In-plane permeability characterization of engineering textiles based on radial flow experiments: A benchmark exercise

TLDR: In this paper, the results of a third benchmark exercise using in-plane permeability measurement, based on systems applying the radial unsaturated injection method, were presented, where 19 participants using 20 systems characterized a non-crimp and a woven fabric at three different fiber volume contents, using a commercially available silicone oil as impregnating fluid.

Abstract: Although good progress was made by two international benchmark exercises on in-plane permeability, existing methods have not yet been standardized. This paper presents the results of a third benchmark exercise using in-plane permeability measurement, based on systems applying the radial unsaturated injection method. 19 participants using 20 systems characterized a non-crimp and a woven fabric at three different fiber volume contents, using a commercially available silicone oil as impregnating fluid. They followed a detailed characterization procedure and also completed a questionnaire on their set-up and analysis methods. Excluding outliers (2 of 20), the average coefficient of variation (cv) between the participant?s results was 32% and 44% (non-crimp and woven fabric), while the average cv for individual participants was 8% and 12%, respectively. This indicates statistically significant variations between the measurement systems. Cavity deformation was identified as a major influence, besides fluid pressure / viscosity measurement, textile variations, and data analysis.

Figures

Table 1: List of participants.

Table 2: Details of the individual set-ups.

Table 3: Variations in textile geometry.

Table 10: Normalized non-parallel cavity deformation. Participant 1 2a 2b 3 4 5 6 7 8 9 in % 1.1 2.2 0.5 0.3 1.9 0.4 0.3 0.4 0.7 0.3 Participant 10 11 12 13 14 15 16 17 18 19

Table 9: Anisotropy values averaged over data of all participants and corresponding cv.

Figure 10: Basic strategies for ellipse modeling – fixed center (left) and floating center (right).

