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Invitation to international textile permeability and compressibility benchmark exercises

News International-French

29 Sep 2016

As an “out-of-autoclave” process, Liquid Composite Moulding (LCM) offers higher efficiency compared to autoclave processes, but improvements are being sought to achieve closer to autoclave production quality and consistency.

In Liquid Composite Moulding (LCM), dry fibre reinforcement is placed in a closed mould and resin impregnated. Different textile reinforcement formats (e.g. woven, multiaxial, braided) made of different fibre types (e.g. carbon, glass, natural, hybrid) are used with a wide range of thermoset resin systems, and increasingly with thermoplastic systems.

LCM process design is highly important to achieve complete saturation, which needs to be completed before the gelation time of a resin system, and curing. To optimise the design of such a process, numerical flow and cure simulations are performed. Simulations need representative textile and resin material input properties to achieve realistic results. Therefore, material characterisation plays a key role in enabling the design of LCM processes and commercial products.
Resin characterisation mainly involves degree of cure and viscosity analysis that are measured by using well established and commercially available offline measurement techniques (e.g. DSC, rheometer). Textile characterisation involves permeability and compressibility measurements. Permeability measurements are needed to determine permeability constants in three different directions (Kx, Ky and Kz), which are important for mould filling simulations. Preform compressibility measurements are required to define the required compaction pressures to achieve desired fibre volume fraction values and to facilitate an accurate approximation of mould deflection.

These fabric properties are measured using a range of measurement techniques as mentioned in [1]. However, to date there are no measurement standards, standardised test rigs, standard reinforcement materials, or standard test fluids available, and textile reinforcement characterisation measurements have not yet been fully transferred to or adopted by industry.

To date, an international benchmark exercise [2] has compared the in-plane permeability results obtained from different in-house built test rigs developed by the participants. As a result of this benchmark exercise, an in-plane permeability measurement procedure based on a channel flow permeability measurement approach has been documented [3]. This procedure was then used for a second in-plane permeability benchmark exercise [4].

From a permeability measurement survey [1] conducted by the United Kingdom’s National Physical Laboratory (NPL) and National Composites Centre (NCC), it has been identified that there is evidence of a need for further benchmark exercises on through-thickness and radial in-plane permeability measurements to compare the results obtained from the existing techniques, and preparation of procedures for future standardisation.

Planned International Permeability and Preform Compressibility Benchmark Exercises
At the 13th International Conference on Flow Processes in Composite Materials (FPCM 13) held in Kyoto, the scientific community agreed to conduct two new international benchmark exercises in support of future standardisation activities.
As a result of this agreement, National Physical Laboratory is organising a through-thickness (Kz) permeability measurement benchmark exercise. This benchmark exercise will allow participants to use their own method, with the aim of highlighting the differences in techniques and results. This work will lead to a baseline for a future round-robin through-thickness permeability exercise. NPL is also organising a preform compressibility measurement benchmark exercise. A preform compaction guideline, which consists of unsaturated and saturated compaction experimental procedures, will be provided to participants.

The Institute for Composite Materials (Kaiserslautern, Germany) is organising an in-plane permeability measurement benchmark exercise. It is planned that participants will perform unsaturated radial flow measurements at constant injection pressure based on provided guidelines. Besides NPL, the University of Nottingham (UK), the University of Delaware (CCM) (USA) as well as KU Leuven (Belgium) are supporting the organisation of the benchmark exercises as members of a steering committee.

In all benchmark exercises, it is planned to use the same textile reinforcements and silicone oil. Saertex is supplying a multiaxial (E-glass) reinforcement system and Hexcel is supplying a 2/2 Twill woven (E-glass) reinforcement system for the benchmarks. Both reinforcements are supplied free of charge. It is expected that all participants will cover their fabric shipment costs. Xiameter PMX-200 silicone oil (100 cSt) will be used as the test fluid. The final participant list will be handed to the silicone oil supplier to ensure that all participants will obtain this silicone oil from the same batch.
For further information and details on how to participate, please feel free to contact us (see details below) by the 28th October 2016.

On completion of these benchmark activities, the results will be jointly published in a peer-reviewed journal and in an international magazine. Also, experimental procedures will be drafted as pre-cursors for future standardisation.

Dr Alper Aktas, for Through-Thickness Permeability Benchmark and Preform Compressibility Benchmark
Dr.-Ing. David Becker, for Radial In-Plane Permeability Benchmark

[1] A Aktas, G Sims, C Lira, M Stojkovic. Survey of procedures in use for permeability measurements in Liquid Composite Moulding processes. NPL Report MAT 82, ISSN 1754-2979, May 2016. Accessible at
[2] R. Arbter, J.M. Beraud, C. Binetruy, L. Bizet, J. Bréard, S. Comas-Cardona, C. Demaria, A. Endruweit, P. Ermanni, F. Gommer, S. Hasanovic, P. Henrat, F. Klunker, B. Laine, S. Lavanchy, S.V. Lomov, A. Long, V. Michaud, G. Morren, E. Ruiz, H. Soll, F. Trochu, B. Verleye, M. Wietgrefe, W. Wui, G. Ziegmann.  Experimental determination of the permeability of textiles: A benchmark exercise. Composites Part A: Applied Science and Manufacturing. Volume 42, Issue 9, p. 1157–1168, September 2011.
[3] JB Alms, N Correia, SG Advani, E Ruiz, CT Gonçalves. Experimental procedures to run longitudinal injections to measure unsaturated permeability of LCM reinforcements. FPCM 2010.
[4] N. Vernet, E. Ruiz, S. Advani, J.B. Alms, M. Aubert, M. Barburski, B. Barari, J.M. Beraud, D.C. Berg, N. Correia, M. Danzi, T. Delavière, M. Dickert, C. Di Fratta, A. Endruweit, P. Ermanni, G. Francucci, J.A. Garcia, A. George, C. Hahn, F. Klunker, S.V. Lomov, A. Long, B. Louis, J. Maldonado, R. Meier, V. Michaud, H. Perrin, K. Pillai, E. Rodriguez, F. Trochu, S. Verheyden, M. Wietgrefe, W. Xiong, S. Zaremba, G. Ziegmann. Experimental determination of the permeability of engineering textiles: Benchmark II. Composites Part A: Applied Science and Manufacturing. Volume 61, p. 172–184, June 2014.