Research On Micro Structure And Mechanical Properties Of3D Face-core Braid Composites

Three dimensional braid composites have good structure designable ability, excellent mechanismperformance, low cost and strong capacity in simulating shapes.3D braid composites with differentfigures has drawn more and more attention along with broadly applied in aeronautics、astronautics、bio-medical engineering and automobile industry, etc.3D face-core braid composite was a new-type structure that based on original3D braidcomposites. Compared with the original3D braid composites, it has its own superiority. In order todesign and use3D face-core braid composites more effectively, an intensive investigation should bemade to its microstructure and mechanical properties.In this thesis, A novel technique was established to divide unit cell for the structure. Amechanical model as well as finite element model was established to predict engineering elasticconstants. The theoretical results were compared with the test data. The chief content can be falleninto three parts as below:In the first part, a model for3D face-core braid composites was established and mechanicalproperties were predicted with the volume—averaging method. The predicted results agree well withthe test data, thus, the correctness of the established model and analysis method has been verified. Atlast a comparison is made with the experimental results, validating the rationality of this model.The second part aims to use FE method to analysis the tension strength of the composites. Thesolid model of3D face-core braid composites unit cell was built. The periodic boundary conditionsare applied to the two-scale models during the3D FE analysis in order to ensure that both thedisplacement and stress are continuous on the boundary surfaces. The maximum principal stresstheory was used and the stiffness reduction of the damaged elements was simulated with theuser-defined material (UMAT) subroutine.In the third part, the RTM technology of3D face-core braid composites was researched.Designed and manufactured a suit of mould for molding3D face-core braid composites. Developedspiral resin injection device for molding tubular composites base on the improving former RTMtechnology. The samples with better quality were made for axial-tensile experiments.