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TFP Strut Qualification

Periodic Reporting for period 2 - SPS_TFP_SQ (TFP Strut Qualification)

Reporting period: 2016-10-01 to 2018-01-31

This activity addresses structural parts which are used for transmitting tension and/or compression forces called struts or tie-rods. The current state-of-the-art is a strut with carbon-fibre reinforced polymer (CFRP) tubes bonded and sometimes riveted to metallic fittings. This technology was established because it was so far not possible to design and manufacture complex geometries at the load introduction points (fittings) in CFRP. The state-of the art product manufacturing involves 4 to 5 processes: filament winding or hand layup, resin injection and curing, metal fitting milling, bonding and in some products riveting. Besides, the manufacturing of the raw fitting material consumes a lot of energy, in particular for the most common type (titanium fittings). For a typical design fittings account for about 70% of the total strut mass. Another disadvantage of the current technology is the interface between metal fitting and CFRP tube. The load introduction between these parts is very inefficient, resulting in a large size of the fitting and additional carbon fibre layers in the tube. Bonding between the tube and the fittings is performed manually and requires special adhesive materials qualified for space applications. Quality assessment of the complete state-of-the-art manufacturing process requires sophisticated expertise and testing. Scientific applications require struts with high thermal stability. To achieve this, the state-of-the art products use Invar fittings, a special nickel–iron alloy that is very expensive and difficult to procure.

The new product will be the first of its kind providing a solution entirely manufactured in CFRP with continuous fibres in one integral part and therefore no internal load introduction interfaces. Manufacturing will involve only two processes: tailored fibre Placement and resin injection with subsequent curing. For a typical strut such approach leads to approximately 75% mass reduction without changing stiffness and strength properties of the strut. The fully integral strut can be manufactured semi-automatically, reducing manufacturing time and simplifying Quality assurance. The thermal stability is intrinsically given due to the low thermal expansion of CFRP material. This project addresses the work programme topic “spinning-in” of terrestrial solutions to challenges in space.

The proposed technology addresses the following problems, creating a business opportunity on the space market:
1. Exceptional mass saving - is critical for all space missions
2. Cost and manufacturing time reduction - is a natural requirement for all business and in particular space endeavours
3. Dimensional stability - is required for precise scientific missions
4. Reducing the environmental footprint - is essential to meet the European and global challenge to protect the environment

The overall objective of this activity is to qualify by extensive testing market relevant strut types.
The performed work and major achievements within this activity have been:
• Requirements definition as fundamental input to the product development process
• Derivation of strut concepts and realisation into detailed strut designs including analytical verification as basis for manufacturing and testing
• Elaboration of qualification test plan and procedures as basis for testing preparation
• Development of an inner core tool. This topic was unsolved for the prototype of Phase 1 and is considered as one of the main achievements in this activity
• Manufacturing of >100 struts representing ten market relevant strut types, manufactured with the tailored fibre placement and hollow core technology
• Estimation on serial production manufacturing cost
• Completion of sample test campaign (bolt preload, insert pull-out, outgassing) that was foreseen to mitigate the risk on any design flaws before full strut manufacturing and qualification test campaign
• Qualification testing of the whole struts under static tension-compression (qualification loads and rupture), mechanical cycling, thermal vacuum including thermal cycling and CTE measurements
• Elaboration of test reports and derivation of the qualification summary
• Project management and continuous updating of project plan to keep track on schedule and cost
• Elaboration of the business plan including a roadmap for exploitation of the results

Dissemination of project activities has taken place continuously throughout the project duration at dedicated events (H2020 Space International Information Day, European Conferences on Spacecraft Structures, Materials and Environmental Testing, SpaceTechExpo Europe). The latter event was used to officially introduce the SpaceStrut concept to the public. For many upcoming events in 2018 participation is confirmed:
• JEC World, Paris, March 2018 - Global composite industry trade show
• FIDAE, Santiago de Chile, April 2018 - Biennial international air show
• Space Symposium, Colorado Springs, April 2018 - Annual space symposium for for more than 30 years
• NewSpaceVision, Berlin, April 2018 - Technology conference focusing on New Space
• ECSSMET, Nordwijk, May 2018 - European conference on spacecraft structures, materials and environmental testing, including a paper presentation about the H2020 SME instrument activity
The SpaceStruts are the first of its kind providing a solution entirely manufactured in CFRP with continuous fibres in one integral part. Therefore no internal joints between indiviual structural parts exist. Compared to the state-of-the-art, this is not just an incremental improvement, but a redefinition of the state-of-the-art. Such ultra-lightweight structures allow cost saving for space missions, reduction of the environmental footprint and are potential enablers of applications that are so far not feasible.
SpaceStruts family