The current issue and full text archive of this journal is available at http://www.emerald-library.com/ft Links between design, pattern development and fabric behaviours for clothes and technical textiles Clothes and technical textiles 217 Hartmut RoÈdel, Andrea Schenk, Claudia Herzberg and Sybille Krzywinski Dresden University of Technology, Dresden, Germany Keywords CAD, Simulation, Garments, Textiles Abstract 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. 1. Introduction The stage of product development and product preparation of clothes requires approximately three times the stage of consumption. In order to compensate for the resulting greater efforts in the product preparation and to react more quickly and flexibly to the latest fashion, the use of complex CAD ± CAM solutions is a must. Today there are lots of existing design programs with various software tools and a wide choice of designing functions. Connected with sketchingsystems so-called two-and-a-half-dimensional presentation programs can give an optical impression of how the colours, motifs and materials look on a scanned model. Steps in production preparation such as pattern construction, grading system, pattern planning and pattern optimisation and the automated cutting are realised by computer assistance. However, CAD-systems available on the market show the following weak spots: . the systems work only two-dimensionally. . the material behaviour and the material parameters are not taken into account. Both these aspects are required for the three-dimensional display of a model with regard to the draping in order to give the designer and model maker a real impression of the model. Optimal possibilities of examing the correct fitting and the form of a model would be the three-dimensional display of a twodimensional pattern construction on a dummy or the development of a threedimensionally constructed model into the two-dimensional level, when the specific material parameters are taken into account. Therefore, the more detailed treatment of physical and mechanical properties and their correct mathematical and physical formulation is of interest. International Journal of Clothing Science and Technology, Vol. 13 No. 3/4, 2001, pp. 217-227. # MCB University Press, 0955-6222 IJCST 13,3/4 218 2. Three-dimensional display of two-dimensional pattern The current procedure to create patterns is a multi-step approach, which involves too many personnel, too much time and costs due to the trial and error phase. The fabric properties enter the design process only via the expertise of the designers. It is absolutely necessary for CAD-systems to be extended with material parameters and to search for possibilities of connecting design and pattern construction in the future. The objective of the research is to create a complete CAD-system for garment manufacturers including 3D-visualization of garments on virtual human beings. An excellent CAD-system for the clothing industry should comprise the following modules: . fabric library relating easy to determine fabric properties to fabric drape configurations; search and sorting routines should be integrated in the library for easy use; . model for the human body, which can be adapted for persons of different sizes; . routines to simulate garment patterns from specific fabrics on the human body with use of data from the fabric library. The following figures, which were made using DesignConcept 3D by CDI Technologies Ltd (recently belonging to Lectra SysteÁmes, France), give an impression of this subject. The software DesignConcept 3D is based on the polygon computation of NURBS (Non-Uniform-Rational-B-Splines). It is considered the state-of-the-art computation method to design complex polygon surfaces. Figure 1 shows a comparison between the drawing of a designer and the simulated skirt. In this program the bending properties in warp and weft direction, the tensile properties in warp, weft, 45ë warp and 135ë warp direction and also the weight per unit are considered in the draping module. Figure 1. Comparison of the sketched and simulated skirt The scale of the property curves depends on the measurement devices (for Clothes and example, KES-FB, Cantilever, Zwick) (see Figure 2). technical textiles A prerequisite for the simulation process is the two-dimensional pattern pieces. They can be prepared with conventional 2D CAD-systems (see Figure 3). Companies have developed 3D body-scanners where the three-dimensional perception of the human body can be realised with a sensor system in a fast and 219 objective way (Figure 4). The DesignConcept 3D enables the user to seam 2D pattern pieces together and drape them over a 3D model. Therefore it is necessary to prepare the 2D pattern piece. Guidelines are used to anchor special lines (for example neckline, waistline) to the 3D body and seam points match different pattern pieces (Figure 5). The next step is to place the 2D-mesh into the 3D space near the 3D body, from which the draping process starts (Figure 6). After this from the draped mesh the user has to generate a surface. The surface can be covered with different colours and/or designs. Figure 7 shows different examples. Figure 2. Fabric properties Figure 3. Two-dimensional pattern IJCST 13,3/4 220 Figure 4. Human body Figure 5. 2D-pattern with guidelines and seams Figure 6. Start position A disadvantage is the high and expensive hardware demands and long calculation times (in some cases up to some hours). Therefore it is necessary to develop those tools with high functionality and with low configuration demands and price and also easy handling. 