Bleed systems decrease pressure and temperature to levels acceptable for downstream pipes and air cooling system. Bleed valves, regulating the pressure, have a strong safety issue: their failures can lead to aircraft depressurisation with the immediate request to land to the closest airport. In addition to all direct consequences on passengers/crews comfort, flight delay and traffic management, failures have a strong economic impact on airliners: a diversion is estimated to cost €150 000. In 2004, 10 diversions, consecutive to valves failure, were reported for the AIRBUS fleet. Valve failures, resulting from ballbearing blockage, are due to fretting and false Brinelling, known to occur in quasi-static assemblies in vibratory environments.
Due to the power increase of new aircraft engines and the extended service life of existing aircraft, vibration levels around engines are becoming extremely strong (about 25g). Temperatures can also reach up to 550oC. Systems surrounding engine zones are therefore submitted to new and extreme environmental constraints. Even if the tendency is to develop more electrical aircraft, most of the aircraft developed today, based on bleed systems, will still be in use during the next 20 years and their issues have to be solved. Today, bearings design and materials have reached their limit.
In the competition with United States (and Japan for bearings suppliers), BEARING was a unique opportunity to maintain European Air Systems and Bearings suppliers leadership by offering superior and affordable European technology, which supports an invaluable strategic advantage for European air-framers and airliners.
The main objective of the BEARINGS project was to develop a new generation of aeronautical bearings for extreme environmental constraints. The project focussed on the understanding of degradation phenomena and the definition of new bearing materials, processes and designs in order to answer the following constraints:
- corrosion and oxidation resistance
- impact resistance
- low friction torque (constant during lifetime)
- load variation resistance (0 to 5000 MPa)
- taking place in extreme environmental working conditions with temperatures of about 550°C and vibration levels at about 25g. An additional constraint will be that only dry lubricants will be authorised.
BEARINGS detailed objectives were:
- to better understand the degradations encountered in bearings, using recent advances in contact modelling;
- to propose innovative materials (bulk, smart sintered, nanomaterials) and adapted processes;
- to propose relevant bearing designs;
- to overcome the limitations, BEARINGS will introduce nanomaterials in aeronautical applications in order to reach the necessary properties in terms of hardness, toughness and strength.
BEARINGS reached the objectives defined due to advanced innovations in:
- Powder design and manufacturing
- Spraying processes
and because of technological developments focused on improving:
- Tribological test-bench capabilities
- Component test-bench capabilities
- Valve design integration.
The innovations can be summarised as:
Innovation No. 1: Adaptation and improvement of a new tribological methodology based on numerical modelling, tribological characterisation and analyses with the objective of proposing a bearing generic model definition.
Innovation No. 2: A better assessment of the local contact solicitations (amplitudes, directions and frequencies).
Innovation No. 3: Measure and introduce new material behaviour laws, which are relevant to the problems with bearings, to greatly improve a new tribological methodology.
Innovation No. 4: Improved understanding and modelling of the formation of the Superficial Tribological Transformations.
Innovation No. 5: Large degree of freedom in designing/conceiving/producing tribomaterial systems adapted to material property expectations.
Innovation No. 6: Responsible nanotechnology approach by using nanomaterials in agglomerated forms to avoid the release of nanoparticles in the environment which may affect human health.
Innovation No. 7: Innovative, smart nano-composite sintered materials with dry solid lubricants.
The main objective of the project was to propose a new generation of bearings, highly reliable, able to answer to the new and extreme constraints on aircraft as: the corrosion and oxidation resistance up to 550°C, impact resistance, low friction torque (constant during life time), contact stress (0 to 5000 Mpa) and vibration level (about 25g). This technological breakthrough was achieved proposing an innovative technology approach that included both scientific and technological aspects as:
- selection and development of new nanostructured materials tailored for the strong requirements needed, and their associated processes (high energy milling, plasma spraying and bulk consolidation) designed to keep the nanomaterials advanced properties;
- understanding of bearings degradation mechanisms of the behaviour of materials under extreme conditions (temperature, tribological in pressure + shearing conditions) through a coupling between modelling and expertises;
- understanding the mechanical, physical, chemical conditions leading to the Superficial Tribological Transformation within the skins of bodies in contact.
BEARINGS provided a unique opportunity to maintain European air systems and bearings suppliers’ leadership by offering a superior and affordable European technology, which supports an invaluable strategic advantage for European airframe manufacturers and airliners. As BEARINGS was a technological breakthrough, they will also have a considerable advantage on the world market.
Advances in the associated scientific/technological fields will give a strong advantage to the equipment supply chain and SMEs by improving their own skills and developing new ones. These competences will also be valid for sectors other than aeronautics.