Design of a High Temperature Test Device for Bidriectional Loading for CMC Samples

Kurzfassung

Since the component mass in space applications is very critical and new developments from CMC materials are on the rise with a high degree of complexity, the exact, detailed analysis of these components is becoming increasingly important to make full use of the material properties. However, material properties of CMC, especially in transverse direction, are often poorly documented, thus leading to compromises with regard to analysis reliability, especially in the use of failure criteria. Due to very limited experience in determination of failure criteria for ceramic matrix composites, it seems necessary to develop a test device to determine those values for material quality assurance and for the verification of analytical prediction tools. To provide a reliable statement about the failure criteria it is necessary to define stress conditions close to the material’s limit. Starting from the one-dimensional stress condition the two-dimensional state is attained by applying a defined shear stress. On the basis of these data a model for the failure of the structure can be derived, which can be part of future design tools of ceramic constructions. At the beginning of the project finite element simulations were performed to optain a suitable sample geometry which provides a reliable prediction of the stress distribution. To reach the favorite stress-case at testing conditions the sample was exposed to combined tension and torsion. It was possible to apply both loads, tension and torsion separately from each other by a special mechanic integrated into the hot test facility. To avoid interactions due to tolerances of manufacturing and the stiffness of the facility, special constructive measures were necessary. The construction of the test facility is suitable for C/C-SIC samples at room temperature conditions and high temperature conditions (up to 1700 K), respectively. The aim of this work was to have on the one side a prediction tool as simple as possible and on the other side to have a simple test opportunity for the verification. This contribution presents an overview of the investigations within the project so far.