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Content archived on 2024-06-11

Mechanics of Bi-Metallic Discs


Bi-metallic discs are of considerable interest for land and aeronautical turbine manufacturers. Their use shouid allow large power (+50%) and efficiency (+10%) gains through: - higher service temperature (50 to 150 K), - simpler architecture, allowing for example an increase of the disk diameter by a factor of two, while keeping stresses as in present designs and lowering operating cost. In a bi-metallic disc, a high creep resistance alloy (with coarse grains eg. CG or single crystals eg. SC) is used for the rim, and a high medium temperatures strength alloy (with fine grains eg. FG) is used for the hub. Today, the main limitation for the introduction of this new technology is the complete lack of suitable testing and design methods and standards for these joints. As a consequence, such components cannot be designed and tested, and thus, not be used. The objective of the Bl-METAL project is to develop the basic scientific knowledge and corresponding methods for mechanical modelling and testing the behaviour and the fracture of bi-metallic joints. Major european land and aeronautical turbine manufacturers, EGT and TURBOMECA will participate as end users in this project. The TECPHY metallurgical firm will participate as manufacturer. The Institute for Advanced Materials of JRC-Petten will participate as testing, modelling (for single crystals to fine grains joints) and standardization research center. The Federal Institute for Material Research and Testing (BAM) from Berlin will study the single crystal behaviour. The Center for Research and Studies on Materials of CEA will contribute as a specialist in fracture mechanics and material testing and modelling, and will focuse on coarse grains to fine grains joints. The Non Destructive Testing team of EMPA will participate to perform suitable non destructive inspection of defects. After the specification and the selection of materials and processes, the raw materials will be supplied and bonded using a previously qualified HIP (Hot Isostatic Pressing) diffusion bonding process. The work will be focused on two joints: CG Udimet 720 or SC MC2 to FG Udimet 720. Mechanical specimens will be designed to allow the measurement of representative properties of the joint. Then, these tests will be performed on joint samples. A mechanical model of the behaviour and of the fracture will be developed from the mechanical and microstructural results of these tests. This model will be calibrated with the numerical data determined from these results. Then, this model will be used to design a validation specimen. This validation specimen will be manufactured and tested to validate the model. Thus, this project will result in validated testing specimens and mechanical models. Such specimens and models will be the scientihc basis necessary for the definition of future lifing methods. Such methods will themselves be the basis of future standards. Such specimens, models, methods and standards are fully original. They have never been developed anywhere, despite they are essential for the industrial application of bi-metallic components in land and aeronautical turbines, and other engineering fields.

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