基于数字图像技术的纤维织物面内渗透率表征

材料渗透率的表征受其结构空间离散性和求解方式准确性的严重影响。基于数字图像技术,评估了纤维织物渗透率的空间分布,并探讨了阶梯铺层对灌注工艺的影响。首先,从恒压单向注射实验的视频流中动态提取了流动前沿的流速分布和流动前沿角,通过织物渗透率与结构的关系仅一次实验便可求得纤维织物的面内局部渗透率分布;其次,利用正态分布函数拟合,建立了基于数字图像技术的纤维织物面内主方向渗透率张量的求解方法,并利用该方法研究了编织形式对渗透率的影响;最后,研究了阶梯铺层和恒定铺层对灌注过程的影响。结果表明:建立的基于数字图像技术的渗透率表征方法可以通过一次实验同时获取面内主方向上的渗透率及其空间离散型;在恒定铺层下缎纹织物渗透率随着纤维层数增大而增大,从厚铺层向薄铺层的灌注方式可以达到最优的灌注时间。      

功能预制结构织物(ES-Fabric~(TM))渗透特性研究

比较了不同纤维体积含量的功能织物毛细渗透高度、毛细压力以及渗透率的大小,通过测试功能织物的渗透性能,研究了定型剂及增韧剂含量、注射压力、铺层方式以及增韧剂涂覆方式对其渗透率的影响。结果表明,毛细压力由纤维体积分数和涂覆颗粒的相互作用决定;在高纤维体分时各种状态的功能织物的毛细压力相差不大,渗透率趋于一致;[0/90]5,[0]10,[45/0/-45/90]2S等不同的铺层方式对面内渗透率Kx,Ky有一定的影响;添加定型剂后的功能织物更趋于各向同性;在相同增韧剂含量的情况下,单面涂覆功能织物的渗透率大于双面涂覆功能织物,这种差异随着体积分数的增加而减少。     

织物预成型体厚度方向渗透特性研究

以达西定律为基础,研究了不同类型织物的织物层数、定型剂质量分数以及铺层角度对织物预成型体厚度方向上渗透性能的影响.实验结果表明,在一定的定型剂质量分数下,测试流体在垂直方向上的流动基本为稳态流动,大体受Darcy定律控制.随着织物层数的增加,流体流速减小,预成型体厚度方向渗透率逐渐增加.随定型剂质量分数的增加,厚度方向渗透率表现出先增大而后又减小的趋势,而且织物的铺层角度对预成型织物厚度方向渗透率也具有较大影响.     

纤维堆积体厚度方向浸渗特性

使用自行设计的夹具对纯树脂沿纤维织物厚度方向的毛细浸渗行为进行了初步研究。通过改变温度、纤维体积分数、纤维类型以及铺层方式,研究了树脂对纤维织物的毛细浸渗规律,并研究了纤维表面浸润剂的影响。结果表明:升高温度和减小纤维含量均有利于提高浸渗速率;而铺层方式的改变对浸渗规律的影响甚小。      

真空导入模塑工艺中织物预成型体的可压缩性

采用真空加载方法研究了循环加载、织物形态、纤维种类、织物层数、铺层方式和混杂方式等参数对真空导入模塑工艺(VIMP)中纤维织物预成型体压缩行为的影响。结果表明: 预成型体纤维体积分数随着压缩循环加载次数的增加而逐渐增大, 但增幅呈现逐渐减小的趋势; 在相同的压缩载荷下, 预成型体的纤维体积分数随着织物层数的增加而增大, 但增幅很小, 对于VIMP制备复合材料构件基本可以忽略; 纤维预成型体在压缩载荷下的响应方式与织物形态、纤维种类、铺层方式和混杂方式等因素密切相关, 单向铺层比正交铺层更容易压缩而获得较高的纤维体积分数, 夹芯混杂比层间混杂方式更容易压缩。      

不同纤维堆积状态下饱和渗透率实验研究

通过调节压力控制纤维体积分数, 用单向饱和流动法对纤维层厚度方向的饱和渗透率进行了测定。考察了纤维体积分数随压力的变化规律, 并分别研究了纤维体积分数、纤维层数、铺层方式和纤维种类对渗透率的影响。结果表明, 当纤维体积分数超过某临界值后其值随压力增大的幅度减小。单向和正交铺层时层数变化对渗透率没有影响, 而平纹布渗透率随着纤维层数的增加而减小。此外, 纤维种类的改变对渗透率有明显影响。      

