Peridynamic Theory And Numerical Analysis On Ablation Problem

The internal structures are in danger of burning because of the huge amount of heat generated by the friction when the vehicles re-entry into the atmosphere.Pyrolysis,oxidation,sublimation and other physical-chemical reactions of the ablative material will be occurred in the high temperature environment.Owing to the loss of their own quality,the ablative material can take away a lot of heat and ensure the safety of the vehicles.In view of the importance of the thermal protection materials,the research on ablation process is becoming more and more extensive.However,the numerical methods used in the studies are all based on the classical continuum mechanics theory.In dealing with the discontinuous problems,some limitations are encountered.Therefore,the ablation model in the peridynamic formulation is established,and the numerical analysis of the ablation process is carried out.The main research contents and achievements are as follows:a.The modified bond-based peridynamic theory based on Voronoi diagram is developed.It is based on the view that there is no direct physical interaction if the particles are not adjacent to each other at the macro scale.The influence between them is passed on by the adjacent one.The theoretical derivation is completed and the expression is improved in this paper.Meanwhile,it is applied to model the fracture problem,and its validity and accuracy are validated.b.Based on the above idea,a new thermal bond only existing between the particle and its contact neighbor is proposed.The modified transient heat transfer theory is derived and the different boundary conditions are imposed.Then the thermal stress caused by the temperature change is introduced,and the thermomechanical response in the peridynamic formulation is established.c.Finally the surface ablation damage model is proposed based on two different ablation criteria,and the damage function is introduced.The description of the autonomous evolution of the moving surface is realized.Thus ablation model based on Voronoi diagram is established in the peridynamic formulation.d.Based on the above ablation model,the flow chart of numerical approach is designed and the computer codes are written in FORTRAN language.First,the heat conduction problem of one-dimensional bar is taken as an example to verify the accuracy of the transient heat conduction theory.Then,two kinds of damage models are used to simulate the ablation process.Based on the simulation results,the change of the ablation rate,temperature field distribution and the stress field distributionare analyzed.