LINKS BETWEEN DESIGN, PATTERN DEVELOPMENT AND FABRIC BEHAVIOR FOR CLOTHING AND TECHNICAL TEXTILES

Transcription

1 LINKS BETWEEN DESIGN, PATTERN DEVELOPMENT AND FABRIC BEHAVIOR FOR CLOTHING AND TECHNICAL TEXTILES Sybille Krzywinski, Hartmut Rödel, Andrea Schenk Dresden University of Technology, Dresden, Germany ABSTRACT In this paper is shown the necessity for the development powerful 3D CAD-systems for the textile and clothing industry. The connection between 2D CAD-systems with 3D CAD-systems enables the user to prepare a collection more quickly and accurately. Applications could be the drape behavior of fabrics, the deformational behavior of fabrics when covering defined surfaces and also technical textiles. Keywords: CAD-system, simulation, material behavior, close-fitting garments, technical textiles 1. INTRODUCTION For garments the phases of product development and preparation of production require approximately triple the time of the actual garment life span. 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 essential. Today there are many existing design programs with various software tools and a wide choice of designing functions. In connection with sketching-systems so called two and a half dimensional presentation programs can give an optical impression how the colors, motifs and materials look on a scanned model. Steps of product preparation such as pattern construction, grading, pattern planning and pattern optimization and the automated cutting are realized with computer assistance. However, commonly used CAD-systems available on the market show the following weak points: the systems work only in twodimensions the material behavior and the material parameters are not taken into account. Both these aspects are required for the threedimensional display of a model with regard to the draping in order to give the designer and model maker a realistic impression of the model. Optimal possibilities to examine the correct fitting and the form of a model would be the three-dimensional display of a two-dimensional pattern construction on a dummy or a development of a threedimensionally constructed model onto the two-dimensional plane, 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 [1, 2]. 1

2 2. THREE-DIMENSIONAL DISPLAY OF TWO-DIMENSIONAL PATTERN The current procedure to create patterns is a multi-step approach which involves much personnel, time and costs due to the trial and error phase. The fabric properties enter the design process only via expertise of designers. It is absolutely necessary for CAD-systems to be extended to material parameters and further search for possibilities to connect design and pattern construction more closely in the future [3, 4, 5]. 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 be comprised of the following modules: a fabric library correlating easily determined fabric properties to fabric drape configurations; search and sorting routines should be integrated in the library for efficient retrieval of information; a 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 using data from the fabric library. The following figures, which were made using DesignConcept 3D [8] by CDI Technologies Ltd. (recently acquired by Lectra Systemes, France), give an illustration of such a CAD-system. 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 for designing complex polygon surfaces. Figure 1 shows a comparison between a sketch by a designer and a simulation of a skirt. In this software program the bending properties in warp and weft direction, the tensile properties in warp, weft, 45 degree warp and 135 degree warp direction and also 2 the weight per unit are considered in the draping module (Figure 2; Table1). The scale of the property curves depends on the measurement devices. Figure 1: Comparison: Designer Sketch and Simulation of Skirt Figure 2: Fabric Properties Properties Parameters [Unit] Tensile Warp LT Weft WT [ gf cm / cm 2 ] Warp 45 RT [ % ] Warp 135 Bending Warp B [ gf cm 2 / cm ] Weft 2HB [ gf cm / cm ] Weight W [mg / cm 2 ] Thickness T [ mm] Table 1: Used Properties

3 A prerequisite for the simulation process is the two dimensional pattern piece (Figure 3). They can be prepared with conventional 2D CAD-systems. Figure 5: 2D Pattern with Guidelines and Seams The next step is to position the 2D mesh into the 3D space near the 3D body, from which the draping process starts (Figure 6). Figure 3: Two Dimensional Pattern Companies have developed 3D bodyscanners where the three dimensional perception of the human body can be realized with a sensor system in a quick and objective way (Figure 4). Figure 6: Start Position After this, the user has to generate a surface from the draped mesh. The surface can covered with different colors and/or designs. Figure 7 shows different examples. Figure 4: Human Body The DesignConcept 3D enable 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 the neckline or waistline) to the 3D body and seam points match different pattern pieces (Figure 5). Figure 7: Examples of Draped Surfaces 3

4 Disadvantages include the high and expensive hardware demands and long calculation times (in some cases, up to some hours). 3. FIT OPTIMIZATION FOR CLOSE FITTING GARMENTS In the mechanical consideration of deformability of fabrics, two directions are distinguished. The first one deals with drape behavior of the fabric and the second one is the deformational behavior of fabrics when covering defined surfaces. This application requires a nearly wrinkle-free draping of the fabric, such as close-fitting garments. For close-fitting garments like underwear, sportswear and swimwear, there are high demands towards fit and pattern construction. The garment size has to be adjusted exactly to the human body, while ensuring optimal comfort and freedom of movement. In pattern construction for closefitting elastic clothing, usually the girth measurements of the garment are configured to be smaller than the body measurements so that the material stretches when worn. Consequently, not only body measurements, but also mechanical properties of the fabric crucially influence the garments fit. The extensibility, i.e. the force - extension relation in case of tensional strain with the corresponding modules, is a significant material parameters. (Figure 8). direction from 1.5 to 2 N per 5 cm fabric width (for underwear, for instance) but it is also possible to use other tensile force values (for example, for clothes with a high pressure effect) [6]. With the help of powerful software the designer is in the position to create an accurate 2D pattern from 3D model surfaces for close fitting body shapes. Problems which are characterized 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 behavior is attributed to the mesh to simulate the development in the twodimensional plane, depending on the used material. First, UV-curves have to be drawn directly on surfaces (Figure 9). Each point on a UV curve has a U and V coordinate, just like each surface point. When the surface is modified, any UV-curves on the surface also change. 5,0 4,0 Force N 3,0 2,0 warp weft 1,0 0,0 0,0 5,0 10,0 15,0 20,0 25,0 30,0 35,0 40,0 45,0 50,0 55,0 60,0 Extension % Figure 8: Force-Extension Relation Investigations into wearing strain on knit clothing show that wearing comfort is optimal when stretching the material in girth 4 Figure 9: Curves on 3D Surfaces

