A new tensile creep testing facility for high temperature measurements of heterogeneous refractories was introduced in order to characterize materials applied for the lining of furnaces and vessels of the steel industry. The machine allowed accurate specimen alignment and holding systems. A uniform loading permitted to avoid bending and uneven stress distribution in the specimen. Prior to the measurements, thermo-mechanical simulations were carried out in order to optimize the testing procedure. Feasibility of the experiments was confirmed with the selection of an optimal heating rate. Observation of temperature and stress distributions in the hot zone and the cold ends confirmed the specimen shape and dimensions chosen. Creep behaviour of magnesia-chromite and magnesia-spinel bricks were measured as a function of tensile stress in the range from 0.2 to 1.9 MPa and as a function of temperature in the range from 1100 °C to 1600 °C. Three creep phases were revealed at these conditions indicating the strain-hardening, the steady state and the strain-softening behaviour of the materials. The procedure developed for the interpretation of the experimental results included the selection of Norton-Bailey creep law, the identification of the creep stages and the calculation of the creep parameters by inverse-estimation using the general reduced gradient (GRG) or Levenberg-Marquardt (L-M) algorithms. A detailed study of creep behaviour of magnesia-chromite material was then carried on with bringing to light the evident correlation existing between the creep strain, the applied stress and the temperature. An approach which consisted on finding the transition points between the creep stages in dependence of stress and temperature can be implemented in a simulation program. The activation energy was evaluated for this material; however it was not evident to conclude about the different mechanisms happening during creep due to their probable simultaneous occurrence in the heterogeneous material. Norton-Bailey creep parameters describing the strain-hardening behaviour of magnesia-chromite were then implemented in the software Abaqus for a thermomechanical modelling of an RH-snorkel. Three models were investigated and compared; the symmetrical tensile, the symmetrical compressive and the asymmetrical creep models. During process the refractory lining endures high thermal stresses. The temperature and stress distributions were evaluated and compared at different moments of the first heat. The asymmetrical creep model was more representative than the symmetrical ones.
|Translated title of the contribution||Kriechmessungen von feuerfesten Baustoffen im Hochtemperaturbereich|
|Publication status||Published - 2016|
Bibliographical noteembargoed until null
- FE simulation
- inverse estimation.