Research On Additive Manufacturing Of Continuous Carbon Fibers Reinforced And Sensing-Integrated Smart Structure And Its Performance

Three-dimensional(3D)printing,as a new additive manufacturing technology,has become a significant supporting technology in the advanced manufacturing field.It can realize the integration and rapid formation of complex structures with a simple process.Fused deposition modeling(FDM)has become one of the most popular 3D printing technologies due to its simplicity,low-cost,and friendly operation.However,FDM products still have deficiencies due to the inherent nature of thermoplastic resins,regarding poor mechanical strength and lack of sensing function,which greatly affect the reliability of the structures.This dissertation focuses on the manufacturing of high-strength and smart structures using additive manufacturing technology to integrate the continuous carbon fibers within 3D printed thermoplastic polymer structures.A kind of 3D printing method for continuous carbon fibers reinforced and sensing-integrated(CCFRS)smart structures was put forward and the mechanical properties of the 3D printed CCFRS structures was investigated.On the other hand,self-sensing characteristics of the 3D printed CCFRS structures based on the electromechanical behavior of continuous carbon fibers were investigated and discussed systematically.Finally,applications of 3D printed CCFRS smart structures were investigated.The main contents and achievements are summarized as follows:(1)Research on 3D printing method for CCFRS structures and their mechanical properties.Two kinds of 3D printers for CCFRS structures printing were developed based on the principle of FDM technology,one was the parallel structure 3D printer,and the other was the double-nozzle 3D printer.Optimum printing process parameters were determined taking an example for TORAY Torayca continuous carbon fibers and polylactic acid(PLA)filament with diameters of 1.75 mm.An improved mixing rule for calculating the tensile mechanical properties of 3D printed CCFRS structures was proposed.As for calculation of flexural mechanical properties of 3D printed CCFRS structures,a method based on the maximum strength theory was presented.The mechanical properties were significantly improved by integrating only one continuous carbon fiber tow within the thermoplastic matrix.(2)Methods for self-monitoring structural conditions of 3D printed CCFRS structures based on the electromechanical behavior of continuous carbon fibers were proposed.The sensing mechanism and electromechanical characteristics of 3D printed CCFRS sensing agents were investigated.A bilinear relationship between the fractional change in electrical resistance and strain was observed.An approach for the real-time monitoring of the external load at different loading positions on 3D printed CCFRS structures was realized by establishing the relationship between the fractional change in electrical resistance and the flexural load in terms of different loading positions.The maximum error was less than 1.28%.In addition,strategies for locating the position and recognizing the deformation field distribution,as well as the damage detection,for the large-scale 3D printed CCFRS structures,have been presented and investigated.(3)Application in self-healing vascular-like system for self-repair of 3D printed CCFRS structures damage was proposed.Three kinds of double-component self-healing system were designed:flat-type,helix-type,and cross-type.The improvements of load bearing capability for these three self-healing systems were 14.04±3.37%,17.00±9.34%,and 18.24±6.19%,respectively.The feasibility of self-sensing and self-healing for the linear-typed CCFRS structures was investigated using three-point bending test.Four stages of electromechanical behavior during the whole loading process were observed:linear increase stage,slow decrease stage,almost constant stage,and dramatic increase stage,which can be used for the structural condition monitoring and the damage healing process prediction.The average self-healing efficiency for this system was 30.15±1.49%,which is expected to be improved when the more suitable self-healing agents are developed or selected.This dissertation established an additive manufacturing technology for CCFRS smart structures,which provided a novel method and approach for producing the high-strength,high-reliability and smart structures.