Experimental characterization to determine the

Transcrição

Nicht zur Verwendung in Intranet- und Internet-Angeboten sowie elektronischen Verteilern.
www.kunststofftech.com
© 2015 Carl Hanser Verlag, München
Zeitschrift Kunststofftechnik
4Autor
Titel (gegebenenfalls gekürzt)
Journal of Plastics Technology
www.kunststofftech.com · www.plasticseng.com
archivierte, peer-rezensierte Internetzeitschrift
archival, peer-reviewed online Journal of the Scientific Alliance of Polymer Technology
eingereicht/handed in:
angenommen/accepted:
12.02.2015
28.04.2015
Dipl.- Ing Dino Magagnato1, Dipl.-Ing Bernd Thoma2, Prof. Dr.-Ing Frank Henning1,2
1
Institut für Fahrzeugsystemtechnik, Karlsruher Institut für Technologie (KIT)
2
Fraunhofer Institut für Chemische Technologie (ICT), Pfinztal
influence of different binder systems on the
preform permeability during RTM
manufacturing
For fixation of the preforms during RTM-manufacturing, mainly adhesive binders are used, where a
uniform layer of these binders are applied between the textile layers. Previous investigations [1 – 3]
showed that the laminar application of binder leads to a reduction of preform permeability for the
injection process. In the following study a new preform fixation approach, called “Chemical Stitching”,
is introduced and its influence to permeability is examined. For the permeability measurements, a 1-D
test setup is used, which is mainly geared to unidirectional fiber textiles. To do the measurements
under suitable conditions, specialized sensors are used to detect the flow front and the pressure
history in the cavity.
Experimentelle Charakterisierung des Einflusses verschiedener Bindersysteme auf die Permeabilität des Preforms bei der RTM-Fertigung
Für die Fixierung von Preformlingen in der RTM-Fertigung werden aktuell hauptsächlich adhäsive
Bindersysteme verwendet, die flächig zwischen die Textillagen appliziert werden. Untersuchungen
von [1 – 3] haben gezeigt, dass der flächige Binderauftrag zur Senkung der Preform-Permeabilität im
Injektionsprozess führt. Im Folgenden wird ein neuartiges Verfahren zur lokalen adhäsiven
Preformfixierung namens „Chemical Stitching“ vorgestellt und dessen Einfluss auf die PreformPermeabilität untersucht. Für die Permeabilitätsmessungen wird ein 1D-Testaufbau verwendet, der
vornehmlich für unidirektionale Faseraufbauten ausgelegt ist. Um die Messungen unter geeigneten
Bedingungen durchzuführen, werden speziell ausgelegte Sensoren verwendet, um die Fließfront und
den Druckverlauf in der Kavität zu verfolgen.
© Carl Hanser Verlag
Zeitschrift Kunststofftechnik / Journal of Plastics Technology 11 (2015) 4
Magagnato, Thoma et al.
Influence of binder on preform permeability
influence of different binder systems on the
preform permeability during RTM manufacturing
D. Magagnato, B. Thoma, F. Henning
1
INTRODUCTION
Fiber reinforced composites are increasingly used for industrial applications due
to the combination of low density and good mechanical properties. For small
series productions it is already possible to realize the economic boundary, but
for large-batch productions like in the automotive industry, the production of
cost-efficient composites parts is still a big challenge. This is because of the
high material and production costs coupled with low degree of automation vis-avis production of metal parts. The Resin Transfer Molding (RTM) process offers
because of good possibilities for automation huge potential for mass production
of high quality fiber reinforced structures.
All RTM-methods combine a low-viscosity thermoset or thermoplastic matrix
with laminar textile reinforcement structures in order to get a fiber composite
part after the curing of the matrix. The process can be divided in following main
steps as: cutting of fiber textiles, the exact placement of dry reinforcement fibers
in a heated cavity, the infiltration of semi-finished fiber materials with matrix
resin and the demolding of the cured fiber composite part.
Textile fabrics are the starting point for the efficient production of complexformed composite parts. These are mostly woven fabrics or non-crimp fabrics of
carbon, glass, aramid or natural fibers as a semi-finished product. The laminar
semi-finished fiber materials are processed into 3-dimensional textile preforms
for the production of complex 3-dimensional formed structures. The fixation of
the semi-finished stack is ensured by sewing or by the use of adhesive binder,
