| In this dissertation, targets made of shipbuilding steel were penetrated, and the materials around the crater were tested by micro-hardness. The deformation and damage around the crater were studied by metallography and SEM. The influence of stress condition and metallurgical quality of material to the damage and fracture in the course of the penetration is also discussed. So we understand systematically the process that shipbuilding steel is penetrated by conical and flat-ended projectiles.The results show that the ductile hole failures and back-surface shearing tear when the conical projectiles penetrated targets. The penetration process is similar to Vickers hardness test, It is triaxial compressive stress condition in the target. The noses of conical projectiles were kept integrity and were treated as rigid projectiles.The failure models and penetration mechanism vary with the projectile velocity when targets were penetrated by the flat-ended projectiles, The process of penetration is similar to the punching extrusion process of metal when the velocity is under the normal projectile velocity. A plug failure is achieved. The penetration mechanism is shearing penetration or punching penetration. When the projectile velocity reaches the normal projectile velocity, the plug failure and erosion-plug failure are the main characters. The penetration behavior is similar to the process penetrated by long rod projectile. The process penetrated is divided into three processes that is crater process, steady penetration process and plugging process.According to the land forces criteria(U.S) for ballistic limit and by the method that the ballistic limit is equal to the average of two velocities. The ballistic limit is determined by both conical and flat-ended projectile. The result shows that all the ballistic limit is in the range of the normal projectile velocities which can be easily reached by average guns. In the sense, the capability ofshipbuilding steel against penetration is not very good.Ballistic limit (m/s)Compressive deformation presents under the condition of conical projectile penetration. The deformation hardening rule of the material around the crater is approximately described with the exponential decay. Material is hardened because of the deformation acutely at the edge of the crater, and the hardness is decreases with the increase of the distance from the crater and to the normal value at last. The hardness at the edge of the crater is increase with the increase of projectile velocity. The reason of the hardness variety maybe is that the strain velocity hardening of material at some range of deformation velocity. The penetration process can be treated as adiabatic process, but the heat effect is not notable, and deformation hardening presents.Shearing deformation along the penetration direction appears under the condition of flat-ended projectile penetration, at the same time, compressive deformation also appears in the material that is in front of the projectile. The change of hardness along the radial direction also approximately coincides with the exponential decay. The flat-ended projectile penetration process can also be treated as adiabatic process. When the projectile velocity is under the normal projectile velocity. For the deformation accumulated the heat effect is notable, the hardness at the edge of the crater decreases with the increase of velocity. When the velocity reaches the normal projectile velocity, the material at the edge of the crater ruptures rapidly, and the deformation to accumulate is restrained. So heat effect is not notable, the hardness is increase.Micro-damage nucleate at the weak location of material such as nonmetal inclusion, rolling segregation, grain boundary, the pearlite and so on. The damage evolution is by the linkage of micro-voids. So those can improve the capability oftarget against scale off which improve metallurgical quality, reduce the segregation degree in the organise and the quantity of nonmetal inclusion. |
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