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| Book | PreJuSER-45778 |
;
2000
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/20627
Report No.: Juel-3788
Abstract: Plasma-sprayed oxide ceramics with porous, fractured, lamellar microstructure exhibit high crack tolerance and excellent thermal shock resistance compared to the sintered bulk materials . However, the extremely low bending strength of only about 20 - 40 MPa restricts their usage under higher external loads. By incorporating an intermediate thermal-sprayed steel layer the strength and the strain tolerance are improved by a factor of five. The reinforcement effect depends on the residual stresses in the ceramic layers due to the difference in thermal expansion coefficient between ceramic and steel. Annealing at high temperatures increases the residual stresses in the three-layered systems. In the present study these Plasmacermet-muhilayerstruCtUres am examined regarding their thermoelastic and thermomechanical behaviour, and the residual stresses in such systems are calculated. The study concentrates on three material combinations (A1203/NiCr 80 20/AI203, Spinell/CrAl 25 5/Spinell and Mg-Zr02/CrA] 25 5/Mg-ZrO2), which are supplied by the company LWK-Plasmakeramik, Gummersbach. The strength of separated steel layers and of the multilayersystems as well as the elastic behaviour of the ceramics and steels are studied as coon of temperature. The thermoelastic parameters enter into analytical elastic sses in the multilayerstructures. Different material a calculations of the residual combinations and steel contents are considered in the calculations for tubular geometries . Microscopical in situ observations of the damage mechanisms under thermomechanical stresses are used to define a failure criterion . This criterion enables to determine layer geometries for which the cracking of the ceramics takes place in the same time than the failure of the steel layers. Besides the analytical calculations of the isothermal stress distribution in mul6layerstructures finite element methods are used to estimate the behaviour of the layered systems under external temperature gradients. Geometrical consequences for the steel layers are discussed.
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