Severin Hofmann

Determination of elastic properties for a wound oxide ceramic composite

Abstract Thanks to its low cost and high flexibility, in the last few years the winding technique has been successfully adapted for the production of complex Ceramic Matrix Composite (CMC) components with load-oriented fibre alignment. Since the winding angle can be adjusted in any direction (from 0° to 90°) during the fabrication process, it is important for the design of components to evaluate the elastic properties of CMCs as a function of the winding angle. In this study, an inverse method based on the Classic Laminate Theory (CLT) has been used for the prediction of the elastic properties, i.e. Young’s modulus, shear modulus and Poisson’s ratio, for a wound oxide CMC material, called WHIPOX® (Wound HIghly Porous OXide ceramic matrix composite). For this purpose the characteristics of an equivalent unidirectional layer (UD-layer) with consideration of fibre volume content (FVC) and porosity were calculated. On the basis of microstructural analysis the computed WHIPOX®UDproperties have been divided into two sets of elastic properties for small (below 30°) and large winding angles (30° and above). Full coverage of the mechanical properties in different wound orientations, non-orthogonal with ±3°/±87°, ±15°/±75°, ±30°/±60° and orthogonal with ±45° and 0°/90°, were evaluated with in-plane tension, and Iosipescu-shear tests. A good correlation between experimental and analytically calculated results is shown in this paper.

Development and Test of Oxide/Oxide Ceramic Matrix Composites Combustor Liner Demonstrators for Aero-engines

Ceramic matrix composites (CMC) offer the potential of increased service temperatures and are thus an interesting alternative to conventional combustor alloys. Tubular combustor liner demonstrators made of an oxide/oxide CMC were developed for a lean combustor in a future aero-engine in the medium thrust range and tested at engine conditions. During the design various aspects like protective coating, thermo-mechanical design, development of a failure model for the CMC as well as design and test of an attachment system were taken into account. The tests of the two liners were conducted at conditions up to 80% take-off. A new protective coating was tested successfully with a coating thickness of up to t=1 mm. Different inspection criteria were derived in order to detect crack initiation at an early stage for a validation of the failure model. With the help of detailed pre- and post-test computer tomography scans to account for the micro structure of the CMC the findings of the failure model were in reasonable agreement with the test results.

Development and Validation of Oxide/oxide CMC Combustors within the HiPOC Program

In the framework of the High Performance Oxide Ceramics program (HiPOC), three different oxide/oxide ceramic matrix composite (CMC) materials are studied for a combustion chamber application in continuation of the work reported in Gerendas et al. [1]. A variation in the micro-structural design of the three CMC materials in terms of different fiber architecture and matrix processing are considered in a first work stream. By modification of the matrix and the fiber-matrix interface as well as the application of an environmental barrier coating (EBC), the high temperature stability is enhanced. Furthermore, design concepts for the attachment of the CMC component to the metal structure of the engine are finalized in a second work stream. Issues like sealing of cooling leakage paths, allowance for the different thermal expansion and the mechanical fixation are addressed. An interim standard of the mechanical attachment scheme is studied on a shaker table. Also the friction coefficient between the metallic and ceramic components is analyzed in order to set the proper tightening torque. The manufacturing of the CMC combustor is improved in several iterations in order to achieve a high quality material with optimized fiber architecture. Afterwards, two CMC materials are selected for the combustion testing and the finalized design of the metallic and CMC components is manufactured. A fit check is performed prior to EBC application and laser drilling of the effusion holes in order to evaluate the impact of the manufacturing tolerances on the function of the sealing and attachment scheme and to correct small issues at this stage. First results from the validation testing in a high-pressure tubular combustion rig up to a Technology Readiness Level 4 (TRL4) are reported.Copyright

DEVELOPMENT AND TEST OF OXIDE/OXIDE CMC COMBUSTOR LINER DEMONSTRATORS FOR AERO ENGINES

Ceramic matrix composites (CMC) offer the potential of increased service temperatures and are thus an interesting alternative to conventional combustor alloys. Tubular combustor liner demonstrators made of an oxide/oxide CMC were developed for a lean combustor in a future aero-engine in the medium thrust range and tested at engine conditions. During the design various aspects like protective coating, thermo-mechanical design, development of a failure model for the CMC as well as design and test of an attachment system were taken into account. The tests of the two liners were conducted at conditions up to 80% take-off. A new protective coating was tested successfully with a coating thickness of up to t=1 mm. Different inspection criteria were derived in order to detect crack initiation at an early stage for a validation of the failure model. With the help of detailed pre- and post-test computer tomography scans to account for the micro structure of the CMC the findings of the failure model were in reasonable agreement with the test results.