增强纤维对用于燃料电池碳纸性能的影响研究

本研究分别采用亚麻纤维、黏胶纤维、ES纤维作为增强纤维与碳纤维复合制得碳纸前驱体(CPP),经树脂浸渍、热压(温度140℃,压力10 MPa)、热处理(氮气保护下,温度980℃)制备了可应用于燃料电池气体扩散层的高性能碳纸,研究了3种增强纤维及其用量对CPP强度以及对碳纸电阻率、孔隙率、拉伸强度的影响。结果表明,增强纤维显著提高了碳纸的拉伸强度,并使碳化后的树脂产生固定作用,降低了碳纸电阻率及孔隙率。亚麻纤维用量20%时,增强效果最优。相比未添加增强纤维碳纸,碳纸的拉伸强度由18. 5 MPa提升至20. 4 MPa,提高了10%;电阻率由36. 7 mΩ·cm降低至34. 2 mΩ·cm,降低了7%;孔隙率由63%下降至56. 4%,降低了10%。     

对压实(股)钢丝绳特性与生产技术难度的认识

压实股钢丝绳具有与匹配滑轮(卷筒)沟槽有较大接触面积、不同层钢丝间接触应力小、更加适应多层缠绕和较高破断拉力等优点,缺点在于钢丝截面存在应力集中、钢丝间相互滑动受阻、塑性变形热对钢丝性能有不利影响和股绳捻距倍数匹配不合理会加大摩擦副的磨损;生产技术难度在于对钢丝质量、润滑油脂质量、压实工装模具质量要求高及结构参数设计难度大,另外,要求捻股机有足够动力。压实钢丝绳具有与匹配滑轮(卷筒)沟槽接触面积大、钢丝绳破断拉力高、更加适合多层缠绕和使钢丝绳抗旋转性能得到改善等优点,缺点在于同层股滑动能力降低、组股相邻层钢丝接触紧密性受影响而降低其疲劳性能;生产技术难度在于对钢丝质量、纤维芯质量要求较高和对组绳股合理间隙控制要求比较严格。     

聚丙烯腈基活性中空碳纳米纤维制备及其性能

为制备具有较高孔隙率的聚丙烯腈(PAN)活性中空碳纳米纤维(AHCNF),以自行制备的PAN为原料,经同轴静电纺丝、预氧化、炭化、活化后制备得到AHCNF,借助X射线光电子能谱仪、扫描电子显微镜、比表面积测试仪研究了致孔剂对其形态与孔结构的影响。结果表明:制备的PAN共聚物环化温度较低,环化放热较缓和,有利于预氧化的进行;炭化过程将PAN表面的碳氧单键转化为碳氧双键,而活化过程将碳氧双键进一步转化为酯基;添加致孔剂和未添加致孔剂得到的PAN活性中空碳纳米纤维横截面呈明显的中空结构,纤维壁较为致密;添加致孔剂后,活性中空碳纳米纤维的总比表面积从55.719 m²/g增加到532.639 m²/g,孔容从0.070 cm³/g增加到0.312 cm³/g,介孔平均孔径从3.408 nm增加到4.309 nm,收率从27.14%降低到9.44%。     

粉料堆积密度与堆积深度关系研究及应用

为了提高粉料包装机械这类机械系统的计量精度,从理论上研究了粉料堆积密度与堆积深度的关系,改进了自然堆积密度试验的测量方法,并对压实密度与压实应力经验公式进行优化。采用等质量分层法,建立物料堆积密度与堆积深度关系的数学模型。在修正多种物料自然堆积密度测量数据的基础上,重新拟合了相关公式。以小麦粉为例,建立了小麦粉的堆积深度与堆积密度的关系式。针对螺旋下料工程应用,提出了一种新的计量方法。     

东华大学在碳纳米纤维孔隙率及电导率方面取得新进展

正多孔碳纳米纤维孔隙和电子结构丰富,其不仅具有无机纳米材料的小尺寸效应、优异的耐热性和化学稳定性等,而且易于形成自支撑的薄膜,避免了因使用粘结剂所带来的界面阻力增加和传质效率降低的缺陷,因此在能源、传感、环境等领域发挥了巨大作用。近日,东华大学纺织科技创新中心俞建勇院士及丁彬研究员带领的纳米纤维研究团队开发了一种基于水系静电纺方法和宏观-微观双相分离技术,制备了具有高孔隙率和高电导率的柔性多孔碳纳米纤维膜。在这项研究中,碳前驱体和造孔剂的均匀混合是控制孔隙率和电导率的关键因素。聚乙烯醇(PVA)、聚     

