Investigation Of Deformation And Fracture Behavior Associated Mechanisms Of The Metal Kinetic Energy Projectiles

Recently, an increasing number of advanced materials and structures have been used in the field of protection,while the deformation and fracture of the penetrators are inevitable during the process of target impact. Although there have been several hundred years of history for the research on the armour-piercing and penetration, most of researches focused on the penetration and perforation caused by rigid projectiles. With more and more high strength and ductility materials and structures are used in the field of armor protection, the influences of deformation and fracture cannot be ignored, which affect the penetration of penetrator seriously. The research on deformation and fracture of kinetic energy projectile in penetration process has became one of the research hotspots in the field of international impact engineering since some researchers paid more attention on this question recently. However, compared with lots of penetration research of rigid projectile, only a few papers involve in the projectile deformation, especially fracture. Furthermore, due to the influence of diversely complex factors, the assumption of rigid target is adopted frequently in order to achieve the deformation and fracture of penetrators conveniently. Even so, the investigations on projectile deformation and fracture behavior in impact test are still limited and patchy. In the actual penetration problem, deformation and fracture can occur for regardless of projectile and target. So it is necessary and meaningful to obtain deformation and fracture behavior of projectiles aimed at deformable targets.Based on the backgrond mentioned above, this thesis will concentrate on the deformation and fracture behavior and mechanisms of kinetic energy projectiles at the sub-ordnance and ordnance speed regime during the process of impacting the rigid targets and several other kinds of typical deformable targets by conducting experiments and numerical simulations, as well as examine the effects of deformation and fracture behaviors of projectiles on penetration ability.According to the method of Taylor impact test, the research on deformation and fracture behavior was conducted for blunt-nosed projectiles with a series of different materials. Deformation and fracture modes and the corresponding speed ranges were obtained for every kinds of projectiles. The fracture mechanisms were primarily revealed for all projectiles by microscopic scanning of typical fracture surfaces. The relationship between deformation and fracture types and material ductility was obtained, as well as a preliminary formula of critical cracking velocities and projectile material parameters was established, such as density, strength, ductility and so on. The numerical simulations were conducted corresponding to Taylor impact tests above. Constitutive relation and fracture criterion with all model parameters were obtained for all involved materials in this thesis by conducting on material performance testing and literature researches. The simulations on Taylor impact tests of various projectiles were achieved and successfully predicted various fracture modes of each projectile. The validity of numerical simulations was verified by comparing with the experimental results, and there was a simple C-L fracture criterion which can predict almost all the fracture modes of various projectiles with different materials. On this basis, the fracture processes and mechanisms were analyzed in detail for the typical fracture modes of each kinds of projectiles, and the sensitivity of some factors that likely to affect deformation and fracture behavior of projectiles were evaluated by numerical simulations.For rod projectiles with two different materials of different strength values penetrated double-layered plates with different hardness values and laminated sequences, the deformation and fracture behaviors were investigated on projectiles and targets, and the effects of deformation and fracture behaviors of projectiles on penetration ability was examined as well. On the basis of experimental achievements, C-L fracture criterion was applied to predict the deformation and fracture of projectiles and targets sucessfully in the numerical simulation.For rod projectiles of high-strength steel penetrated armored steel targets，two kinds of nosed shapes were adopted in the research. Typical deformation and fracture modes, feature sizes of projectiles and targets were obtained by experiments, which were reproduced by C-L fracture criterion that has been verified previously. Based on this, typical fracture processes of projectiles and targets were analyzed in detail and fracture mechanisms was revealed by numerical simulations. Besides, the velocity range was extended appropriately by numerical simulations and the deformation and fracture behaviors of projectiles and targets in the wider speed range were obtained in numerical simulations.Research results of this thesis can provide some accumulations of data and experiences for the research field of deformation and fracture of kinetic energy projectile. Meanwhile, the results can also provide some data references and methods for the pre-research, especially material selection and structure design of kinetic energy rod projectiles.