Experimental Study And Failure Analysis Of Mechanical Properties Of Acupuncture C/C Composites Under Biaxial Loading

Needle punched C/C composites have been widely used in aerospace and defense industry as an important structural component due to their low density,good chemical and thermal stability,ablative resistance,and strong fracture toughness.With the extensive use of acupuncture C/C composite materials,the acupuncture C/C composite materials in service are usually in a complex load environment,and the traditional uniaxial load experiment cannot simulate the complex stress state of the composite structure,so that Researchers may not fully understand the true load-bearing level of composite materials under complex stress,which makes the formulation of material technology and structural component design lack the necessary theoretical basis;at the same time,the establishment of material strength criteria also requires some complex stress conditions Strength value,so it is particularly important to carry out the corresponding biaxial loading experimental research.In view of the above deficiencies,the main research contents of this article are as follows:First of all,the manufacturing process of the needle punched C/C composite material is introduced,the microscopic structure and morphological characteristics of the needle punched C/C composite material are observed and analyzed,and the internal defects of the material are studied.Conduct basic mechanical properties experiments of acupuncture C/C composites,including out-of-plane stretching,out-of-plane compression,and interlayer shear mechanical properties experiments.The longitudinal tensile/compressive strength,longitudinal tensile/compressive elastic modulus and interlaminar shear strength of the needle-punched C/C composite under uniaxial load were obtained.After the experiment,the fracture characteristics of the material were studied and analyzed to determine the failure mechanism of the needle-punched C/C composite under different load conditions;the trend of the stress-strain curve of the material during the stress process was studied to determine the needle-punched C /C composite material elastic modulus changes in each experiment.Then,the biaxial statics experiment analysis was carried out on the needle-punched C/C composites.Firstly,the out-of-plane normal stress-shear stress coupling experimental scheme design of acupuncture C/C composites was carried out,and then the out-of-plane tensile-shear and out-of-plane compression-shear tests under different biaxial load ratios were carried out to obtain acupuncture.Biaxial tensile shear strength and biaxial compressive shear strength of C/C composite materials under various loading ratios.Through the analysis of the experimental data,it was found that in the out-of-plane tensile-shear experiment,the tensile strength and shear strength of the needle-punched C/C composite material showed a biaxial weakening phenomenon;in the out-of-plane compression-shear experiment,The out-of-plane compressive strength shows a biaxial weakening phenomenon,and the shear strength shows a biaxial strengthening phenomenon.The trends of the biaxial tensile and compressive strength and shear strength of the material with the stress ratio are summarized separately.Finally,according to the fracture characteristics of the sample after the experiment,the failure mechanism of the needle-punched C/C composite material under complex load environment was analyzed,which provided experimental support for the establishment of the room-temperature strength criterion of the needle-punched C/C composite material.Secondly,combined with the biaxial load experimental data of the needle-punched C/C composite material and the commonly used three-dimensional macro strength criterion,the failure failure of the needle-punched C/C composite material is studied,and the applicability of various strength criteria to the experimental data is analyzed.The results show that in the out-of-plane compression-interlayer shear experiment,the Christensen strength envelope is in good agreement with the experimental data,and can be used as the failure criterion for out-of-plane compression-interlayer shear of needle punched C/C composites;In the out-of-plane compression-interlayer shear experiment,it was found that the commonly used composite strength standards are in good agreement with the experimental data,but the deviation of the Christensen strength criteria is small.By correcting the Christensen strength criterion,when the correction coefficient C=3,the corrected Christensen strength envelope is consistent with the out-of-plane tensile-interlayer shear experimental data.Finally,the strength envelope of the out-of-plane normal stress-interlayer shear stress of the complete needle-punched C/C composite is drawn.Finally,the finite element software ANSYS was used to analyze the temperature distribution of the biaxial specimen in electromagnetic induction heating,which made a foundation for the subsequent high-temperature biaxial mechanical performance experiments.The design of the induction coil was optimized through orthogonal experiments.Since the induction coil designed by the original scheme could not achieve the requirement of uniform temperature,the design of the induction coil was completed by adding a graphite induction heating body to the biaxial sample.Use the optimized induction coil to electromagnetically heat the biaxial tensile-interlaminar shearing and out-plane compression-interlaminar shearing biaxial samples to obtain the temperature field distribution when the sample is heated to 1600? Perform homogenization analysis on the gauge length of the sample.The results show that the optimized coil can make the biaxial specimen achieve uniform temperature requirements during electromagnetic induction heating.