The ability of porous brittle materials to absorb and withstand high energy density pulse

Abstract

The high energy density pulse input into brittle structural materials will propagate as a shock wave. It induces compression fracture and function failure. In this work, voids are introduced to significantly enhance the shock plastic deformability of brittle structural materials, so that brittle structural materials can effectively absorb the shock wave energy, and restrain the propagation of shock-induced cracks. A lattice-spring model is established to investigate the mechanism of shock plastic, and the processes of energy absorbing and crack expanding in porous brittle materials. The shock wave inside porous brittle material splits into an elastic wave and a deformation wave. The deformation wave is similar to the plastic wave in ductile metal, however, its deformation mechanism is of volume shrinkage induced by voids collapse, and slippage and rotation deformation of scattered tiny scraps comminuted by shear cracks. We calculate the shock wave energy based on particle velocities and longitudinal stresses on nine interfaces of the modeled brittle sample, and further obtain the absorbed energy density. The absorbed energy density curve is composed of two stages: the absorbing stage and the saturation stage. The absorbing stage corresponds to the deformation wave, and the saturation stage corresponds to the shock equilibrium state (Hugoniot state). The energy absorb abilities of the dense sample and porous samples with 5% and 10% porosities are compared based on calculation results. It shows that the ability of the porous brittle material to absorb high energy density pulse is much higher than that of the dense brittle material. The ability of porous brittle materials to restrain the propagation of the shock fracture is also explored. The goal of this design is to freeze the propagation of the shock fracture in the middle of the brittle sample, so that the other parts of the sample keep nearly intact during the shock. Inside the protected area, the designed functions of brittle materials can be accomplished without the disturbance of the shock fracture. This design is used under the short pulse loading condition: the rarefaction wave on the rear of the short pulse will catch up and unload the deformation wave if it moves slowly; the deformation wave and the shock fracture propagate synchronously; when the deformation wave is unloaded, the shock fracture will be frozen in the middle of the porous sample. Under the short pulse loading condition, compared with the dense brittle material, whose entire regions are destructed, the porous brittle material can restrain the propagation and impenetration of the shock fracture, with the cost of increasing the damage extent in part of the sample. This is helpful to avoid the entirely function failure of the brittle structural material.