关键词: 2.5维机织, 复合材料, 屈服准则

Abstract: 2.5D woven composites are now in wide use, yet their failure mechanism is not clearly understood. From the tensile tests of 3D woven composites, the original yield condition and criteria of 2.5D woven composites loaded in weft are deduced based on the hypothesis that the matrix and fiber within the warp curved layers possess equal stress along the weft. To verify the original yield condition and the yield criteria, 12 samples of 2.5D woven composites with three different structures are selected for tensile tests in which the samples are loaded in the weft direction. Experiment results of these tests and examples in literatures are in good agreement with the outcome of the yield criteria. The conclusion is drawn that transverse cracks of the matrix is the direct reason of original yield. Original yield criteria of 2.5D woven composites are relative only to the fracture volume of warp in warp curve layers, the modulus of fiber and matrix, and the strength of the matrix, and they seem to have no relationship with the number of layers and warp direction. The strain of the matrix is larger than that of the composites because of the different moduluses of its components when it is loaded in weft. Original cracks begin at places crowded with fibers, and spread in resin channels, which are prevented by fiber when they spread to tows.

Key words: 2.5D woven, composite, yield criteria