Failure And Fracture Characteristics Of Ad95 Ceramics Under Impact Loading

Recently,AD95 ceramics are widely used in various domains,including the aerospace industry and armor protection,due to its low density,high strength,high-temperature tolerance and corrosion resistance.As a typical brittle material,there are initial micro-voids,micro-cracks,grain boundaries and other defects inside the AD95 ceramics.The fracture mechanism is complicated because of the severe asymmetry in tensile and compressive strength and stress concentration in the position of initial defects under impact loading.Consequently,there is a requirement to study its dynamic properties,microstructure and fracture mechanism.In this article,the dynamic mechanical properties and the scale of fracture of AD95 ceramics under impact loading were researched based on the experiment and theoretical analysis and the dynamic damage and fracture mechanism of the material were revealed combined with numerical simulation.Firstly,the dynamic tensile/compression experiments under one-dimension stress wave loading were conducted on split Hopkinson pressure bar(Hopkinson)to study the dynamic tensile/compression mechanical properties of AD95 ceramics and the strain rate effect of the material’s tensile / compressive strength was obtained.Secondly,the average radius and number of broken particles at different strain rates were obtained by the soft recovery of the crushed samples under dynamic compression and the fracture scale was analyzed by DID model.It is found that the compression strength and tensile strength are of obvious strain rate effect and the value of compression strength is approximately 20 times that of tensile strength.By analyzing the microstructure of the material,it is found that this obvious imbalance is mainly caused by factors such as the shape of microscopic particles,grain boundaries and the size of micro-voids.The 3D numerical simulation results shows that the damage of the ceramic specimen begins in the position of the stress concentration at the end edge of the material and then gradually expands to theinside,which eventually leads to the complete failure and fracture of the specimen.Finally,the symmetrical plate impact experiment of AD95 ceramic was carried out.The plane shock wave velocity and the Hugoniot curves under high-speed impact of the material were obtained by the internal pressure sensor.By recovering the fracture particle samples,it is found that the fracture scale of AD95 ceramics under plane shock loading was concentrated between 300 μm and 1000 μm and the total number of broken particles increased with the increase of impact pressure.By the nonlinear finite element software AUTODYN,the ceramic specimen under plane impact loading was numerically simulated and the complete damage history of the material was obtained.It is found that a high stress area is formed on the front of the specimen under the high-speed impact of the flyer and the failure and fracture of the sample are mainly caused by insufficient compressive strength;with the propagation of the stress wave,the loading of side rarefaction wave along a specific path and the spallation inside the sample lead to the tensile failure of the material.