Research On The Forming And Properties Of High-strength Head C/C-SiC Composites

Carbon fiber reinforced carbon-silicon carbide(C/C-SiC)composites combine the excellent mechanical properties of carbon fiber and good thermal/chemical stability of ceramic matrix,due to its good performance of high specific strength,low coefficient of thermal expansion,and good ablation resistance.C/C-SiC composites were widely used as thermal structure materials of interior combustion chamber of liquid fuel ramjet.With the rapid development of technology concerns weapon equipment,the condition of thermal protection of ramjet is getting more and more harsh.The ablation and mechanical denudation of the head of interior combustion chamber are becoming more and more serious.In order to improve the overall compressive strength of the head of combustion chamber under transient large overload condition,meet the requirements of ablation resistance and realize the unity of structure and function.C/C-SiC composites were prepared by chemical vapor infiltration(CVI)combined with precursor infiltration and pyrolysis(PIP).The tensile properties and interlaminar peel properties of needled NOL ring preforms were analyzed by mechanical test and mathematical simulation.The flexural and shear properties of C/C-SiC composites were characterized.Based on the hydraulic test and finite element simulation,the failure mechanism of C/C-SiC composite rings and head were analyzed.The ablation resistance of C/C-SiC composites was tested by oxyacetylene ablation test.Researches and results are as follows:(1)Firstly,the effects of carbon cloth laying mode,needle density and needle depth on the overall tensile strength and interlayer peel strength of needled NOL ring preforms were studied.Secondly,the response surface model of overall tensile properties,interlaminar peel properties and preform preparation parameters of needled NOL ring preforms was created.Finally,the preparation parameters of the preform with the best comprehensive mechanical properties were obtained.The results show that the carbon fiber needled preform has the comprehensive mechanical properties with 15.25 pin·cm^-2of needle density,12.86 mm of the needle depth,and 0.26 of the proportion of non-woven cloth.The interlaminar peel strength is 398.04 N·m^-1,and the overall tensile strength is 5.31 MPa.On the basis of response surface equation of preform preparation parameters and comprehensive mechanical properties of needled NOL ring preform.Combination of needle density of 17 pin·cm^-2,needle depth of 12 mm,and the proportion of non-woven cloth of 0.25 were selected based on the response surface equation of preform preparation parameters and comprehensive mechanical properties of needled NOL ring preform.The overall tensile properties and interlaminar peel properties were predicted,and the error between the predicted values and the actual values is less than 6%,proved the high accuracy of the model.(2)The effects of SiC matrix content on ablation properties,bending properties and in plane shear properties of C/C-SiC composites were studied.The results show that with the increase of SiC matrix content,the ablation rate,bending strength and in plane shear strength of C/C-SiC composites increased at first and then decreased.The material with SiC ceramic matrix content of 24.23%have the best comprehensive properties,with 300 s linear ablation rate of 0.0034 mm·s^-1,300 s mass ablation rate of 0.0011 g·s^-1,bending strength of 181.1 MPa and horizontal shear strength of 25.8 MPa.The bending strength and in plane shear strength of the material can be improved by appropriately increasing the non-woven cloth and needle density,reducing the needle depth within a certain range.Compared with the sample of control group without optimization of preform preparation parameters,the bending strength and in plane shear strength of the sample increased by22.2%and 23.3%,respectively.(3)Firstly,the hydraulic burst pressure of C/C-SiC composite rings and head were tested,meanwhile,the finite element model of hydraulic blasting process was established.Finally,the factors affecting the overall bearing capacity of the composites were explored.The results show that the optimization of preform preparation parameters can significantly improve the overall bearing capacity of composites.The hydraulic burst pressure increased from 1.9 MPa to 2.3?2.4 MPa,Longitudinal cracks appeared in all the four groups of composite rings,and the circumferential tensile stress was greater than the axial compressive stress when the composite rings cracked,and its circumferential tensile strength had a significant impact on the hydraulic bursting pressure of the composite rings.The head with the optimization of preform preparation parameters and SiC matrix content shows excellent overall pressure-bearing performance,with hydraulic burst pressure of 1.7MPa.The crack of the head is mainly due to the fact that the axial tensile stress near the component arc surface is much greater than the circumferential tensile pressure,which leads to the circumferential crack in this area.The modes of the crack of C/C-SiC composite rings and head were predicted by finite element simulation,it has a good similarity with the results of hydraulic burst test.