Failure Waves In Alumina Ceramics Subjected To Shock Compression

Ceramics are extensively used in national defense engineering and military science with their excellent physical and mechanical capabilities, so it is a widely attentional subject in dynamics circles to research on the dynamic responses and failure behavior of ceramics under impact loading. Especially the failure waves, which propagate in impacted glasses and ceramics below their Hugoniot elastic limits (HELs) and refer to mechanical, material and physical science, were discovered in the 1990s. So far the study on the failure wave has focused on accumulating acquaintance with its physical and mechanical characters monitored in experiments with restriction of experimental conditions of high pressure loading and monitoring techniques for high resolving wave profiles. And there is not a perfect model to explain the formation and propagation of the failure wave and the mechanism of interaction between failure wave and material, even to numerical model the basic mechanical response characters behaved in experiments satisfactorily. This is the emphasis and difficulty in the study on failure waves, and main reason why scholars at home and abroad are interested in failure waves so many years.In this dissertation, normal and oblique plate impact experiments of polycrystalline alumina ceramics were proposed and performed on the basis of the research at home and abroad on failure waves and inelastic deformation in shocked glasses and ceramics. Then the physical and mechanical mechanism of failure waves forming and propagating in glasses and ceramics were analyzed associated with the failure wave phenomena in glasses, and the gradual crushing model was proposed to describe failure waves based on material heterogeneity and high singularity of stress in mesoscope. The main work and conclusions in this dissertation are as follows:(1) The failure wave in shocked glasses below their HELs and the particular inelastic responses in shock-loaded ceramics were reviewed on the related literature. The physical mechanism of failure waves formation and propagation, mechanical characters and mathematic models were investigated specially.(2) The basic physical and mechanical parameters of alumina were measured in ultrasonic experiments. The material components were analyzed by energy spectrum and the microstructures were observed by scanning electron microscope. The components and structures of alumina are strongly heterogeneous in mesoscope.(3) With the help of the National Defense Science and Technology Key Laboratory of Shock Wave Physics and Detonation Physics in China Academy of Engineering Physics, normal and oblique plate impact experiments of alumina ceramics were proposed and performed. In the experiments, the free surface velocity histories of alumina under 1D-strain shock loading with Φ100 light gas gun were monitored by VISAR and the recovered specimens were observed by scanning electron microscope in order to analysis the inelastic deformation and failure behavior in alumina and the meso-structure characters of damaged and post-failure materials. As a result the failure wave propagation was observed in alumina, and it propagated at higher velocity under stronger shock loading.(4) In oblique plate impact experiments, the electromagnetic induced electromotive force histories of particles in alumina specimens under combined compress-shear loading with Φ57 light gas gun were traced by embedded electromagnetic particle velocity gauges. The influence of copper flyer on induced electromotive forces was found out and then eliminated. The recovered specimens were observed by scanning electron microscope to analysis the influence of shear component of shock loading on the inelastic deformation and failure behavior of alumina. Then the conclusion that shear impaction promoted the microcracks nuclearing and expanding in alumina was drawn.(5) The evolution of the HELs of brittle ceramics was discussed on the basis of experimental results from the inelastic deformation and failure behavior of shocked alumina and ma...