2.5维机织复合材料纬向拉伸过程初始屈服准则

Original Yield of 2.5D Woven Composites Loaded in Weft

2.5维机织复合材料已有较为广泛的应用,而目前对该类复合材料的破坏机理和失效原因尚未形成统一的认识。根据三维机织复合材料的拉伸试验现象,基于经纱曲面层板纬向纤维和树脂应力相等的假设,建立了2.5维机织结构复合材料纬向拉伸过程的初始屈服条件和屈服准则。通过对2.5维机织复合材料3种结构12个试件进行纬向拉伸试验及文献中的三维机织复合材料拉伸试验,与计算预测结果的对比表明本文中建立的初始屈服准则的合理性。研究表明,树脂横向裂纹是2.5维结构复合材料纬向拉伸过程初始屈服产生的直接原因;2.5维机织复合材料出现纬向拉伸屈服的条件仅和经纱曲面板内的经纱体积含量、纤维和基体的弹性模量及基体的拉伸破坏强度等因素有关,而与经纱曲面板的走向和层数无关。因为组分弹性模量不同,在纬向拉伸过程中,树脂应变高于复合材料的应变。树脂的初始横向裂纹首先发生在纤维密集处,并向富树脂区扩展;裂纹在向纤维方向扩展过程中受到纤维的阻碍而受到限制。

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. 513 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 out＇come 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.