The Microstructure Analysis And Process Design Of 3D Five-Directional Braided Composite

The microstructure of three-dimensional (3-D) five-directional braided composites produced by the four-step 1×1 braiding technique have been studied by means of the CCD Microscope and the control volume method, and then the process of braiding design was given.Firstly, a series of cross-section images of 3-D five-directional braided composites were captured by the CCD Microscope, and then the yarns' arrangements, their section patterns and their trends were analyzed.Secondly, 3-D five-directional braided preforms were studied systemically by the control volume method according to the yarn carriers' movements of the four-step 1×1 3-D five-directional square braiding process, attaining the structure of the preform's unit cell. And then the relationship between the microstructure and the braiding parameters were established based on the captured images. Then the braiding yarns' sections were analyzed according as the braiding yarns and the axial yarns were selected when their proportions are different. The fiber volume fraction, the pitch length, the pitch width, the geometrical dimension etc were calculated, it turns out that the microstructure model correct.Finally, the effect of 3-D braided composites' geometry parameter on the fiber volume fraction, the pitch length, the pitch width, the geometrical dimension etc were analyzed via the former parameter relationship, and then the process of design was given.In this thesis, the microstructure of three-dimensional (3-D) five-directional braided composites was established. It can be applied in the parameter selection, the properties' design, and the structural optimization of this material during the manufacture process, and to push the further application of three-dimensional composites in the aerospace industry.