Study On Impact Failure Mechanism Of Al₂O₃/SiC Composite

Ceramic materials are widely used in various armor protection structures due to their low density,high strength and high modulus.With the advancement of material science and the innovation of related industrial technology,ceramic matrix composites based on alumina have gradually become a popular choice for new armor protection materials due to their superior mechanical properties and cost performance.In recent years,a large number of researchers have focused on the sintering process,microstructure and mechanical properties of alumina matrix composites,and the research on the impact failure mechanism of materials needs to be further studied.In particular,the relationship between macroscopic and microscopic failure mechanism of composite ceramics,the effect of second reinforcement on material properties and its role in crack propagation are still unclear.In this paper,Al₂O₃/SiC composite ceramics with 5wt%SiC content of the second phase particles were selected as the research object.The dynamic failure mechanism and fracture behavior of Al₂O₃/SiC composite ceramics under impact load were studied by combining experiment,theory and numerical simulation.Firstly,the dynamic compression and tensile tests of Al₂O₃/SiC composite ceramics were carried out by SHPB loading device.Affected by the inertia effect of cracks,the dynamic compressive and tensile strength of the material increase exponentially with the strain rate,and the strain rate effect sensitivity index is close to 1/3.SEM scanning electron microscope was used to analyze the micro-damage of multiphase ceramics at different fracture positions after impact loading.It was found that sparse waves would lead to more intergranular fractures,and the micro-damage deformation of materials showed unique inelastic deformation response characteristics.The dynamic compression test sample fragments were recovered,and the DID debris scale theory prediction model was revised.The crushing characteristics and average particle size distribution of multiphase ceramics under one-dimensional stress waves were obtained,which are in good agreement with the theoretical results.Secondly,the dynamic failure mechanism of composite ceramics under one-dimensional plane waves was studied by designing a plane impact loading device and specimen.The results show that at high stress level,more local plastic deformation characteristics such as shear slip and step cleavage fracture appear in the composite ceramic.The grain damage deformation around the fracture core is affected by the side sparse wave,and the micro deformation of the multiphase ceramics is jointly controlled by the loading rate and stress state.At the same time,the composite ceramics showed obvious second phase particle effect,and the reinforcement changed the propagation of microcracks.The fracture samples of composite ceramics under plane shock wave were statistically analyzed.Based on the DID model,a theoretical correction model for predicting the size of debris under one-dimensional strain state was proposed.The theoretical results are in good agreement with the experimental data.Finally,the ballistic impact test of Al₂O₃/SiC multiphase ceramic target was carried out by ballistic gun device.The results show that Al₂O₃/SiC composite ceramics have good anti-elastic properties.With the increase of projectile velocity,the number of radial and circumferential cracks in the target plate increases.The theoretical prediction of ceramic cone angle is in good agreement with the experimental data.The impact process of projectile on Al₂O₃/SiC composite ceramic target was simulated by AUTODUYN software,which found that the impact compression wave and the reflected tensile sparse wave jointly act on the target to form a broken cone.The microscopic analysis of Al₂O₃/SiC composite ceramic target shows that the fracture surface of the broken cone and the fracture position of the radial crack have different microscopic fracture modes due to different stress states.There are a large number of intergranular fractures on the fracture surface of the broken cone,and the radial crack propagation fracture position is mainly transgranular fracture,but the two fracture positions have the microscopic damage deformation characteristics such as slip line and cleavage fracture.By analyzing the microstructure of the fracture core grains,it can be seen that the sparse wave has an important influence on the propagation of radial cracks and the formation of ceramic crushing cone.