Full text

Accepted Manuscript
In-Plane Permeability Characterization of Engineering Textiles Based On Ra-
dial Flow Experiments: A Benchmark Exercise
D. May, A. Aktas, S.G. Advani, D.C. Berg, A. Endruweit, E. Fauster, S.V.
Lomov, A. Long, P. Mitschang, S. Abaimov, D. Abliz, I. Akhatov, M.A. Ali,
T.D. Allen, S. Bickerton, M. Bodaghi, B. Caglar, H. Caglar, A. Chiminelli, N.
Correia, B. Cosson, M. Danzi, J. Dittmann, P. Ermanni, G. Francucci, A. George,
V. Grishaev, M. Hancioglu, M.A. Kabachi, K. Kind, M. Deléglise-Lagardère,
M. Laspalas, O.V. Lebedev, M. Lizaranzu, P.-J. Liotier, P. Middendorf, J.
Morán, C.-H. Park, R.B. Pipes, M.F. Pucci, J. Raynal, E.S. Rodriguez, R.
Schledjewski, R. Schubnel, N. Sharp, G. Sims, E.M. Sozer, P. Sousa, J. Thomas,
R. Umer, W. Wijaya, B. Willenbacher, A. Yong, S. Zaremba, G. Ziegmann
PII: S1359-835X(19)30079-X
DOI: https://doi.org/10.1016/j.compositesa.2019.03.006
Reference: JCOMA 5360
To appear in:
Composites: Part A
Received Date: 24 October 2018
Revised Date: 1 March 2019
Accepted Date: 9 March 2019
Please cite this article as: May, D., Aktas, A., Advani, S.G., Berg, D.C., Endruweit, A., Fauster, E., Lomov, S.V.,
Long, A., Mitschang, P., Abaimov, S., Abliz, D., Akhatov, I., Ali, M.A., Allen, T.D., Bickerton, S., Bodaghi, M.,
Caglar, B., Caglar, H., Chiminelli, A., Correia, N., Cosson, B., Danzi, M., Dittmann, J., Ermanni, P., Francucci, G.,
George, A., Grishaev, V., Hancioglu, M., Kabachi, M.A., Kind, K., Deléglise-Lagardère, M., Laspalas, M., Lebedev,
O.V., Lizaranzu, M., Liotier, P.-J., Middendorf, P., Morán, J., Park, C.-H., Pipes, R.B., Pucci, M.F., Raynal, J.,
Rodriguez, E.S., Schledjewski, R., Schubnel, R., Sharp, N., Sims, G., Sozer, E.M., Sousa, P., Thomas, J., Umer, R.,
Wijaya, W., Willenbacher, B., Yong, A., Zaremba, S., Ziegmann, G., In-Plane Permeability Characterization of
Engineering Textiles Based On Radial Flow Experiments: A Benchmark Exercise, Composites: Part A (2019), doi:
https://doi.org/10.1016/j.compositesa.2019.03.006
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In-Plane Permeability Characterization of Engineering
Textiles Based On Radial Flow Experiments: A Benchmark
Exercise
D. May
a,*
, A. Aktas
b
, S. G. Advani
c
, D. C. Berg
d
, A. Endruweit
e
, E. Fauster
f
,
S. V. Lomov
g
, A. Long
e
, P. Mitschang
a
, S. Abaimov
h
, D. Abliz
d
, I. Akhatov
h
,
M.A. Ali
i
, T. D. Allen
j
, S. Bickerton
j
, M. Bodaghi
k
, B. Caglar
l
, H. Caglar
l
,
A. Chiminelli
m
, N. Correia
k
, B. Cosson
n
, M. Danzi
o
, J. Dittmann
p
, P. Ermanni
o
,
G. Francucci
q
, A. George
r
, V. Grishaev
h
, M. Hancioglu
l
, M. A. Kabachi
o
, K. Kind
s
,
M. Deléglise-Lagardère
n
, M. Laspalas
m
, O. V. Lebedev
h
, M. Lizaranzu
m
, P.-J.
Liotier
t
, P. Middendorf
p
, J. Morán
q
, C.-H. Park
n
, R. B. Pipes
u
, M. F. Pucci
v
,
J. Raynal
w
, E. S. Rodriguez
q
, R. Schledjewski
f
, R. Schubnel
w
, N. Sharp
u
, G. Sims
b
,
E. M. Sozer
l
, P. Sousa
g
, J. Thomas
i
, R. Umer
i
, W. Wijaya
j
, B. Willenbacher
a
,
A. Yong
b
, S. Zaremba
s
, G. Ziegmann
d
a
Institut für Verbundwerkstoffe GmbH, Germany
b
Materials Division, National Physical Laboratory, United Kingdom
c
Department of Mechanical Engineering and Center for Composite Materials, University of
Delaware, USA
d
Department of Polymer Materials and Plastics Engineering, Technische Universität
Clausthal, Germany
e
Faculty of Engineering, University of Nottingham, United Kingdom
f
Processing of Composites Group, Montanuniversität Leoben, Austria
g
Department of Mechanical Engineering, Katholieke Universiteit Leuven, Belgium
h
Center for Design, Manufacturing and Materials, Skolkovo Institute of Science and
Technology, Russia
i
Khalifa University of Science and Technology (KUST), Abu Dhabi, UAE
j
Centre for Advanced Composite Materials, University of Auckland, New Zealand
k
Composite Materials and Structures Group, INEGI, Portugal
l
Department of Mechanical Engineering, KOÇ University, Turkey
m
ITAINNOVA Instituto Tecnológico de Aragón, Spain
n
Department of Polymers and Composites Technology & Mechanical Engineering, IMT
Lille Douai, France
o
Department of Mechanical and Process Engineering, ETH Zürich, Switzerland
p
Institute of Aircraft Design, University of Stuttgart, Germany
q
Institute of research in Materials Science and Technology, Universidad Nacional de Mar
del Plata, Argentina
r
Faculty of Manufacturing Engineering Technology, Brigham Young University, USA
s
Chair of Carbon Composites, Technische Universität München, Germany
t
Mines Saint-Etienne, Université de Lyon, CNRS, UMR 5307 LGF, Centre SMS,
Departement
MPE, F-42023 Saint-Etienne, France
u
Composites Manufacturing & Simulation Center, Purdue University, USA
v
C2MA, IMT Mines Ales, Univ. Montpellier, Ales, France

