Preparation And Investigation On The Properties Of Three-Dimensional Braided Quartz Fiber Reinforced Composites

Fiber-reinforced composites possess excellent mechanical properties, such as high specific strength and high specific stiffness. Among kinds of fiber-reinforced composites, laminated composites are most widely used because of their good in-plane mechanical properties. But laminated composites also have a significant disadvantage-lower interlaminar stress, which has limited uses of laminated composites to a large extent. So in order to overcome this shortcoming, three dimensional(3-D) braided composites emerge as the times require. Besides traditional mechanical features as well as laminated composites, the most significant feature of 3-D braided composites is excellent anti-shear resistance, which has been widely used in many fields, such as aviation, aerospace and national defense.Comprehensive epoxy-based composites reinforced with 3-D braided quartz fibers are prepared by Vacuum Assisted Resin Transfer Molding (VARTM) process. Mechanical properties, influence of fiber surface treatments on 3-D braided SiO2/EP composites, curing technology and the application of fractal theory in quantitative analysis of bending fracture mechanism of composites are investigated systematically.Through studies of quartz-fiber single fiber composites, it is detected that a positive coorelation exists between the shear stress and the tensile strain of single fiber composites. Based on this result, the optimum chemical surface treatment technology on quartz fibers is founded with the help of SPSS software. SEM images of quartz fiber and analysis of infrared spectrum and X-ray diffraction show that physical and chemical states of quartz fiber surface are changed by chemical surface treatments. The results of mechanical test indicate that chemical surface treatments have a good effect on 3-D braided SiO2/EP composites, improving both interfacial bonding strength and tensile and flexural properties.In order to acquire epoxy resin with uniform internal crosslinking structure and density, the dynamic curing behavior of epoxy resin is detected by Differential Scanning Calorimeter. With Kissinger equation, Crane equation and Ozawa equation, the reaction mechanism of curing process and main technological parameters (temperature and time) are discussed, and a numerical model representing the curing process is developed, which will provide important theoretical grounds for both simulating the changing process of internal parameters in various technological conditions and supervising the curing process of epoxy resin.This paper also systematically investigates the application of fractal theory in quantitative analysis of bending fracture mechanism of composites. Based on fractal theory, the binary image fractal dimension Df is determined by Box-counting method with MATLAB to process SEM images of fracture appearance. The cracks of composites possess obvious characters of ductile fracture, which is in accordance with the phenomenon observed in the three-point bending experiment. As far as it is concerned, fractal dimension Df could conduct as a quantitative parameter characterizing fracture surface of composites.This paper investigated the influence of chemical surface treatments on mechanical properties of 3-D braided SiO2/EP composites, and creatively introduced fractal into the analysis of mechanism of flexural failure, which will provide references for developing advanced products.