复合材料带筋壁板预成型体压缩性与渗透性对树脂流动的影响

以航空碳纤维增强树脂基复合材料典型结构件带筋壁板为研究对象,通过对U3160单向织物的组织结构进行分析,根据纤维束的受压变形状态对其压缩响应进行理论建模,然后以纤维束压缩模型为基础,预测了U3160单向织物按0°/45°/90°/-45°铺层时预成型体在压缩应力作用下厚度变化的响应行为。建立了压缩应力作用下纤维预成型体的渗透率解析模型:在织物压缩模型的基础上,建立了纤维束等效渗透率模型;根据张量理论,分别建立了0°、±45°和90°铺层织物等效渗透率模型;运用渗透介质串并联关系,建立了带筋壁板各特征区域渗透率综合表征模型。基于PAM-RTM流动模拟软件,进行分区渗透率定义,在充模过程中对树脂在带筋壁板预成型体中的流动行为进行模拟,优化工艺参数,确定出最终充模方案,并制作带筋壁板实验缩比件进行成型实验,验证了充模方案的合理性。研究结果为制件的成功制作提供理论依据,从而指导生产实践。      

真空压力下液体沿炭纤维织物铺层厚度方向的渗透特性

使用自行设计的装置对真空压作用下液体沿单向织物厚度铺层方向的渗透特性进行了初步研究, 通过一系列实验对设备和操作方法进行了规范。通过改变所加真空压力的大小, 研究了蒸馏水、酚醛溶液、丙三醇三种流体对炭纤维织物铺层的渗透规律。结果表明, 随着真空压力增加, 流体对单向织物堆积体的渗透速率增加。相同真空压力条件下, 三种流体中蒸馏水的渗透速率最快; 在5 kPa 和20 kPa 真空压作用下丙三醇的渗透速率快于酚醛溶液; 在40 kPa 和60 kPa 真空压力下, 酚醛溶液的渗透速率快于丙三醇。      

传感监测LCM成型厚铺层结构增强体内部渗透性能研究

采用传感监测系统辅助对厚铺层结构纤维增强体内部流动情况进行了实验研究.结果表明:渗透率随铺层厚度的增加逐渐减小,并趋于平缓;测试液在铺层厚度增强体顶层和底层渗透存在一定量的差异,并随铺层厚度的增加而增大.在不影响结构要求的前提下,导流布与长丝毡的配合使用是改善厚铺层结构渗透性能的有效方法.     

传感监测LCM成型厚铺层结构增强体内部渗透性能研究EI

采用传感监测系统辅助对厚铺层结构纤维增强体内部流动情况进行了实验研究.结果表明:渗透率随铺层厚度的增加逐渐减小,并趋于平缓;测试液在铺层厚度增强体顶层和底层渗透存在一定量的差异,并随铺层厚度的增加而增大.在不影响结构要求的前提下,导流布与长丝毡的配合使用是改善厚铺层结构渗透性能的有效方法.     

Lattice Boltzmann method based computation of the permeability of the orthogonal plain-weave fabric preforms

Changes in the permeability tensor of fabric preforms caused by various modes of fabric distortion and fabric-layers shifting and compacting is one of the key factors controlling resin flow during the infiltration stage of the common polymer-matrix composite liquid-molding processes. While direct measurements of the fabric permeability tensor generally yield the most reliable results, a large number of fabric architectures used and numerous deformation and layers rearrangement modes necessitates the development and the use of computational models for prediction of the preform permeability tensor. The Lattice Boltzmann method is used in the present work to study the effect of the mold walls, the compaction pressure, the fabric-tows shearing and the fabric-layers shifting on the permeability tensor of preforms based on orthogonal balanced plain-weave fabrics. The model predictions are compared with their respective experimental counterparts available in the literature and a reasonably good agreement is found between the corresponding sets of results.     

Analysis of Transversal Permeability for Different Types of Glass Fiber Reinforcement

In some of the new processes to produce elements in composite materials, the innovation is due to the fact that the resin flow is perpendicular to the plane of the reinforcement during the impregnation.So a very important parameter is the transversal permeability of the reinforcing materials used in these processes. In fact for a high value of this parameter it is possible to increase the product quality and to reduce the process time.In this work, using Darcy's law and a particular permeameter, the transversal permeability of preforms constituted by fabric and mat layers of fiber glass has been valued for different injection pressures. In particular, the permeability of two types of preform, consisting respectively of only mat layers and of only fabric layers, have been determined by tests and calculated by Kozeny–Carman equation. The research has been also focalised on the evaluation of the permeability of preforms constituted by a mix of the two different types of reinforcement. Furthermore an analytical model has been studied to calculate the permeability of preforms consisting of layers of different reinforcement types, starting from the permeability data characterizing the single reinforcement type and determined by the tests or by Kozeny–Carman equation.     

Optimization of Cut-Out Shape on Composite Plate Under In-Plane Shear Loading

The wing in flight condition is subjected to heavy aerodynamic loads that in turn lead to a shear flow over the wing ribs that support it. Cut-outs change the mechanical behavior of plates, as they redistribute the stresses and are influenced by the shape of the cut-out. A three-dimensional displacement-based finite element analysis is performed to study the symmetric, laminated composite plate of 20 layers. The analysis is performed to obtain the in-plane and out of plane performances of the laminate. Five basic cut-out geometries, viz., circle, square, diamond, ellipse with major axis along the y-axis, and another ellipse with major axis along the x axis were used for the numerical analysis. A cut-out geometry is generated based on the results of analyses performed on five basic geometries to optimize the performance. The optimized cut-out is associated with the least Tsai-Hill and Hashin failure index as compared with the five basic geometries.     

