风力发电机叶片用玻璃纤维织物的渗透率

通过改变纤维层数来改变纤维织物的孔隙率,采用一维饱和流动方法测量了风力发电叶片用玻璃纤维织物(WindstrandTM)三个方向(x、y和z)的饱和渗透率大小.考察了孔隙率、模具尺寸以及纤维方向(平行于和垂直于2％的纤维束两个方向)对其饱和渗透率的影响.结果表明:渗透率随孔隙率的降低而迅速降低；当孔隙率为34.6％～54.7％时,模具尺寸对y向饱和渗透率影响不大；改变2％的纤维束方向(由平行到垂直),当孔隙率为34.6％～54.7％时,对饱和渗透率有一定影响.当孔隙率为45％～55％时,玻璃纤维织物x和y方向的饱和渗透率约为z方向饱和渗透率的3～7倍.     

Si与Mg含量对离心铸造原位颗粒增强Al-xSi-yMg复合材料组织与耐磨性能的影响

采用离心铸造方法制备了不同Si、Mg含量的Al-xSi-yMg复合材料筒状铸件, 考察了不同成分铸件的宏观组织和微观组织, 并测试了不同成分铸件的耐磨性能, 分析并计算了Al-xSi-yMg合金中形成初晶颗粒的条件。结果表明: 除Al-15Si-5Mg外, 其他各成分铸件内侧均形成了含有初晶Si或Mg₂Si颗粒的增强层, 外侧为不含颗粒的非增强层。不同成分Al-xSi-yMg铸件中形成的初晶颗粒、颗粒增强层的相对厚度值(k)以及颗粒的体积分数各不相同。随着铸件内层初晶颗粒体积分数的逐渐增加, 材料的耐磨性能显著提高。计算结果表明, 当x≥12.8＋0.49y且y≥5时(15≤x≤30, y≤8), 合金中形成初晶Si、Mg₂Si两种颗粒; 当x<12.8＋0.49y且y≥5时, 合金中只形成初晶Mg₂Si颗粒; 当x≥12.8＋0.49y且y<5时, 合金中只形成初晶Si颗粒; 当x<12.8＋0.49y且y<5时, 合金中不形成初晶颗粒。     

铌酸钾钠基透明上转换陶瓷材料制备及性能

采用热压烧结工艺, 以LiBiO₃作为烧结助剂, 制备了铌酸钾钠基透明上转换陶瓷K_0.5(1-y)Na_0.5(1-y)Li_yNb_1-yBi_yO₃- Er_0.005Yb_0.005x(Er³⁺/Yb³⁺:KNNLB, x=0~3, y=0~0.09)。并对其微观结构、光学透光率和上转换效应等进行了研究。结果表明该透明陶瓷具有正交钙钛矿型结构, 晶粒尺寸约0.5 μm, 致密度较高。该材料在红外区和可见光区有良好的透明性, 但是随着铒镱掺杂量的增加, 可见光区透光率呈明显的下降趋势。当y=0.06、x=0时, 在可见光范围内透过率可达到45%(样品厚度为0.5 mm), 红外光区域透过率达到95%以上。铒镱共掺杂透明陶瓷实现了在波长900 nm氙灯光源激发下的上转换效应。     

层间纳米纤维膜对玻纤预制体渗流特性的影响

为了研究层间纳米纤维膜对玻纤织物渗流特性的影响,使用超景深三维显微镜表征了纳米纤维含量对玻纤织物微观结构的影响,采用径向法测量了纳米纤维膜夹层玻纤织物预制体的渗透率,重点分析了纳米纤维含量对玻纤织物预制体渗流模式的影响。结果表明:玻璃纤维束间的毫米尺度区域被纳米纤维膜填充而离散成微米尺度区域;预制体孔隙率及渗透率值均随着纳米纤维含量的增加而减小;随着纳米纤维含量的增加,复合预制体表现出的各向异性程度逐渐减小;树脂宏观流动前沿内部分饱和区域面积比例随纳米纤维含量的增加而增大;相同纳米纤维含量预制体的部分饱和区域面积比例随注入时间的增加呈先增大后减小趋势。     

