The Coupled Thermo-chemo-mechanical Analysis Of UHTCs’ Ablation Based On Peridynamic

Ultra-high temperature ceramics（UHTCs）have the characteristics of ultra-high temperature resistance,high thermal conductivity and high strength.They can be used as heat bearing structural components such as nose cone and wing leading edge of reusable spacecraft.UHTCs’ablation is a very complex physicochemical process including mechanical behavior,temperature effect and chemical reaction.Therefore,studying the constitutive relation of multi field coupling of thermal,mechanical and chemical behaviors of ceramic materials in ultra-high temperature environment and establishing an appropriate numerical simulation model are vital.The current research shows that the chemical reaction in the process of ceramic super ablation has a great impact on the ablation resistance of ceramics,but there is a lack of numerical simulation research that can describe the coupled effect of chemical reaction,structural deformation and temperature change in the process of ceramic ablation.In this paper,under the framework of peridynamic theory,combined with the oxidation kinetics model of single-phase ZrB₂ ceramics,a simplified coupled thermo-chemo-mechanical bond-based peridynamic model based on the ablation of single-phase ZrB₂ ceramics is proposed.The main research contents and achievements of this paper are as follows:1.The oxidation kinetic model of ZrB₂ in high temperature environment and the fully coupled thermo-mechanical theory of peridynamic are studied.A coupled thermo-chemo-mechanical bond-based peridynamic model based on single-phase ZrB₂ceramic ablation is established.Firstly,based on the oxidation kinetic model of ZrB₂ceramics and bond-based peridynamic model,the coupled thermo-chemo-mechanical calculation equation of ZrB₂ ceramics is deduced.Then,an improved peridynamic damage criterion is proposed,in which the temperature bond is not completely equal to the force bond.Finally,a coupled thermo-chemo-mechanical bond-based peridynamic model is established.The model includes not only the interaction between temperature and deformation,but also the influence of oxide growth caused by chemical reaction on structural deformation.2.The numerical implementation scheme of coupled thermo-chemo-mechanical bond-based peridynamic model based on single-phase ZrB₂ ceramic ablation is given,and the reliability of the numerical algorithm of the coupled model is verified by three groups of numerical examples.Firstly,the discrete format and numerical calculation flow of the coupling model are given,and the calculation program of the coupling model is written in Fortran language.Then,based on the fully coupled thermo-mechanical calculation of plate under temperature load,the effects of horizon size and particle spacing on the numerical calculation are studied.The results show that the coupled thermo-chemo-mechanical model can give consideration to the calculation accuracy and efficiency under the appropriate selection of calculation parameters.Finally,the reliability of this model is verified by the fully coupled thermo-mechanical analysis of two-dimensional plate under temperature load,the crack propagation simulation of ceramic plate under cold impact load and the evolution calculation of oxide layer thickness of ZrB₂ ceramic under high temperature environment.3.The effect of oxide layer formed by chemical reaction on the ablation resistance of ceramics and the effect of chemical reaction growth coefficient on the calculation results were studied.Firstly,the temperature and damage calculation results of coupled thermo-mechanical model and coupled thermo-chemo-mechanical model under the same calculation conditions are compared,and the research significance of coupled thermo-chemo-mechanical model is proved.Secondly,the effect of oxide thickness on the ablation resistance of ceramics was studied by presetting different oxide thickness.Finally,the influence of chemical reaction growth coefficient on the calculation results is studied.It shows that the influence of chemical reaction on the stress and strain of oxide layer directly affects the thermal shock resistance of ceramics.