INFUCOMP

Simulation based solutions for industrial manufacture of large infusion composite parts.

Seventh framework programme priority

A CEC Framework VII collaborative research project to develop new technologies and simulation tools to predict Liquid Resin Infusion (LRI) of large aircraft composite structures

• GA number: ACP8-GA-2009-233926
• Collaborative project: Small or medium-scale focused research project
• Coordinator: Anthony Pickett (Engineering Systems International, Eschborn, Germany)
• Dissemination: Hexcel and ESI Group
• GA number: ACP8-GA-2009-233926
• Duration: 1st October 2009 to 30th September 2013

Summary

To date, manufacture of advanced composites in the Aerospace industry mostly uses pre-impregnated composite materials, tape laying technologies and autoclave curing for the production of large, high performance structures and components. These combined technologies allow toughened resins to be uniformly dispersed in a well controlled fiber system with a high fiber content, producing excellent mechanical stiffness, strength and fatigue resistance properties. However, there are drawbacks, including high material costs, limited shapeability, complex, expensive and time-consuming manufacturing, and short materials shelf life. As a consequence alternative manufacturing methods are being sought based on Liquid Resin Infusion (LRI) technologies in which the resin is infused only after all dry textiles are assembled to form the final composite component configuration. This assembly, prior to infusion, is called a preform. The advantages are lower material and material storage costs, indefinite shelf life (for the textiles) and the ability to manufacture integrated structures having complex geometries only limited by shapeabilty of the dry preforms.
Currently, LRI of large composite structures require 'trial and error' testing and considerable experience on the part of designers and manufacturers to get the correct set-up. The high cost and risks involved will often lead to overly conservative infusion designs with associated cost and performance penalties; or may lead to alternative, less competitive, manufacturing technologies and materials being adopted.
The scientific aim of the CEC INFUCOMP project (CEC, 2010) is to provide a full simulation chain for LRI manufacture of large aerospace composite structures dedicated to solutions required by the European Aircraft industry.  Extensive materials testing for a range of dry fabrics and permeability characterization is being conducted from which new constitutive laws will be developed. Software developments will be implemented into an existing infusion code PAM-RTMTM (ESI Group 2009), which has essentially been developed for Resin Transfer Molding (RTM) processes. Some other specific developments include process optimization, cost analysis and predictive tools to characterize imperfections such as porosity and residual stresses. One major software development is extension of current scalar computing capabilities so that advantage may be taken of State-of-the-Art massive parallel computers; this will allow a step change to full 3D infusion modeling involving tens of millions of elements. The new capabilities will be validated by a series of demonstration studies on representative parts using the different infusion technologies actively used at the four industrial partners sites.

Infusion methods for composites

Infusion of dry fabrics may be undertaken using a variety of processes. The first popular method is Resin Transfer Molding (RTM) which is widely used for the manufacture of small to medium sized components and is especially suited to automation and the manufacture of relatively high production volumes. High injection pressures can be used to reduce infusion time, but is in practice limited by stability of the tooling and effects such as porosity and fiber distortion which may occur especially in the vicinity of the injection ports. The main limitations are high cost and size (weight) of the two part tooling, and relatively long cycle times needed to cure the resin before the part is sufficiently stable to be extracted from the mould. The key steps in RTM are shown in Figure 1 below and involve shaping the preform, extraction and trimming of the preform, and resin infusion in sealed matched (usually metal) tooling.
 

Fig. 1.  Steps in pre-forming and RTM infusion (Rudd, et al. 1997).

As mentioned some limitations of RTM are high cost, weight and complexity of tooling. Liquid Resin Infusion can overcome these problems and requires only one sided tooling, which may be significantly lighter and therefore cheaper. Figure 2 below shows the essential features of LRI. A dry fabric is laid up in the tooling, usually with a low permeability flow medium to aid infusion, and a peel ply and/or release ply to help separation of the final composite and flow medium after curing of the final part. The complete setup is sealed in a vacuum bag that prevents air entering the system; vacuum is applied at one location (outlet port) and draws resin from an inlet port through the dry fabric. Large complex parts invariably need a system of inlet and outlet ports which may use synchronized opening and closing to enable complete infusion of the large volume. Also shown in Figure 2 is an intermediate stage of the infusion of an aircraft composite fairing, described in more detail (Alonim, 2005).

Fig. 2.  The LRI infusion set-up and an industrial example (Courtesy IAI).

Dissemination articles and further reading

• Press release published by ESI Group on March 2nd, 2010 

References

• 1. Advani, S., Bruschke, M., & Parna, R. (1994). Resin transfer molding. In S. Advani, Flow and rheology in polymeric composites manufacturing (pp. 465–526). Amsterdam: Elsevier Publishers.
• 2. Alonim, J., Arnon E., David A., Gold E., Green A.K., Hackman N. and Leibovich H. (2005). Development of a Business Jet Component by Resin Infusion using a Stitched Preform, Proc. 26th Intl. SAMPE EC Conf., Paris, 9A, (pp. 476).
• 3. CEC. (2010). Simulation based solutions for industrial manufacture of large infusion composite parts. INFUCOMP CEC project ACP8-GA-2009-233926.
• 4. ESI Group. (2009). 99 Rue des Solets, Silic 112, 94513 Rungis-Cedex, France.
• 5. Mathur et al. (2001). Flow front measurements and model validation in the vacuum assisted resin transfer molding proces. 22 (4), 477-490.
• 6. Rudd, C., Long, A., Kendall, K., & Mangin, G. (1997). Liquid moulding technologies. Cambridge, England: Woodhead Publishing.