Design Analysis And Experimental Study Of High Temperature Ablation Coupling Biaxial Tensile Loading Device

As a strategic structural material,thermal protection materials are widely used in high-precision equipment in the field of aerospace and defense because of their excellent high temperature mechanical properties,and the service environment of the materials not only includes extreme high temperature,but also often accompanied by the comprehensive effect of complex mechanical loads,exploring and revealing the mechanical property changes and damage failure mechanism of thermal protection materials in extremely complex service environments is of great significance for its application and developmentFor a long time,the environmental performance test at home and abroad is basically to replace the real service environment performance with high temperature performance under air,vacuum or inert protective atmosphere,which is a big gap between the real service conditions of the material,which is not enough to fully simulate the oxidative damage and complex load action of the material,which will lead to the lack of authenticity of the test results,and the full environmental factor test that is completely equivalent to the actual working conditions is costly and costly.Therefore,it is very urgent to develop the performance simulation test technology of materials in close to the real service environment and clarify the performance and evolution law of materials in the service environment,and this paper designs and constructs a test device that can simultaneously carry out high-temperature ablation and biaxial tensile load coupling loading of thermal protection materials in the service conditions of simultaneous ablation and complex mechanical load coupling,which provides a method for mastering the performance test of thermal protection materials in close to complex service environment.In this paper,a uniaxial tensile test was carried out on the carbon/carbon(C/C)composite,the basic mechanical parameters of the material were obtained,the basic size of the specimen was determined according to the working range of the biaxial load loading platform,the shape and size of the biaxial carbon/carbon composite were designed and optimized by finite element software,and the influence of two different transition forms and the thickness of the thinning zone of the specimen on the specimen was analyzed,and finally the optimized specimen parameter combination was obtained.Aiming at the characteristics of carbon/carbon composite anisotropy,the threedimensional structural model of the material was constructed by using COMSOL software,and the temperature field distribution of the material under the action of external heating source were simulated.Secondly,the clamping scheme of the biaxial specimen under high temperature flame ablation is designed,the fixture is loaded through the wedge facing the specimen,the water-cooled runner is designed inside the fixture for cooling,and the mechanical strength of the fixture and the temperature distribution under high temperature loading are simulated by finite element software,and the results show that the mechanical properties and heat dissipation capacity of the fixture meet the design requirements.The test device for coupling loading of high temperature flame ablation and biaxial tensile load was designed and established,mainly including high temperature flame ablation module,biaxial load loading platform,strain measurement system and multidimensional temperature measurement module based on DIC technology,by optimizing the spatial layout,reducing the interaction between the loading and measuring systems.The structure of the water card calorimeter was designed,and the flow field and temperature field were analyzed by finite element software.The heat flux density of oxyacetylene flame was measured by water card calorimeter,and the temperature field distribution of the flame was measured by using a thermal external thermal imaging camera,and the performance parameters of the flame ablation module were obtained.The coupled loading test of high temperature flame ablation and biaxial tensile load at 1500°C was carried out,and the strain and temperature field information in the center area of the specimen were obtained synchronously by DIC strain measurement system and infrared thermal imager,and the stress-strain curve of the material was drawn.At the same time,a comparative test of vacuum high temperature and biaxial tensile load coupled loading at 1500°C was carried out,and the test showed that the tensile strength of the specimens with flame ablation and biaxial tensile coupling loading is 59.3MPa,which is about 19.9% lower than the uniaxial tensile strength at room temperature,the tensile strength of the specimen with vacuum high temperature and biaxial tensile coupled loading is 117.2 MPa,which is increased by about 49.9%compared with the uniaxial tensile strength at room temperature,and the tensile strength of the material in the flame ablation coupling loading test is reduced by about 46.6%compared with the vacuum high temperature environment.Laser confocal microscopy,SEM and EDS were used to characterize and analyze the failure specimens under flame ablation coupling and vacuum high-temperature coupling loading,and the line ablation rate and volume ablation rate of the material were 0.0273mm/s and 0.0287g/s,respectively,and SEM found that grooves and oxides appeared on the surface of the specimen after flame ablation coupled loading,accompanied by the disappearance of matrix,fiber sharpening and obvious characteristics of sheath structure,and analyzed the reasons for the formation of microstructure under the two test conditions.Its macroscopic mechanical properties are explained.