2
w
Institut de Soudure Group, France
*Corresponding author mail: david.may@ivw.uni-kl.de, phone: +49 631 31607 – 34
Abstract
Although good progress was made by two international benchmark exercises on in-plane
permeability, existing methods have not yet been standardized. This paper presents the
results of a third benchmark exercise using in-plane permeability measurement, based on
systems applying the radial unsaturated injection method. 19 participants using 20 systems
characterized a non-crimp and a woven fabric at three different fiber volume contents, using
a commercially available silicone oil as impregnating fluid. They followed a detailed
characterization procedure and also completed a questionnaire on their set-up and analysis
methods. Excluding outliers (2 of 20), the average coefficient of variation (c
v
) between the
participant’s results was 32% and 44% (non-crimp and woven fabric), while the average c
v
for individual participants was 8% and 12%, respectively. This indicates statistically
significant variations between the measurement systems. Cavity deformation was identified
as a major influence, besides fluid pressure / viscosity measurement, textile variations, and
data analysis.
Keywords: A. Fabrics/textiles; B. permeability; D. Process Monitoring, E. Liquid
composite moulding, E. Resin flow

3
1. Introduction
Liquid Composite Molding (LCM) processes are employed for the manufacture of fiber
reinforced polymer composites (FRPC), since they allow to efficiently manufacture
components of different complexity and size at higher rates than autoclave processes. To
obtain fast and complete saturation of the reinforcement with liquid resin in LCM, a suitable
process design is desirable, which requires knowledge about material properties. The textile
permeability is particularly important. It is defined by Darcy’s law, which correlates the
phase-averaged flow velocity  with the impregnating resin pressure gradient , its
dynamic fluid viscosity , and the textile permeability, which quantifies the conductance
of the porous media for liquid flow (Eq. 1).
  
󰇡


󰇢
 
(1)
The permeability of fiber structures, such as textiles, is generally direction-dependent and
therefore described by a second-order tensor. Commonly, textile symmetry conditions are
taken into account so that the tensor can be diagonalized, which leads to four remaining
values describing flow in any direction within a fiber structure (assuming absence of
coupling between in-plane and out-of-plane flow):
 Highest in-plane permeability (K
1
), in-plane refers to the textile layer;
 Lowest in-plane permeability (K
2
), oriented perpendicular to K
1
;
 Orientation angle of K
1
(β), relative to the production direction of the material (0°);
 Out-of-plane permeability (K
3
), oriented perpendicular to K
1
and K
2
.
The present paper focuses on the characterization of the in-plane permeability (K
1
, K
2
and
β).
Despite the relevance of accurate permeability characterization for process efficiency,
existing in-plane permeability characterization methods have not yet been standardized.
Following several smaller regional benchmark studies [1-5], the results of the first truly

4
international benchmark exercise on in-plane permeability measurement were published in
2011 [6]. In this exercise, same fabric was used by all participants, but no specifications
were made regarding the measurement method and the test parameters. This resulted in a
scatter of the measured permeability values of more than one order of magnitude. A second
international benchmark exercise with a predefined measurement procedure [7] followed.
The participants were required to apply an unsaturated linear injection method. In
unsaturated linear injection of a fluid into a dry reinforcement sample, one-dimensional flow
develops. The resulting flow front movement can be tracked, and the permeability along the
specimen axis can be derived using a 1D formulation of Eq. (1). This benchmark exercise
showed - for this specific test method - that by defining minimum requirements for
equipment, measurement procedure and analysis, satisfactory reproducibility of data
obtained using different systems can be achieved [8]. In-plane permeability characterization
based on radial flow experiments is an alternative approach, where the test fluid is injected
through a central injection gate into a tool cavity containing the reinforcement sample.
Advantages of this approach are that only one test is required for full textile characterization
including K
1
, K
2
and β and that the possible influence of race-tracking on test results is
reduced. Hence, it was agreed at the 13
th
International Conference on Flow Processes in
Composite Materials (FPCM) in Kyoto (2016) to perform a third international benchmark
exercise, focusing on unsaturated in-plane permeability characterization based on radial flow
experiments. This benchmark exercise was organized by the Institut für Verbundwerkstoffe
(IVW, Kaiserslautern, Germany), and strongly supported by the National Physical
Laboratory (UK), the University of Nottingham, the University of Delaware (CCM), the
Montanuniversität Leoben and KU Leuven as members of a steering committee.
Furthermore, the organizers were strongly supported by the Department of Polymer

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "In-plane permeability characterization of engineering textiles based on ra- dial flow experiments: a benchmark exercise" ?

