Investigation On Thermal Shock Resistance Of ZnS Wave-transparent Ceramic Antenna Window And Ultra-high-temperature Ceramics

In order to study the combined effect of aerodynamic heating, pneumatic pressureand external constraint on the thermal shock resistance (TSR) of ZnS wave-transparentceramic which is used as antenna window of near space vehicle in its actual serviceprocess, the theoretical model was established by introducing the analytical solution oftransient heat conduction problem of ZnS plate under aerodynamic heating into itsthermal stress field model. The numerical simulation was also conducted not only toexamine the theoretical model, but also to study how to improve the TSR.In chapter II of this paper, the influences of constraint and pneumatic pressure hadbeen studied and the effects of loosing constraint and active cooling had been focusedon. The study shows that the critical rupture temperature difference of simply supportedZnS plate will form wave peak; the TSR of ZnS plate is obviously optimized whenloosing constraint method has been adopted, and the effect of pneumatic pressure onTSR is closely related to the change of failure region; active cooling is an effective wayto improve the TSR of ZnS plate and the stronger pneumatic pressure, the better TSR,but active cooling can’t be too violent.In chapter III of this paper, the present work mainly focused on the influences ofconstraint, size and aspect ratio on the critical rupture temperature difference of ZnSplate subjected to aerodynamic heating and pneumatic pressure. The results show thatthe large heat transfer condition corresponds to the poor TSR unless the constraint is toostrong; the square plate provides the better TSR in case of different pneumatic pressures;a reasonable side length according to the range of pneumatic pressure would lead to thebetter TSR.The thermal shock resistance of ceramics depends on not only the mechanical andthermal properties of materials, but also the external constraint and thermal condition.So in order to study the actual situation in its service process, a temperature-dependentthermal shock resistance model for ultra-high temperature ceramics considering theeffects of thermal environment and external constraint was established based on theexisting theory. Furthermore, the model was validated by finite element method.In chapter IV of this paper, the present work mainly focused on the adjustment ofstress reduction factor according to different thermal shock situations. The influences ofexternal constraint on both critical rupture temperature difference and the second thermal shock resistance parameter in either case of rapid heating or cooling conditionshad been studied based on this model. The results show the necessity of adjustment ofstress reduction factor in different thermal shock situations and the limitations ofapplicable range of the second thermal shock resistanceparameter.