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Development of an optimized large scale engine CFRP annulus filler

Final Report Summary - ORCA (Development of an optimized large scale engine CFRP annulus filler)

Executive Summary:
An annulus filler is a rotating part on modern jet engines. It smoothens the airstream and is vital for proper functioning of the rotor system. Designed to be as lightweight as possible, yet stable enough for impact of small to medium birds and hailstones, the current state of the art are metallic designs.
The main task of the ORCA project was to design, manufacture and test a composite annulus filler. After several design iterations, a composite design was considered mature enough to be manufactured and tested on the Advanced low pressure system (ALPS) engine of the (sustainable and green engine) SAGE3 project.
The targets set at the beginning of the project were overfulfilled. In comparison to the best existing design, the ORCA filler reduces the weight by over 40%, whilst providing the same excellent impact and fatigue behaviour. Cost wise, the part is competitive to existing designs, with possible further cost reduction summing up to a lighter and less expensive part.
The part has been awarded with the international JEC award on innovation in aeronautics in 2014, and sets a new benchmark for cost- and quality efficient production routes for CFRP parts.
The part has been on display at exhibitions, and several lectures and conference contributions were published. Three patents were filed protecting the generated foreground.

Project Context and Objectives:
As part of the ALPS engine, the composite annulus filler was to provide significant weight improvements at the same mechanical behaviour as the benchmark solution. Whilst the annulus filler is a rather lightweight part already (typically below 0.5 kilograms even for the largest engines), and often exchanged during maintenance, the sheer number of 18-25 fillers (same number as fan blades) per engines allows a significant system weight reduction, but also a manufacturing process capable of high annual production rates, yet also very narrow tolerances due to balancing issues. Within the proposed scope of work, the ORCA project had to tackle several tasks in order to verify the suitability of an CFRP (Carbon-fibre reinforced plastic) annulus filler.
1) Material innovation
The major driver for rotating devices is the self-imposed, centrifugal load created through the high revolutions of modern jet engines. While this quasi-static loading can be compensated by intelligent fibre orientation and layup, the second major design driver, the impact resistance, implies challenges on brittle composite systems. The proposal included an modification approach of the raw resin system to improve the toughness whilst keeping the processability and the mechanical properties at the same level.
2) System integration innovation
While the part itself is a one-shot part already, there are several metallic add-on parts to be installed. The work required for the associated bonding operations is taking over 20 percent of the actual manufacturing time, it is a promising optimization area.
3) Process innovation
The major part of workhours for production of CFRP parts are associated with the preforming. Examples from the packaging industry, from innovative furniture design and graphic design demonstrate a potential for use in the production of preforms. Articles such as cartons, pieces of furniture, boxes, clothing etc have been designed drawing on ideas developed from the art of origami, which lead to finished products with fewer folding and assembly steps following the cutting out of the flat blanks of raw material. In making thick-walled components with complicated geometry by the RTM process there can be faults in the fibres, and their positioning can depart from the ideal. These defects affect the strength and the behaviour under load of such thick-walled components. Since each such component presents its own particular problems in this regard, it is necessary to develop an evaluation strategy to obtain information about the effects of these defects and to obtain a measure of the extent to which they are admissible. To do this the tooling must be analysed to identify joints and sharp bends, to estimate their potential for causing defects of this kind, and to set up rules for the design of tooling.
4) Part innovation
After tackling tasks 1-3, a suitable design for a real part needed to be constructed, analysed, build and tested. Whilst composite annulus filler designs have been around since the early 1990ies, no working concept could yet be demonstrated. The final aim of the ORCA project was to bring a composite design to a level where enough confidence in the general concept was established, that a test series (including a flying test bed) proving the flight worthiness could be justified.
The approach was to start with virtual design and analysis, to verify critical design elements with sub-component tests , provide process data on the basis of simple lab trials and scaled technology demonstrators and finally confirm the analysis results by static and dynamic ground testing.