This paper presents the results of a third benchmark exercise using in-plane permeability measurement, based on systems applying the radial unsaturated injection method. 

Q2. What future works have the authors mentioned in the paper "In-plane permeability characterization of engineering textiles based on ra- dial flow experiments: a benchmark exercise" ?

Global Method yes average 15 Weitzenböck et al. Reference Time Step Method no average 16 Weitzenböck et al. Global Method yes average 17 Weitzenböck et al. Elementary Method yes average 18 Adams/Rebenfeld Global Method yes average 19 Chan/Hwang Global Method yes target 1for detailed explanation the authors refer to these publications: Chan/Wang: [ 19 ] ; Adams/Rebenfeld: [ 18 ; 20-22 ] ; Weitzenböck et al. [ 23, 24 ] 2for detailed explanation they refer to Ferland et al. [ 17 ] 3When fitting an ellipse to the flow data there are two possibilites: Either fix the ellipse-center to the injection point ( yes ) or to allow the location of the ellipse center to deviate from the injection point ( no ) 4Refers to the way how injection pressure is considered in permeability calculation Average: 

Q3. What is the dominant component of the overall pressure?

It must be noted that textile compression pressure is the dominant component of overall pressure, because it easily exceeds the maximum injection pressure of 0.4 MPa and acts on the complete surface. 

Q4. What is the effect of the axial stiffness on the cavity height?

While relatively stiff systems remain closer to the target cavity height of 3.00 mm, the less stiff ones show increasing cavity height, presumably related to tool deflection. 

Q5. How many layers can have an influence on the measured permeability?

While the number of layers can have an influence on measured permeability, due to effects of nesting between layers and edge effects at the fabric-tool interface [18], such influence is assumed to be negligible for this benchmark, as eight layers or more are used. 

Q6. How many different systems did the coefficient of variation (cv) between the permeability values?

Averaged over all 12 test cases (highest and lowest in-plane permeability of two textiles at three levels of nominal Vf), the coefficient of variation (cv) between the permeability values determined with the different system was 32% and 44% for NCF and WF, respectively. 

Q7. What is the influence of Vf on the cavity?

This influence of Vf is presumably related to increasing cavity deformation resulting from increasing textile compression and also from increasing injection pressure. 

Q8. What is the permeability calculation algorithm used for step 3?

One of the permeability calculation algorithms is applied to the data of each pair of subsequent time steps and allows calculation of the permeability values based on the differences between the data sets at both time steps (esp. flow front progression). 

Q9. What are the main causes of the difference in permeability?

Several causes for this difference were identified, leading to the conclusion that strategies to minimize differences in permeability values obtained using different systems will have to focus on these points:- Cavity deformation is presumably the largest influence and strongly varies amongparticipants. 

Q10. What is the alternative approach to characterization of in-plane permeability?

In-plane permeability characterization based on radial flow experiments is an alternative approach, where the test fluid is injected through a central injection gate into a tool cavity containing the reinforcement sample. 

Q11. What is the effect of the pressure sensor on the permeability of the preform?

Opposing the assumptions underlying the application of Darcy`s law, differences in viscosity could have secondary effects on the permeability, e.g. different deformation behavior of the preform or variations in wetting behavior. 

Q12. What is the definition of a pressure difference between the vessel and the tool?

Pressure loss in the feed line between the pressure vessel and the tool can cause deviations of the actual injection pressure from the target pressure set at the vessel. 

Q13. What is the impact of the deformation on the variation of the results?

The impact of the deformation on the variation of the results becomes clear when only the 10 systems with a deviation from target cavity height smaller than 2% are considered for statistical analysis: 

Q14. What is the difference between linear and radial injection tests?

Compared to linear injection tests, radial injection tests allow by far more variation in these steps, due to the more complex flow front shape and accordingly more complex mathematics.