Study of the bending induced gap in fiber preforming of woven fiber mats

In the preforming of an RTM process, the configuration of the fiber mats should deform in order to conform to the mold surface. Several deformation modes may occur during a forming process. It can be characterized by factors such as the local surface curvature of the mold, the loading condition and the type of reinforcement. It has been suggested that fiber deformation modes may include fiber stretching, fiber straightening, shear slip, and buckling. As the fiber is bent at the bending edge in the preforming, a small gap may emerge from the outer side owing to the movement of fiber bundles. Studies on the relation between the channel gap formation and the bending angle together with the effect of the fiber content were investigated in order to establish a useful guide for the design of mold with bending edges. A model with a slip factor was proposed to estimate the bent fiber thickness.     

Modeling of pore structure evolution within the fiber bundle during chemical vapor infiltration process

Taking into account the gas diffusion parallel and perpendicular to the bundle axis, a two-dimensional model combining the non-conservative level set method and the steady-state diffusion equation is presented for evolving pore structure in the bundle cross-section. Parametric studies have been conducted to determine the sensitivity of residual porosity within the bundle to the structure parameters. Sheldon and Besmann's approach is revised and more realistic approximated expressions depicting the accessible and total porosity evolution inside the bundle are given. Such expression can serve as useful estimate of pore structure evolution for modeling the CVI process.     

Investigation of the compaction behavior of carbon fiber NCF for continuous preforming processes

This paper describes the experimental investigation of the compaction behavior of dry single‐ply and multi‐ply fabric stacks (preforms). Utilizing four biaxial (two 0°/90° and two ±45°) and one triaxial (0°±45°) carbon fiber NCF, differing in weight (300 g/m², 600 g/m²) and type of stitching (tricot, pillar, hybrid), the influence of compaction speed, pre‐compaction cycles, number of layers, and stacking sequence on compaction force was examined. In contrast to other studies, the area of interest is limited to 40–50% fiber volume content (FVC), which is based on current continuous preforming conditions. The results showed that higher testing speeds result in increased compaction forces. Pre‐compaction cycles (up to 8) significantly reduce (up to 69%) the required compaction forces of preforms for continuous preforming. Furthermore, at an equal total superficial density (1800 g/m²), 6‐ply preforms (300 g/m² each ply) require 75–88% higher compaction forces than 3‐ply preforms (600 g/m² each ply). This relation remains constant with decreasing or increasing total superficial density (ply number). Also the stacking sequence of 6‐ply preforms (300 g/m² each ply) remarkably influences the compaction force, whereby the stitching seam pattern and their alignment (superposition) to each other were the main influencing factors. POLYM. COMPOS., 38:2609–2625, 2017. © 2015 Society of Plastics Engineers     

Modeling of the impregnation process during resin transfer molding

A model has developed for simulating isothermal mold filling during resin transfer molding (RTM) of polymeric composites. The model takes into account the anisotropic nature of the fibrous reinforcement and change in viscosity of the polymer resin as a result of chemical reaction. The flow of impregnating resin through the fibrous network is described in terms of Darcy's law. The differential equations in the model are solved numerically using the finite element technique. The Galerkin finite element method is used for obtaining the pressure distribution. A characteristics based method is used to solve the non-linear hyperbolic mass balance equation. The finite element formulation facilitates computations involving the motion of the polymer resin front characterized by a free surface flow phenomenon.     

Modeling the deformation of thermoformable random fiber reinforcements during preform manufacture

Liquid molding processes have been identified by the automotive and aerospace industries as having potential for structural and semistructural applications. Of the several obstacles to their more widespread use, the major drawback is the lack of an automated and reliable technology for producing reinforcement preforms. Current preform technology is usually based on the forming of continuous fiber mats or fabrics between matched molds. This can result in defects within the fiber structure including wrinkling, thinning, and, in extreme cases, tearing. To understand and eliminate these defects, it is necessary to develop a simulation of the preforming process. This paper is aimed at developing a mathematical model of the deformation of thermoformable continuous filament random mat. The analysis presented is based on plasticity theory, suitably modified to describe the behavior of fiber reinforcements. This is demonstrated for the stretch-forming of reinforcement using arbitrary axisymmetric punch and die profiles. Experimental work is included to demonstrate the effect of varying a range of process parameters, including rate of forming, reinforcement temperature, and stack thickness. The Validity of the model is demonstrated for a number of punch geometries.     

