Application of stitch-bonded multi-plies made by using the extended warp-knitting process: influence of pattern and knitting yarn tension on the geometry of the textile fabric

This paper is part of a series dealing with the application of the extended warp‐knitting process for the production of textile fabrics for composites. Further studies will examine the properties of thermoplastic composites and textile reinforced concrete made of stitch‐bonded multi‐plies. It is known that knitting yarn pattern and knitting yarn tension during fabric production affect the properties of stitch‐bonded multi‐plies and composites made thereof. This paper describes the effects of those two parameters on the fabric as produced with the extended stitch‐bonding process. It can be shown in which way pattern and yarn tension can be chosen to reduce compression of the warp threads in the fabric as well as to avoid unwanted displacement of threads caused by handling.     

扁平经纱在织机上无捻加工的解决方案

这个项目所取得的结果展示了如何采用扁平经纱织造致密面料的方法,这种方法既可实现高产量和高质量,又可改善材料的各种特性.因此,这种织物的应用领域可进一步拓展.这些改造采用的都是市场上有售的部件,无需特别的手段.改造之后,经轴和织造区之间的自由纱段最小化、经纱张力更均匀.经轴和织造区之间根据扁平纱的几何形状设置导纱器,并应用了特殊的综丝,明显减少或避免了经纱在整个经纱方向出现捻度.     

间隔机织物的卷绕、切割和存储系统

描述了间隔机织物的新型卷绕、切割和存储系统的设计.这种系统的关键问题是间隔织物包含织物结构如间隔,即所谓的交联.为了防止玻璃纤维-聚丙烯混纺纱线中玻璃纤维被破坏,必须避免交联塌陷.这种织物被用作热塑性纺织增强复合材料模件的预型件.     

The effect of the discharge rate on the electrochemical properties of AB3-type hydrogen storage alloy as anode in nickel–metal hydride batteries

In this work, the ternary CeY₂Ni₉ alloy was prepared and served as anode materials in the Ni–MH battery system. The effect of the discharge rate on the electrochemical proprieties of CeY₂Ni₉, such as activation capability, polarization, discharge capacities, hydrogen atomic diffusion capability and redox parameters, were also investigated systematically during activation and long cycling. Charge–discharge measurement showed that this alloy is characterized by fast activation and requires only three cycles to be activated regardless of the discharge rate, the maximum discharge capacity was obtained for the medium discharge rate (C/10). An important correlation was observed between the evolution of the electrochemical parameters and that of the kinetic parameters, such as the hydrogen atomic diffusion capability and the exchange current density.The total substitution of La by Ce in LaY₂Ni₉ parent alloy enhanced its activation, polarization and stability despite the decrease of its discharge capacities, especially at high rates.     

Improved interface conditions for 2D domain decomposition with corners: a theoretical determination

This article deals with a local improvement of domain decomposition methods for 2-dimensional elliptic problems for which either the geometry or the domain decomposition presents conical singularities. The problem amounts to determining the coefficients of interface boundary conditions so that the domain decomposition algorithm has rapid convergence. Specific problems occur in the presence of conical singularities. Starting from the method used for regular interfaces, we derive a local improvement by matching the singularities, that is, the initial terms of the asymptotic expansion arond the corner, provided by Kondratiev theory. This theoretical approach leads to the explicit computation of coefficients in the interface boundary conditions, which have been tested numerically. This final numerical step is presented in a companion article [4]. This article focuses on the method used to compute these coefficients and provides detailed examples for a model problem. C. Chniti was supported by the Tunisian Government and the école Polytechnique and visited IRMAR-Rennesl as a post-doctoral assistant.     

Multi-criteria fuzzy algorithm for energy management of a domestic photovoltaic panel

This paper presents a fuzzy algorithm which makes decision so as to connect domestic apparatus on either the electrical grid or a photovoltaic panel (PVP). The decision is made in real time with respect to multi-energy save criteria and upon the PVP maximum available power and apparatus states. The algorithm is validated on a 1 kW peak (kWp) PVP and domicile apparatus of different powers installed at the Energy and Thermal Research Centre (CRTEn) in the north of Tunisia. Criteria are verified on the system behaviour during days covering the different seasons of the year. The power audit, established using measures, confirms that the energy save during daylight reaches 90% of the PVP available energy.     

High performance thermoplastic composite from flat knitted multi-layer textile preform using hybrid yarn

Modern flat knitting machines using high performance yarns are able to knit fabrics including the reinforcement yarns arranged differently into knit structures. Due to their improved mechanical properties, composites made from multi-layer knit fabrics show great potential in lightweight applications. This paper reports on the development of flat knitted multi-layer textile preforms for high performance thermoplastic composites using hybrid yarns made of glass (GF) and polypropylene (PP) filaments. Such textile preforms with different reinforcements were used to consolidate into 2D thermoplastic composites. Moreover, the mechanical properties of these composites were studied. The mechanical properties of 2D composites were found to be greatly affected by different arrangements of reinforcement yarns. The integration of reinforcement yarns as biaxial inlays (warp and weft yarns) is found to be the best solution for knitting, whereas tuck stitch shaped and unidirectional arranged reinforcements offer also promising application possibilities.     

Numerical simulation of yarn tensile force for dynamic yarn supply systems of textile machines

During the production of textiles, quality problems arise with increasing machine speed due to high dynamic stresses in the yarn supply system. Based on the large number of influencing factors in this process, an analysis of the cause of the errors is only possible with high experimental effort or, due to sporadic errors, not at all. The yarn tensile force is the critical parameter and its simulation in the entire yarn supply process opens a wide range of opportunities for analysis and optimization. First, a mathematical model based on the invariance of the mass of a yarn piece and the non‐linear elongation behavior of the yarn is constructed and the influencing factors of the essential elements of yarn supply cone, feeder, and eyelet on the yarn tensile force are described. The simulation is carried out using the software package Matlab/Simulink in which the created sub‐elements can be combined optionally and can be duplicated, which allows a simple and quick adjustment of any yarn supply system in textile machinery. On the basis of comparative measurements, it is shown that the simulation predicts the yarn tensile force, for example extreme situations in the yarn supply process, such as the insertion of the yarn into knitting machines, in a very good approximation to reality. The simulation is transferable to other yarn supply systems of the textile technology by extending the yarn supply sub‐element database.