Multiscale COmponents-MATerials-COntact interactions in braking systems and aircraft compressors – CoMatCo

The approach is based on the following key points:
- Development and elaboration of «model materials' representative of industrial materials but with reduced formulation and process
- Microstructure characterization of materials (including X-ray tomography) and their mechanical, thermal and tribological properties. For this purpose original devices are required, compatible with the materials, constraints of size and solicitation. Instrumentation at macro and microscopic scales is privileged to access several magnitudes scales (particularly by field measurements). Link of these characterizations with modeling of heterogeneous materials by multi-scale numerical approches (finite element method) and homogenization techniques, theoretical and semi-analytical.
- Tests on proven tribometers with material and interface (third body) characterization (including their gradients), after or during the loading, using creative ways to rheological characterization (rheometer and meso-tribometers). Link with a digital multi-scale approach and multi-physics considering the evolution of materials and interface with the solicitation.
- Integration of multi-scale approaches in systems modeling of the treated industrial applications and results.

'- Reduced formulation materials have been developed and characterized to have a fine description of the microstructures, which is a necessary step for modeling.
- On the basis of the complementarity of microstructural analysis, material properties characterization and heterogeneous modeling, an original methodology has been proposed binding properties and role of components. The idea was to develop means of heterogeneous calculations related microstructural analysis to identify the components playing a role on the properties, and not necessarily include all components.
- Original ways of characterizing materials and interfaces have been proposed, under compression and shear solicitation, coupled with field measurements to obtain bulk and local properties. These means are extendable to other materials.
- About heterogeneous modelling, theoretical and numerical methods have been developed and compared to each others with a relevance associated with the type of material considered.
- About characterizations by friction, progress has been made regarding the relevance of «micro-tribology« testing to obtain friction and wear indicators «controlled«.
- A numerical multi-scale methodology has been developed with interactions between the response of the complete system and heterogeneities across the contact. Macro Finite Element models are combined with resolution at he mesio scale by semi-analytical methods. This strategy has been validated for mechanical resolutions and extended to the thermomechanical part. It has the advantage of being quickly integrated into industrial practice.
- Finally it was shown the necessity to consider the evolution of materials with loading sequence, which has never been considered in the literature. Experimental and modelling methodology have been extended to this aspect.

According to the socio-economic issues of reducing material consumption and pollutant emissions, the main benefits of the project are:
- a methodology to «design« friction materials for braking applications and turbojet casing,
- a multi-scale modeling of heterogenous material and contact interface, that could be integrated into industrial methods.
Methodology should also reduce the costs of materials development.
From the scientific point of view, the major benefit is a «homogenization tribological interpretations« that will be a first in tribology.

The production includes scientific publications (see list below) and communications in scientific and industrial conferences (19 to 31/07/2016).
Some creative ways to characterize materials and interface may be the subject of patent applications.
Some of multiscale simulation resources will be promoted by integration into industrial methods.

1. Role of constituents of friction materials on Their sliding behavior entre room temperature and 400 ° C Mat and Design 65 (2015)
2. Limit analysis and homogenization of porous materials with Mohr-Coulomb matrix. Part I: Theoretical formulation of the J Mech and Physics of Solids 91 (2016)
3. Limit analysis and homogenization of porous materials with Mohr-Coulomb matrix. Part II: Numerical bounds and assessment of the theoretical model of the J Mech and Physics of Solids 91 (2016)
4. A method for multiscale mechanics of frictionless touch rough surfaces Trib Int 96 (2016)

In turbojet aircraft engines, reducing fuel consumption and specific emissions of CO2 and NOx need to control the clearance between rotor and stator and consequently to master the blade-casing interactions. These interactions are strongly conditioned by the choice of the coating inside the casing.
With regard to braking systems, regulations intend to reduce environmental impacts (noise, particulate emissions) and to increase performance of energy dissipation (high speeds). These specifications need to master the phenomena of friction and the choice of materials in contact. The solutions implemented by manufacturers are based on the use of feedback based approaches and "trial and error" that led to the development of "recipes of heterogeneous materials” performance, with regard to brake lining and turbojet casing coating. However, in the absence of a real understanding of phenomena, such "black box" approaches are facing the new technical and environmental requirements. Besides it generates high development costs due to the number of trials needed.
The project objective is to develop a methodology to design multi-scale friction materials. This methodology fills in the missing link within the process of understanding and modelling systems (brakes and rotor-stator assemblies for jet engines) in order to increase their energy efficiency and to reduce environmental pollution (noise, pollution...) while maintaining reliability as part safe.
Due to high complexity, the approach relies on the one hand on the identification of physical dominating phenomena and, on the other hand, on an experimental-numerical dialogue. Manufacturers (Snecma, FBF-Bosch and FTG-Faiveley) and some academic teams already have an extensive experience with the targeted applications and knowledge of the physical phenomena involved (LaMCoS and LML-ER5). They propose to add skills of other research teams on multi-scale approaches (IJLRDA and LML-ER4) and in the physical chemistry of surfaces (KUL).
The approach is based on the following key points:
- Definition of "model materials" representative of industrial material formulations reduced and controlled, which will be characterized in terms of heterogeneities and properties.
- Approved friction tests with quantitative characterization of material properties and interface (third body) and their gradients. Innovative ways to rheological characterization will be implemented (rheometers and meso-tribometers).
- Multi-scale multi-physics numerical innovative approach considering the heterogeneity of materials and interface. This will be done through multi-scale numerical and semi-analytical homogenization.
The main benefits are to achieve:
A methodology to "design" friction materials for brake applications and casing coatings for turbojet engine.
A multi-scale modelling of material - contact interface, integrated into the industrial methodology for analysing performance of brake systems and aeronautic engines.
From a scientific perspective, the major benefit is a "homogenization tribological interpretation" that will be a first in tribology.