In-plane permeability of sheared fabrics

Shear is the main mode of deformation in the draping of fabrics over complex mould geometries in composites manufacturing. Hence, the measurement and prediction of the in-plane permeability of sheared fabrics is a crucial task for the design of resin transfer moulding and other composites processing techniques of complex shaped articles. A mathematical model has been developed and applied to predict the in-plane permeability in the two principal directions and the angle of the flow ellipse for sheared assemblies of bi-directional woven fabrics that are in-plane isotropic to flow when unsheared. Modelling was accompanied by in-plane permeability measurements for unsheared and sheared woven fabric assemblies, and a comparison of this experimental permeability data with the proposed model proved encouraging. A study into the change of the areal density of different woven fabrics with shear angle has also been included.     

Temperature Dependence of Resin Flow in a Resin Film Infusion (RFI) Process by Ultrasound Imaging

Ultrasonic imaging in the C-scan mode was used in conjunction with the amplitude of the reflected signal to measure the temperature dependence of resin flow rate in single layers of woven carbon fabric. The RFI samples were vacuum-bagged and scanned in a water tank at 50°C, 60°C, 70°C, and 80°C. The measured flow rates were plotted versus inverse viscosity to determine the permeability in the thin film, non-saturated system. The permeability values determined in this work were consistent with permeability values reported in the literature. Capillary flow was not observed at the temperatures and times required for pressurized flow to occur. The flow rate at 65°C was predicted from the measured flow rates, and then measured in a 10-layer laminate. The investigation demonstrates that ultrasonic imaging in the C-scan mode in conjunction with the amplitude of the reflected signal is an effective method for measuring resin flow through fabric.     

国产CCF300碳纤维单向织物液体成型工艺性及其复合材料力学性能

选取国产碳纤维CCF300所制备的2种单向织物,单向无纬织物U3160及单向无屈曲织物KUC160,分别对其预成型体进行压缩特性和渗透特性测试,以研究2种单向织物的液体成型工艺性,并采用树脂传递模塑(RTM)工艺制备2种单向织物/双马来酰亚胺树脂基复合材料,测试并对比其面内力学性能。结果表明:预成型体压缩试验中,嵌套效应受压力及织物层数影响较大,压力越高、层数越多,嵌套效应越显著。U3160织物的嵌套效应较KUC160织物更为明显,在较高压力下,KUC160织物预成型体的纤维体积分数较U3160织物的下降了约20%。渗透率测试结果表明:相比U3160织物,KUC160织物0°方向的渗透率较高,而90°方向的渗透率有所降低;这是由于经编线的绑缚作用能促进0°方向的宏观流动,而阻碍90°方向的微观渗透。此外,KUC160织物的经编线与U3160织物的纬向纱线的导流作用也对渗透率有影响。力学性能试验结果表明:相比U3160织物增强复合材料,KUC160织物增强复合材料0°方向的拉伸、弯曲和压缩性能均有所下降,拉伸强度和弯曲模量降幅最大,分别约为11%和21%;而层间剪切强度有小幅提高,增幅约为8%。      

彩色图像中椭圆的快速检测算法

椭圆检测是图像处理中常用的技术,由于自然界很多物体都可以用椭圆进行拟合,所以也成为图像分割和目标提取的关键技术.该文分析了椭圆的解析结构,利用椭圆长短轴之间的几何关系,从边缘点集合中选取全局性的参数,快速生成椭圆.算法针对彩色图像,引入了彩色边缘增强算法和基于图搜索的边缘追踪算法,生成封闭的边缘轮廓曲线,对每段曲线进行椭圆拟合,通过拟合评估,形成拟合判决,确定图像中的椭圆区域.算法计算量小,检测速度快,对多椭圆和椭圆弧都能准确检测.     

Effective permeabilities of multilayer fabric preforms in liquid composite moulding

A homogenisation method was developed to predict effective permeabilities of multilayer fabric preforms by considering interlayer continuity and coupling between in-layer flow and trans-layer flow. A simplified approach was addressed first, from which the common approaches of arithmetic mean formation and harmonic mean formation can be deduced to define the effective permeability by neglecting coupling between in-layer flow and trans-layer flow. For multilayer preforms in liquid composite moulding, the permeability predicted by such an approach, however, is generally different from the actual one because of neglecting effects of micro-structure between layers and synchronisation between in-layer flow and interlayer flow. A conceptual model for interlayer flow, based on the hydraulic radius theory, was then proposed to quantitatively characterise the effect of interlayer micro-structure on the effective permeability of multilayer fabric preforms. The predictions show good agreement with experimental results available in literature.