which is applied laminar between the semi-finished stacks. Analysis of preform
permeability showed that preforms produced with the help of adhesive binders
have a lower permeability compared to stitched preforms or preforms without
binders. This results in a longer and time consuming subsequent infiltration
process. The main reason for that is the laminar application of the binder [1 - 3].
Due to the fact that a big part of the RTM cycle time is claimed by injection and
by curing of the resin/hardener combination, it is reasonable to investigate new
preform fixation technologies that might have a less negative influence on the
preform permeability. A new approach for an automatic fixation of dry fiber
structures is examined in the Fraunhofer Innovations cluster KITe hyLITE. The
so-called “Chemical-Stitching” approach is based on a local application of a
liquid and fast curing adhesive.
Journal of Plastics Technology 11 (2015) 4
257
For this approach the preform is produced by inserting specific amount of
adhesive at predefined points, hence resulting in fixation of several
reinforcement fiber layers. The required amount, flow and position of adhesive
point are ensured with an application unit which is presented in Thoma [4]. In
this approach, a consistent coherence of the laminar semi-finished fiber material
is created by the cohesion and adhesion forces of the adhesive material unlike
the binding force produced by continuous stitching thread. As there is no sewing
thread which remains under tension, the ondulation of fibers is reduced
significantly. Furthermore, to implement the adhesive, a needle cannula with a
diameter far below 1 mm is used, which is smaller than in the case of the
sewing process to implement the sewing thread hence reducing the fiber
disorientation significantly. Due to the possibility of the introducing of a flexible
and local binder, the improvement of the textile permeability and, therefore, the
improvement of the flow behavior of the matrix material is expected during the
infiltration process.
Figure 1: Chemical stitching - Process flow
The step by step process for the application of adhesive is shown in Figure 1.
The curing energy (Ec) as shown in the above figure can be in the form of heat
or UV radiation. It must be ensured that the adhesive is not reducing the drape
properties of the textile and, furthermore, does not have a negative influence on
the mechanical properties of the final composite part. The choice of an
appropriate adhesive is therefore of high significance.
258
2
EQUATIONS
The injection process during the RTM manufacturing is described by the law of
Darcy [5]:
K 
 ∇( p )
v = − 
 ϕµ 
(1)
Where, v is the velocity of flow front [m/s], ϕ is the porosity [-] and p is the
pressure field [Pa] in the cavity. Relevant material parameters are the viscosity,
µ [Pa s] of the resin and the permeability, K [m²], of the fibers, which is an
anisotropic tensor of second degree. In the principal coordinate system there
are three relevant parameters: K1, K2 and K3. For the unidirectional fibers the
direction with best permeability, K1, is parallel to the fibers and the worst
permeability K2 is normal to the fiber direction. The permeability in thickness
direction, K3, can be neglected, because of the small thickness of the
composites parts [6]. Unfortunately, there is yet no standard norm to determine
the permeability experimentally [7, 8], which results in a certain confusion at the
calculation. In this study a new permeability measurement setup is used, which
is able to measure the permeability directly during RTM manufacturing. This
guarantees a process-oriented approximation of the permeability behavior. The
viscosity of the resin-hardener is a function of temperature and curing degree.
In this study, a replacement fluid with nearly constant viscosity is used to avoid
the influence of the curing process of the resin.
3
EXPERIMENTAL SETUP
The used raw materials, the preparation of the tested samples as well as the
permeability measurement setup are explained in the following chapters.
3.1
Materials:
Glass fiber fabric of the type 92146 with FK800 finish manufactured by P-D
Interglas GmbH is used as the textile reinforcement structure for this study. The
areal density of the fabric is 425 g/m². The weave structure is a plain weave
with warp to weft ratio of 90:10. In context of the analysis of permeability, three
different types of adhesive are examined:
•
Co-polyamide-binder fleece PA-1541 (Manufacturer: Spunfab Ltd)
•
Epoxy-binder powder Epikote 05311 (Manufacturer: Momentive Specialty
Chemicals)
•
Acrylat PB 4468 (Manufacturer: DELO Industrie Klebstoffe GmbH)
259
To minimize the experimental efforts for permeability measurements, Mesamoll
(Manufacture: Lanxess AG) is used, instead of epoxy resin. Mesamoll is a fluid
with nearly the same fluid mechanical properties at room temperature (RT) as
epoxy resin at typical RTM temperatures (~80°C). Typically, silicon oil is used
for permeability measurements [7, 8], but as shown in Magagnato [9], Mesamoll
shows even better agreement with epoxy resin. To minimize the influence of
temperature changes during permeability measurements, the viscosity of
Mesamoll was determined beforehand with a rotation rheometer of the type
MCR501 (Manufactured by Anton Paar) at different temperatures [9]. During the
permeability measurements, the temperatures are recorded with pressure
sensors and subsequently regarded in the evaluation algorithm.
3.2
Preform manufacturing
The preform permeability measurements were conducted on flat dry preform
stack containing six glass fiber fabric layers with a main fiber direction of 0°. The
geometry of the specimens is 520 mm x 222 mm. The specimens are fixed
locally by chemical-stitching (see Figure 2), as well as laminar fixation with
binder powder and binder fleece. The preforms, which are locally bindered by
chemical-stitching, are produced with the help of an application unit as
presented in Thoma [4]. The liquid acrylat-adhesive PB 4468 is introduced
locally in the dry, six layered fabric stack compacted under vacuum foil and is
in-situ hardened with the help of UV-radiation. The duration of exposure of the
adhesive to the UV radiation is 10 seconds in each case. The matrix of the
adhesive points for fixation is 10 mm in x- and y-direction. Preforms with
adhesive doses of were further manufactured for permeability measurements.
Figure 2: Stack of glass fiber woven fabric fixed by chemical stitching
The doses of 4 mg; 7 mg and 8 mg for each adhesive point further corresponds
to the areal density of 6 g/m²; 10 g/m² and 12 g/m² respectively for the defined
stack and fixation matrix. As a reference to the locally bindered preforms, the
laminar bindered preforms (with Co-polyamide fleece PA-1541 and Epikote
260
05311) are also produced with similar areal density of the adhesives. The
binder materials are introduced preferably homogeneous and laminar between
each glass fiber layer. Afterwards, the packages of plies are compacted
between two steel plates, heated up to 110 °C and kept at this temperature for
15 min for binder fixation and then cooled.
3.3
Measurement setup
For this study a measurement setup [9] was used, which is able to determine
permeability by tracing the flow front with specialized pressure and temperature
sensors of the type MTPS 7868- STS (Manufacturer: FOS Messtechnik GmbH).
Apart from the permeability measurement, the setup is also constructed to
produce RTM plates by injection of a curing matrix material (for example epoxy
resin). The cavity is a plate with 540 mm x 200mm x 2 mm in dimension and
both parts of the tool are made of steel and 100 mm thick to guarentee that
there is no deformation during the injection process.The pressure sensors are
located in level with the cavity on the top part of the tool. Their signals are
transferred by an amplifier type pT-Amplifier-7Ch-S (Manufacturer: FOS
Messtechnik GmbH) and voltage measurement device of the type NI 9205
(Manufacturer National Instruments Germany GmbH) to a computer system.
The tool is placed in a hydraulic press with a maximum press force of 3000 kN
to reach necessary locking force. In this study, the test fluid phenyl ester (trade
name Mesamoll) is pumped up through an injection line into the cavity by a
pressure pot. The schematic of the entire permeability measurement setup is as
illustrated in Figure 3.
Figure 3: Schematic of the permeability measurement setup
Reprinted from [9], Copyright © 2015 Trans Tech Publications Ltd
261
The measurements were done at room temperature with a constant pressure
difference of 5.5 bars, which is high enough to keep the influence of capillary
effects down. The capillary forces have to be considered in permeability
measurements with less than 1 bar injection pressure [10]. In Figure 4 the
