【作者】 葛朝阳；

【导师】 胡红；

【作者基本信息】 东华大学 ， 纺织工程， 2014， 博士

【摘要】 天然材料通常表现为正泊松比,即拉伸时材料变窄,压缩时变宽。近几十年来发现了一些具有负泊松比性能的材料,并于1991年被Evans等人命名为拉胀材料(Auxetic material),其泊松比的绝对值越大,负泊松比效应越明显。研究发现,拉胀材料除具有负泊松比外,与传统材料相比,还具有其他独特性能,如剪切刚度、断裂韧性、抗压痕性、能量吸收能力(超声波、声、阻尼)等都有所提高。以上优良的力学性能使得拉胀材料可望应用于航空航天、环保、生物医学及其他国防领域,从而使拉胀材料的开发和研究具有重要意义。本课题旨在设计开发一种具有负泊松比效应的三维织物结构,研究其产生负泊松比的压缩变形机理并讨论其结构参数对负泊松比的影响。该结构包括经纱、纬纱及捆绑纱,其结构特点是经纬纱多层排列,不进行交织,层间垂直交叉排列,层内纱线一隔一或完全平行排列,同时由织针在垂直于经纬纱交叉排列平面的方向编织经编编链结构形成捆绑纱。标记经纬纱其中一组纱线一隔一排列的结构为结构A,经纬纱同时一隔一排列的结构为结构B。定义该织物的结构松弛率为理想状态下即经纬纱都完全平直情况下织物的厚度与下机后织物的厚度差占理想状态下织物厚度的比例,则影响织物的相关结构参数有：经纬纱半径、不同层相邻经纱间的水平距离、不同层相邻纬纱间的水平距离、经纬纱弹性模量、结构松弛率。本课题研究工作主要分为四部分：(1)设计一种具有负泊松比效应的三维织物结构,建立该结构的二维几何模型,考察该结构中各参数对其泊松比性能的影响。制造三维织机实现以上结构的织造。(2)通过手工和机械的方法编织出14种不同结构参数的试样,并对以上试样进行压缩实验测试,研究织物产生负泊松比的变形机理以及结构参数对负泊松比的影响。(3)根据经典弹性理论和接触理论建立该结构的二维力学模型,比较该模型所得结果与二维几何模型及压缩实验结果的差别。(4)利用有限元分析方法建立该结构的有限元模型,讨论其结果与二维力学模型及压缩实验结果的差别。研究主要结论：(1)三维织物结构在二维几何原理上能够展现负泊松比效应。二维几何模型表明,该结构的负泊松比随着压缩应变的增加而增加。该结构经纱半径增加,不同层相邻经纱间的水平距离减小,同时避免纬纱半径及其结构松弛率过大就可得到负泊松比更明显的织物。(2)该类结构在一向具有负泊松比。结构在压缩过程中产生负泊松比性能的原因是弯曲刚度大的一组纱线一隔一排列。手工编织试样与三维织机织造试样压缩试验对比发现,两种编织方法得到的试样都能使三维织物结构的展现负泊松比性能。但由于编织方法的不同,相同编织参数织物的结构松弛率有所不同,其泊松比性能也有些微差异。经纱半径和不同层相邻经纱间的水平距离对织物泊松比的影响与二维几何模型具有相同变化趋势：随着以上参数的增加织物负泊松比性能增加。但纬纱半径对泊松比影响的变化趋势则刚好相反。(3)三维织物结构的二维力学模型计算结果与实验结果显示相同的变化趋势,随着压缩应变的增加,结构的负泊松比效应愈加明显。但其二维力学模型所得负泊松比略大于、受力明显大于实验结果。二维力学模型研究发现经纱半径的增加、纬纱半径的减小,不同层相邻经纱间的水平距离的减小,经纱弹性模量的增加,纬纱弹性模量的减小都使该结构负泊松比效应增加。结构松弛率的增加虽能增加结构的负泊松比性能,却使结构的最大压缩应变降低。(4)有限元分析表明,以该结构的最小单元作为有限元模型足以模拟该结构的泊松比、受力状况与压缩应变的关系。结构A和结构B在结构参数相同时,具有几乎相同的泊松比—压缩应变曲线及受力—压缩应变曲线。有限元模型中结构参数变化对结构泊松比—压缩应变关系的影响趋势与压缩实验结果和二维力学模型结果相同。更多还原

