3D Printing Of Continuous Fiber Reinforced Lattice Structure And Study On Its Mechanical And Shape Memory Properties

In recent years,the continuous fiber reinforced composite materials prepared through 3D printing technology has rose great research interest,and the introduction of intelligent printing substrates can expand the functions and application prospects of those composite materials.Continuous fiber can be customized to produce lightweight and high-strength composites with the aid of printing technology,and the structural material is integrally formed which may also reduce costs.By introducing the shape memory smart polymer substrate and continuous fibers into the printing process,the structure could achieve shape changes under specific stimuli,and can be used to design self-expanding or self-adaptive functions of enhanced structures.It has huge application potential in aerospace and other fields.However,previous studies have shown that the printing process has higher requirements for continuous fibers,and there are obvious defects in the prepared composite structure;and the printed composite structure of the smart substrate is still in its preliminary stage.Therefore,how to optimize the design of continuous fiber 3D printing path and the mechanical properties of the structural composite fabricated by continuous fiber and smart substrate,and how to construct lightweight and high-strength structures,and related application development,etc.,have important inspirations for the guidance and development of intelligent 3D printing intelligence and high-strength structural composites.In this thesis,the printing process of lattice structure composite was optimized by designing the printing path and the extrusion amount of lattice structure composite for preparing the lattice structure composite with uniform fiber distribution.Continuous fiber reinforced lattice structure composites were designed and prepared by using shape memory polylactic acid(PLA)and continuous Kevlar fiber.The effects of printing parameters and structural parameters on the mechanical properties and shape memory properties of the composites were systematically studied.Finally,in order to achieve the remote and direct driving of the intelligence lattice structure composite,the electro-induced carbon fiber reinforced auxetic structure composite was prepared,and the performance of the composite structure and its application potential as a remote driving deformation device were explored.The main research contents and conclusions are as follows:(1)A novel printing strategy based on cycle overlapping continuous fiber printing path and extrusion configuration was proposed.Diamond-filled lattice structure composites with different path configuration were prepared with continuous Kevlar fiber and polylactic acid as its reinforcement and matrix respectively.The effect of printing path configuration on printing quality and mechanical properties of continuous fiber was studied.The results show that the composite structure designed by "trapezoid-like" path has most uniform fiber distribution,good printing quality and ideal mechanical properties,and the path design idea can be used to fabricate continuous fiber reinforced lattice structure composites with different filling patterns and uniform fiber distribution.(2)Continuous fiber reinforced triangle-filled shape memory lattice composite with uniform fiber distribution was designed and prepared based on the optimization of printing process.The effects of structural parameters and printing parameters on the tensile mechanical properties of the composite structure were studied,and the failure mode of the composite structure under tensile load was analyzed by finite element numerical simulation.The effects of structural parameters and printing parameters on the bending properties and shape memory properties of triangle-filled lattice composites were investigated respectively.It was found that the fiber in the composite structure act as the main bearing part during tensile test,and the main stress concentration is observed at the lap joint of the strut,which is consistent with the failure position in the experimental tensile test;The relative density of the structure decreases with the increase of the cell length of the printing structure,but the tensile strength of the composite witness an oppsite trend;With the decrease of the printing layer height,the fiber content of the sample increase with the decrease of the printing layer height,leading to the significant increase of tensile strength;the increase of cell length can change the stiffness of the grid structure,and with the increase of cell length,the bending performance of the composite structure shows an upward trend,while the shape memory recovery rate shows an opposite trend;With the decrease of printing layer height,the fiber content in the composite increases from 3.65% to 16.32%,and the relative maximum load and relative bending of the composite structure can bear The modulus increases nearly 2 times and 3 times respectively,while the shape recovery rate decreases significantly from 74.62% to 53.88%.(3)In order to achieve remote driven of the smart lattice structure composite,thermoplastic polyurethane(TPU)and multiwalled carbon nanotube(MWCNT)were introduced into the shape memory polylactic acid matrix to prepare electro-induced shape memory composite filaments for 3D printing.Continuous carbon fiber reinforced auxetic composite was designed and prepared by continuous fiber 3D printing technology.The mechanical properties and electrical/thermal shape memory properties of carbon fiber reinforced shape memory composites were studied respectively.Furthermore,the mechanical properties and negative Poisson’s ratio effect of the auxetic lattice structure under tensile load are investigated,and the remote driven shape memory effect of the auxetic composite is explored.The results show that the carbon fiber reinforced composite substrate has good mechanical properties and thermal/electro-induced shape memory performance.And the shape recovery ratio of the composite substrate could reach 94% within 25 s under 10 V voltage stimulation;The printed auxetic composite shows a negative Poisson’s ratio effect under tensile load,and the established mathematical model can well predict the Poisson’s ratio during the tensile test;The composite structure can recover from the temporary shape to the initial shape under electro stimulus,and the specific parts of the lattice structure composite materials could be activated by applying electro stimulus to the selective ends of the printed auxetic structure.This work combined shape memory polymer substrates with continuous fibers,optimized the continuous fiber 3D printing path,and studied the performance of 3D printing continuous fiber reinforced shape memory lattice structure,which is important for the development of 3D printing smart high-strength materials.It has important guiding value for the development of3 D printing smart high-strength materials,also lays a good foundation for the future design of self-expanding or self-adapting materials for reinforced structures and their applications in aerospace and other fields.