Numerical Simulation And Prediction Of The Thermo-mechanical Behavior Of Porous Mullite Refractories At High Temperature

Refractories are inelastic or elastoplastic and exhibit quasi-brittleness at normal temperature.However the melting of glass phase softens the refractories and making the materials show a certain visco-plasticity at high temperatures.The pore structure and the air filled in pores of the light insulation materials have an important influence on their thermo—mechanical behavior.In this paper,porous mullite refractory materials were used as the research object.By constructing a gas-solid binary model with different pore structures,the thermo-mechanical coupling simulation method was used to study the effects of different pore structure parameters(porosity,pore size,acentric factor of pore diameter and departure factor of pore position)on the thermo-mechanical behavior,such as thermal mechanical strength,thermal shock resistance,and high-temperature elastoplastic deformation of porous materials.And combined with experiments,the mechanism of thermal mechanical damage and thermal shock damage of porous mullite refractory was discussed.The simulation results were fitted calculation to obtain the models for predicting the thermo-mechanical behavior parameter of porous mullite refractories with different pore structures.The main conclusions of the paper are as follows:(1)The gas-solid binary model could better characterize softening behavior of porous mullite refractorie at high temperature.Buckling analysis,strain-life method and multilinear kinematic hardening model could accurately predict the thermo-mechanical behavior parameters of porous mullite refractories.Therefore,it was reasonable and effective to study the thermo-mechanical behavior of porous mullite refractories by using a gas-solid binary model and the thermo-mechanical coupling simulation.(2)In the state of three-point bending,the crack started from the middle position at the bottom and then extended upwards to cause cracking of the material structure.Under uniaxial compression,the irregularity of crack distribution and the fragmentation of material were caused due to the disordered distribution of stress.The larger the pore diameter,the lower its high-temperature strength,and the more unstable the structure when the pore diameter is in the range of 0.18?0.42mm.The larger the porosity,the larger the amount of buckling deformation,which made the strength of the materials reduce.The chaotic distribution of pore diameters and pore positions was prone to stress concentration,which reduced the critical stress(3)The mechanism of thermal shock damage was that the material was subjected to tensile/compressive alternating stress under repeated cycles of heating and cooling,causing damage to occur.The temperature gradient and thermal expansion mismatch between the solid and air leaded to residual thermal stress concentration and damage initiation at the solid/air interfaces.When the porosity P=50%and d=0.18?0.42mm,the thermal shock resistance increases first and then decreases.And the number of thermal shock cycles is the largest when d=0.3mm.The higher or lower porosity had no positive effect on the thermal shock resistance of the porous material;When d=0.3mm,number of thermal shock cycles with a porosity of 20%is the largest.When porosity exceeds 40%,the thermal shock resistance decreased rapidly.The chaotic distribution of pore diameter and pore location resulted in thermal stress concentration,which reduced their thermal shock resistance(4)The high-temperature elastoplastic deformation curve rose faster in the elastic phase and the change of strain were small.And the variation of strain was large and rose slowly in the plastic phase.The middle position of the upper end of the material yielded first,and the plastic deformation was the largest.When the pore diameter d=0.30mm,the ability to resist external force was the strongest.The larger the porosity,the more concentrated the yield stress distribution,and the elastic modulus and plastic stress gradually decrease.The more chaotic the distribution of pore diameter and pore position,the more chaotic the distribution of yield stress,which made their strength decreases(5)Eureqa software was used to fit the simulation results to determine the intrinsic relationship among the four pore structure parameters corresponding to the thermo-mechanical behavior parameters.Four specific models were obtained to predict the thermal critical stress,the number of thermal shock cycles,and the elastic modulus of porous mullite refractories under four different pore structure parameters,and they are as follows,respectively:109+166c2+0.0226b+9.76c62-660b-0.092d3b2-P=0770+16.6c+22.2db+84.6d2-22.3b-519d-30.9b2-P=099c+0.293 d+0.039d2b2-541-1.34db-1.78b2-0.521db2-P=0557-0.073dc+0.543c2+0.04d2-8.02d-12c-0.44bc-P=0Where P is porosity of the materials,%.d means the pore diameter,mm.And b,c are acentric factor of pore diameter and departure factor of pore position,respectively.