3. Fit optimization for close fitting garments In the mechanical consideration of deformability of fabrics, on principle, two directions are distinguished. The first deals with drape behaviour of the fabric Clothes and technical textiles 221 Figure 7. Examples of draped surfaces (chapter 2) and the second is the deformational behaviour of fabrics when covering defined surfaces. This application requires a nearly wrinkle-free draping of the fabric, as, for example, close fitting garments. For close-fitting garments like underwear, sportswear and swimwear, there are high standards of fit and therefore also of pattern construction. The garment size has to be adjusted exactly to the human body, while in optimal comfort wearing and freedom of movement have to be secured at the same time. In pattern construction for close-fitting elastic clothing usually the girth measurements of the garment are constructed so as to be smaller than the body measurements, so that wearing will extend the material. Consequently, not only body measurements, but also the mechanical properties of the fabric crucially influence the garment's fit. Here, the extensibility, i.e. the force-extension relation in case of tensional strain with the corresponding modulus, is a significant material parameter (see Figure 8). Investigations into the wearing strain on knitted clothes showed that the wearing comfort is optimal when stretching the material in girth direction at Figure 8. Force-extension relation IJCST 13,3/4 222 Figure 9. Curves on 3D surfaces 1.5 to 2N per 5cm fabric width (for example, underwear) but it is also possible to use other tensile force values (for example, for clothes with a high pressure effect). With the help of a powerful software the designer is in a position to create accurate an 2D pattern from 3D model surfaces for close fitting body shapes. Problems which are characterised by large deformations may be described by incremental formulations to determine the state of deformation and tension stress. For this purpose, a mesh is generated on the component surface to be shaped. The mesh may be generated automatically or interactively. The accuracy of computation depends on the triangle size. Material behaviour is attributed to the mesh to simulate the development in the two-dimensional level depending on the material type. First, you have to draw UV-curves (curves on surfaces) directly on surfaces or create them via Converters functions. UV-curves cannot be drawn across surface boundaries, however. When you modify the surface, any UV-curves on the surface change too (see Figure 9). With the region function it is possible to create accurate 2D pattern pieces from 3D model surfaces. Regions in 3D grow over model surfaces, confirming to surface contours and crossing the boundaries of adjacent surfaces as directed. Once a 3D region is created on a surface model, it may be ``flattened'' to produce a 2D region counterpart (see Figure 10). The next step is to apply the mechanical properties for the knitted fabric to a 3D region mesh. The simulation process is an advanced flattening technique that determines deformation strain and stress and develops a mesh from 3D to 2D based on the mechanical properties applied in the grain and crossdirections. The stress or strain analysis colours show the 3D mesh stress or strain based on the development status of the 2D mesh (see Figure 11). In terms of visualisation, you can apply material properties and maps to regions in order to enhance the realistic appearance of a model. For example, if you apply a patterning fabric image to a 2D pattern, the ``stripes'' appear on the Clothes and technical textiles 223 Figure 10. Regions on surfaces Figure 11. Flattening process associated 3D surface just as they appear on the pattern, regardless of the orientation of the 3D surface (see Figure 12). 4. Technical textiles Lightweight structures including textile construction methods offer definite advantages for the development of curved structural elements, in particular, in the automobile and aircraft industry. This is achieved when textile reinforcing structures, which can be arranged and combined very flexibly, are specifically draped. Owing to the insufficient design experience and the largely high material cost, the potential fields of application, in particular, in the mechanical engineering and the car industries have not been opened up at all. IJCST 13,3/4 224 Figure 12. Visualisation of the realistic appearance At present, after the structural element has been designed, the desired design variant is implemented in several iterations. As a result, the development of the structural element most frequently takes a rather long time and involves considerable costs as well. In order to guarantee the required variety of models and to make the structural component adequate to load without at the same time increasing the involved time for industrial engineering, the development of efficient tools for product simulation is of predominant importance. Since 1997 a research team supported by the German Research Foundation (DFG) has been working at Dresden University of Technology under the headline Textile Reinforcements for High-Performance Rotors in Complex Applications. 