positions of the sensors in the mold cavity are presented. The analysis of the
permeability is done by the seven sensors in the middle corridor of the plate.
Figure 4: Positions of the integrated sensors
left: topview of the RTM tool, right: pressure history of the sensors
Reprinted from [9], Copyright © 2015 Trans Tech Publications Ltd
The two sensors (S2b and S5b) along the edge are to ensure a homogeneous
flow front. On the right side of the Figure 4, a representative pressure history of
the integrated sensors is shown. For the permeability calculation the arrival time
of the flow front at each sensor is entered into the analytic solution for the flow
in a plate with a line injection, which is derived from Darcy’s law [5]. After
transposing the equation, the permeability in flow direction at each sensor
position can be determined with formula 2.
x 2s (t )φµ
K=
2( p 0 − p s )t s
(2)
where p0 is the injection pressure, ps is the pressure at sensor, ts is the arrival
time when the flow front passes the sensor and xs is the sensor position.
The output permeability is an average value over all sensors. The output
permeability is an average value over all sensors.
262
3.4
X-ray computed tomography
The analysis is conducted with the help of a x-ray computer tomography (“CT”)
type „SkyScan 1076“ (Manufacturer: Bruker). The detector of the device has an
image area of 1024 x 1024 pixels. During the image capture, the x-ray source
and the detector are rotating around the specimen in an angle of 180°. The
chosen step size of 0.7° leads to 257 single images. The acceleration voltage is
60kV, with a current of 0.17 mA. For reconstruction of the taken single images,
the software „3D-Creator“ is used. The voxel size has an edge length of 9 µm.
The analysis of geometry of the adhesive points is done by image processing.
4
RESULTS AND DISCUSSION
In the following section the obtained results concerning textile permeability are
presented and discussed.
4.1
Results
4.1.1
Permeability measurements
For this study, preforms with the three different binder systems (Epikote,
Spunfab and chemical stitching; see chapter 3.2) are tested against a reference
sample without binder. Furthermore the amount of binder is varied from 6 g/m²
up to 12 g/m², which is the usual range for industrial applications. For each
binder-textile combination at least four permeability measurements in each fiber
orientation (0° and 90°) are done for statistical coverage. As usual for these
kinds of measurements there is a coefficient of variation of around ±10 %. In
Figure 5, the results of permeability measurements in 0°-direction (K1) are
presented. The reference sample without binder has the best permeability. The
permeability deteriorates with increasing amount of binder for all three kinds of
binders.
Especially at a low amount of binder, the samples prepared with the “Chemical
Stitching” technology show here a significantly better flow behavior than the
laminar bindered preforms. Whereas at 12 g/m² the permeabilities of the three
binder systems are nearly equal. For permeability measurements normal to
fibers (K2) also as seen in Figure 6, the permeability decreases with increasing
amount of binder. Here all three kinds of binders are nearly on the same level. It
seems that the permeability of laminar bindered samples is even slightly higher
than of the samples fixed by chemical stitching, especially at a binder amount of
12 g/m².
263
Figure 5: Permeability depending on binder system at 0° fiber orientation (K1)
Figure 6: Permeability depending on binder system at 90° fiber orientation (K2)
264
4.1.2
X-ray computed tomography
Figure 7 shows the results of the X-ray computer tomography measurements
for the chosen adhesive, which has a processing viscosity of 7 Pas. The
adhesive column is shown from top view as well as a cut in 90° and 0° direction.
It is clearly evident, that the applied adhesive points cause a resin-rich zone,
which spreads in an elliptic form in direction of the main fiber direction.
Figure 7: X-ray computed tomography measurements for the adhesive system
Delo 4468
4.2
Discussion
Based on theoretical considerations [4], a significant improvement of the
permeability for the locally bindered preforms is estimated. Also, after a haptic
265
perception of the produced specimen, a better permeability of the local fixed
specimens in both directions is expected. This is, as seen in Figure 6, only
partially the case. It is quite a surprising result that the K2 permeability of the
