Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - AllOxITD (Development and Manufacturing of an All-Oxide Inter Turbine Duct for Aeroengines)

Teaser

Ceramic Matrix Composite materials (CMCs) have excellent properties at high temperatures. In contrast to metallic materials they do not lose in strength up to 1000°C. This behaviour is making CMCs interesting for components in the hot gas section of gas turbines. Due to...

Summary

Ceramic Matrix Composite materials (CMCs) have excellent properties at high temperatures. In contrast to metallic materials they do not lose in strength up to 1000°C. This behaviour is making CMCs interesting for components in the hot gas section of gas turbines. Due to higher allowable material temperatures the effort for cooling air can be significantly reduced in contrast to metallic components. This is increasing the turbine efficiency by using as much air as possible for the thrust producing main flow direction. The objective of the project is the development of an all-oxide Ceramic Matrix Composites (CMC) inter turbine duct for testing in a demonstrator engine.

Work performed

As a starting point, the design and the general boundary conditions of a typical metal ITD were analysed. On this basis the design, attachment and sealing concepts of the metal part had to be adapted for the CMC-material. This involved a number of challenges including the different thermal expansion of the ceramic and surrounding metal structures. Thus, special care had to be taken to prevent thermal restraints and maintaining a gas-tight seal, whereby the last-named matter has not yet been resolved.
Furthermore a suitable design sketch was chosen. This design is currently undergoing detailed thermomechanical analysis to see if it can withstand the thermal and mechanical loads in the gas turbine for the required life-time. The fabrication process of CMC is much more similar to the processing of fibre reinforced polymers than metals and the geometries and fibre architecture which can be produced from CMC material had to be considered in the design stage. Consequently, the CMC design looks very different in comparison to the metal design, yet fulfils the same requirements.
During the second period various thermomechanical simulations were generated to comprehend the strains and stresses inside the CMC-component and to investigate weak spots. Highest stresses could be localized in the flanks in axial and especially in circumferential direction. Studies with various boundary conditions were performed and a mesh optimization served to enhance the simulation model.
Within the thermomechanical simulation the material properties of a commercially available oxide CMC (FW12) were used. Later on these values were exchanged by material data generated by characterisation of the developed pre-preg CMC.
The thermomechanical simulations served to evaluate the CMC-component design. The simulations gave support in the design development with regard to a CMC-appropriate design, thermomechanical loads and manufactural aspects. Design modifications were discussed with the objective to reduce stresses at critical regions. At the end of the second reporting period most design parameters were defined so that the manufacturing tools could be developed to produce a first series of hardware parts.

Within the first reporting period the manufacturing process of wound material had been started. Several sample plates with different winding parameters, fibre bundle types and matrix systems were produced for initial testing to optimize the mechanical properties of the material. Also parameter studies for the manufacturing of pre-preg material were carried out. First plates with optimized fabrication parameters were manufactured and delivered to the project partners for testing.
At the beginning of the second reporting period it was decided to focus on the pre-preg CMC for manufacturing of ITD demonstrator parts. The pre-preg CMC was optimised in terms of mechanical properties and manufacturing technologies to realise the designated geometry which were developed during the project. Standard Operation Procedures (SOP) and acceptance limits have been installed for the test materials and process steps for varying geometry levels to ensure the material quality.

The characterisation of the materials produced within this project is focused on the thermomechanical and thermophysical properties at application-relevant conditions. This data is required for further FEM simulations and verification of the demonstrator component. A suitable test matrix and a time schedule were developed at the beginning of the project, including preliminary tests with dummy specimens. Based on the current test results and other factors affecting the time schedule of the project, the test matrix is constantly being reviewed and amended when necessary.
For wound and pre-preg CMC preliminary material data was collected (static thermomechanical and thermophysical characterisation). Dynamic properties (e.g. creep behaviour) were determined for pre-preg CMC additionally.
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Final results

A successful demonstration of an all oxide ceramic ITD at ground testing was not described in literature before and will have great importance for the scientific community.
Up to date, the availability of ceramic fibre braids is very limited and mostly restricted to biaxial braids. Within the EU, this project is the first to produce tri-axial oxide ceramic fibre braids.