Mechanical Properties Research Of 3D Six-Directional Rectangular Braided Composites

The three-dimensional six directional rectangular braided composites have good structural integrity,which can not only effectively overcome the weaknesses of the traditional laminated composites,such as low interlayer strength and easy stratification,but also help to reduce the weight of the structure.Therefore,it has a broad application prospect in aerospace and other fields.As a new type of lightweight and high-strength structure,the basic mechanical properties of the material are the important foundation and premise for applying this material to structural design.However,the microstructure of materials is extremely complex,which significantly increases the difficulty of material design and analysis.Therefore,it is of great academic value to establish the mechanical analysis model of material based on the characteristics of the three-dimensional six direction braided composites' macrostructure,and to study the influence of the material process parameters and structural parameters on the mechanical properties of the material..In this dissertation,according to the four step knitting process,the spatial motion and distribution pattern of the yarn are analyzed,and the cellular parameterized entity cell model is established.Then,the elastic properties analysis model based on the internal cell is established by using the cross scale mechanical modeling idea combined with the periodic boundary conditions.A nonlinear finite element model for progressive damage analysis of cells is established through the failure criterion and performance degradation scheme of embedded materials.The validity and applicability of the 3D six directional braided composite mechanical model based on cell is proved by an example.Finally,the influence of the material technological parameters(braiding angle and fiber volume content)on the elastic properties and the macroscopic stress and strain behavior of the material is discussed,and the effect of the material on the tensile and shear progressive damage behavior and the failure mechanism of the material is analyzed in detail..The research in this dissertation shows that the prediction model of elastic properties and strength of 3D six directional braided composites based on inner cell is reasonable and effective.On the one hand,the model and method can be used in the design and analysis of multi-directional braided composites,in order to shorten the design period and save the cost of development.On the other hand,this work has laid an important theoretical foundation for the structure design of multi-directional braided composites.