Abstract: Based on the hypothesis of the rectangle and biconvex section shape of the yarn , and different collocations
between the inner warp and outer warp , thickness , section shape of the same st ructure being considered especially ,a geomet ric cell model for 2. 5D woven st ructures is developed. This model can be used to calculate the configuration of each yarn system , including the orientation angle of the constituent yarns and the fiber volume f raction. To verify the geomet ric model , 28 samples of 2. 5D woven composites with 8 various st ructures are selected and the fiber volume f raction is measured. The experiment result s are in good agreement with the outcomes of the model . Further , the geomet rical model is used to calculate and analyze the fiber volume f raction and oriental angle of three various structures. A conclusion is drawn that the interweaving times of the fiber in a cell is the important factor for the fiber volume f raction , and the tropism angle of the straight2joint structure?s warp is lower than the bend2joint structure?s.