参数化单胞计算三维编织预制件纤维体积含量

在Pro/E中建立了三维编织预制件的内部单胞、表面单胞和棱角单胞的3D实体模型,并对模型进行了参数化设计。当编织工艺参数改变时能自动生成新的单胞模型,单胞纤维体积由Pro/E的模型分析功能直接输出。提出了基于参数化单胞计算预制件纤维体积含量的公式。计算了长方体形预制件的纤维体积含量,并与实测值进行比较,理论计算与实验结果吻合良好。计算了扇环形预制件的纤维体积含量,为复杂外形预制件纤维体积含量的计算提供了新方法。     

经编四轴向玻璃纤维织物的渗透行为和渗透率

为研究经编四轴向玻璃纤维织物的渗透行为同织物结构的关系,采用径向法和单向法对不同铺层数和铺层角度的预制件进行面内渗透率以及单向渗透率的测试,并结合复合材料横截面切片对织物凹凸表面效应对流动的阻碍作用进行分析。采用以体积分数为自变量的经验公式对多层铺层织物的单向渗透率进行预测。实验结果表明：对于低铺层数的预制件,渗透率和纤维体积分数无直接关系,与织物表面在压缩作用下形成的平行于流动方向的流道数量密切相关;对于铺层角度不同的预制件,平行流道数目最多的预制件具有最大的渗透率;经验公式较Kozeny-Carman公式更能准确的预测经编四轴向织物的单向渗透率。     

36吨压路机在填石路基上的有效压实深度研究

随着我国公路建设的迅速发展,公路不断向经济欠发达的山区延伸,施工时路基填筑材料多为路堑开挖产生的石方及征用土场取石方作为填石路基填料。在类似的项目工程上采用重型压实设备不仅可以保证压实效果,而且可以有效提高工作效率。本项目基于国道京漠(樟岭至西林吉)A1标段的填石路基,通过测量36吨重型压路机在不同压实厚度下碾压振动的压力变化,对其在填石路基上有效压实深度进行研究。     

基于GA-BPNN算法的碳纸原纸性能指标建模预测研究

本研究通过改变碳纤维长度、碳纤维占比、分散剂用量等工艺参数,制备不同碳纸原纸,探究不同工艺参数对其抗张强度、孔隙率、透气性、电阻率的影响,采用遗传算法改进反向传播神经网络算法（GA-BPNN算法）,构建了碳纸原纸性能预测模型。结果表明,碳纤维长度与碳纸原纸抗张强度、孔隙率、透气性呈正相关,与电阻率呈负相关;碳纤维占比与碳纸原纸抗张强度呈负相关,与孔隙率、透气性、电阻率呈正相关;分散剂用量与碳纸原纸抗张强度、电阻率呈正相关,与孔隙率、透气性呈负相关;碳纸原纸抗张强度、孔隙率、透气性、电阻率预测模型平均相对误差（MRE）分别为5.49%、5.75%、5.21%、5.54%,预测模型MRE均小于10%,与实验得到的工艺参数对碳纸原纸性能的关系趋势一致。     

热塑性聚氨酯中空纤维膜性能测试与分析

将热塑性聚氨酯/聚乙二醇(TPU/PEG)熔融共混纺丝制得中空纤维膜,并对中空纤维膜的微孔结构及其压力响应性能进行测试与分析。研究结果表明:中空纤维膜壁上存在大量的微孔,其横截面微孔为均质结构,表面孔的孔隙率高,孔径较大;且中空纤维膜的孔径随压力变化而扩张或回缩,导致中空纤维膜的水通量具备压力响应性。     

Dimensional stability of multiaxis 3D-woven carbon preforms

Multiaxis 3D-woven carbon preforms are fabricated using prototyped multiaxis weaving. The fabricated preform has structural instability at thickness. For this reason, the structural parameter and processing parameters were evaluated to make uniform preform and to understand the preform-process relations. The important process parameters are identified and described to enhance the preform and unit cell architecture. Also, preform structural parameters are analyzed in terms of fiber cross-section and fiber tow size, bias angle, and fiber waviness. The useful recommendation is also to make uniform multiaxis 3D-woven preform for composites.     

