Research On The Continuous Braiding Process And Trajectory Of Carriers For Braiding Preform With Multi-type Structure

Textile structures are known for their unique combination of light weight and flexibility and their ability to offer a combination of strength and toughness.Textile preforms not only play a key role in translating fiber properties to composite performance but also are the structural backbone for the toughening and net shape manufacturing of composites.3D braiding,3D weaving and 3D knitting are the textile technologies to realize light-mass,cost-effective and high-volume of 3D fiber composite preform.The development of track-and-column braiding,3TEX braiding,hexagonal braiding and array braiding based on maypole have enriched the processing technology of 3D braiding preforms,especially the development of array braiding equipment has made it possible to form continuous 3D braiding fabrics with variable structure.In this thesis,based on array type rotary forming principle of braided fabric,the motion characteristics of the carriers in the process of braiding 、 the interweaving mode of yarn 、 the realization of the 3D braided fabric with multi-type variable geometric structure,so as to explore a new technology of forming of 3D braided fabric with multi-type variable-structure on array rotary braiding machine,and the properties of 3D braided composites with different track splicing structures are compared.The specific research content is as follows:（1）According to the most basic track type and the trajectory direction of the carrier,the possibility of cross combination between different track types is studied,and three basic track units with different interweaving forms are obtained: the oblique track,the 484 cross break track and the diagonal closed track.According to the running state of the switches between horn gears,the carrier arrangement characteristics which can describe the period of the carrier arrangement in the process of track splicing are obtained,and the overall model of track splicing topology for braided system is formed.When horn gears with four slots are arranged in the track,the maximum number of carriers on the braiding machine can be guaranteed by analyzing the interweaving relationship of yarns in the process of braiding track splicing and combination.（2）In order to effectively control the motion of carriers in the braiding process of array rotary braiding machine,the specific arrangement of carriers in different track configurations is studied on the basis of the known number of the period of the carriers arrangement in the track,so as to ensure no interference between carriers in different track configurations.By establishing the mathematical models of the carriers’ locations at Sc P and Mt P,firstly,the form of the 484 cross break track is decomposed into corresponding basic track crossing segments,and then,by defining the position of the crossing segments of each type of the 484 cross break track and the motion direction of the carrier in the track,and the 18 motion relationship between the carriers at the intersections of different tracks are obtained,which can ensure that the carriers can be fully arranged in the slots of the track without interference with each other.（3）The non-stop switching between different carrier arrangement laws can be realized by adding extra tracks.Different carrier arrangements can be used to produce different braided fabrics.In order to realize the smooth transformation between different carrier arrangement laws in the track,take the carrier arrangement A（"10101010"）to carrier arrangement B（"10100101"）as an example,the number of extra tracks to be added is calculated,and the conversion between the initial state and final state is completed through 22 steps of detailed analysis.A more concise method of carrier arrangement law conversion is obtained also.（4）The influence of different track splicing configurations（splicing methods）on braided fabric structure in array rotary braiding is studied.The track splicing configuration and the carrier arrangement are the necessary design variables in three-dimensional braiding process.By analyzing different carrier configuration obtained from different track splicing configuration,full carrier configuration in array rotary braiding track can be realized,and then the differences of the yarn interweaving density and the yarn topology can be studied accordingly.The difference of yarn topology can be eliminated by changing the orientation of track splicing point or adding axial yarn into the 3D braided preform.（5）The structure model of three-dimensional braided fabric with multi-type variable geometry structure is established.The track splicing mechanism based on the track transformation method is given: the track in the shape of the cross section of the fabric is connected,while the track outside the shape of the cross section of the fabric is blocked.According to the state of the switches at the intersection point of the tracks,the method of yarn adding or subtracting during braiding is analyzed,and the law of track crossing transformation and the yarn number change in the process of variable structure braiding are obtained.Take 3D braided fabric with variable structure that is "rectangle-circular-rectangle" as an example,when it is necessary to change the shape of the cross section of the 3D braided fabric,it is need to change the switches’ state at the edge of the shape of the target cross-section before the carrier moves to the switches’ area,the cross transformation of tracks can be realized.At this point,the number of yarns involved in braiding changes twice as much as the number of horn gears.（6）By studying the position relationship among horn gear,switches and carriers in the array rotary braiding process,and according to the time and position of the carrier before and after passing through the switches,the position of two adjacent carriers in the same track are represented as the motion trajectory of the carriers,the topological structures of yarn in braided space are obtained,and the corresponding models of unit cell are obtained.Based on the multi-scale homogenization theory,the tensile strength prediction model of 3D braided composites with three different track configurations are established,and the corresponding three-dimensional fabrics are braided and the composite material specimen prepared,and the validity of the simulation model is verified by testing the tensile properties of the specimens.To sum up,this paper focuses on the continuous whole production of the diversity of the braided preform with multi-type variable structure,and it provides a theoretical reference for the formation of braided fabric with diverse variable structure on the array rotary braided machine,the optimization design of array rotary braided machine,and the design of braided composite material with different yarn interweaving forms.