Elastic Moduli of anisotropic materials at high temperatures

Research project P 14294 Elastic moduli of anisotropic materials at high temperatures Karl KROMP 26.6.2000 In the course of the rapid progress in e.g. aerospace and communication technologies during the last decade specific high Performance materials for special applications were developed. The materials e.g. intermetallics, high Performance ceramics and ceramic composites, an predominantly anisotropic. For design purposes Of constructive parts under load e.g. by FE calculations the elastic constants (the components of the elastic stiffness tensor) in dependence on orientation and on temperature have to be known (the technical "elastic moduli" directly can be calculated from these elastic constants). Thus there is a strong interest in Practicable procedures for the determination of the elastic constants in dependence On Orientation and on temperature. The "Resonant Beam Technique" (RBT), applied at the institute of materials Physics, University of Vienna, was extended in. the frame of the Previous project P 9920-PHY, tied up in the action COST 510, so far that it can be performed up to 2000 OC in dependence on orientation, thus for anisotropic materials. A Software was developed, so that the appropriate sets of moduli can be detected half-automatically. The main disadvantage of the technique is that it is restricted to thin long bar-shaped specimens, cut out from the material along the main axes of symmetry. Thus for specific materials, it is not possible to achieve the I set of elastic constants, because some of the relevant specimens cannot be prepared for geometrical reasons. With the "Resonant Ultrasound Spectroscopy" (RUS) small rectangular parallelepiped-shaped specimens with the main axes of symmetry oriented parallel or perpendicular to the sides of the specimens can be investigated. In principle the full set of elastic constants can be achieved from one single specimen. This fact will be the main advantage compared to the RBT. With RUS the full set of elastic constants is determined by minimising the difference between observed and calculated resonant frequency spectra (spectra of eigenfrequencies), using a least squares method. The disadvantage of the RUS technique is that some of these elastic constants or some of the eigenlrequencies have to be identified before to start the calculation of the full set of eigenfrequencies. If then the set of eigenfrequencies is not known very precisely, the fit will not be unique and there arise too many different (wrong) possibilities, so that the problem cannot be, solved at all. The aim of the project is to combine the "Resonant Beam Technique", RBT and the "Resonant Ultrasound Spectroscopy", RUS to solve this problem. The procedure proposed is to start measurements with thin long bar- shaped specimens, oriented along specific main axes of symmetry in directions where the cutting out of such specimens is possible, to achieve a subset of eigenfrequencies. With this subset of results the RUS-investigation can be started in the same equipment which will be designed and built up in rive the frame of this project and the results can be successfully exploited. For this exploitation the Software equipped with a graphical user interface will be developed. The novel method will be verified e.g. on C/C composites out of the nozzle of the booster of the Ariane V in the frame of a direct cooperation, already started with the RBT-technique, to achieve the full set of elastic constants in dependence on. temperature.