Sybille Krzywinski

Links between design, pattern development and fabric behaviours for clothes and technical textiles

Shows the necessity of developing powerful 3D CAD‐systems for the textile and clothing industry. The connection between 2D and 3D CAD‐systems enables the user to prepare a collection more quickly and accurately. Applications could be the drape behaviour of the fabric, the deformational behaviour of fabrics when covering defined surfaces and also technical textiles.

Development of a process chain for the realization of multilayer weft knitted fabrics showing complex 2D/3D geometries for composite applications:

The use of thermoplastic components with a complex three-dimensional (3D) shape, manufactured efficiently with thermo-presses, has been increased steadily. Flat knitting technology using reinforcing hybrid yarns in the horizontal and vertical direction is especially suited for producing near-net-shape or fully-fashion multilayer weft knitted fabrics – MLGs (abbreviated from the German word Mehrlagengestrick, meaning multilayer weft knitted fabric). The other advantages of manufacturing such MLGs, using flat knitting technology, are reduced waste and desired reinforcing fibre alignment to obtain improved mechanical properties for high-performance applications. Before knitting 3D shaped MLGs, it is necessary to transfer the 3D component geometry into a suitable two-dimensional (2D) pattern cut by implementing parting lines. The use of computer-aided design (CAD) programs enables an effective development of complex components preforms. The generated 2D pattern cuts are analyzed with the consideration of net-shape preforming processes on V-bed flat knitting machines. The development of a segmented take-down system for effective production of 3D MLG preforms is also discussed.

Simulating the Drape Behavior of Fabrics1

This paper is the result of an interdisciplinary research project at the Institute of Textile and Clothing Technology and the Institute of Solid Mechanics. The aim of this project is to describe and simulate the deformation behavior of flexural fabrics ( espe cially woven fabrics). For the simulation model, the shell theory is taken as a basis. Simulating drape behavior presents a geometrically nonlinear field problem with con siderable displacements. The deformation theory and its application for fabrics is used as a practicable approach for simulating drape. Investigations of the description of the materials behavior and its properties are a further necessary focus.

Seams and Bending in Cloth Simulation

Accurate modeling of bending behavior is one of the most important tasks in the field of cloth simulation. Bending stiffness is probably the most significant material parameter describing a given textile. Much work has been done in recent years to allow a fast and authentic reproduction of the effect of bending in cloth simulation systems. However, these approaches usually treat the textiles as consisting of a single, homogeneous material. The effects of seams, interlining and multilayer materials have not been considered so far. Recent work showed that the bending stiffness of a textile is greatly influenced by the presence of seams and that a good cloth simulation system needs to consider these effects. In this work we show how accurate modeling of bending and seams can be achieved in a state-of-the-art cloth simulation system. Our system can make use of measured bending stiffness data, but also allows intuitive user control, if desired. We verify our approach using virtual draping tests and garments in the simulation and comparing the results to their real-world counterparts. Furthermore, we provide heuristics derived from measurements that can be used to approximate the influence of several common types of seams.

Simulation of drape behaviour of fabrics

In this paper a model is presented for the calculation by approximation of a drape test standardized in the textile industry. As woven fabric is of low thickness compared with the other dimensions, the fabric can be considered to be a two‐dimensional continuum. For the simulation model, the shell theory is taken as a basis. Simulating the drape behaviour presents a geometrically non‐linear field problem with considerable displacements.

Decoupling the bending behavior and the membrane properties of finite shell elements for a correct description of the mechanical behavior of textiles with a laminate formulation

Drape simulation of textiles is a field of research, which is known in the clothing sector for a long time. The ongoing development of high-performance composites made of textile reinforcements and matrix materials focus the interests on a serial production in many industrial sectors, such as aviation and automotive industries. Challenges occur mainly in the serial production technologies and in supplying concepts for the preform architecture and shape. Research aims on the acceleration of preform manufacturing and the reduction of expensive pretests. Numerical simulation models can help to improve the composite development chain with structure and process simulation. A special challenge in drape modeling is the bending behavior of textiles. This study introduces a novel approach for modeling single textile layers as laminates to gain a correct mechanical behavior, where all deformation mechanisms are uncoupled. The implementation in the finite element software LS-DYNA® is described. An algorithm is introduced which provides the membrane stiffness for each layer of a laminate to fit the measured cantilever bending stiffness of textiles in every bending direction and bending side. The calculated parameters for the laminate formulation result in the requested bending stiffness for the textile layer. The cantilever bending stiffness can be used directly for dimensioning the model.