腈纶生产中硫酸钠结晶工艺的调控

根据结晶原理及工业结晶的控制要求,分析了硫氰酸钠( NaSCN)二步法腈纶生产中硫酸钠( Na2 SO4)结晶工序的失控原因,并提出了调控措施.结果表明:生产中结晶工序沉降槽底部晶浆过量去除破坏了Na2 SO4的结晶平衡,导致Na2 SO4不能有效去除;添加固体无水Na2 SO4,培养晶种,保持沉降槽底部Na2sO4质...     

涤纶短纤棉纺脱落物研究

综合文献资料及实验工作对涤纶短纤维棉纺加工中脱落物的发生及其危害进行论述,对重点发生部位如并条脱落物及细纱白粉的成分进行了分析,对其成因和解决措施进行了讨论。     

Modeling and process simulation of hollow fiber membrane reactor systems for propane dehydrogenation

We report a detailed modeling analysis of membrane reactor systems for propane dehydrogenation (PDH), by integrating a two‐dimensional (2‐D) nonisothermal model of a packed bed membrane reactor (PBMR) with ASPEN process simulations for the overall PDH plant including downstream separations processes. PBMRs based on ceramic hollow fiber membranes—with catalyst placement on the shell side—are found to be a viable route, whereas conventional tubular membranes are prohibitively expensive. The overall impact of the PBMR on the PDH plant (e.g., required dimensions, catalyst amount, overall energy use in reaction and downstream separation) is determined. Large savings in overall energy use and catalyst amounts can be achieved with an appropriate configuration of PBMR stages and optimal sweep/feed ratio. Overall, this work determines a viable design of a membrane reactor‐based PDH plant and shows the potential for miniaturized hollow‐fiber membrane reactors to achieve substantial savings. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4519–4531, 2017     

Modeling and control of CO2 separation process with hollow fiber membrane modules

A multi-stage model is developed for CO₂ separation by hollow-fiber membrane. The model permits rapid solution of the governing differential mass and pressure distribution in hollow-fiber gas separation modules using a computational scheme that does not rely on commercial software and conventional numerical methods such as shooting techniques. For 1-stage, 2-stage and 3-stage configurations the changes of required separation areas according to stage cuts are computed. A simple model predictive control technique is employed to provide optimal operation conditions based on the proposed model. Values of stage cuts can easily be identified for various desired mole fractions and recovery rates. From the results of numerical simulations, we can see that the proposed model can be effectively used in the control of gas separation process by hollow-fiber membrane modules.     

凝胶染色过程中腈纶沿纺程的结构性能变化的研究

采用湿法纺丝工艺制备腈纶(即聚丙烯腈(PAN)纤维),研究了凝胶染色过程中PAN纤维在不同工序段的结构和物理性能.结果表明:沿着纺程,PAN纤维的直径逐渐减小,纤维的玻璃化转变温度和结晶度逐渐提高;在水洗后PAN纤维表面有明显的微观结构缺陷、且无定形区占比高;经过热拉伸和干燥致密化之后,纤维致密化,结晶度大大增加,凝胶...     

纤维增强塑料注射充模过程中纤维对模具的冲蚀磨损模拟

针对塑料模具在玻璃纤维冲蚀下造成的表面磨损问题,运用有限元软件ANSYS/LS-DYNA建立了模具材料多颗粒冲蚀有限元模型,进行三维显式冲击动力学计算,研究纤维在不同冲蚀速度和冲蚀角度下对模具的冲蚀规律,分析冲蚀机理。结果表明,玻璃纤维对模具的冲蚀过程以微切削为主;玻璃纤维对模具的冲蚀磨损率随着冲蚀速度的增加而增加,随着冲蚀角度的增加而呈现先增加后减小的趋势。     

Influence of fiber slippage coefficient distributions on the geometry and performance of composite pressure vessels

In this article, the effects of several slippage coefficient distributions on the geometry, fiber trajectories, and the structural efficiency of non‐geodesic domes are evaluated for composite pressure vessels. Several functions, which ensure C¹ continuity of the winding trajectories, are respectively used to describe the slippage coefficient distributions along the fiber paths. With the aid of the fiber slippage law and the optimality condition of equal shell strains, the differential equations that govern the non‐geodesics–based dome shapes and related fiber trajectories are formulated. The meridian profiles and winding angle developments of the carbon–epoxy domes are obtained based on the given slippage coefficient distributions; their structural performances are then determined and compared with each other. The results conclude that the non‐geodesic dome designed using the maximum constant slippage coefficient exhibits better performance than those using other slippage coefficient distributions; this is mainly triggered by maximum utilization of the longitudinal strength of the laminate. It is also revealed that the structural efficiency of domed pressure vessels can be improved using non‐geodesics that provide higher degrees of freedom in the design of filament wound structures. POLYM. COMPOS., 315–321, 2016. © 2014 Society of Plastics Engineers     

