Study on the Forming Principles of 3D Hexagonal Braided Fabric and Its Composite Properties

Author:Li Zheng Ning

Supervisor:chen ge frank ko

Database:Doctor

Degree Year:2019

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Pages:164

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The large scale application of textile composite is originated from the invention of high performance fiber.In order to take the advantage of the properties of high performance,it is common to fabricate it into three dimensional(3D)preform.There are three kinds of fabrication technology,such as 3D brading,3D weaving and 3D knitting,especially 3D braiding technology has the best comprehensive properties.The fabrication technology of 3D braided preform is developed from trackand-column braiding technology and rotary braiding technology to state-of-the-art hexagonal braiding technology,and also the braiding machines.Compared with other kinds of braiding technology,hexagonal braiding technology has obvious merit on yarn density,and it has a great potential on fabrication of high interlacement ration fabrics.However,the study on hexagonal braided fabric and its process is not profound because of its short history.In this thesis,based on basic hexagonal theory,some topics has been studied,such as the dynamic characterization of yarn carrier and yarn interlacement,simulation and optimization of circular hexagonal braided fabric structure,the establishment of hexagonal braiding machine,the fabrication of hexagonal fabric and the composite with additive hexagonal braided structure.In that case,the hexagonal braiding process,the characterization of hexagonal structure,control principle of braiding machine,the fabrication process and mechanical property of additive composite has been articulated.Specific study content in this thesis are as follows:The geometrical parameters and arrangement density of horngear were analyzed to study the possibility of horngears with different notches.It was proved that only horngears with four notches or six notches could be arranged as compact array to keep the high yarn carrier density and yarn interlacement ratio.The relationship of horngear(plate)rotation and yarn interlacement was analyzed.Within the 180 degree’s rotation of adjacent plates of 2D rotary braiding process,there was once yarn interlacement,but within 60 degree’s rotation of adjacent horngears of hexagonal braiding process,there were twice yarn interlacements.Hence,hexagonal braiding technology is better to fabricate fabric with compact structure.In order to control the process of hexagonal braiding effectively,based on the analysis of dynamic property of yarn carrier in 2D rotary braiding machine,the acceleration and speed of yarn carrier in hexagonal braiding were studied.The analysis result showed that the speed curve of yarn carrier in hexagonal braiding process could be classified into two types,and both types of curves were too close to the square wave.The virtual machine of hexagonal braiding machine was built,and ADAMS was applied in the simulation on acceleration and speed curves of yarn carriers,which validated the theoretical curves.The circular hexagonal braided fabric was established,acoording to the coordinates on the bedplate of hexagonal braiding machine.Following the time sequence of horngear rotation and fabric take-up speed,a series of spatial coordinates were obtained,which could be connected to create yarn trajectories and hexagonal fabric structure with 30 yarns.B-spline was utilized to make the yarn trajectory smoother,and in order to make the fabric more compact,the algorithms of coordinate conversion and matrix conversion were applied.The fiber volume faction of fabric with 30 yarns was improved from 18% to 57% after optimization,which validated the optimization algorithm for hexagonal structure.Likewise,the circular hexagonal braided fabric structure with 72 yarns and 132 yarns were established,and the fiber volume fraction before and after optimization was also compared.In order to analyze the hexagonal structure more intuitively,the solid model of hexagonal fabric with 30 yarns was built in SolidWorks,and then fabricated with additive manufacturing technology.The composite fabrication process based on additive manufacturing was studied.The fabrication process like traditional textile composite was designed.Following this process,track-and-column braided composite and hexagonal composite specimens were made and the compression property was tested.Through the variation of materials to additive reinforcement(PLA,CPLA)and matrix(Epon-828 resin,UDMA/TEGDMA,E-51 resin and TDE-85 resin),the macro-characterization of breakage cross-section and compression property were studied.The result showed that additive reinforcement would not change the tendency of compression strain stress curve.The binding condition between two components would affect the initial modulus and ultimate stress.Generally,the variation of braiding angle had no direct relationship with compression property of composite with additive reinforcement.In order to validate the simulation structure of circular hexagonal braided fabric,the hexagonal braiding machine with 19 horngears was established.Focused on mechanical structure design and control unit design,the details of hexagonal braiding machine were analyzed,such as the combing parameter of horngear and yarn carrier,drive force of horngear and the cascade of control board.The circular hexagonal braided fabric was fabricated with hexagonal braiding machine,which validated the structure of simulation model and real fabric.Also,the fabric with 30 yarns was fabricated with aramid to test the tensile property.The test result showed the breakage force of fabric would decrease along with the braiding angle’s increase.Moreover,the slippage of yarns would lead to the larger breakage elongation of fabric than that of aramid yarn.In summary,this thesis combined theory,simulation and experiment to articulate the forming principle of hexagonal braided fabric and its composite properties,which enriched the hexagonal braiding technology and could offer effective theoretical and practical references on hexagonal braided fabric design,hexagonal braiding machine development,additive textile composite design and property.