【Abstract】 Natural materials usually exhibit positive Poisson’s ratio; that is, such materials tend to contract or expand in the transverse direction if they are stretched or compressed, respectively, in the longitudinal direction. In recent decades, some materials with negative Poisson’s ratio (NPR) have been found, and named as auxetic materials by Evans et al in1991. The greater the absolute values of Poisson’s ratio of auxetic materials have, the higher the NPR effect. Compared with common materials, in addition to NPR, auxetic materials possess other unique properties, such as high shear stiffness, high fracture toughness, high resilience and energy, ultrasound, sound absorption capacity, etc. These excellent mechanical properties make auxetic materials good candidates for the applications in aerospace, environmental protection, biomedicine and other defense field. Hence, the development and study of auxetic materials are of great significance.The study aims to design and develop an innovative kind of three dimensional fabrics with negative Poisson’s ratio, and analyze their deformation mechanism under compression process and influences of structure parameters on the NPR effect. The fabric structrure is composed of three yarn systems, i.e., weft yarns, warp yarns and stitch yarns. The structure features include:1) the weft and warp yarns layers are not interlaced;2) the weft and warp layers are fully or partially arranged in each layer;3) the weft and warp yarns are bound by the stitch yarns through the fabric thickness direction. Two kinds of structures, structure A and structure B, were suggested and produced. In structure A, the weft yarns are fully arranged, and the warp yarns are partially arranged. In structure B, both of the weft and warp yarns are partially arranged. The relaxation rate of the two kinds of stuructures is defined to describe the initial state of the fabric at which the weft and warp yarns are crimped or completely straight. The structural parameters including radiuses of the weft and warp yarns, the spacing of two adjacent warp yarns in the same layer, the spacing of two adjacent weft yarns in the same layer, the Young’s modulus of the weft and warp yarns and structure relaxation rate, are the factors affecting auxetic effect of the fabric structures. The study includes four parts. An innovative three dimensional structure with NPR was first designed and developed. In the first part, a geometric model was established, and the effects of structural parameters on NPR of the fabrics were discussed based on the model established. Then, a machine to produce this kind of3D fabric structure was manufactured to produce. In the second part, fourteen fabric samples were manufactured manually and produced using the machine, respectively, and compressed using an Instron5566machine. The reasons for the fabric structure with axuetic effect under compression and the affecting trends of structural parameters on negative Poisson’s ratio were experimentally analyzed. In the third part, a2D analytical model was established based on the classical theory of elasticity and contact theory, and compared with the experimental results and the above mentioned geometric model. In the last part, a finite element model was built, and the simulation results were compared with the results from the compression tests and the2D analytical model.The main conclusions of the study are as follows:(1) The results of the geometric model confirm that the innovative structure has a negative Poisson’s ratio which increases with the compression strain. To obtain more obvious auxetic effect of the structure, the radius of the warp yarns and the spacing of two adjacent warp yarns should be increased,, and the radius of the weft yarns and structure relaxation rate should be not too high.(2) The innovative three-dimensional structure can only have NPR in one direction for both the structure A and structure B. The axuetic effect under compression results from a group of yarns with higher bending stiffness and alternately arranged. Comparative experiments between the fabrics produced by hand and the fabrics manufactured by machine show that all the samples have NPR. The fabrics with the same structural parameters having different structural relaxation rates lead to different Poisson’s ratios. The increase of radius of warp yarns and the spacing of two adjacent warp yarns in the same layer enhances the auxetic effect and this trend agrees well with the prediction of the2D geometric model.(3) The results from the2D analytical model showed that the theoretical Poisson’s ratio-compression strain curves had the same trends as the experiment results. Auxetic effect of the structure was more obvious with the increasing the compressive strain. But the NPR values obtained from this2D analytical model are slightly greater than the experiment results, and the force of unit cell is significantly greater than that from experiment. In addition, the results showed that increasing the radius and elastic modulus of the warp yarns, and decreasing the spacing of two adjacent warp yarns in the same layer and the radius and elastic modulus of the weft yarns have a significant and positive impact on the NPR ratio effect. Although the structural relaxation rate at the initial state had significantly improved the NPR performance of the fabric structure, it can affect the compressive strain rate of the fabric structure to a certain extent.(4) The finite element analysis showed that using the smallest unit cell of the structure to simulate Poisson ratio and stress in compression process was reasonable. Additionally, structure A and structure B with the same structural parameters have the same trends in the Poisson’s ratio-compressive strain and stress-compressive strain relationships. The influences of structural parameters on Poisson’s ratio in the finite element model had the same trend as the results of compression test and2D analytical model.更多还原