feeder, this paper proposes a method for automated yarn addition and reduction using “glue‐bonding for yarn‐addition and cutting for yarn‐reduction.” Experiments involving glue‐bonding and cutting were conducted with an auto yarn addition and reduction device. The effects of blade angle, blade speed, cutting position, fiber length, and pre‐tension on fiber cutting were tested. A three‐dimensional finite element model simulated the damage mechanisms during the addition and reduction process, and experimental and simulation results were compared and analyzed. The study also investigated fiber fracture at the constrained end during yarn reduction. It was found that a 70‐degree blade cut, lower pre‐tension, closer cutting points to the constraint end, and shorter fiber lengths significantly improved cutting performance for yarn reduction. An experiment with cyclic cutting of carbon fibers revealed an increase in cutting force of approximately 0.046 N per cutting cycle. The tensile resistance of carbon fibers glued with epoxy‐based UV‐curable adhesives under quasi‐static and dynamic loading was studied, showing good bonding performance capable of withstanding tensions generated during yarn reduction. The study concludes that the automated method of using UV‐curable adhesives for yarn addition and blade cutting for yarn reduction is applicable to variable cross‐section three‐dimensional braided technology, providing a theoretical basis for the active yarn feeder to achieve addition and reduction yarn functions. Highlights Introduced an automated method for the addition and reduction of yarn. A finite element model for addition and reduction yarn has been established. The study has unveiled the mechanism of shear fracture in carbon fibers. Reveals the fracture mechanism at yarn‐reduction sites. Provides a basis for optimizing addition and reduction yarn performance.