Studies On Dynamic Behavior Of High-speed Projectile Penetrating Into Concrete Target

The high-speed projectile penetrating into concrete usually has significant mass loss and nose blunting, which dramatically decreases its ballistic performance. Since the1990s, with considering mass loss and nose blunting, the dynamic behavior of high-speed projectile has already drawn great interests in the academic and engineering communities. The objective of this dissertation is to study the dynamic behavior of high-speed projectile with considering mass loss and nose blunting. The projectile is ogival long-rod projectile or the Concept Projectile for High-speed Penetration (CPHP) made of high-strength alloy steel. The corresponding target is plain concrete target assumed as semi-infinite. The striking velocity of projectile is usually below1500m/s.The experimental data of ogival long-rod projectile are further analyzed. It is found that the mass loss of projectile is proportional to its initial kinetic energy, and the proportional coefficient increases with the Moh’s hardness of aggregate increasing. Furthermore, the nose shape of residual projectile could be approximated as ogive. The corresponding CRH value of residual projectile nose decreases, falling between0.5(hemisphere) and the CRH value of origin projectile nose. Therefore, the total mass loss of projectile could be predicted according to the projectile nose shape before and after penetration, and vice versa.A model for total mass loss of projectile is constructed by introducing Moh’s hardness of aggregate into Jones Model. Specially, the mass loss and nose blunting of projectile are ignored during analyses. There are six parameters in the model, i.e., the initial striking velocity of projectile, CRH value of origin projectile nose, melting heat of unit mass of projectile material, the density, unconfined compressive strength and Moh’s hardness of aggregate of concrete target. Two conclusions are obtained through parametric analysis. Firstly, the influence of target density upon relative mass loss of projectile can be ignored. Secondly, the parameters’influences on relative mass loss descend, i.e., the Moh’s hardness of aggregate in concrete target, CRH value of projectile nose and unconfined compressive strength of target. When limited in the applicable range of deep-penetration projectile, the relative mass loss of projectile is affected most by the unconfined compressive strength.Assuming the nose shape of ogival long-rod projectile keeping ogival with decreasing CRH value during penetration, an incremental model is constructed to simulate nose blunting and mass loss of projectile by extrapolating the model for total mass loss to predict mass loss of projectile at any time during penetration. The dynamic behavior of projectile is also simulated. The model predictions respectively coincide with the experimental results, including the time history of projectile acceleration, CRH value of residual projectile nose and total mass loss of projectile. The acceleration is further discussed. It is found that the absolute value of acceleration may increase in tunnel stage, which indicates that the model prediction may be quite different from analysis of ideal rigid projectile. Further investigation indicates the variation of pulse shape of acceleration with parameters increasing resembles that of mass loss and nose blunting of projectile, which denotes that mass loss and nose blunting of projectile affect the pulse shape of acceleration.A model for the rate of frictional work on unit projectile surface is constructed based on the energy conservation law. Inserting it into Jones model and discretizing penetration process in time and space scales, a numerical model is constructed to simultaneously simulate nose blunting, mass loss and dynamic behavior of projectile in terms of receding in projectile surface. This model is independent of any assumption of nose blunting. The shape of residual projectile, DOP and mass loss of projectile obtained by the numerical model agree with that obtained by experiments, respectively. Two schemes of distribution of refractory material in projectile nose are analyzed. The refractory material is overlaid outside the projectile nose to protect the inner material in the first scheme. The projectile nose is made of a fictitious gradient material with decreasing melting heat from nose tip to shank in the second scheme. Both schemes could decrease nose blunting and increase DOP of projectile.Finally, the CPHP normally penetrating into concrete is experimentally studied with striking velocities between1130m/s and1650m/s. The mass of projectile is approximately1.83kg. After penetration, there are significant marks of mass loss overall the outside surface of CPHP, which is much different from ogival long-rod projectile. The metallurgical observation of residual projectile indicates that the heat generated by interaction of target and projectile is the main cause of HAZ and the mass loss of CPHP still mainly comes from the peeling of molten surface layer of projectile. Moreover, there are a few Adiabatic Shearing Bands (ASBs) around the nose tip. Although a small quantity of ASBs have minor influence on mass loss of projectile, they may cause small part of projectile to suddenly fall off and then lead to asymmetrical abrasion of projectile nose and descending of DOP if their distribution is asymmetrical. Further analysis of the experimental data indicates that the total mass loss of projectile, mass loss of nose and shank of projectile are all proportional to the initial kinetic energy of projectile, and a model is also constructed to predict the residual shape of CPHP. The model predictions agree with the experimental results, respectively.