Jan Hausding

Application of stitch-bonded multi‐plies made by using the extended warp knitting process: reinforcements with symmetrical layer arrangement for concrete

With the development of the extended stitch‐bonding process, an important modification of the production process for stitch‐bonded fabrics was realized. Through the introduction of a lateral shift of the needle bar, the stitch‐bonding process is essentially being changed compared with the working method used before. This has made possible the manufacturing of optimally adjusted textile semi‐finished products for numerous applications in the field of composite material. One such application – the usage of stitch‐bonded fabrics as a textile reinforcement for concrete – is analyzed in this article. It was observed that promising possibilities for the use of the extended stitch‐bonding process result from overcoming the known restrictions during the production with conventional stitch‐bonding machines. A markedly improved quality of textile reinforcement is achieved through the new binding patterns and the free arrangement of the layers. The reinforcement shows a verifiable better bonding behavior than the conventional method. Therefore, it is guaranteed that there is no spalling on the concrete surface at service load, which is an important prerequisite for the practical use of textile‐reinforced concrete.

Improvements in the warp-knitting process and new patterning techniques for stitch-bonded textiles

Stitch-bonding technology offers a highly effective process of manufacturing reinforcement textiles for composite materials. This innovative technology is based on joining layers of threads and fabric with a knitting thread to create a layered structure, a multi-ply. Thus far, the knitting thread has restricted the positioning of individual layers in the fabric. It has been impossible, until now, to position warp layers symmetrically in one step as the outer layers of the fabric. It has been accomplished as a multi-step process, which in turn compromises productivity and quality. With the needle shift technique as an extension of the stitch-bonding process, all previous restrictions on multi-plies are eliminated. Both outer warp layers can be secured in one procedure by incorporating a shift of the needle bar during the stitching process, creating endless possibilities for the arrangement and patterns in the stitch-bonding process. For the numerical description and diagramming of the new patterning techniques, we have reworked and expanded previous illustration models.

Vorimprägnierte textile Halbzeuge (Prepregs)

Vorimpragnierte textile Halbzeuge, sogenannte Prepregs, sind ein wichtiges Ausgangsmaterial fur die Herstellung von duroplastischen und thermoplastischen Verbundwerkstoffen. Es handelt sich hierbei um vorgefertigte, meist ebene, flachige Halbzeuge, die eine Verstarkungsstruktur aus endlichen bzw. endlosen Fasern aufweisen, die bereits mit der fur die Bauteilfertigung benotigten duro- bzw. thermoplastischen Matrix kombiniert ist. Als Ausgangsprodukt konnen sowohl Kurzfasern oder Endlosfilamentgarne als auch textile Flachengebilde wie Gewebe und Multiaxial-Kettengewirke zum Einsatz kommen. Grundprinzip der Verwendung dieser speziellen Form der textilen Halbzeuge ist die Trennung des Trankungsvorgangs bei der Verbundwerkstoffherstellung vom eigentlichen Herstellen der Bauteilform.

Warp-Knitted Semi-finished Products and Warp-Knitting Technologies

The production of warp-knitted semi-finished products is based on classical warp knitting processes, in which warp yarns of one or several groups are simultaneously and parallelly transformed into loops. This basic principle is used to connect yarn layers and/or other fabrics, such as nonwovens or pre-impregnated fiber layers by means of these loops. The main advantages of warp-knitted semi-finished products are their highly productive manufacture, the adjustability of the angles at which the individual yarn layers can be arranged respective to one another, and the versatile combinations of layer structuring and layer arrangement. Typical products are made from glass or carbon filament yarns and find applications in rotors in wind energy plants, in boat and vehicle construction, sports equipment, and construction.

Stress-strain behavior of carbon filament yarns under high strain rates

Fiber-reinforced composites used in numerous technical applications have to meet the ever increasing safety requirements. Resistance to extreme stress under high velocity impact loads assumes even greater significance. Previous studies on the behavior of fiber-reinforced composites under impact loads provide little insight about the properties of filament yarns, a basis for many composite applications. Hence this paper focuses on the development of a suitable test method for performing high speed tensile tests on all filament yarn types, and the acquisition and analysis of the test results. This will enable the derivation of material models for their usage in the field of composites applications. Initially, the widely used carbon fiber filament yarns have been tested. The conclusive test results with a reduced yarn clamp mass and high stiffness of the test apparatus indicate that tensile strength and modulus of elasticity of carbon filament yarns increase with higher strain rates.

Pre-impregnated Textile Semi-finished Products (Prepregs)

Pre-impregnated semi-finished textile products (prepregs), are an important base material for the manufacture of thermoset and thermoplastic composite materials. They consist of a usually flat and planar textile reinforcement structure and are combined with thermoset or thermoplastic matrices required for the production of the final component. Both short fibers or continuous filaments and textile fabrics, such as woven fabrics or multiaxial warp-knitted fabrics, can be used as base material. The basic principle of using this special textile semi-finished product is to separate the step of impregnating the reinforcement structure with the matrix during composite material production from the final step of producing the component form.

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.

Gewirkte Halbzeuge und Wirktechniken

Gewirkte Halbzeuge fur Leichtbauanwendungen basieren in ihrer Herstellung auf dem klassischen Kettenwirkverfahren, bei dem die Faden eines oder mehrerer Wirkfadensysteme gleichzeitig und parallel zu Maschen umgeformt werden. Diese Grundlage wird genutzt, um Fadenlagen und/oder andere Flachengebilde wie beispielsweise Vliesstoffe oder vorimpragnierte Faserlagen mittels Maschen zu verbinden. Die wesentlichen Vorteile der gewirkten Halbzeuge liegen in ihrer hochproduktiven Herstellung, der Einstellbarkeit der Winkel, unter denen die einzelnen Fadenlagen zueinander angeordnet werden konnen, und den vielfaltigen Kombinationsm oglichkeiten beim Lagenaufbau und der Lagenanordnung. Typische Produkte bestehen aus Glas- oder Carbonfilamentgarn und kommen beispielsweise in den Rotoren von Windenergieanlagen, im Schiff- und Automobilbau, bei Sportartikeln sowie im Bauwesen zum Einsatz.