【作者】 陈思；

【导师】 龙海如；

【作者基本信息】 东华大学 ， 纺织工程， 2015， 博士

【摘要】 经编间隔织物具有优异的抗压缩、抗冲击性能和较高的生产效率，用其作为增强体的复合材料在厚度方向具有较好的力学性能，能明显的提高层间剪切强度，且在受到外界载荷特别是动态载荷作用时，不会出现分层的现象。良好的结构完整性、抗冲击性以及低廉的生产成本使经编间隔织物增强聚氨酯复合材料有望成为一种新型缓冲材料。但是与其它纺织结构增强复合材料相比，有关经编间隔织物增强复合材料的研究寥寥无几。因而本论文对经编间隔织物增强聚氨酯复合材料缓冲性能的研究有重要的意义，旨在为该复合材料缓冲性能的优化设计提供理论指导和实验支持。为了研究不同经编间隔织物结构和参数对复合材料缓冲性能的影响，本论文设计并编织了8种具有不同结构和参数的经编间隔织物，包括3种不同的间隔梳栉针背横移针距数、4种不同的表面组织、2种间隔丝直径以及2种织物厚度。采用手糊成型的方法，完成了经编间隔织物与聚氨酯泡沫的复合成型，制备出了10种经编间隔织物增强聚氨酯复合材料试样。在复合材料成型固化的过程中，由于基体体系中低分子基团的存在或成型工艺的缺陷，可能造成固化成型后复合材料的密度分布不均。这种密度分布的不均匀可以明显降低复合材料的各项力学性能，包括抗弯曲性能、抗压缩性能和抗冲击性能等。因此，成型后的复合材料密度分布均匀度对复合材料力学性能有显著的影响。本论文选用意大利IMAL公司生产的DPX300-LTE型密度扫描仪对固化成型后复合材料的密度分布情况进行研究。根据密度测试结果可知，复合材料上、下表面层的密度值远大于间隔层的密度值，这是因为间隔织物由间隔丝将两个织物表面层连接在一起，间隔织物的间隔层只存在间隔丝，因此间隔层的密度值要小于表面层，进而造成复合材料的上、下表面层的密度值大于间隔层。但复合材料上表面的密度值和下表面的密度值很接近，同时复合材料间隔层的密度值基本保持不变。由此可知，通过手糊成型法所制备的经编间隔织物增强聚氨酯复合材料的密度分布是均匀的，可以满足实际工程应用的需要。采用长春科新WDW3020型万能材料测试仪对复合材料试样进行了准静态压缩性能测试，以考察其抗压缩及能量吸收特性。同时，分析了不同结构与参数对复合材料压缩性能的影响。通过研究发现，复合材料的结构与参数对其压缩性能有显著的影响，间隔梳栉针背横移针距数较大、表面组织为六角形网孔、间隔丝直径较小、聚氨酯泡沫体系中开孔剂含量较少的复合材料试样，在小应力值下具有较高的能量吸收率。反之，间隔梳栉针背横移针距数较小、表面组织为菱形网孔、间隔丝直径较大、聚氨酯泡沫体系中开孔剂含量较多的复合材料试样更适合在大应力条件下作为能量吸收材料使用。厚度对复合材料试样能量吸收性能的影响随着压缩应力值的变化而变化。因此通过改变及优化间隔织物结构与参数及聚氨酯基体参数可以明显提高复合材料的能量吸收性能。本论文以文克尔弹性地基模型为理论基础，根据复合材料中间隔丝的排列方式，建立了经编间隔织物增强聚氨酯复合材料压缩性能的理论方程，进而得到理论压缩应力-应变曲线，并将其与实验得到的压缩应力-应变曲线进行对比，结果显示出两者之间具有较高的吻合度，这说明本文所建立的压缩模型能较好的模拟复合材料实际的受力情况，可为实际工程应用提供理论指导。作为缓冲材料，经编间隔织物增强聚氨酯复合材料的抗冲击性能尤为重要。本论文以国标GB/T8171-2008为依据，在Instron公司生产的Dynatup9250HV落锤冲击试验仪上设计并安装了标准平面冲头，以模拟缓冲材料与物体的冲击情况。研究分析了不同结构与参数对复合材料抗冲击性能的影响以及在不同冲击能量下复合材料的冲击响应。对复合材料冲击后的损伤形态及剩余压缩应力进行研究以表征复合材料冲击后的损伤程度。复合材料冲击实验结果显示，不同的复合材料试样具有不同的冲击力峰值和能量吸收特性。一般地，间隔梳栉针背横移针距数较大、表面组织为菱形网孔、间隔丝直径较大、厚度较大、聚氨酯泡沫体系中开孔剂含量较多的复合材料试样，在冲击的过程中产生较小的冲击力峰值，可以吸收较多的冲击能量，更加适合作为缓冲材料。但并不是间隔梳栉针背横移针距数越大越有利于吸收能量，间隔梳栉针背横移针距数过大，在受到冲击载荷时，复合材料更容易发生变形进入密实区，反而降低了复合材料的能量吸收能力。理论上，表面组织网孔越大，复合材料的抗冲击性能越好，但是网孔过大的表面组织，使间隔丝更多的暴露在外，这样就增加了间隔丝受到损伤的几率，从而降低了复合材料的抗冲击性能。受到冲击后，复合材料的压缩应力-应变曲线与冲击前具有相同的形态，只是压缩应力值略小，且冲击前、后复合材料压缩应力值的大小顺序相同，说明冲击前抗压缩性能好的复合材料冲击后的剩余压缩应力值大。在压缩和冲击实验研究的基础上，利用有限元方法和ANSYS软件，对典型的间隔织物增强聚氨酯复合材料的压缩和冲击性能进行了模拟分析。在假定复合材料宏观连续均匀的前提下，选取了间隔丝的一个最小循环及所包含的聚氨酯材料作为一个代表体单元来建立有限元分析模型。其方法是根据间隔丝实际的排列方式，先对间隔织物进行几何建模，再对聚氨酯基体部分建模，最后将两部分模型装配在一起，从而保证了两部分在界面上的节点完全重合。间隔丝的模型由空间三维几何线段组成，建模时考虑了相邻的间隔丝之间不接触，以免造成相邻间隔丝内部各个节点重合。如何确定材料属性也至关重要。根据弹塑性力学理论，本文将本构关系呈非线性的聚氨酯基体定义为各向同性材料。对增强体间隔织物的面板与间隔丝分别定义，即面板定义为正交各向异性体，间隔丝定义为正交各向同性体。利用有限元软件的分析与计算，可以得到经编间隔织物增强聚氨酯复合材料在压缩和冲击过程中的应力分布情况及压缩应力-应变(冲击力-位移)曲线。从复合材料的受力应力云图可得，复合材料在受到压缩载荷时，经编间隔织物是压缩载荷的主要承载体；在受到冲击载荷时，与冲头接触区域的应力值最大，且应力向复合材料边缘区域扩散。有限元模拟的压缩应力-应变曲线和冲击力-位移曲线与实验结果有较高的吻合度。更多还原

【Abstract】 Warp-knitted spacer fabrics possess superior compression resistance, impact resistance and high productivity. Therefore, the composites reinforced by these fabrics exhibit promising mechanical performances. Due to the better interlaminar shear strength, the composite delamination can be fully avoided when subjected to impact loading. As for superior anti-impact properties, integrity and low-cost, the composites reinforced with warp-knitted spacer fabrics are expected to become a new kind of cushioning material. However, the researches on warp-knitted spacer fabric composites are limited compared to other textile-structure reinforced composites. Therefore, this thesis is important to investigate cushioning properties of polyurethane composites reinforced with warp-knitted spacer fabrics and would offer theoretical guidance and experimental supports for designing cushioning properties of the composites.To better understand the effect of structure and parameter on the cushioning behaviors of warp-knitted spacer fabric polyurethane composites, eight warp-knitted spacer fabrics with different structures and parameters