二维二轴编织铺层复合材料压缩性能研究

发布时间：2018-08-11 18:29

【摘要】：编织铺层复合材料,国外学者大多称其为Over-braiding composites materials,它的应用领域越来越广泛,研究它的力学性能是目前国内外学者面临的主要问题之一。而且压缩性能作为力学性能中较难测定的难题之一,也是我们研究的重点方向。本课题主要是对编织铺层复合材料的压缩性能进行探讨,目的是得推导出一套表征或者能够在一定程度上定量描述其压缩时的弹性性能的计算方法,并对其压缩破坏模式作简要分析。首先,在立体式二维编织机上编织,设计编织所用芯模的尺寸,编织不同层数的编织铺层复合材料,在MTS 647 Hydraulic Wedge Grip仪器上进行压缩试验,测试不同编织层数的试样,得到编织铺层复合材料的压缩数据。其次,通过在体式显微镜下,观测编织铺层复合材料纱线走向,考虑纱线在交织处屈曲起伏,纤维轴向模量会有部分损失,提出纤维轴向模量损失系数ξ。通过测量编织复合材料中的基本参数,结合复合材料细观结构、弹性力学、迭层理论和多层等效弹性力学模型,利用推导出一套比较简单而实用的二维两轴编织铺层复合材料平均压缩模量的计算方法。最后,分析讨论多层碳纤维/环氧树脂编织铺层复合材料的压缩性能。主要考虑不同层数下不同编织角度的编织铺层复合材料平均压缩模量的变化规律及编织铺层复合材料的压缩破坏模式。结论分析表明:一、提出了一套较为精确地计算2×2结构编织铺层复合材料单层和多层的压缩弹性性能的方法,结果表明,该套计算方法与实测结果非常接近,是可行的。该套计算方法比较简单,适合于工程应用,比如复合材料制备过程中的性能评价,复合材料制备工艺的控制与改进,复合材料产品的设计等。二、对于编织铺层复合材料的进行压缩试验后可知:(1)在纤维体积分数基本保持一致的情况下,同一块板内,若编织角有差异,则编织角影响复合材料的压缩性能。编织角大的平均压缩模量小。随着层数增加,厚度增大,编织铺层复合材料的平均压缩模量呈下降趋势。(2)材料在未压缩破坏前,应力-应变曲线呈线性状态,在压缩初始阶段呈现弹性变形,随着应变的增加,应力迅速上升到最高值,达到最高值,下降相对于来说比较缓慢。(3)编织铺层复合材料压缩破坏过程,最主要的破坏形式是分层现象,这种破坏时分层现象的程度是介于单向布铺层复合材料和三维编织复合材料之间的。在同一试验条件下,随层数增加,层数多的编织铺层复合材料的破坏程度比层数少的严重些。在同一层中,编织角小的内侧破坏比编织角大的外侧厉害些。裂纹与加载方向呈一定角度,裂纹扩展未超过有效压缩长度。
[Abstract]:The braided laminated composite is often referred to as Over-braiding composites material by foreign scholars. Its application is becoming more and more extensive, and the study of its mechanical properties is one of the main problems faced by scholars at home and abroad. As one of the difficult problems in mechanical properties, compression performance is also the focus of our research. This paper mainly discusses the compressive properties of braided laminated composites. The purpose of this paper is to deduce a set of calculation methods which can describe the elastic properties of braided laminated composites or describe quantitatively the compressive properties of braided composites to a certain extent. The compression failure mode is analyzed briefly. First of all, braiding on the three-dimensional two-dimensional braiding machine, designing the size of the core die for braiding, braiding different layers of braided laminated composites, and carrying out compression tests on the MTS 647 Hydraulic Wedge Grip instrument to test the samples with different braiding layers. The compression data of braided laminated composites were obtained. Secondly, by observing the yarn direction of braided laminated composite yarn under the shape microscope, considering the buckling and undulating of the yarn at the interlaced place, the axial modulus of the fiber will be partially lost, and the coefficient 尉 of the axial modulus loss of the fiber is put forward. By measuring the basic parameters of braided composites, combining the microstructure of composites, elastic mechanics, lamination theory and multi-layer equivalent elastic mechanics model, A simple and practical method for calculating the average compression modulus of two-dimensional two-axis braided composites is derived. Finally, the compressive properties of multilayer carbon fiber / epoxy braided composites are analyzed and discussed. The variation of average compression modulus of braided laminated composites with different braiding angles and the compressive failure mode of braided laminated composites are considered. The results show that: firstly, a set of methods to calculate the compressive elastic properties of 2 脳 2 braided composite materials are presented. The results show that this method is very close to the measured results and is feasible. The method is simple and suitable for engineering applications, such as the evaluation of properties in the preparation of composite materials, the control and improvement of the preparation process of composite materials, the design of composite products and so on. Secondly, the compression tests of braided laminated composites show that: (1) when the fiber volume fraction is basically the same, if the braiding angle is different, the braiding angle will affect the compression properties of the composites. The average compression modulus with large braiding angle is small. With the increase of layer number and thickness, the average compression modulus of braided laminated composites decreases. (2) the stress-strain curve of braided laminates shows linear state before compression failure, and shows elastic deformation at the initial stage of compression. With the increase of strain, the stress rises rapidly to the highest value and reaches the highest value, and the decrease is relatively slow. (3) the main failure form of braided composite is delamination. The degree of delamination is between unidirectional laminated composites and three-dimensional braided composites. Under the same test conditions, with the increase of the number of layers, the degree of failure of the braided composite with more layers is more serious than that of the number of layers. In the same layer, the inner side with a small braiding angle is more destructive than the outer side of the braided angle. The crack is at a certain angle to the loading direction, and the crack propagation is no longer than the effective compression length.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB332

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