Document 6459781

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