液体模塑成型工艺用纤维织物厚度方向饱和渗透率的预测模型液体模塑成型工艺用纤维织物厚度方向饱和渗透率的预测模型

树脂在复合材料预成型体厚度方向的渗透能力对复合材料液体模塑成型工艺（LCM）的成功实施至关重要。本文采用连续加载的方式,研究了玻璃纤维增强树脂基复合材料液体成型过程中多轴向无屈曲织物（NCF）和斜纹织物（WF）的压缩响应行为,并建立描述该行为的数学模型。采用自制测试装置对预成型体在重力等不同注射压力驱动下的厚度方向渗透率进行测试,考察了预成型体纤维体积分数、测试流体注射压力等对预成型体厚度方向渗透率K_z的影响。基于预成型体压缩响应数学模型和厚度方向渗透率与注射压力的关系,对Kozeny-Carman公式进行修正,提出了变注射压力条件下的厚度方向渗透率预测模型。结果表明:预成型体厚度方向渗透率随着纤维体积分数的增大而减小,与Kozeny-Carman方程结果相符合。当纤维体积分数为0.42≤V_f≤0.58时,注射压力对厚度方向渗透率影响较大,实验结果验证了本文提出的预测模型;当纤维体积分数V_f≥0.58时,注射压力对厚度方向渗透率影响较小,厚度方向渗透率趋于恒定。      

碳纤维复合材料超声振动辅助RTM工艺的浸润特性

研究了织物类型、纤维体积分数和超声振动对树脂在碳纤维织物中流动特性的影响规律,设计了超声振动辅助RTM工艺过程中单向渗透率测量装置,开展了16组渗透率测试实验,并结合COMSOL软件仿真分析了织物中的树脂流动特性。研究表明,在相同纤维体积分数水平下,斜纹编织物的纤维束间隙通道比平纹织物的更宽,2/2斜纹编织织物渗透率比平纹织物提高了约21.5%。纤维体积分数与织物渗透率呈负相关,其函数关系与半经验公式Kozeny-Carman(KC)方程吻合较好。树脂流动过程中加入超声振动,其超声空化效应、加速度效应和微射流效应作用于纤维丝束表面,提高了织物渗透率约58.2%。有限元仿真模拟了椭圆形和近矩形纤维束截面设计的织物模型的流动过程,结果发现近矩形纤维束截面高流速区域范围更广,流体向纤维布夹层浸渍的速度分量更大。超声作用于织物纤维可能带动纤维丝束蠕动,使纤维束截面趋于近矩形状,从而提高了树脂对纤维织物的浸润性。上述研究结果对优化碳纤维复合材料成型工艺和成型性能具有一定的指导意义。      

电弧离子镀Cr1-xAlxN硬质薄膜的成分、结构与性能

采用电弧离子镀的分离靶弧流调控技术在硬质合金基体上制备了4组不同Al含量的Cr_1-xAl_xN硬质薄膜, 采用SEM、XPS、GIXRD、Nanoindenter及划痕仪分别表征了薄膜的形貌、成分、相结构和力学性能。结果表明: 4组薄膜厚度分别为1.28、1.42、1.64和1.79 μm; 成分x随着Al靶的弧流相对增大而增大, 分别为x=0.41、0.53、0.64和0.73; 相结构与成分密切相关, 当x=0.41时, 薄膜呈单一的c-(Cr,Al)N相, 而当x≥0.53时, 则由c-(Cr,Al)N相和hcp-AlN相混相构成; 随着Al含量增加, 晶粒尺寸先减小后增大, 在x=0.64时达到最小值8.9 nm; 相应地硬度则先增大后减小, 在x=0.64时达到峰值35.3 GPa; 4组Cr_1-xAl_xN薄膜的膜基结合良好, 结合力均在60 N以上。综合测试结果发现, 当x=0.53时, Cr_1-xAl_xN薄膜的韧性最佳, 弹性恢复系数最高为57.4%, 同时兼具较高的硬度34.7 GPa, 此时薄膜具有最佳的综合性能。     

液体模塑成型工艺二维径向非饱和流动数值模拟

通过引入沉浸函数建立了双尺度多孔介质非饱和流动模型,并采用有限元/控制体积法实现了恒压及恒流注射条件下液体模塑成型（LCM）工艺二维径向非饱和流动的数值模拟,得到了不同注射条件下纤维织物内的压力场分布及半饱和区域长度随时间的变化规律,并将双尺度非饱和理论结果与单尺度饱和理论结果进行对比。结果表明：非饱和流动过程中,半饱和区域内的压力和压力梯度明显下降;半饱和区域长度随时间逐渐增加随后保持稳定,当流动前沿到达出口后半饱和区域长度开始逐渐减小;当两个主方向渗透率不同时,沿主方向半饱和区域长度也不同,渗透率越大该方向的半饱和区域长度也越大,纤维织物完全浸润时间取决于较小的渗透率。研究结果对合理预测树脂填充过程中压力分布及纤维预制件的浸润具有指导意义。     

