To prevent functional failure, the macroscopic shock response of ceramics needs to be understood. We explored the mesoscopic deformation features of porous ceramics, which are responsible for the measured macroscopic “plastic” wave profiles, using polycrystalline modeling and experiments. A polycrystalline model is established that considers the influence of two major microstructures (multi-voids and grain boundaries) in the porous ceramics. Shock experiments with the recovery of shocked porous lead zirconate titanate ceramics were conducted. The computational results show that shear cracks nucleate around voids under shock because of severe shear stress concentrations. Broken fragments fill the voids and lead to void collapse. Representative long-distance extended cracks and thick crevices are observed in the recovered sample subjected to 3.3 GPa compression. These representative features are reproduced by the polycrystalline model. An initial transgranular crack translates into an intergranular crack after a certain propagation range to form a long-distance extended crack. Intergranular cracks branch from the main transgranular crack during main crack propagation to form a thick crevice. The simultaneous propagation of main and branching cracks results in a more effective shock energy dissipation. Slippage and rotation deformation induced by multi-cracks allows the shocked porous ceramic to deform even after all the voids have collapsed. Mesoscopic deformations of porous ceramics induce significant stress relaxations and lead to macroscopic “plastic” wave profiles. The polycrystalline model will aid microstructures design and provide guidance for preventing the shock failure of functional ceramics.

The rapid propagation and coalescence of cracks and catastrophic fractures, which occur often under shock compression, compromise a brittle material's design function and restrict its scope of practical application. The shock plasticity of brittle materials can be improved significantly by introducing and designing its microstructure, which can help reduce or delay failure. We used a lattice-spring model, which can describe elastic deformation and brittle fracture of modeled material accurately, to study the influence of void distributions (random, square, hexagonal, and triangular void patterns) on the macroscopic shock response and the mesoscopic deformation feature of brittle materials. Calculated results indicate that the void patterns dominate two inelastic deformation stages on the Hugoniot stress-strain curves (the collapse deformation stage and the slippage deformation stage). It shows that the strain localization is not strong and that the broken media are closer to a round bulk when the samples exist in random and triangular void patterns. This favors an increase in deformation during the slippage deformation stage. For the samples with square and hexagonal void patterns, the strain localization is strong and the broken media are closer to columnar bulks, which favors an increase in deformation during the collapse deformation stage.

The mechanical properties of a material are closely related to its internal micro-structure. Enhancing shock plasticity by designing appropriate micro-structure will help to slow down or delay shock failure of brittle material. In this paper, we put forward a method of designing and improving shock plasticity of brittle material by implanting specific micro-voids. A lattice-spring model is adopted, which can represent mechanical properties of brittle materials quantitatively. Simulations reveal how the arrangement modes of micro-voids can affect the shock response of brittle material. By implanting randomly arranged voids, porous brittle material has significantly higher shock plasticity than dense brittle material and the design of the regular arrangement mode of voids will help to enhance the shock plasticity further. The dominant mechanism corresponding to the void collapse in the shocked brittle material is shear slip caused by shear stress concentration, which features the occurrence of shear cracks around the voids. Features of mesoscopic deformation in the sample with 5% porosity indicate that the shock plasticity of porous brittle material comes from the volume shrinkage deformation caused by void collapse and the slippage and rotation deformation caused by extension of shear cracks. The inter-permeation of voids and volume shrinkage deformation play a leading role in the sample with regularly arranged voids. While the shear cracks extends over long distance, slippage and rotation deformation take place dominantly in the sample with randomly arranged voids. The two samples with different arrangement modes of voids both have three stages of response in the Hugoniot stress-strain curves in this paper, i. e., linear elasticity stage, collapse deformation stage, and slippage and rotation deformation stage. The sample with higher porosity has a higher shock plasticity than the sample with lower porosity. When the samples have the same porosity, the collapse deformation stage makes greater contribution to the overall shock plasticity if voids are regularly arranged, while the slippage and rotation deformation stage make greater contribution to the overall shock plasticity if the voids are randomly arranged. The principle of enhancing shock plasticity of brittle material by arranging voids regularly in this paper provides physical knowledge for the designing and preparing new types of brittle materials, thereby helping to prevent the function failure induced by shock in brittle material.