The Micro Structure And Mechanical Properties Of 3D Woven Composites

3D woven composites, with good mechanical properties, is produced by connecting yarns of different systems together with weaving method to form spatial reticulate structure which is then compounded with matrices under some conditions. Resulting from the good quality of the whole structure, mechanical properties of textile are well improved in direction of thickness, and the disadvantages of traditional laminate composites, such as inter-bedded weaknesses and poor resistance to impact loading, are also overcome; in addition, 3D woven composites is suitable for large production because of its simple loom and low cost. Moreover, the composites have a strong capacity in simulating shapes. In light of these advantages, 3D woven composites, as a kind of structural material, has drawn more and more attention at present, and is broadly applied in aeronautics,astronautics,bio-medical engineering,automobile industry, etc. So in order to design and use 3D woven composites more effectively, an intensive investigation should be made to its real microstructure and mechanical properties.In this paper, a new mechanical model is established for 3D woven composites based on the real shape of yarns, and its properties is analyzed with experimental research accordingly. The chief content can be fallen into three parts as below:In the first part, shapes of cross-section of 3D woven composites and its track are deduced by using photographic method to slices. Firstly, the RTM molding technology is studied, then test specimens made from 3D woven composites will be sliced along yarns direction at fixed intervals, and every cross-section will be photographed. Finally, special software will be used to simulate the photos obtained in order to get micro-shapes and real direction of yarns.In the second part, volume—averaging method is used to analyze mechanical properties of 3D woven composites. Firstly, a new model is established combining with real yarn shapes, and elastic properties are analyzed based on this model. Next, according to Tsai—Wu tensor theory, averaging calculating method is used for the theoretical analysis of the stretching, compression and inter-bedded shear strength of the composites, at last a comparison is made with the experimental results, validating the rationality of this model.The third part aims to investigate experimentally the mechanical properties of 3D woven composites. A number of specimens have been made for the stretching, compression and inter-bedded shear experimentations. These experiments are conducted in different cases with different structures, textile parameters and kinds of raw material. Finally, an analysis is made to the experimental phenomena and data, and many valuable conclusions can be obtained.