Study On Filament Winding And Automated Fiber Placement Process Of Grid Structure

With the development of aerospace technology,composite materials and structures have been widely used.The grid is a typical form of strengthening structure.In the 1950 s,the grid structure of metal materials was used in the aircraft structure to reduce the weight of the structure.Nevertheless,the load-bearing efficiency of the grid composite structure is higher.It has been widely used in aerospace structures in foreign countries.This thesis will focus on the process and mechanical properties of the grid composite structure,aiming to establish the mathematical characterization and process model of the grid structure,and design and build the winder and fiber placement system for the grid structure.Firstly,the method of characterizing the grid density by using the number of circumferential ribs and helical ribs was proposed.And the relationship between grid density and the dimensions of cylindrical structures was also deduced.In order to analyze the axial carrying capacity of the grid structure,a general subroutine of cylindrical grid structure analysis was developed by using apdl language.The analysis results show that the axial carrying efficiency of the rectangular pattern grid structure is the highest,the grid structure of the regular triangle pattern is the next,and the diamond grid pattern is the worst.By increasing the grid density,the axial carrying efficiency of the grid structure can be appropriately increased.When the grid density reaches a certain value,the grid density is further increased,and the efficiency is limited.The structure at the stiffener node intersections was studied,and the process route for reducing the buildups and stacking of fibers near the nodal points was determined.Secondly,the mathematical model of the filament winding of the grid structure was established.The mathematic model of the winding pattern of the diamond pattern grid structure was established,and the rules of covering helical ribs were analyzed.The winding process of helical circumferential grids was improved,and a multi-feeding winding scheme in which the circumferential ribs and the helical ribs are wound at the same time was proposed.According to the winding tempo of the circumferential ribs and the helical ribs,the relationship between the thickness of one layer of fiber required to helical ribs and circumferential ribs was derived.And a tabletop four-axis winder with multi-feedeye was designed and built.Then,a fiber placement head suitable for the grid structure was designed according to the process characteristics of the grid structure.The fiber placement head has basic functions such as clamping,re-feeding and compacting.It adopts a modular design with an independent yarn path and independent roller,and can be expanded according to the grid structure fiber placement process.In addition,the fiber placement experiments were carried out on the prototype.Finally,according to the structural dimensions of the cylindrical grid structure,a gypsum-silicone combined mold was prepared.The cylindrical grid structure was formed by dry winding using a tabletop multi-feedeye winder,and the weight of the prepared grid member was 63.62 g.And axial compression experiments were performed: the experimental results show that the prepared grid structural has a maximum axial load of 19744.99 N,and a load-to-weight ratio of 310.36N/g.Furthermore,the failure of the structure is mainly caused by the delamination and fracture of the helical rib near the intersection.