The Study Of The Penetration Behaviors Of A Ship-building Steel

Targets made of ship-building steel, which is concerned, were penetrated by conical and flat-ended projectiles. The damage and failure behaviors of targets have been studied systematically by micro-hardness, metallography and scanning electron micrography.The results show that the ductile hole failures and back-surface petal failures are achieved when targets penetrated by the conical projectiles. The penetration process is similar to Vickers hardness test. It is triaxial compressive stress condition in the target and can be maintained as long as the noses of conical projectiles keeping integrity, thus, the plastic deformation continues under such stress state, In our test, the noses of conical projectiles keep integrity in the rang of all velocity, the conical projectiles can be treated as rigid projectiles. The penetration mechanism is ductile penetration.The failure models and penetration mechanism vary with the projectile velocity. Under the condition of penetration by flat-ended projectiles, the noses of flat-ended projectiles keep integrity when the velocity is under the normal projectile velocity. Also, the flat-ended projectile can be treated as rigid projectile under this condition. The penetration process is similar to the punching extrusion process of metal. At first, the shear deformation presents in the target along the penetration direction, then, when the deformation depth reaches to a critical value, the material in front of the projectile will be shear failure, thus a plug failure is achieved. The penetration mechanism is shearing penetration or punching penetration in this case. When the projectile velocity reaches to the normal projectile velocity, the projectiles fracture crushingly, the penetration process is similar to the process penetrated by long rod projectile and can be divided into three processes that is crater process, steady penetration process and plugging process. The erosion failure and plug failure of target are the main character under this condition.According to the land forces criteria(U.S) for ballistic limit and by using the method that the ballistic limit is equal to the average of two velocities that are partly penetration velocity and completely penetration velocity respectively, the ballistic limit is determined targets penetrated by both conical and flat-ended projectile, the result can be in the table. The result show that all the ballistic limitis in the rang of the normal projectile velocities which can be easily achieved by average guns so, in this sense, the capability of material against penetration is not very good.Ballistic limit (m/s)Vi-iVl-2VIMVlI-2325399535902Based on the analysis of failure model of ductile target penetrated by conical projectile, a new energy function is obtained, as follows, ?88.4547The ballistic limit can be predicted using the function and satisfactorily accords with the actual results.Compressive deformation presents under the condition of conical projectile penetration. The change of the micro-hardness along the radial direction approximately coincides with the exponential decay, that is at the edge of the crater the hardness is the highest and 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 increases with the increase of velocity and approximates to the liner function of the velocity. The penetration process can be treated as adiabatic process, but the heat effect is not notable.When targets penetrated by flat-ended projectile, shear deformation along the penetration direction appears, at the same time compressive deformation also appears in the material that is in front of the projectile. The compressive deformation begins at the back surface of the target and spreads inward. The change of hardness along the radial direction also approximately coincides with...