浸浆制备过程中陶瓷膜厚度控制及其模型化

在毛细过滤和薄膜形成机理的基础上,采用化学工程实验与模型化方法,对浸浆成型法制备多孔α-Al₂O₃陶瓷膜过程中,膜厚与影响因素之间的关系进行了理论分析和实验研究. 结果表明：膜厚受到制膜液粉体浓度、制膜液黏度、粉体粒径大小、载体纯水渗透性能以及涂膜过程中浸浆时间和载体提升速度等因素的影响. 通过膜厚与影响因素间的数学模拟,建立了膜厚控制模型. 并以ZrO₂粉体为原料,采用相同方法制备ZrO₂陶瓷膜对模型进行了验证,模拟计算值与实测值基本一致.     

盐水液滴降压蒸发析盐过程数值模拟

盐水溶液的降压蒸发广泛应用于海水淡化和工业制盐等领域,因此研究盐水在降压过程中的蒸发特性具有重要意义,有助于解决我国水资源缺乏问题。本文通过数值模拟的方法研究了降压环境下盐水液滴蒸发析盐过程,获得了盐析质量和液滴温度随时间的变化。采用的工质为饱和盐水,液滴的初始温度分别为20℃、15℃、10℃;环境压力从0.1MPa降至2000～10000Pa。通过与实验数据相对比,验证了本文模型的有效性。通过该数学模型,分析了影响析盐率和液滴温度变化的主要因素。结果表明:液滴直径越大,在蒸发过程中其析盐率越高,但温度变化越慢;压降速率越快,液滴蒸发速率越快,析盐率越大,温度变化也越快;液滴初始温度越高,蒸发速率越快,液滴表面析盐率越高,但不同初始温度的盐水液滴,在蒸发过程中其最终温度趋于一致。     

湿法腈纶质量控制的影响因素

浅析了影响腈纶生产质量稳定的控制因素,主要包括原液质量、纤维成形工艺等。正常生产中,控制聚丙烯腈(PAN)浆化液质量分数为26%,PAN溶液质量分数为13.5%,凝固浴硫氰酸钠质量分数为8%～12%,以及严格控制其他工艺条件,有利于生产稳定。     

ESCA characterization of polyacrylonitrile-based carbon fiber precursors during its stabilization process

Oxidation process control plays a key role in influencing the development of carbon fiber properties. The characterization of oxidized fibers is difficult because of their poor solubility in organic solvents and strong absorbance. X-ray photoelectron spectroscopy (XPS) has been used in the surface characterization of carbon fiber precursors during the oxidation or stabilization process. The changes in surface elemental composition and functionalities of carbon and oxygen have been identified. Quantitative changes have been noticed in surface functional groups as the oxidation process proceeds. © 1994 John Wiley & Sons, Inc.     

Modeling the delamination process during shear premixing of nanoclay/thermoset polymer nanocomposites

As shear premixing is an important process for the dispersion of nanoclays in polymeric resins, this article studies the effect of temperature, duration, speed of premixing, and also the interlamellar spacing of clay platelets on the dispersion of organoclay in epoxy by using a high speed premixing technique which can generate high shear. The quality of dispersion and intercalation/exfoliation of organoclay in epoxy after premixing (before adding hardener) was analyzed by means of X‐ray diffraction (XRD) and rheological measurement. The dispersion and intercalation/exfoliation of organoclay in the epoxy nanocomposites (ENCs) after curing were characterized by TEM. The results illustrate that the intercalation/exfoliation of organoclay in epoxy at the premixing step is very much depending on the premixing parameters. This article also presents a model which takes into account the parameters such as the interlamellar spacing of clay platelets, the viscosity of the epoxy‐clay mixtures, and the velocity of the mixer to explain their effect on the dispersion of clay in epoxy resin. The study focuses on the flow of epoxy clay in the high shear mixer to describe a model for predicting the processing conditions necessary for achieving delamination of the clay layers. Experimental results on the dispersion of clay are also provided to validate the model. The model provides a guide for the premixing parameters necessary to separate the clay layers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011