Generalized geometric modeling of three-dimensional orthogonal woven preforms from spun yarns

Through the thickness mechanical properties of composites have been improved with the advance of 3D woven preforms incorporating through-thickness reinforcement element compared to 3D woven composites from stack of 2D fabrics. In this study, a generalized geometric model considering non-jammed and jammed constructions of 3D orthogonal woven preforms from spun yarns was developed to predict fiber volume fraction (FVF) of structure constituents, preform thickness, preform areal density, and minimum thread spacing (x-, y-, and z-yarn spacing) to achieve jammed construction in terms of weave factor, number of layers, and constituents’ variables (y- and z-yarn sequence, linear densities, packing factor, and fiber volumetric density). Numerical results are presented to demonstrate the generalized model potential as a design tool to achieve broad range of constituents FVF that controls composite performance.     

基于一元二次函数的层联机织预制体细观结构表征

织物预制体结构参数之间的相互关系是高性能复合材料设计需要解决的关键问题。为建立层联机织预制体的细观几何关系,通过显微观察和结构分析提出基于一元二次函数的抛物线凸透镜形纬纱横截面、抛物线形经纱路径等假设,通过研究典型的多层平纹层间联锁结构层联机织预制体,建立预制体全厚度单胞模型,推导其细观结构参数的几何表达,获得纱线横截面变异系数、预制体厚度和纤维体积含量的计算方法,从而实现预制体结构的细观设计。通过实测值和理论预测值的对比,验证了该细观模型的有效性和合理性,并确定了层联机织平纹预制体的纱线填充因子取值区间为0.73~0.87。     

Development of automatic weaving technique of tapered circular tubular woven graft: a preliminary validation

The tapered circular tubular (TCT) woven fabric has been applied successfully as the components in vascular prostheses. The application of tapered tubular woven fabric based on the existing weaving technology requires the densification of a large end to ensure porosity uniformity through the tapered tubule. Although the previously proposed equal-cover-factor (ECF) design technique overcame some disadvantages of the conventional densification methods, such as the protruding portions of the dropped yarns as well as the change of both fabric porosity and tensile strength, the off-loom weft density significantly deviates from the on-loom value. On the basis of ECF design technique and the basic shed geometry, this study rebuilt the relative motion relationship among the front rest, the cloth fell, the back rest, and the take-up length, and modified the weft density on loom to achieve continuous weaving process of TCT fabric as well as the uniform porosity. And then, a computerized weaving procedure based on the rebuilt relationship was developed to automatically weave TCT fabric with different weaves on the customized shuttle loom. As a result, the uniform porosity of those samples validated the proposed weaving techniques.     

Non-destructive infrared inspection of dry multilayer carbon fibre preforms

Thermography was used for performing non-destructive inspection of dry carbon fibre textile preforms used in manufacturing carbon fibre polymer-matrix composites (CF-PMCs). The aim was to probe the feasibility of identifying defects in thick carbon fibres preforms made from multiple layers of industrial textile reinforcements, before composites are manufactured. Inspecting dry preforms will not replace the inspection of final CF-PMC parts but it can avoid costly and wasteful manufacturing of CF-PMC parts from defective preforms, as the defects sought in this paper cannot be observed by visual inspection. The preforms tested were made of two or four layers of industrial carbon fibre textile reinforcements. They featured defects of different widths, types and orientations. Results show that thermography can identify defects in preforms successfully, and that detection is influenced by the orthotropic thermal conductivity of carbon fibres, by yarn and fabric architecture, by the relative orientations of defects and yarns, and by the number of layers.     

Structural Analysis of 3-D Braided Preforms for Composites Part II: The Two-step Preforms

In Part I of this series of papers, structures and geometries of the four-step preforms were studied and analysed. In this part, an account is given of similar work conducted on the two-step preforms. Theoretical models for both regular and tubular two-step preforms are established with a few assumptions. Structural geometries of the preforms are analysed and discussed according to the theoretical models developed. Mathematical relations between the structural parameters, such as the fibre orientation, yarn-volume fraction, and preform contour sizes, as well as their dependence on operating conditions, are derived. It is found that the preform structures are determined by the constituent yarns, the braiding arrangements, and the process operating conditions. The extreme values of the parameters in the jamming conditions are also discussed. To verify the validity of the analytical models, experimental investigations were also carried out. The experimental results strongly support the theoretical predictions.     

