Microstructure Analysis and Multi-Unit Cell Model of Three Dimensionally Four-Directional Braided Composites
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Microstructure Analysis and Multi-Unit Cell Model of Three Dimensionally Four-Directional Braided Composites Kun Xu & Xiaomei Qian
Received: 21 November 2013 / Accepted: 11 April 2014 # Springer Science+Business Media Dordrecht 2014
Abstract In this paper, a new multi-unit cell model of three dimensionally braided composites is presented on the basis of the microstructure analysis of 3D braided preforms produced by four-step 1 × 1 method. According to a new unit cell partition scheme, the multi-unit cell model possesses five kinds of unit cells, namely interior, exterior surface, interior surface, exterior corner and interior corner unit cells. Each type of the representative volume cell has unique microstructure and volume fraction in braided composites. On the basis of these five unit cell models, the structural geometry parameters of the preforms are analyzed and the relationship between the structural parameters and the braiding parameters in different regions are derived in detail, such as the braiding angles, fiber volume fraction, yarn packing factor, braiding pitch and so on. Finally, by using the multi-unit cell model, the main structural parameters of braided composites specimens are calculated to validate the effectiveness of the model. The results are in good agreement with the available experimental data. In addition, the effect of braiding angle on the squeezing condition of braiding yarn is analyzed. The variations of the volume proportion of five unit cells to the whole specimen with rows and columns are discussed, respectively. The presented multi-unit cell model can be adopted to design 3D braided composites and predict their mechanical properties. Keywords Textile composites . Braided composites . Microstructure analysis . Geometrical model
1 Introduction Three-dimensional (3D) braided composites have great potential applications in the aeronautics and astronautics industries because of their excellent mechanical performances, such as better out-of-plane stiffness, strength and high impact resistance, etc. To make 3D braided composites more widely applied in the industries, many models were developed to analyze their microstructures and mechanical performance. However, due to their complicated K. Xu (*) : X. Qian School of Aeronautics and Astronautics, University of Electronic Science and Technology of China, Chengdu 611731, People’s Republic of China e-mail: [email protected]
Appl Compos Mater
architectures and anisotropic nature, it is difficult to establish a theoretically perfect microstructure model used for predicting the mechanical properties of 3D braided composites. Especially, the microstructures of 3D braided composites greatly depend on the braiding process parameters, such as braiding angle, pitch length and fiber volume fraction, which make modeling the microstructure difficult. Even so, many researchers have spent great efforts on the understanding of the microstructure of braided performs, and many models have been developed in the past [1–15]. Ko [1] first proposed a cuboi
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