Research On Fatigue Properties Of Advanced Ceramic Wave Transmitting Materials Based On Meso CT Images

As two kinds of advanced ceramic wave-transmitting materials,silicon nitride（Si₃N₄）ceramics and Si O_2f/Si O₂composites have excellent wave-transmitting,thermal protection,and load-carrying properties,which are widely used in radome structures.The radome faces complex thermal,static,and dynamic loads during high-speed aerodynamic flight.It is essential to accurately evaluate the fatigue performance of such materials under service conditions.Due to the complex preparation process,the microstructure characteristics of Si₃N₄ceramics and Si O_2f/Si O₂composites are often shown as uneven material distribution,unsatisfactory fiber arrangement,and different pore morphology,so the mechanical behavior of them have large dispersion,poor consistency,and complex failure mechanism,which brings great uncertainty to the application of advanced ceramic wave permeable materials.In this paper,the micro-component structure and defects of the material are characterized by X-ray computed tomography（X-CT）,and the tensile-tensile（T-T）fatigue properties of composites are analyzed.Firstly,the Si₃N₄ceramics,2.5D and 3D needle-punched（3Dn）Si O_2f/Si O₂samples are scanned by X-CT.According to the Computed Tomography（CT）images,the meso-component structures and defect characteristics of different materials were summarized.The threshold segmentation algorithm is used to extract the component material and defects,and the binary image is output.The in-plane content of each component is calculated,and the change curve with different slices is drawn.Then the binary images are stacked to realize the three-dimensional reconstruction,and the three-dimensional volume content is calculated.Secondly,T-T fatigue and residual tensile strength tests of Si₃N₄ceramics are carried out at room temperature,800°C,1000°C,and 1200°C.The fatigue life,residual tensile strength,failure location,and macroscopic fracture morphology of silicon nitride ceramics were analyzed based on CT images.The crack source often emerges from large defects,and it is more likely to occur in the middle of several defects that are very close to each other.The fatigue behavior of Si₃N₄ceramics at different temperatures is analyzed,the brittle-ductile transition temperature of Si₃N₄ceramics is between 1000°C and 1200°C,and the fatigue limits at room temperature,800°C,1000°C,and 1200°C are obtained.Finally,the fatigue properties of 2.5D and 3Dn Si O_2f/Si O₂have been investigated experimentally,and the fatigue behavior is analyzed by the stress-strain curve.Combined with Micro-CT images,the differences between the microstructures of 2.5D and 3Dn are studied to investigate their effect on macroscopic fracture.The results show that the fracture position is affected by pore defects.The content of fiber bundles that parallel to load direction has a significant influence on the fatigue performance of Si O_2f/Si O₂composites.And the discreteness of the fatigue properties of Si O_2f/Si O₂composites is closely related to the degree of irregularity of the microstructure.