Hybrid Yarns and Textile Preforming for Thermoplastic Composites

In the recent years, the use of textile structures made from high performance fibers is finding increasing importance in composites applications. In textile process, there is direct control over fiber placements and ease of handling of fibers. Besides economical advantages, textile technologies also provide homogenous distribution of matrix and reinforcing fiber. Thus textile performs are considered to be the structural backbone of composite structures. Textile technology is of particular importance in the context of improving certain properties of composites like inter-laminar shear and damage tolerance apart from reducing the cost of manufacturing. Textile industry has the necessary technology to weave high performance multifilament fibers such as glass, aramid and carbon, which have high tensile strength, modulus, and resistance to chemicals and heat into various types of preforms. Depending upon textile preforming method the range of fiber orientation and fiber volume fraction of preform will vary, subsequently affecting matrix infiltration and consolidation. As a route to mass production of textile composites, the production speed, material handling, and material design flexibility are major factors responsible for selection of textile reinforcement production. This opens a new field of technical applications with a new type of semifinished material produced by textile industry. Various types of hybrid yarns for thermoplastic composites and textile preforming methods have been discussed in detail in this issue. Information on manufacturing methods, structural details and properties of different hybrid yarns are presented and critically analyzed. Characterization methods used for these hybrid yarns have been discussed along with the influence of different processing parameters on the properties being characterized. The developments in all areas of textile preforming including weaving, knitting, braiding, stitching and nonwovens techniques are presented and discussed along with the characterization techniques for these preforms. The techniques used for manufacturing composites using hybrid yarns and textile preforms are discussed along with the details on compaction behavior of these structures during consolidation process. The structure of hybrid yarns and the textile preforms have direct influence on the properties of the composite made from them. The reported literature in this aspect is discussed in detail. In the end, the potential application areas and their trends for thermoplastic composites are discussed and analyzed.     

2.5维预制体结构参数的设计方法

由于缺少三维织物的设计理论,使确定2.5维预制体结构参数的确定成为三维纺织复合材料预制体设计人员面临的难题。为此,给出了相似2.5维预制体的定义,按纤维体积含量保持不变推导出相似2.5维预制体结构参数的关系式,以便根据原织物的结构参数计算出新织物的结构参数,特别是可以准确预测新织物的厚度。同时用3个实例验证了该关系式。研究结果表明,所得到的相似2.5维预制体结构参数关系式具有实用价值。     

变径变纬密管状织物的控制模型及其算法实现

为满足管状织物变径变纬密的织造要求和自动化生产需要,建立了其控制模型,分析并实现了控制算法。首先针对织物的变径特性,设计了一种可无级变径机构,并据此推导出了旋转角度与时间的变化关系。然后分析了纬密变化方式,建立了牵引速度与时间的关系函数。基于广义回归神经网络来逼近织物的非线性形状曲线,采用Matlab进行仿真分析,验证了模型和算法的可行性,通过编程实现了控制参数的自动计算和输出。该控制模型和算法具有运算快、结构简单、精度高等优点,能很好满足碳纤维复合材料预成型体织造等领域的要求。     

Establishment of acoustic characteristic model of activated carbon fiber felts

Abstract

In order to analyze two basic characteristic acoustic parameters of activated carbon fiber felts: propagation constant and characteristic impedance, the theoretical model of characteristic impedance concerning the two parameters was established by means of motion and continuity equations based on the propagation theory of acoustic waves in activated carbon fiber materials. On the basis of acoustic theories proposed by Zwikker and Kosten, taking into account of the vibrating influence occurring among fibers and modifying the effective air density and the effective bulk modulus, theoretical model of characteristic acoustic parameters of activated carbon fiber materials was established. Surface acoustic impedance was tested with an impedance tube when activated carbon fiber materials were subjected to an acoustic range of 250–2500?Hz frequencies, then propagation constant and characteristic impedance of activated carbon fiber materials were defined by the method of double thickness. Statistics of two acoustic characteristic parameters in theory and trial were compared and contrasted, which showed that the theoretical model had its feasibility and could provide reference for developing and designing the activated carbon fiber materials with sound absorbing properties.