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Abstract: Mechanical properties of three-dimensionally (3D) four-directional and five-directional braided quartz preforms reinforced silica (SiO2f /SiO2) composites were compared. Mechanical properties tests were carried out under various loading conditions, including tensile, flexural and shear loading. The mechanical testing results indicated that the tensile strength, flexural strength and shear strength of the 3D five-directional braided SiO2f /SiO2 composite was superior to that of 3D four-directional braided SiO2f /SiO2 composite; especially the tensile strength (increased by 24 percentage points). Both 3D four-directional and five-directional braided SiO2f /SiO2 composites exhibited graceful failure under loading. Shear failure behavior between these two composites differed entirely, because of the existence of the 5th yarns in 3D five-directional SiO2f /SiO2 composite. The fiber placement in the preform strongly affected the mechanical property and failure behavior of the composite. 3D five-directional braided SiO2f /SiO2 composite had better strength and toughness than 3D four-directional braided SiO2f /SiO2 composite. [Copyright &y& Elsevier]