were designed and produced, including three lapping movements of spacer-guide-bar, four surface structures of spacer fabrics, two thicknesses of fabrics and two diameters of spacer yarns. The composite samples from eight warp-knitted spacer fabrics and three polyurethane materials were fabricated by hand lay-up method.Due to the low molecular groups existed in polyurethane matrix and the defects of manufacturing technology, the sample density may be uneven after curing of composites, which can reduce the mechanical properties of composites, including the anti-compression, shear and impact resistance behaviors. Thus, the composite uniformity plays an important role in the mechanical properties of composites. A compact X-RAY density profile analyzer (IMAL DPX300-LTE, Italy) was used to evaluate the density of composites. It can be seen that the density values in surface layers of composites are higher than that in spacer area. This phenomenon can be explained with the fact that the density values in the outer layers of spacer fabrics are higher as compared to that in spacer area, resulting in higher density values in the surface layers of composites. However, it is obviously observed that the density values in the spacer area of composites are nearly constant along thickness direction, indicating that the density distribution of composites was uniform in the spacer area of composites. Additionally, the density values in top and bottom layers of composites are also very close to each other. All the results significantly demonstrated that the density is fairly well-distributed in the finished composites, which can meet the end-use requirements.The forming composites have been characterized for compression properties by using the Ke-xin WDW3020universal material test instrument to investigate the compression resistance and energy absorption properties of composites. Furthermore, the influence of structure and parameter on the anti-compression and energy absorption behaviors of composites has been thoroughly investigated as well. The results show that the structures and parameters have strong influence on the compression performances of composites, the composites with larger underlapping of spacer yarns, hexagonal mesh in surface layers, finer spacer yarn, lower opening-agent content in polyurethane foam are suitable for absorbing energy at a lower stress level with higher efficiency. In contrast, the composites with smaller overlapping of spacer yarns, rhombus mesh in surface layers, coarser spacer yarn, higher opening-agent contained in polyurethane foam can be used to absorb energy at a higher stress level. The effect of sample thickness on the energy absorption properties varies with the changes of stress level. All the findings obtained indicate that the energy absorption properties of composites can be adjusted to meet the end-use applications by varying the structures and parameters of composites.Based on the Winkle elastic foundation theory, a compression analysis model of composites was established according to the arrangement of spacer yarns. The compression stress-strain curves obtained from the theoretical model were compared to the experimental results. The results show that the theoretical model is in good agreement with the experimental data, indicating that the predicted model can successfully simulate the compression behaviors of composites and offer the references for designing and producing the warp-knitted spacer fabric polyurethane composites for cushioning applications.As cushioning material, the impact resistance and energy absorption behaviors of composites are important. Taking GB/T8171-2008as