基于Micro-CT图像的缎纹织物细观结构分析及渗透率预测

建立了确定显微计算机断层扫描技术(Micro-CT)扫描最合适分辨率的方法,并基于CT图像分析了3K五枚缎纹织物的结构,预测了渗透率。首先,将织物理想单胞模型转换为不同分辨率二维切片,考察分辨率对单胞结构、渗透率表征的影响,提出了确定Micro-CT扫描最合适分辨率的方法;其次,采用确定的分辨率对织物进行Micro-CT扫描,获取织物细观结构;最后,使用CT三维细观结构进行厚度方向渗透率数值预测,研究了织物结构的空间离散性对厚度方向渗透率的影响。结果表明：对于本文所用五枚缎纹织物,采用15μm分辨率进行Micro-CT扫描最合适;通过Micro-CT可准确获取织物纤维束的路径及截面变化;多层织物的孔隙沿3个主方向均呈现周期性排布,且束间孔隙率均值为16.6%;使用真实CT模型的厚度方向渗透率预测结果与实验值具有良好的吻合性。     

Al含量对CrFeNiAlxSi系高熵合金性能的影响

选取与天然铬铁矿粉有效成分相近的Al、Cr、Fe、Ni、Si元素为高熵合金成分,采用激光烧结技术制备CrFeNiAl_xSi系高熵合金,研究了Al含量对CrFeNiAl_xSi系高熵合金的物相结构、显微组织、密度和孔隙率、显微硬度、耐磨和抗高温氧化性能的影响。结果表明：CrFeNiAl_xSi(x=0.2、0.4、0.6、0.8、1.0)系高熵合金由BCC+FCC相构成,随着Al含量的提高FCC相减少;x=0.6的合金硬度最高,为813.3HV;合金的密度降低孔隙率提高,x=0.2的合金密度最大,为4.21 g·cm^-³,孔隙率最低,为26.46%;x=0.6的合金耐磨性能最佳,磨损率为69.50 mg·cm^-²;随着Al含量的提高,合金的抗高温氧化性能明显提高。     

The effect of fabric and fiber tow shear on dual scale flow and fiber bundle saturation during liquid molding of textile composites

In Liquid Composite Molding (LCM) processes, a fibrous reinforcement preform is placed or draped over a mold surface, the mold is closed and a resin is either injected under pressure or infused under vacuum to cover all the spaces in between the fibers of the preform to create a composite part. LCM is used in a variety of manufacturing applications, from the aerospace to the medical industries. In this manufacturing process, the properties of the fibrous reinforcement inside the closed mold is of great concern. Preform structure, volume fraction, and permeability all influence the processing characteristics and final part integrity. When preform fabrics are draped over a mold surface, the geometry and characteristics of both the bulk fabric and fiber tow bundles change as the fabric shears to conform to the mold curvature. Numerical simulations can predict resin flow in dual scale fabrics in which one can separately track the filling of the fiber tows in addition to flow of resin within the bulk fabric. The effect of the deformation of the bulk fabric due to draping over the tool surface has been previously addressed by accounting for the change in fiber volume fraction and permeability during the filling of a mold. In this work, we investigate the effect of shearing of the fiber tows in addition to bulk deformation during the dual scale filling. We model the influence of change in fiber tow characteristics due to draping and deformation on mold filling and compare it with the results when the fiber tow deformation effect is ignored. Model experiments are designed and conducted with a dual scale fabric to characterize the change in permeability of fiber tow with deformation angle. Simulations which account for dual scale shear demonstrate that the tow saturation rate is affected, requiring longer fill times, or higher pressures to completely saturate fiber tows in areas of a mold with high local shear. This should prove useful in design of components for applications in which it is imperative to ensure that there are no unfilled fiber tows in the final fabricated component.     

GM T 熔融浸渍中熔体在玻纤毡中的流动

通过改装毛细管流变仪建立了专门的实验装置, 研究高温高压下熔体在纤维床层中的流动行为。采用一维恒压流动实验分别测量了不饱和及饱和流动状况下玻纤毡厚度方向聚丙烯熔体的渗透率, 考察了玻纤毡空隙率、单丝直径、针刺等几何结构对渗透率的影响。根据实验结果进一步讨论了GM T 片材熔融浸渍过程中的气泡形成以及浸渍工艺参数的选择。      

Transverse Tensile Properties of 3 Dimension-4 Directional Braided C<Subscript>f</Subscript>/SiC Composite Based on Double-Scale Model

In this thesis, a double-scale model for 3 Dimension-4 directional(3D-4d) braided C/SiC composites(CMCs) has been proposed to investigate mechanical properties of it. The double-scale model involves micro-scale which takes fiber/matrix/porosity in fibers tows into consideration and the unit cell scale which considers the 3D-4d braiding structure. Basing on the Micro-optical photographs of composite, we can build a parameterized finite element model that reflects structure of 3D-4d braided composites. The mechanical properties of fiber tows in transverse direction are studied by combining the crack band theory for matrix cracking and cohesive zone model for interface debonding. Transverse tensile process of 3D-4d CMCs can be simulated by introducing mechanical properties of fiber tows into finite element of 3D-4d braided CMCs. Quasi-static tensile tests of 3D-4d braided CMCs have been performed with PWS-100 test system. The predicted tensile stress-strain curve by the double scale model finds good agreement with the experimental results.     

