Multimaterial airframes based on 3D joints between AM metals and carbon-fiber composites

Project Information

MIMOSA

Grant agreement ID: 101091826

DOI

10.3030/101091826

Project closed

EC signature date 18 November 2022

Start date 1 December 2022

End date 30 November 2025

Funded under

• Digital, Industry and Space

Total cost

€ 5 475 469,25

EU contribution

€ 5 475 469,25

Coordinated by

POLITECNICO DI TORINO
Italy

Periodic Reporting for period 1 - MIMOSA (Multimaterial airframes based on 3D joints between AM metals and carbon-fiber composites)

Reporting period: 2022-12-01 to 2024-05-31

Summary of the context and overall objectives of the project

The aim of MIMOSA Project is the development of joined multi-material structures with new concepts able to achieve higher technological and economic performances with respect to current traditional joints. Furthermore, MIMOSA will lead to the application of circularity of materials and production by integrating the recycling, starting from the ideation phase of product and business. These ambitions needs will be achieved with innovative process for joining AlSi10Mg alloy from AM and CFRP without rivets or adhesives. The project proposes also the after-service materials regeneration (50% of metals and 90% of CFRP), the weight (-51%) and lead time (-65%) reduction and the overall process environmental footprint reduction. A prototype of aircraft vertical stabilizer (VS) will be fabricated as business case.

Many primary flight control (PFC) structures of aircrafts, are composed of CFRP skin and internal metal parts coupled by rivets. However this kind of joint has some drawbacks: (1) long time for assembling, (2) loss of fibers integrity due to holes, (3) rivets payload, (4) surface treatment with paints, (5) rivets failure, (6) hard inspection and maintenance. MIMOSA will go beyond the state of the art about: (1) the research-driven integration of different fabrication processes (LB-PBF, APPD, CFRP autoclave) and their certification guidelines. (2) New AM-CFRP inter-locked joint concept, with prevention of corrosion, fatigue, inhomogeneity, adhesion issues. (3) Materials recycling to reduced waste and generate economic value. (4) Improvement of the process: energy consumption, lead-time and cost. (5) Fabrication of prototype with the new MIMOSA joint, also used as business case (OB8).

Project objectives:
OB1. Design of innovative AM-CFRP joints supported by multi-physical modeling and simulation
OB2. Optimization and application of LB-PBF process for AlSi10Mg alloy
OB3. Optimization and application of APPD coating to metals
OB4. Fabrication of the joint with CFRP autoclave curing and fabrication of the prototype
OB5. Pre-standardization and establishment of safety levels for regulation and certification
OB6. After-service recycling of materials with the creation of technological and economic value
OB7. Validation of KPIs of samples and prototype (vertical stabilizer, VS) by testing campaign
OB8. Development of business plan for Project’s exploitation; economic validation through the prototype

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Design and simulation activities provide:
● weight reduction of 1.27g/mm2 (-51% compared to riveted joint);
● tensile mechanical strength of 36MPa (+60.5%/+ 51.5% operational performance);
● uniform stress distribution with target 215MPa/safety coefficient;
● 1.5 ratio between the thermal expansion of materials.

LB-PBF process:
● to optimize the LB-PBF process on AlSi10Mg for hybrid structures with material density = 99.95%;
● validation of fatigue on 170 samples items;
● optimization of fitting structures for vertical stabilizer prototype.

APPD coating optimization:
(a) improved wetting to epoxy precursors and adhesion to epoxy matrix, (b) corrosion protection with "self-healing" capacity in case of damage. The coating is applied by aerosol-assisted APPD.

AM metal – CFRP joints fabrication:
• to optimize the autoclave-cured prepreg process;
• to build the AM-CFRP samples;
• to build the prototype (vertical stabilizer) by autoclave-curing.

Certification methods and tests for materials/products/processes:
• to define normative requirements related to the Project;
• to define the actions needed to get multi-disciplinary optimization of the production process.

Joints disassembling and metal recycling by AlSi10Mg powder regeneration

Recycling of composites (size < 1mm at 90% of vol. fraction, particles recycling efficiency = 90%).

Operative tests on materials and components (characterization of materials and processes, static tests on CFRP by ASTM D3039, joints strenght test by ISO 22841 and ASTM D3528, fatigue test on CFRP and joints by ASTM D3479 and ISO 9664.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Expected results:
- Models of the joint (thermo)mechanical performances
- Optimized LB-PBF process for AlSi10Mg parts fabrication
- Optimized APPD coating of metal parts
- Optimized process for AM-CFRP joints
- Certification guidelines
- Optimized atomization process
- Optimized CFRP recycling process
- Results of testing campaigns on samples and prototype
- Economic results of the prototype (business case), and business plan for MIMOSA exploitation

The Project contributions in the long term (4 years after conclusion) are:
- EI1. (Technological). Resilient, sustainable & secure (critical) raw materials value chains for EU industrial ecosystems.
- EI2. (Technological/scientific). New sustainable-by-design materials with enhanced functionalities and applications in a wide range of industrial processes & consumer products.
- EI3. (Environmental, societal). Leadership in producing materials that provide solutions for clean, toxic/pollutant free environment, decarbonizing industry, & safeguarding civil infrastructures.
- EI4. (Economic). Leadership in circular economy that strengthens cross-sectorial cooperation along the value chain and enable SMEs to transform their activities and business models.
- EI5. (Technological). Increased adoption of key digital and enabling technologies in industrial value chains and strategic sectors, paying particular attention to SMEs and start-ups.

Production of composite samples for mechanical testing

CFRP samples for tensile tests

Recylcing phase of aluminum parts 2

Aluminum samples from AM process

Composite lamination process

Recylcing phase of aluminum parts