chemical stitched preforms is even lower compared to the laminar bindered
preforms. The CT-images of the chosen adhesive system described in chapter
3.4 deliver an explanation. As illustrated in the schematic Figure 8, the adhesive
binder spreads out elliptically. The big main axis (l1 ) of the ellipse is thereby
extended along the main fiber direction and the small main axis (l2 ) is extended
across. This can be explained by the expansion of the fiber rovings in
combination with the high fiber stiffness that leads to a local cavity and
ultimately to the adhesive enrichment in fiber direction. Another reason is that
the permeability in the K1-direction of the preform without binder is generally
higher than in the K2-direction.These adhesive volumes cannot be infiltrated by
the test fluid and could act like local disorders in the flow front and result in
pressure losses. The drag coefficient of these volumes at the 0°-preforms is
significantly less than the 90°-preforms, where the major axis of the ellipse is
normal to the flow direction. During the infiltration of the textiles in K1 -direction,
the fluid is forced in a preferred flow direction, which is a sort of a flow channel,
because of the introduced adhesive points. In contrary, the adhesive points in
Figure 8 (Infiltration in K 2 –direction (right)), are forming flow barriers. This is
also the explanation for the amplifying of the described effect with increasing
amount of adhesive. With an increasing amount of adhesive, the flow channels
between the adhesive points are getting narrow, which results in an increasing
flow resistance.
Figure 8: Schematic illustration of orientation of adhesive geometry
Infiltration in K1-direction (left) and in K2- direction (right)
In addition to that, losses that result from the inhomogeneity of the flow front
play a less important role at the 0°- fiber direction. The flow here is inhomo-
266
geneous by itself because of varying wide gaps between the fiber rovings that
result in dual scale flow [11, 12]. In 90°- fiber direction, the flow front is relative
homogeneous by itself so that these local disorders have a bigger influence.
5
SUMMARY AND CONCLUSIONS
The results of the measurements show that the application of binder reduces
the preform permeability significantly. Derived from Darcy’s law, a reduced
permeability has a negative effect to the cycle times for mold filling process
during RTM manufacturing. This results in increased production costs for high
performance composite materials. The chemical stitching approach offers
potential to reduce this effect. Particularly in fiber direction, the negative
influence of chemical stitching to the preform permeability is less compared to
other binder technologies. In addition to that, the chemical stitching process
needs less binder to reach the same fixation strength [4]. So, generally, less
binder must be used during preforming, which, again, has a positive impact on
the permeability. However the adhesive dose and the disposal of the adhesive
points must be carefully chosen. Especially normal to the fiber direction, the
adhesive points should not be arranged too close to each other, to avoid local
disorders in the flow front. Through local application of adhesive, flow channels
can be placed where they are needed. So it is possible to set a targeted flow
behavior and to improve the mold filling process in that way. Regarding the
future process chain for the sequential preforming of textile semi-finished
products to 3d-complex preforms, the chemical stitching approach could be
integrated directly into a textile handling unit. So an in-situ fixation of textile
patches or sub-preforms could be realized.
6
ACKNOWLEGDEMENTS
These investigations are carried out through the R&D activities of KITE hyLITE
Plus project. This project is funded by the European Union through the program
“European Funds for Regional Development” as well as state government of
Baden-Wuerttemberg in Germany. Administrative agency of this program is the
Ministry of Rural Development, Food and Consumer Protection.
267
Literature
[1]
Rohatgi, V.;
Lee, L. J.
Moldability of Tackified Fiber Preformlinge in Liquid
Composite Molding
Journal of Composite Materials 31 (7), 1997, pp. 720744
DOI: 10.1177/002199839703100705
[2]
[3]
Morris, S.;
Sesco, R.
Preform Binder Technology
Shih, C.;
Lee, L. J.
Tackification of Textile Fiber Preformlinge in Resin
