| In the nature,a large number of organisms have evolved biological structures with high strength,high toughness and good energy dissipation mechanism in order to resist the damage of predators and adapt to the complex and changeable environment.Among them,the nacre in the shell has a biological structure with good impact resistance.It is a composite material composed of brittle aragonite and soft organic matter,and has a complex hierarchical structure at the micro scale.In this paper,nacre-like ceramic/polyurea composite plates was designed by simulating the “brick-and-mortar” microstructure of nacre and replacing the aragonite with the alumina ceramic of high strength,high hardness,low density and chemical inert and the soft organic matter with the polyurea of high toughness,low density,wear resistance and corrosion resistance.Based on numerical simulation,the influence of structural parameters of target and projectile parameters on the impact resistance of nacre-like ceramic/polyurea composite plate were studied.Also,a nacre-like ceramic/polyurea composite plate was prepared,and a high-velocity impact test was performed by using the one-stage light gas gun as loading equipment to study the mechanical behaviors of the nacre-like composite plate under high-velocity impact.The main work of this paper is as follows:Firstly,nacre-like ceramic/polyurea composite plates with the same overall size and different internal structural parameters were established.Based on Smoothed particle hydrodynamics(SPH)method,the process of the composite plates subjected to high-velocity impact of flat-nosed projectile was numerically simulated.The effects of polyurea thickness,ceramic tile size and layer number on the impact resistance of nacre-like composite plate at different impact velocities were analyzed,and the impact resistance of composite plates and pure ceramic plate was compared.The results show that under different impact velocities,the effects of polyurea thickness,ceramic tile size and layer number on the impact resistance of composite plates are different.Overall,the influence of polyurea thickness and number of ceramic tile layer on the impact resistance of composite plate is more significant than that of ceramic tile size.When the impact velocity is relatively low,the impact resistance of composite plate is better than that of pure ceramic plate.When the impact velocity is high,the impact resistance of pure ceramic plate may be better than that of composite plate with certain structural parameters.From the point of view of increasing the ballistic limit velocity of nacre-like composite plate,in the range of the parameters studied in this paper,it is preferable to take a larger thickness of polyurea,a larger number of ceramic tile layers,and a smaller ceramic tile size.At the same time,the influence of the shape of ceramic tile was analyzed,and the impact resistance of the nacre-like composite plate with quadrilateral and hexagonal ceramic tiles was compared.The results show that when the thickness of polyurea is small,the impact resistance of hexagonal composite plate is better;when the thickness of polyurea is large,the difference in impact resistance between the two is dependent on impact velocity.In addition,the effect of toughness of polyurea material on impact resistance of nacre-like composite plate was discussed.The results show that the toughness of polyurea material has obvious influence on the impact resistance of nacre-like composite plate,and the influence is greater when the impact velocity is low.Then,for a given nacre-like ceramic/polyurea composite plate,the process of four kinds of projectiles with the same mass while different shapes penetrating into the nacre-like composite plate was numerically simulated based on SPH method.The influence of projectile shape on the impact resistance of the nacre-like composite plate was studied,and the ballistic limit velocities of the composite plate under different shapes of projectiles were predicted.The simulation results show that the ballistic limit velocity for the ball-shaped projectile penetrating the composite plate is the largest,and then the order from big to small is ogival-nosed projectile,the hemispherical-nosed projectile and the flat-nosed projectile.The damage area of composite plate caused by hemispherical-nosed projectile impact is the largest,and the damage area caused by ogival-nosed projectile impact is the smallest.The diameter of bulge at the back of the composite plate caused by the impact of the four types of projectiles is basically the same,and the bulge area is limited to the ceramic tile corresponding to the impact point and its adjacent ceramic tiles;The shape of damage area at the back of the composite plate is conical under the impact of flat-,hemispherical-and ogival-nosed projectiles,but the conical distribution is not obvious under the impact of the ball-shaped projectile.Furthermore,based on the SPH method,the oblique penetration process of nacre-like composite plate with different shapes of projectiles was numerically simulated.The influence of projectile inclination angle on the impact resistance of the composite plate was studied,and the variation of residual velocity and ricochet angle of projectile were analyzed.The numerical simulation results show that with the increase of projectile inclination angle,the residual velocities of projectiles with different shapes decrease,and the decrease rate increases gradually.When the impact velocity is 903.9 m/s,the critical angle of projectile ricochet is between 70° and 75°.Finally,96 alumina ceramic and SWD 9526 polyurea were used as experimental materials to prepare nacre-like ceramic/polyurea composite plate samples.The one-stage light gas gun system was used as the loading equipment,and the impact process of the projectile on the target was recorded by high-speed camera.The high-velocity impact test of the nacre-like composite plate was carried out.The high-velocity impact mechanical behavior of the nacre-like composite plate was studied,and compared with that of the pure ceramic plate with similar areal density.The results show that the overall structure of the nacre-like composite plate is intact under the high-velocity impact of the projectile,and the diameter of the damaged area is less than 3.5 times of the diameter of the projectile.However,the pure ceramic plate is completely damaged,and the central area of the plate has been comminuted,resulting in a hole larger than 7 times of the diameter of the projectile.This indicates that the nacre-like composite plate has advantages over the pure ceramic plate in resisting multi-point impact of the projectile.The residual velocity of projectile penetrating the nacre-like composite plate at 343.9 m/s is 227.7 m/s,while the residual velocity of projectile penetrating the pure ceramic plate at 310.4 m/s is 157.5 m/s,which indicates that the anti-penetration ability of the nacre-like composite plate prepared in this paper is lower than that of the pure ceramic plate.Therefore,it is still necessary to further optimize the selection of polyurea material,the structural parameters of the composite plate and the preparation process,so as to improve the anti-penetration ability while maintaining the advantage of small damage.At present,there are few public reports on high-velocity impact tests of nacre-like ceramic composite structures.The experimental data obtained in this paper can provide important insight into the subsequent related research. |
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