CERFAC's major challenge is the design and manufacturing of strong and cost-efficient joints for high performance CFRP aero-structures. In particular, transfer of distributed loading along rivets lines in the assembly of flat or curved thin-walled stiffened panels, and introduction of concentrated loads for connecting lugs with thicker laminates are special & frequent problems.
CERFAC focuses on applications with significant volume and occurrence (butt straps & splices, orbital and longitudinal multi-functional joints, single and multiple bolts attachments), such that an increase of the strength to cost ratio of joints could lead to overall significant cost and weight savings.
CERFAC's high level objectives are:
- To increase the strength to cost ratio and damage tolerance of fastener areas in CFRP structures without weight, thickness and stiffness penalty;
- To reduce the number or fasteners (10 to 100% reduction), the local thickening of fastener areas and minimize the manufacturing & assembly costs (20% reduction).
This will be achieved thanks to advanced and rigorous research & development activities with the following major deliverables and outputs:
- A catalogue of validated reinforcement solutions at the locus of fastener holes or edges leading to lighter, stronger and more damage tolerant designs;
- This contribution would then help reducing further the number of fasteners, while increasing the load bearing capacity and damage tolerance of the assembly, with a significant step towards a reduced manufacturing cost. Repair and disassembly will be considered as mandatory requirements in this contribution;
- Upgraded design, analysis and testing methodologies as well as pragmatic guidelines for future exploitation of the new concepts in the next generation of aircrafts.
Better fasteners safely transfer loads
Composite aircraft structures are joined together with a variety of techniques and materials. EU-funded scientists are improving the reinforcement of fasteners for lighter aircraft and cost-effective assembly and maintenance.
The widespread use of carbon fibre-reinforced plastics (CFRPs) in the aerospace industry has enabled significant savings in weight and associated fuel consumption and emissions. Despite inherently superior mechanical properties in terms of stiffness-to-weight ratio, for full exploitation of CFRPs more efficient joining systems are needed to ensure damage-tolerant structures.
Critical components in aircrafts such as the fuselage and wings have several interfaces that require safe transfer of loads between composite parts with reduced weight and cost. This is necessary to increase the competitive position of the EU aircraft industry. Scientists are investigating reinforcement and joining solutions to address these issues with EU funding of the project 'Cost effective reinforcement of fastener areas in composites' (http://research.cenaero.be/~cerfac (CERFAC)).
Researchers are focusing on reducing either the weight or number, or both, of reinforcements in three application areas. These are generic butt straps for assembling thin-walled structures, advanced joints for final assembly of fuselage shells or barrels, and thicker laminates or thickened zones of thin-walled parts for more efficient and safer transfer of concentrated loads.
Scientists also focused on the development of solutions for small- to medium-sized sample parts as well as designs for the three applications for eventual testing. Design of reinforcement solutions was supported by advanced modelling using finite element methods and experimental analysis of reinforcement strength to characterise assembly. Extensive research was devoted to preparation of test specimens of composite materials with reinforcements. These were subjected to bending and pulling, open hole tension analysis, compression loading and preliminary fatigue testing. As a result of the test campaign, several solutions have been selected for further development in the upcoming project phase.
CERFAC expects to deliver advanced reinforcement solutions for aircraft composite structures that enhance the performance while reducing the number of fasteners required. This will also enable cost-effective manufacturing and assembly solutions through substantial reductions in weight, fuel consumption and emissions. As a result, the manufacturing, assembly, and inspection and maintenance costs of the aircraft industry will be reduced considerably.