Thermal And Mechanical Performance Characterization And Ablation Simulation Of High Density And High Silica/phenolic Composite

When the launch vehicle is launched,wake flame of the engine will produce high heat flow and high impact force,which the heat shield to withstand the combined action of high heat flow and high impact force when the rocket is launched.Faced with such a harsh service environment for tail flames,the performance requirements to materials of rocket heat shield are put forward.For rocket heat shields,thermal protection materials need to be considered for its performance.How to develop composite materials with high density,high heat flow and high mechanical strength is the focus research of rocket heat shield material.High silica/phenolic(VSF/PR)composite material is a typical resin-based thermal protection composite material.Because of its low thermal conductivity and good heat absorption capacity,it gives the material with high thermal stability and ablation resistance.And in the production process,the material preparation cost is low,the cycle is short,it is often widely used in ablation and heat protection systems.Under high heat flow conditions,a series of physical and chemical changes will occur during the service of high silica/phenolic composite materials:the gradual thermal decomposition of phenolic resin,the flow and diffusion of pyrolysis gas,the pore flow and boundary layer of porous materials Move and other processes.At the same time,when the material is subjected to high heat flow and high load,the mechanical properties of the materials will change.Therefore,in order to meet the service requirements of mechanical and thermal properties,the method of layup optimization is adopted to design different composite material layup structures to prepare high silica/phenolic composite materials to improve the ablation performance and mechanical load-bearing capacity of the materials,and using this method researches the ablation behavior of the high silica/phenolic composite material during the entire ablation process,which is of great significance for the research on the ablation performance of silicon-based ablation materials.Aiming at the service conditions of rocket heat shields,a method of combination of experimental preparation,material characterization and numerical simulation are used to prepare high silica/phenolic composite materials,and the thermal,mechanical and ablation properties of the materials are researched.The specific research contents are as follows:(1)According to the performance requirements of rocket heat shields,the density and mechanical properties of ablation materials need to be improved.By optimizing the form of high silica fiber reinforcement,selecting high silica fiber mesh cloth/needle felt to optimize the layup and using phenolic resin to impregnate the high silica fiber reinforcement to form a preform,using a compression molding process of setting three different temperature stages of preheating,heating and cooling prepares ablation and heat protection material with ablation-bearing integration.(2)The density,thermal properties(thermal conductivity,thermogravimetric analysis,specific heat capacity),mechanical properties(compressive strength,compressive modulus,flexural strength,flexural modulus)of high silica/phenolic composite materials)and ablation performance(surface temperature,backside temperature,mass ablation rate,linear ablation rate)are studied by using a series of characterization methods.The results show that the density of the four composite materials is 0.8-1.2g/cm~3,and the thermal conductivity is 0.14-0.21W/m·K,the compressive strength is greater than 50MPa,the bending strength is greater than20MPa,and the influence of different layup methods on the properties of the material is analyzed.(3)The surface temperature and the temperature at 12mm of the experiment and the simulated are compared by Designing a 2.5 MW/m~2ablation experiment to verify the validity of the ablation simulation calculation model.Based on this simulated performance parameter,by using Open FOAM+PATO software,the ablation behavior of the material under the condition of high heat flow of 4.8MW/m~2is studied.Based on the material with a structural thickness of 12mm,the mass loss is less than 40%,and the temperature change is less than 250?,which can meet the performance requirements of rocket heat shields.