5 With the region function, it is possible to create accurate 2D pattern pieces from 3D model surfaces. Regions in 3D grow over model surfaces, conforming to surface contours and crossing the boundaries of adjacent surfaces as directed (Figure 10). Once a 3D region is created on a surface model, it may be flattened to produce a 2D region counterpart. Figure 11: Flattening Process Figure 10: Regions on Surfaces The next step is to apply the mechanical properties of the knit fabric to a 3D region mesh. The simulation process is an advanced flattening technique that determines deformation strain, stress and develops a mesh from 3D to 2D based on the mechanical properties applicable to the grain and cross directions. The stress or strain analyses colors show the 3D mesh stress or strain based on the development status of the 2D mesh (Figure 11). Figure 12: Visualization of the Realistic Appearance 4. TECHNICAL TEXTILES In terms of visualization, one can apply material properties and map to regions in order to enhance the realistic appearance of a model (Figure 12). For example, if you apply a patterning fabric image to a 2D pattern, the stripes appear on the associated 3D surface just like they appear on the pattern, regardless of the orientation of the 3D surface. Textile reinforced light weight structure offer significant advantages among others in automobile and aircraft construction, especially for the design of curved components. This is achieved when textile reinforcing structures, which can be arranged and combined very flexibly, are specifically draped. Owing to insufficient design experience and the high cost of material, the potential fields for application in particular in 5

6 mechanical engineering and the auto industry have not been explored. 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. In order to guarantee the required variety of models and to make the structural component adequate for loading, 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 [7]. 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 behavior! cutting! stacking! prefabrication and placing of the z reinforcement! 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. shape according to the required load and thus avoiding rework (Figure 13). Three-dimensional CAD programs are mainly applied to design complex components (AUTOCAD 2000, CATIA.)[9,10]. The data obtained by the above remarks programs may be transferred to the simulation program via suitable interfaces (IGES- Initial Graphics Exchange Specification, VDAFS interface suited for the exchange of free forms and curves) [8, 9]. Figure 13: 3D component The textile preform should be in most exact accordance with the component geometry desired. In particular, for the realization of free-form 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). 4.2 Pattern Construction under Consideration of the Material Behavior 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 6 Figure 14: Conical shell shearing of a carbon fabric

7 Shearing in the pattern as well as material tension stresses and stretching may be analyzed to provide the designer with information that enables one to produce suitable patterns from the reinforcing textile material. The material data obtained for the shearing, the material tension stress and also the stretching behavior may be implemented in the simulation program by scanning the measurement curves and subsequent scaling or by loading a file in the ASCII format [11]. This investigation starts from an orthotropic structure for the majority of fabrics tested. When high modulus carbon yarns are processed (E modulus > N/mm 2 ), a starting point is the knowledge that of potential deformation between the two-dimensional cutting and the multicurved component surface results from the shearing deformation. After the computation has been completed, the shearing in the shaped patterns may be analyzed. 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 for the component surface. Another sample product is a spherical segment (Figure 15). One can see the developed pattern and also get information about its behaviors. For the flattening process, a shear angle of approximately 40 degree is necessary. Figure 15: Spherical Segment 5. CONCLUSIONS The working methods outlined in this research can assist designers with work and also enable designers to deal with the implementation of designs in view of pattern construction, without limiting creativity. 6. REFERENCES [1] Schenk, A.: Berechnung des Faltenwurfs textiler Flächengebilde, Dissertation TU Dresden, [2] Brummund, J.; Schenk, A.; Ulbricht, V.: Beitrag zur Modellierung des Fallverhaltens in der Textilindustrie, Proceedings GAMM 1998, Bremen, Germany. [3] Krzywinski, S.: Design und Materialverhalten Gestaltungseinheit zur Schnittentwicklung, Mittex 4/1999, S [4] Krzywinski, S.; Rödel, H.; Schenk, A.: Design und Materialverhalten Gestaltungseinheit zur Schnittentwicklung DWI Reports 2000, S [5] Krzywinski, S.: Design und Materialverhalten, Bekleidung und Wear (2000)3, S [6] Kirstein, T.; Krzywinski, S.; Rödel, H.: Pattern construction for close-fitting garments made of knitted fabrics Melliand English 3/1999, S. E 46 - E 48. [7] Krzywinski, S.; Herzberg, C.; Rödel, H.: Computer-aided product development and the making-up of multilayer 3D-preforms for composites, AUTEX CONFERENCE, Technical Textiles, Juni 2001, Portugal. [8] Reference Manual DesignConcept3D, Volume II, Grand Rapids, [9] Reference Manual AUTOCAD 2000, San Rafael, CA [10] CATIA Dassault Systems, 2001, [11] ASCII, Joan G. Stark, 2001, 7

8 Prof. Dr.-Ing. habil. H. Rödel, Technische Universität Dresden, Institut für Textil- und Bekleidungstechnik, D Dresden, Deutschland, Tel.: +351/ , Fax: +351/ , Dr.-Ing. S. Krzywinski, Technische Universität Dresden, Institut für Textil- und Bekleidungstechnik, D Dresden, Deutschland, Tel.: +351/ , Fax: +351/ , Dr.-Ing. A. Schenk, Technische Universität Dresden, Institut für Textil- und Bekleidungstechnik, D Dresden, Deutschland, Tel.: +351/ , Fax: +351/ , 8