4.1 Textile preform The following steps are necessary to make a textile preform with the component design being very complex: . pattern design in accordance with material behaviour; . cutting; . stacking; . prefabrication and placing of the z reinforcement; and . assembly of the 3D preform. Most of the components may be produced using various procedures. Material considerations, design and economic aspects should determine the procedure chosen. 4.2 Pattern construction under consideration of the material behaviour If curved element contours of lightweight textile structures are covered with an undefined shape of the reinforcing textile, the mechanical component properties may deteriorate. The patterns should be developed directly on the object to apply the reinforcing structures to the desired 3D shape according to the Clothes and required load and thus avoiding rework. technical textiles Three-dimensional CAD programs are mainly applied to design complex components (AUTOCAD 2000, Pro Engineer, Thinkdesign 4.0, CATIA). The data obtained by the above programs may be transferred to the simulation program via suitable interfaces (IGES ± Initial Graphics Exchange Specification, 225 VDAFS ± interface suited for the exchange of free forms and curves). The textile preform should be in most exact accordance with the component geometry desired in the end (Figure 13). In particular for the realisation of freeform surfaces it is necessary to cut the fabric or multiaxial structures, so that it may be shaped later without irregular folds. After the patterns have been developed with regard to functional requirements using a three-dimensional model, surface generation and the development of the two-dimensional patterns are made feasible by an efficient software tool (Figure 14). Shearing in the pattern as well as material tension stresses and stretching may be analysed to provide the designer with information that enables him to produce suitable patterns of the reinforcing textile material. The material data obtained for the shearing, the material tension stress and also the stretching behaviour may be implemented in the simulation program by scanning the measurement curves and subsequent scaling or by loading a Figure 13. 3D component Figure 14. Conical shell ± shearing of a carbon fabric IJCST 13,3/4 226 Figure 15. Spherical segment file in the ASCII format. This investigation starts from an orthotropic structure for the majority of fabrics which have been tested so far. When high modulus carbon yarns are processed (E modulus > 650.00N/mm2), we may start from the fact that the potential deformation between the two-dimensional cutting and the multiple curved component surface results from the shearing deformation. After the computation has been completed, the shearing in the shaped patterns may be read. A comparison with the critical shearing angle, which indicates how far the share of threads can be twisted or compressed without folds, helps the designer to decide if the pattern is suited to the component surface. Another sample product is a spherical segment (Figure 15). Here you can see the developed pattern and you also get information about the behaviours. For the flattening process, a shear angle of approximately 40ë is necessary. Bibliography Brummund, J., Schenk, A. and Ulbricht, V. (1998), ``Beitrag zur Modellierung des Fallverhaltens in der Textilindustrie'', Proceedings GAMM, Bremen, Germany. Cusick, G.E. (1968), ``The measurement of fabric drape'', Journal of the Textile Institute, Vol. 59 No. 6, pp. 253-60. Fischer, P. (1997), ``Ermittlung der mechanischen KenngroÈûen textiler FlaÈchen zur Modellierung des Fallverhaltens unter BeruÈcksichtigung konstruktiver, faserstoffbedingter und technologischer AbhaÈngigkeiten'', Dissertation TU Dresden. Fischer, P., Krzywinski, S., RoÈdel, H., Schenk, A. and Ulbricht, V. (1999), ``Simulating the drape behavior of fabrics'', Textile Research Journal, Vol. 69 No. 5, pp. 331-4. Kirstein, T., Krzywinski, S. and RoÈdel, H. (1999), ``Ermittlung des Zusammenhanges zwischen Gestrickparametern, rechnergestuÈtzter Schnittgestaltung und Sicherung der Passform von Untertrikotagen zur QualitaÈtsverbesserung'', Vti aktuell, Vol. 3, p. 10. Krzywinski, S. (1999), ``Design und Materialverhalten ± Gestaltungseinheit zur Schnittentwicklung'', Mittex, Vol. 4, pp. 9-11. Krzywinski, S. (2000), ``Design und Materialverhalten'', Bekleidung und Wear, Vol. 3, pp. 12-17. Krzywinski, S., RoÈdel, H. and Schenk, A. (2000), ``Design und Materialverhalten ± Gestaltungseinheit zur Schnittentwicklung'', DWI Reports, pp. 182-9. Krzywinski, S., Schenk, A., RoÈdel, H. and Fischer, P. (1999), ``Links between cloth design, pattern development and fabric behaviours: modern applied mathematics techniques in circuits, systems and control'', World Scientific and Engineering Society Press, pp. 396-400. Magloth, A. (1997), ``Design-Idee und Materialverhalten als Gestaltungseinheit'', Bekleidung & Wear, Vol. 20, pp. 13-14. RoÈdel, H., Ulbricht, V., Krzywinski, S., Schenk, A. and Fischer, P. (1997), ``Simulation of drape behaviour of fabrics'', Conference Proc. Advances in Fibre and Textile Science and Technologies, Mulhouse, France. RoÈdel, H., Ulbricht, V., Krzywinski, S., Schenk, A. and Fischer, P. (1998), ``Simulation of drape behaviour of fabrics'', International Journal of Science and Technology, Vol. 10 No. 3/4, p. 201. Schenk, A. (1996), ``Berechnung des Faltenwurfs textiler FlaÈchengebilde'', Dissertation, TU Dresden. Clothes and technical textiles 227