FEM simulation of the thermo-mechanical behaviour and failure of refractories—a case study

Ceramic refractory materials are applied for the lining of furnaces and vessels of the steel industry, such as teeming ladles considered here. Due to a rather coarse grain/matrix structure characterised by a maximum grain size of several millimetres and defect sizes up to a similar order of magnitude, these materials show a rather low strength, but can exhibit significant resistance against crack propagation. The thermo-mechanical response of refractory materials to a service load typical for a teeming ladle has been studied by means of FEM (finite element model) analysis. Two major types of thermo-mechanical loading have been considered here. The first one occurs during the initial heating-up of a cold ladle. In this case the thermo-mechanical stresses can be influenced by the dimension of expansion gaps. The second is due to the thermal shock caused by the liquid steel poured into the ladle. Material behaviour was described by the Drucker–Prager plasticity model combined with a tension cut-off criterion. The fracture behaviour under tension was modelled applying the fictitious crack model according to Hillerborg. All material properties were taken as temperature dependent. Several axisymmetrical and three-dimensional unit-cell models have been used to simulate stress and temperature fields as well as the resulting crack patterns. The relations between the obtained results and the corresponding thermal boundary conditions, the material parameters and the lining design give a good insight into the reasons of material failure and help to find counter-measures.