the reference, standard plane striker, was designed and installed in the drop striker impact tester (Instron Dynatup9250HV) in order to simulate the impacts between striker and cushioning materials. The influences of structures and parameters on impact properties of composites at different impact energies were investigated. Moreover, damage performance and residual compressive strength of composites were also studied to describe the damage after impact. The results show that different composites exhibit vary peak impact-force and energy absorption properties. The composites made with larger underlapping of spacer yarns, rhombus mesh in surface layers, larger fabric thickness, coarser spacer yarn, higher opening-agent content in polyurethane foam display lower peak impact-force, thus can absorb more impact energy during the impact process. However, it is stressed that the energy absorption properties will not rise with increasing of underlapping number of spacer yarns all the time. The composites with over-larger underlapping of spacer yarns are easy to enter the dense area when suffered impact load, resulting in the decrease of energy absorption. The energy absorption capacities increase as the size of mesh in outer layers increases. However, the larger size of mesh in surface layers, the more spacer yarns exposure, which makes the spacer yarns damage more easily, leading to a decrease of impact resistance capacities of composites.The compression-after-impact curves of composites exhibit the same configuration as the compression curve without impact, except the peak force value. The sequence of residual compression strength of composites is the same as that of composites before impact, indicating that the composites with higher compression strength also keep higher residual compression strength.Based on the compression and impact tests, the finite element method and ANSYS software were involved to analyze the compression and impact performances of warp-knitted spacer fabric composites. It is assumed that the composites are homogeneous and continuous on macrostructure, a representative volume element having a spacer yarn cycle and polyurethane was taken to set up analysis model. The spacer yarn model was established firstly according to their actual arrangements, and then the polyurethane was modeled. And the final analysis model can be obtained by gluing these two parts together. The spacer yarn model consisted of several pieces of three dimensional geometrical curves. To avoid that the nodes inside the spacer yarns was not coinciding, the two neighbor spacer yarns could not be intersected. Besides the modeling, the definition of material characteristics is also very important. In this study, the non-liner polyurethane was defined as the isotropic materials according to the principle of elastic-plastic mechanics, while the reinforced warp-knitted spacer fabric was divided into two parts: surface of fabric and spacer yarn were defined as orthogonal anisotropic material and isotropic one respectively. The Von Mises contour nephogram and stress-strain (force-displacement) curves were obtained from the finite element analysis. According to the Von Mises contour nephogram, it can be found that the warp-knitted spacer fabrics in the composites bore the main compressive loads. When the composites suffered impact loads, the peak loads were found in the contact area between the striker and composites, and the loads spread to the edge of composites. The predicted compression stress-strain curves and impact force-displacement curves by the finite element analysis model were in reasonable agreement with experimental results.更多还原