Garment prototyping based on scalable virtual female bodies

Purpose – The aim of the research is the development of 3D virtual models of lower female bodies from scanned data of different body types for computer‐aided 3D product development of loose‐fitting garments.Design/methodology/approach – In order to develop reproducible construction of fashionable/functional outerwear (e.g. ladies’ trousers) on the basis of generated scalable 3D virtual female models, 3D‐CAD methods have to be developed. In doing so, the variable parameters are predefined and the block pattern of a trouser design can be modified by changing the parameters for the variety of trouser models. Two‐dimensional (2D) pattern pieces are then automatically generated and modified if necessary. According to morphological changes, the whole process proceeds automatically up to 2D patterns and thus corresponds to a grading in 3D.Findings – The generated 3D virtual model and trouser design corresponding to a basic design or block pattern can be offered to the garment industry. The task of the designer o...

Analysis and finite element simulation of the draping process of multilayer knit structures and the effects of a localized fixation

Fiber reinforced composites (FRC) are an interesting alternative for numerous applications due to their lightweight character. However, there are currently several challenges for a serial production. The manufacturing process still requires a high percentage of manual labor which greatly restricts the reproducibility. Additionally, high-quality standards necessary for many applications cannot be met due to the low displacement resistance of the textiles. Structural fixation could greatly improve the displacement resistance and therefore the handling of the material layers. This paper reports on a model used for draping simulations of nonfixed and fixed multilayer knits using the commercial finite element software LS-DYNA®. The aim of this model is to improve the development process of FRCs. With a standardized specification, the basic macromechanical properties can be modeled with finite shell elements. A material model is introduced that accounts to the characteristic mechanisms of the deformation of biaxial fibrous structures. A fixation of the fabrics is achieved by melting the thermoplastic hybrid yarns embedded in the textile structure with infrared radiation. This process improves the handling of the textiles. It is of great benefit when such a structural fixation is applied locally. The process of choosing local fixation zones is described in this paper and the applicability of this process is illustrated.

Modellierung und Simulation

Dieses Kapitel beschreibt grundlegende Aspekte und Methoden zur Modellierung und Simulation textiler Verstarkungsstrukturen und Faserkunststoffverbunde (FKV). Auf Grund der anisotropen Werkstoffeigenschaften ist die Simulation des Deformationsverhaltens der textilen Verstarkungsstrukturen sehr komplex. Unterschiedliche Ansatze werden vorgestellt und Simulationsmoglichkeiten auf der Basis kinematischer Modelle ausfuhrlich diskutiert. Der Schwerpunkt dieser Ausfuhrungen zielt auf die Unterstutzung der Konstrukteure bei der Preformauslegung fur komplexe FKV-Bauteile. Um den Verbundwerkstoff entsprechend der Belastung des Bauteils mittels Finite Element Modellen (FEM) richtig zu konfigurieren, sind derzeit umfangreiche experimentelle Untersuchungen zur Quantifizierung der Verbundeigenschaften erforderlich. Der Beitrag widmet sich deshalb daruber hinaus Modellierungs- und Simulationsverfahren auf Basis mehrskaliger Betrachtungsweisen zur Ermittlung mechanischer Materialkennwerte.

Weft-Knitted Preforms Adapted for Crash and 3D Applications

Multilayer-weft-knitted reinforcing structures arouse interest in the composite industry for their excellent drapability, impact resistance, and near-net-shape manufacturability. The research into those structures is one main focus at the Institute of Textile Machinery and High Performance Material Technology at Technische Universitat Dresden starting from machine development up to the whole production chain, taking into account the knitting ability of the used high performance glass/ polypropylene hybrid-yarns. Those fabrics combine the advantages of non-crimp fabrics and conventional weft-knitted fabrics. Due to the straight inlay yarns in horizontal (weft) and vertical (warp) direction these structures ideally suit as reinforcing structures for composite application with improved mechanical properties.