Transfer Molding
Composites 2006 Convention and Trade Show,
American Composites Manufacturers Association, St.
Louis, 2006
Journal of Composite Materials 35 (21), 2001,
pp. 1954-1981
DOI: 10.1177/002199801772661452
[4]
[5]
Thoma,B.;
Weidenmann,K.;
Henning, F.
Chemical-Stitching, ein vielversprechender Ansatz für
die automatisierte Preformfertigung,
Darcy, H.
Les fontaines publique de la ville de Dijon
Journal of Plastics Technology 5 (8), 2012, pp. 490514
Dalmant, Paris, 1856
[6]
JIANG,J.,
WANG, Z.
Measurement of Transverse Permeability of Fabric
Preforms Using Ultrasound Monitoring Technique in
LCM Processes,
Advanced Materials Research Vols. 311-313, pp.
214-217
DOI: 10.4028/www.scientific.net/AMR.311-313.214
[7]
Arbter,R.,
Experimental determination of the permeability of
Beraud,J.M.,
textiles: A benchmark exercise
Binetruy, C., et al Composites Part A: Applied Science and
Manufacturing, Volume 42(2011), pp. 1157-1168
DOI: 10.1016/j.compositesa.2011.04.021
268
[8]
Vernet N.,
Ruiz E.,
Advani S., et al.
Experimental determination of the permeability of
textiles: benchmark 2,
Composites Part A: Applied Science and
Manufacturing, Volume 61 (2014), pp. 172-184
[9]
Magagnato D.,
Henning F.
Process-oriented determination of preform
permeability and matrix viscosity during mold filling in
resin transfer molding
Materials Science Forum, Volumes 825-826 (2015),
pp. 822-829
[10] Amico S., Lekakou An experimental study of the permeability and
C.
capillary pressure in resin-transfer moulding
Composites Science and Technology, Volume 61
(13), 2001, pp. 1945-1959
DOI: 10.1016/S0266-3538(01)00104-X
[11] Markicevica B.,
Heidera D.,
Advani S., et al.
Stochastic modeling of preform heterogeneity to
address dry spots formation in the VARTM Process
Manufacturing, Volume 36(2005), pp. 851-858
[12] Drapiera S.,
Monattea J.,
Elbouazzaouia
O., et al.
Characterization of transient through-thickness
permeabilities of Non Crimp New Concept (NC2)
multiaxial fabrics
Manufacturing, Volume 36 (2005), pp. 877-892
Bibliography
DOI 10.3139/O999.03042015
Zeitschrift Kunststofftechnik / Journal of Plastics
Technology 11 (2015) 4; page 256–270
© Carl Hanser Verlag GmbH & Co. KG
ISSN 1864 – 2217
269
Stichworte:
Permeabilität, Chemical Stitching, Resin Transfer Molding (RTM), Preforming,
Binder, Hochleistungsfaserverbunde
Keywords:
Permeability, Chemical Stitching, Resin Transfer Molding (RTM), Preforming,
Binder, high performance composite
Autor/author:
Dipl.-Ing. Dino Magagnato
Dipl.-Ing. Bernd Thoma
Prof. Dr.-Ing. Frank Henning
E-Mail: [email protected]
homepage: http://www.fast.kit.edu/lbt/
phone: +49 (0)721/608-45384
fax: +49 (0) 721/608-945905
Karlsruher Institut für Technologie
Institut für Fahrzeugsystemtechnik
Lehrstuhl für Leichtbautechnologie
Rintheimer Querallee 2
76131 Karlsruhe
Herausgeber / Editors:
Editor-in-Chief
Prof. em. Dr.-Ing. Dr. h.c. Gottfried W. Ehrenstein
Lehrstuhl für Kunststofftechnik
Universität Erlangen-Nürnberg
Am Weichselgarten 9
91058 Erlangen
Deutschland
Phone: +49 (0)9131/85 - 29703
Fax: +49 (0)9131/85 - 29709
Europa / Europe
Prof. Dr.-Ing. Dietmar Drummer, responsible
Lehrstuhl für Kunststofftechnik
Universität Erlangen-Nürnberg
Am Weichselgarten 9
91058 Erlangen
Deutschland
Phone: +49 (0)9131/85 - 29700
Fax: +49 (0)9131/85 - 29709
Amerika / The Americas
Prof. Prof. hon. Dr. Tim A. Osswald, responsible
Polymer Engineering Center, Director
University of Wisconsin-Madison
1513 University Avenue
Madison, WI 53706
USA
Phone: +1 608/263 9538
Fax: +1 608/265 2316
Verlag / Publisher:
Carl-Hanser-Verlag GmbH & Co. KG
Wolfgang Beisler
Geschäftsführer
Kolbergerstraße 22
D-81679 München
Phone: +49 (0)89/99830-0
Fax: +49 (0)89/98480-9
Redaktion / Editorial Office:
Dr.-Ing. Eva Bittmann
Christopher Fischer, M.Sc.
Beirat / Advisory Board:
Experten aus Forschung und Industrie, gelistet unter
270

Experimental characterization to determine the

Transcrição

Documentos relacionados

Factormed - Detalhes de produto

SAC3 - Cable Tie Mounts self adhesive/screw fixing

Zeitschrift Kunststofftechnik Journal of Plastics

NetBotz Door Switch Sensors for APC Racks (NBES0303)

ArmaSound Industrial Systems

Scanning Electron Microscopy Evaluation of the - FORP

Click Bond`s CLICK PATCH

MOLECULAR STRUCTURE OF LIGNOSULFONATES

Influence of adhesive system in bond strength of fiber glass posts to

Intestinal permeability and systemic infections in critically ill patients

ARTICLE IN PRESS