玻璃纤维增强聚乙烯复合材料力学及摩擦性能的研究

本文制备了结构-性能不同的纤维增强聚乙烯基复合材料,研究了纤维含量及纤维取向对聚乙烯基复合材料力学性能和摩擦性能的影响.实验结果表明:纤维含量及取向对玻纤增强的聚乙烯基复合材料的摩擦磨损性能影响较大.沿垂直纤维方向摩擦时磨损量最少,沿平行玻纤方向摩擦时摩擦系数μ最低.玻纤含量为30%的聚乙烯基复合材料耐磨性好,摩擦系数低,综合力学性能优良,是一种有应用前景的高分子抗磨材料.     

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。      

Study of saturated and unsaturated permeability in natural fiber fabrics

The main goal of this work is to understand how the main processing variables are affected when glass fibers are replaced by natural fibers in reinforced plastics. In this publication, a jute fabric was characterized in terms of its saturated and unsaturated permeability. It was found that fluid absorption and swelling are mechanisms present in natural fibers that reduce both permeabilities. Fluid absorption removes fluid from the main stream as it travels through the reinforcement, acting as a sink component and thus decreasing flow velocity during the unsaturated flow. Also, the saturation of the natural fibers cause swelling, reducing the porosity and increasing flow resistance during saturated flow.     

编织碳纤维/环氧树脂复合材料热扩散仿真

对编织碳纤维/环氧树脂(CF/EP)复合材料的三维热扩散性能进行有限元仿真研究。通过TexGen软件创建20层编织CF/EP复合材料三维仿真模型,计算了不同孔隙率样品的有效体积比热和热导率来设置材料属性,并使用幅值曲线模拟周期性点光源进行仿真。首先以孔隙率为0%的样品为例,采用非线性拟合求解热扩散系数,选出最优的调制频率范围为0.1~2 Hz。在此基础上研究了孔隙率对复合材料热扩散性能的影响。结果表明,编织CF/EP复合材料在平面内的热扩散系数随着孔隙率的增大而减小,孔隙率小于1.55%时,孔隙率每增加1%,热扩散系数下降5.4%。孔隙率大于1.55%时,下降速度变慢,仅为2.4%。在平面内沿着经纱和纬纱方向的热扩散较快,经(纬)纱45°方向的热扩散较慢,而在垂直方向上,由于点光源的穿透性使法向的热扩散最快,体现了热扩散的各向异性。      

Permeability of natural fiber reinforcement for liquid composite molding processes

We investigate the influence of liquid type on the saturated permeability of natural fabrics in liquid composite molding processes. The permeability of flax woven fabric was characterized with two different liquids which have different viscosity, wettability, and sorption characteristics with flax fiber. From the experimental data, it was observed that the saturated permeability values were different for the liquid type. The fiber swell during the mold filling process and the corresponding change of fabric microstructure were assumed to be the main reason for this dependency of saturated permeability on the liquid type. The fiber swell due to the liquid sorption was characterized as a function of time, and the corresponding change of fiber diameter was investigated. The effective fiber volume fraction of wet natural fabric was defined in terms of fiber swelling ratio. The predictions by the classical Kozeny–Carman model and by the modified Kozeny–Carman model with two model constants were compared with the experimental data. It was shown that the modified Kozeny–Carman equation considering fiber swell could predict very well the saturated permeability of natural fabrics regardless of liquid type.     

An analytical model for the longitudinal permeability of aligned fibrous media

This paper presents an analytical series solution of the longitudinal fluid flow in porous media consisting of aligned rigid fibers, which, in turn, is used to establish a relationship for the longitudinal permeability as a function of the fiber packing geometry, fiber volume fraction and the fiber radius. The analytical series solution is developed for rectangular and staggered packing arrangements of the fibers using the boundary collocation method where the constants in the series solution are solved for numerically. As the number of boundary collocation points is increased, the analytical solution is shown to converge with a finite element solution of the identical flow situation for all fiber volume fractions and packing arrangements. In addition, the permeability results are presented in a dimensionless form as a function of the fiber volume fraction and fiber packing arrangement for a general applicability and easy use of the results for predicting the longitudinal permeability of fiber tows consisting of aligned rigid fibers.