Research On Penetration Mechanisms Of High-Velocity Projectiles Impacting Concrete-like Materials

The intensification and deep underground of important military targets have greatly promoted the development of penetration technology and earth penetrating weapons.The significant deformation,mass loss and fragmentation of projectile has been observed in the high-velocity penetration into concrete targets with increasing impact velocity.The depth of penetration does not increase linearly with velocity,but instead great drop.The assumption of rigid projectile penetration as well as the relevant theory is inappropriate in the case of high-velocity penetration.In the present dissertation,the high-velocity impact mechanics of concrete-like materials are deeply and systematically investigated by combining the theoretical analysis and experimental study method.The outline of this dissertation is as follows:(1)The p-alpha equation of state(EOS)and constitutive relationship which can reflect the pore compaction effect of sand and concrete are establishedBaesd on equivalent model of porosity evolution and generalized Mises strength criterion,the p-alpha EOS and dynaminc constitutive relationship are established.The influence regularity of the compressibility in the shock compression process are also discussed.It is showed that in plastic deformation stage,the p-alpha model in this dissertation is similar like Herrmann’s model.Comparing to the available Hugoniot experimental data in the literature,the accuracy of the porosity evolution EOS is verified.(2)The impact compression tests of cement mortar material are conducted,and the p-alpha EOS and Griineisen-type EOS considering the initial porosity compaction are establishedThe impact compression tests of cement mortar material under different velocities are conducted,and the stress wave propagation feature and shock Hugoniot relationships under uniaxial strain condition are analysed.It is showed that the stress wave of different position found in the experiment is on rapid rise to the peak then decays with time and the propagation distance.Moreover,the p-alpha EOS and high-pressure polynomial Griineisen-type EOS for cement mortar considering initial porosity compaction are given.(3)The rigid penetration model based on p-alpha EOS and nonlinear yield criterion has been presentedBaesd on the dynamic spherical cavity-expansion model,p-alpha EOS and nonlinear yield criterion,the depth calculation methods for concrete penetration by the rigid projectiles and influence regularity of the constitutive parameters on penetration are established.It is shown that the model is suitable for predicting the DOP into concrete targets by rigid projectiles below the critical erosion striking velocity.It is also confirmed that the spherical cavity expansion model based on the p-alpha EOS and nonlinear yield criterion can describe the dynamic behavior of concrete better.The influences of constitutive parameters on the DOP show the compacted pressure and shear stength influence the penetration process strongly.(4)Experimental study of high-velocity projectile penetration into mortar targets in the speed range of 1200-2400m/s.The experiments of steel projectiles at 1200～2400 m/s into mortar targets using the two-stage light-gas gun are carried out to investigate the effect and mechanisms of penetration.The DOP,carter parameters and the mass of the recovered projectiles are obtained.Investigation and analysis show that the DOP has increasing-reversing-running to the limit regularity with the striking velocity increasing,but the crater parmeters always increases with the increase of striking velocity.It is conclude that impact velocity less than 1720 m/s is related to the rigid penetration stage where the mass loss of projectile could be ignored,and the mass loss rate reached 30～60%when impact velocity larger than 1720 m/s.(5)The speed range of high-speed penetration is defined and the calculation model of penetration depth at different velocity ranges is givenThe model is modified for the projectile penetration in a pseudo-hydrodynamic state.The modified model could be used to describe the target medium transform from elastic-plastic state to the internal friction state,then to the fluid dynamic state,and it could also be used to define the range of the speed of the high-velocity penetration.The mechanical phenomena of high-velocity penetration characteristics are presented,sunh as the penetration depth reversal due to the mass loss of projectile,and the penetration depth tending to the limit as a result of the projectile erosion.The methods to calculate the depth and corresponding formulas are presented and verified.