Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ARCTIC (Advanced Bearing Technologies to Increase Capabilities)

Teaser

The development of Very High Bypass Ratio (VHBR) engines is a promising engine concept to fulfil the objectives of the Sustainable and Green Engines (SAGE) programme. From an engineering point of view, the significant environmental benefits of this new engine are synonymous...

Summary

The development of Very High Bypass Ratio (VHBR) engines is a promising engine concept to fulfil the objectives of the Sustainable and Green Engines (SAGE) programme. From an engineering point of view, the significant environmental benefits of this new engine are synonymous with an increased speed and rolling contact stress capabilities.
In terms of engine performance, the design, sizing and capacities of the rolling element bearings can affect the whole engine architecture. The rolling element bearings have been clearly identified as crucial components with respect to reliability.
Nowadays, new engine architecture developments are possible only if they take into account new technologies and developments for engine’s component parts.
The main scope of ARCTIC proposal is thus: “to develop and demonstrate various unique rolling bearing technologies that overcome current design rules of aero-engine bearings and allow the development of a VHBR engine (or other high performance architectures)”.
ARCTIC project will also contribute to the raising of the Technology Readiness Level (TRL) of the proposed bearing technologies, meaning that the overall whole engine system reaching TRL 6.
ARCTIC is full in line with the Clean Sky 2 programme, since it will support the key Societal Challenge. It will enable cutting edge bearing solutions for further gains in decreasing fuel burn, CO2, NOX, noise emissions and strongly contribute to the renewed ACARE SRIA. ARCTIC proposers are committed to support future global leadership of the European aeronautical industry supply chain, creating jobs through and reinforced competitiveness.
The new bearing technologies to be developed in ARCTIC will demonstrate the following specific objectives (in comparison to current bearing baseline solution):
- 15% to 30% improvement in terms of rolling contact stress capability in back-to-back comparison with current baseline solution. This should be accompanied with an enhanced bearing behavior in cases of degraded running conditions (poor or polluted lubrication, high temperature) and a 25% increase in rolling bearing speed capacity.
- to provide analysis tools for component life prediction based on a fine study of failure mechanisms, and integrating developed new bearing technologies. This should be achieved by the delivery of a utilizable model and associated new bearing design rules for industrial implementation.

Work performed

The ARCTIC project is a 5-year project basically decomposed in two main activities. The first 24 months are dedicated to material screening, new steels development and elementary evaluation. The surface engineering (including thermal and mechanical treatment) is also part of the scope. Then, the 3 next years are used to test to developed advanced steels and to validate their performances.

The first project period ended after 18 months and was mainly dedicated to steel developments to reach the project performance objectives.
Two main approaches will be used: traditional VIM-VAR processing of novel alloys and PM-HIP processing of novel alloys.

For the VIM-VAR route, new steel compositions have been designed and produced. Two series of three and four experimental melts have been assessed.
The experimental alloy compositions were designed using the Thermo-Calc software, bearing in mind the requirements described in the “Ideal Aero-Engine Bearing Steel” report.
Basically, the “chromium and nickel equivalent” were part of the design criteria, to ensure that a corrosion resistance level, that the delta-ferrite content was likely to be low and that the Ms temperature of the carburised case would not be too low.
The two series of experimental melts were made. The homogenization temperature was investigated to keep an acceptable level of δ-ferrite and the melts have been hot rolled. The Ms temperature have also been evaluated.
At the end, few variants are potential candidate as a high capacity steel for hybrid bearings for aero-engines.
The activities on the heat treatment have also started.
The next steps will be a whole mechanical and metallurgical evaluation of the potential candidates to select the final steel composition for anindustrial VIM-VAR melt.

Regarding the Powder Metallurgical (PM) routes, firstly, a screening of existing grade and PM steels properties have allowed to choose potential existing PM grades.The results of Single-ball test using AMS6560 grade has demonstrated a very high rolling contact fatigue resistance for raceway or rolling elements compare to AMS 6490 (M50) steel.
A whole PM process analysis have been initiated to make a risk analysis and to evaluate the existing gaps for a potential introduction of PM steels on Mainshaft bearing applications.

Finally, a modelling approach have been initiated to be able to reproduce and explain the effects of material and surface characteristics on performances. This objective will be achieve by developing a rolling contact semi-analytical model (integrating the heterogeneities, the elasto-plastic behaviour and the residual stresses profiles) based on existing promising scientific researches at the INSA of Lyon (LaMCoS laboratory).
The rolling contact model is now available and need to be feed by some experimental data. Cleanliness analysis and micro-compressive tests have been initiated to support the numerical activities.

Final results

The main impact of this proposal is to provide key bearing steel, heat treatment and raceway finishing technologies for the development of a VHBR engine and other next generation engines to meet the objectives of the Clean Sky 2 programme in terms of environmental benefits and European competitiveness.
The technical impacts of ARCTIC project are potentially huge and because several major advances/innovations will be necessary to achieve the technological step requested.

- The possibility offered by ARCTIC project technologies to design new environmentally friendly aero-engines (such as a VHBR engine).
- A full exploitation of components potential in terms of performance (a totally leakage free, power and weight optimized solution) and life estimation through increased knowledge of the material fatigue behaviour.

The envisaged technical exploitation of the results is significant as there will be:
a) Direct exploitation of cutting edge rolling bearing technologies: newly developed materials (steels & ceramics) and associated surfaces treatments,
b) A breakthrough in terms of rolling bearing performance and design possibilities,
c) Additional exploitation of some stand-alone results: experimental database results and back-to-back comparison of PM-HIPed steel with conventional remelt steel technology; application of state-of-the-art mechanical contact modelling,

It is also important to note that the developed technologies in this project (material and surface engineering development) can be directly transferred, like elementary bricks, to improve performances of other engine technologies (for example gears) or in other sectors (i.e railwayautomotivemaritime).

Employment will be directly linked to the economic impact of ARCTIC project at the European and global levels. ARCTIC project will maintain and create jobs for aero-engine manufacturers and also for rolling bearing and material suppliers.
Employment of highly skilled personnel will be required for some of the proposed technologies.
ARCTIC project will promote education by involving a university/research centre, INSA of Lyon.