Project Results:
1) Material innovation
Within the material selection phase, the first question to solve was if an untoughened resin system could deliver enough performance to survive hail and bird strike requirements, or if a toughened system, which comes with a cost- and processing disadvantage, would deliver improved performance. This has been tested at IWK Rapperswil with standard-CAI-tests (compression after impact) on commercially available, aerospace-qualified products.
Four candidate materials were identified, meeting the qualification requirements and being supplied in acceptable quantities.

The results were not as expected, as an unmodified epoxy resin with standard HTA fibres would deliver approximately the same performance, as the more expensive, less process-able resin systems do. This can be explained by the unique design of the annulus filler, which tries to transfer the impact away from the aerodynamic lid to the substructure (see appendix figure 1)
It was therefore decided to use the most economic material, as the slight mechanical advantage given by the more expensive materials could not justify their usage cost wise.
2) System integration innovation
In order to stay compatible with the finalized shape of fan blade and fan disk, not all possible integrations could be realized. However, several add-on parts were already integrated in the main body, reducing the bonding operation to the bonding of seals and effectively eliminating over 5 hours of manufacturing time per part. The integrational design was a key point for a possible commercial success, and detailed solutions have been included in the patent filings.

3) Process innovation
The primary approach of near-net-shape preforming could only be achieved partly. Main reason were the narrow tolerance requirements, which could not be achieved without post-demoulding machining. However, an improvement to existing preforming strategies could be implemented: with a sophisticated use of different CTE (coefficient for thermal expansion) in the main tooling, the preforming stabilization step was integrated into the main RTM tooling, effectively reducing both investment costs (for the preforming line) and process time
The preforming strategy was long debated. Finally, an optimized layer cut procedure with an automization approach for the preformhandling reduced the preforming time to less than one hour, including the stabilization cycle. This reduced the throughput time per part to less than two days, effectively allowing mass production of fillers.

4) Part innovation
With a high degree of design freedom, several potential solutions for composite annulus fillers were designed (see appendix Figure 2)

3 major designs were intensively analysed, resulting in an highly integrated composite annulus filler.
The part approach allows a direct comparison to an existing metal filler, as it has been designed to replace metallic fillers on existing engines. The results were highly promising:
• The weight could be reduced by over 40%.
• The final part costs are comparable.
• The manufacturing process proved to be very stable, even when the resin & fibre quality is reduced on purpose.
• The target throughput time was undercut by over 10 percent.
• The transfer from research environment to production facilities was established without quality reduction or cycle time rise.

Alltough the ground testing has been very successful (see Appendix fig. 3), the ultimate confirmation of the flight worthiness will be a successful flight test, which is currently scheduled for Q3/2014.

Potential Impact:
The lightweight design improves jet engine fuel efficiency at no significant cost rise, therefore it is perfectly contributing to the goals of CleanSky and SAGE.
The partners within the consortium experienced excellent cooperation, resulting in continued joint research activity within cross-border funding schemes (M.era-net EUREKA and Horizon 2020).
The economic impact for FACC can be considered very important. Not only that the potential portfolio of manufacturing has been extended, the know-how gained in the production of very-high-volume parts has already been transferred to other serial production projects. In addition, not only the topic manager, but also competitors have already set up preliminary negotiations to exploit the use of comparable parts on their engines. A transfer into serial production is currently aimed for in 2015/16, which would result in an economic advantage for FACC and its supply chain, as the machinery and tooling required for a full scale serial production would result in a net investment of approx. 6 Mio Euro within Europe.
For university of Rapperswil, the research conducted has been published in various conferences, strengthening the reputation of an expert research facility in composite design and manufacturing. A peer review publication of the whole research within ORCA is currently under review in Applied composite materials journal.
The final outcome received major attention in the composite industry with the JEC Award in 2014. The composite annulus filler has been awarded as the Innovation breakthrough product in aeronautical applications, exactly 10 years after the first award for FACC (see app. Fig. 4).

List of Websites:
public website: N/A
Contact details:
for HSR Rapperswil: Prof. Dr. Markus Henne; Oberseestrasse 10, CH-8640 Rapperswil; mhenne@hsr.ch
for FACC AG : Konstantin Horejsi, Office park 1/10, AT-1300 Flughafen Wien; k.horejsi@facc.at