MODELLING OF NONLINEAR BEHAVIOUR AT HIGH TEMPERATURE OF REFRACTORY MASONRIES WITHOUT MORTAR
Résumé
Some vessels used in steel industry are protected against the hot products they contain by a refractory masonry built without mortar. The gap between bricks allows a free thermal expansion during the beginning of heating. If the masonry is modelled with a continuum material that has the behaviour of the bricks, the stresses will be overestimated. If each brick is modelled, the computation time will be too important and the computation will probably not succeed due to too numerous contacts. Therefore the masonry was replaced by a homogeneous material that has a behaviour equivalent of that of the set bricks and dry joints (joints without mortar) using a periodical homogenisation technique [1]. The behaviour of this equivalent material depends of the state of the joints (open or closed) and of the temperature [2]. In a first step the brick behaviour was assumed as elastic linear. A steel ladle (containing liquid steel at 1650°C) was modelled using the finite element method and replacing the masonry by an orthotropic equivalent material. This model has shown the influence of the masonry design (joint thickness, orientation of bricks) on the stresses in the steel shell and in the different refractory linings. It is also possible to observe the progressive joint closure.
In a second step, the real nonlinear brick behaviour at high temperature is taken into account. This behaviour is modelled using an elastic-visco-plastic law [3]. This model applied to the previous steel ladle allows to determine the evolution of stresses during time (creep) and over cycles.
References
[1]Anthoine A (1995). Derivation of the in-plane elastic characteristics of masonry through homogenization theory. International Journal of Solid and Structures 32(2): 137-163.
[2]Nguyen T, Blond E, Gasser A, Prietl T (2009). Mechanical homogenization of masonry wall without mortar. European Journal of Mechanics A/Solids 28: 535-544.
[3] Blond E, Schmitt N, Hild F, Blumenfeld P, Poirier J (2005). Modelling of high temperature asymmetric creep behavior of ceramics. Journal of the European Ceramic Society 25: 1819-1827.