Research On The Blast Loadings And The Response Of Multi-layer Protective Structure

The impulsive load inside a naval vessel is due to an explosion, which is clearly a major hazard that can result in severe structural damage and even sinking. The explosion source is assumed to be an anti-ship missile, striking the hull just above the water line. Internal blast occurs when the hull is breached before detonation. Anti-ship missiles designed to explode inside the vessel have armor piercing or semi-armor piercing capability with delayed action detonation to maximize the caused damage. These anti-ship missiles often have out-standing ability in See Invisibility and hit precision. Under such situations the combined effect of blast pressure and fragment impact on the structure is possibly more severe than the effects of blast or fragments alone, particularly for the close-range internal explosions.Considering the serious damage effects caused by the anti-ship missile, multi-layer protective structures have been applied to the large surface ships. The main function of the multi-layer protective structure of a ship is to prevent the inner cabins from being destroyed by the weapons. Although concept of the multi-layer protective structures has been advanced in the world for several decades, its defense objects are some traditional anti-ship arm, i.e. torpedo, mine and anti-ship missile. Moreover, an appropriate design of multi-layer protective structures, which is severed as ’guard’ structure under the threat of modern weapons, should be based on a reasonable study of its mechanism. A method that can precisely calculate and analyze the response of protective structure under the explosion loadings is the key to investigate the mechanism of anti-explosion structure, estimate the effect of protection and get reasonable structure.Generally speaking, there are three basic scientific problems lie in the response of multi-layer protective structure under explosion loadings, namely the loadings from the warhead of anti-ship missile, the dynamic characteristic of materials under impact and the reasonable calculation method of structure response. In this paper, these problems are mainly considered theoretically, experimentally and numerically.Good resolution of steep gradients is important in numerical calculation of shock wave propagation. The high resolution LCPFCT algorithm is employed to solve the problem of steep gradients. Additionally, the Euler-FCT solver in Autodyn code is adopted to calculate the propagation process of shock wave inner a cabin with an venting hole in the cabin wall. An experiment was conducted to validate the accuracy of the numerical method in investigating the blast load in the cabin with an venting hole, which is used to simulate the rupture of the cabin wall.A reasonable constitutive model is of great important in calcaulation of the strcutre response, by which the mechanics behavior of material under dynamic load can be presented appropriately. In this paper, a constitutive model in the form J-C model is acquired based on the experiemtal investigation of material’s dynamic mechanical properties. The parameters of the constitutive model are validate by comparing the numerical results with the Taylor cylinder test.Explosively driven fragmentation of ductile metals is a very complex phenomenon in which the fragmenting material is plastically deformed by the intense shock followed by high-rate plastic deformation that ultimately leads to fracture. The damage effect of explosive filling metal casing mainly includes the fragments and shock wave. In the conditions of near field explosion, the spatial distribution of fragments with powerful penetrability has considerable influence on the failure pattern of the target. Many circumstances arise where a much more sophisticated treatment is necessary to predict the fragmentation features accurately over the entire length of a cylinder including the ends. Such calculation may be required to investigate the differences in initiation sites of the high explosive, properties of casing materials, and irregular shapes of casing. However, there are no corresponding theoretical analysis models. In this paper, the Smoothed Particle Hydrodynamics (SPH) method is used to investigate numerically the fragmentation process of a cylindrical metal casing with ends. After applying the numerical method to predict the propagation of detonation wave, the expansion and rupture process, the expansion velocity of metal casing, the leakage of detonation products and the fragment distribution, the fragment mass distribution is validated by comparing the numerical results with experimental data in the literature. Additionally, an experiment was conducted with the same explosive fragmentation geometry as modeled. Thus, the equivalent bare charge and fragment loading can be determined in the calculation of response of multi-layer structure. The double cabin model is manufactured to conduct the explosion experiment with different shape and mass of explosive charge, and the influence of three connection patterns of the corner structure on the converge of shock wave is studied. The explanation of shock wave convergence is given by the method of images. The interaction process between the blast loading and the structure is analyzed. Based on energy analysis and combination of MOI method, the equivalence energy of the charge is determined. Besides, the analytical model of calculation the outflow of blast pressure is proposed. The calculation method of blast pressure in cabin, which is relate to the relative position between charge site and the venting on the wall of cabin, is presented eventually.In order to investigate the synergistic effect of blast wave and fragment impact loadings on the multi-layer protective structure. An experiment is conducted in which the metal casing filled with TNT charge (MCTC), which is used to simulate the warhead of anti-ship weapon, explodes inside an empty cabin of the first layer of the multi-layer protective structure. A protective structure model with four layers and the MCTC model are designed and manufactured. According to the distribution of fragments and the equivalent bare charge of the MCTC determined by a numerical method, the MCTC model is placed appropriately in the experimental structure. From the experimental results, the failure pattern of the multi-later protective structure under the synergistic effect of blast wave and fragment impact loadings, the releasing effect of the venting hole in the transverse bulkhead, the function of the liquid cabins in the multi-layer protective structure and the shock responses of the cabins are investigated. The synergistic effect of blast wave and fragment impact loadings for the stiffened plates is also presented in the experiment by comparing the deformation and the rupture of the air-backed and water-backed plate. Finally, some conclusions are drawn and some suggestions for the design of multi-layer protective structure are put forward.The experiment of a multi-layer protective structure under the synergistic effect of blast and fragment loadings is numerically simulated by using of fluid-structure coupling and the method of multi solvers processing. The fargemt loading is obtained by the numerical mentod described in Chapter4and apply to the structure by combining the SPH and Shell slover. Besides, the balst load from equivalent bare charge is imposed to the structure by Euler-Shell coupling. A numerical method that can simulate the response and rupture of a multi-layer protective structure under the synergitci effects of blast and fragment impct loadings is presented.In this paper, based on the velocity loss analysis and Wen-Jones model, taking the influence of pressure produced by the moving fragment on the anti-perforation ability of inner-plate into account, a criterion is given to determine whether the guarding fluid cabin is effective. Besides, numerical simulations were conducted to investigate the process of single and double fragments penetrate the water cabin. The results indicate that there is an apparent additive effect of shock wave in water cabin caused by the impact of double fragments, and the position with high pressure of shock wave occurs is related to the distance between fragments. The double fragments impacting overpressure of shock wave and the pressure endured by inner plate are two times more than that of single fragment case. The present research laid the groundwork for the future study of the response of fluid cabins under fragments impact.