DESIGN OF THERMALLY HIGH-LOADED CERAMIC COMPONENTS FOR GAS-TURBINES

The excellent high-temperature properties of ceramics offer great pote ntial for their application in gas turbines. However, ceramics lack th e ability to reduce local stress concentrations by plastic deformation . As a result, stresses that are caused by different local thermal exp ansions can reach critical values, especially in the hot-section compo nents. To improve the reliability of ceramic components, the temperatu re differences have to be reduced. Ar the Institut fur Thermische Stro mungsmaschinen (ITS) a systematic methodology for designing thermally high-loaded components has been developed. The principles of the desig n procedure include a segmentation of the parts according to the load and a three-layered construction of the component's wall. The inner ho t-gas ducting layer consists of a high-temperature resistant ceramic m aterial which is embedded into a metal containment by a flexible ceram ic fibre insulation. By adjusting the individual thicknesses of the ce ramic and the insulation layers according to the local boundary condit ions on the hot-gas side, the local temperature differences in the cer amic can be considerably reduced Finite element analyses of the temper ature and stress distribution for first stage nozzle guide vanes and t he vaneless scroll of a racial gas turbine are shown. Compared with co nventional designs, the calculations clearly demonstrate that the hybr id wall construction and an ingenious segmentation of the components l ead to a significant reduction in the stress level. The reliability im provement is documented by failure probability calculations performed using the ITS fracture statistics code CERITS. (C) 1997 Elsevier Scien ce Limited.