Investigation On The Dynamic Responnse Of Long Ogive-nosed Projectiles Penetrating Into Semi-infinite Concrete Targets

As concrete is widely used in both military,industrial and civil engineering structures due to its outstanding performances.It is of great importance to study the dynamic response of concrete under high speed penetration.In this study,both theoretical analysis and numerical approaches on penetration into semi-infinite concrete targets were developed in conjunction with published experimental data.A staged penetration equation of penetration depth was developed on the basis of a parametric correlation on penetration resistance of rigid projectiles,in which both target inertia and diameter effect of projectiles were introduced.For deformable projectiles,an analytical model on both homogeneous mass loss and nose shape change of projectile noses was developed.In addition,on the basis of a meso-scale composite model of concrete,the dynamic response of projectiles under asymmetric load was studied.A numerical study on the resistance of rigid projectiles penetrating into semi-infinite concrete targets was performed by AUTODYN2 D hydrocode.On the basis of the numerical model with a two-staged pre-drilled hole which consists of a conical crater and a following cylindrical crater,the depth of entrance phase at the front of the target was quantitatively studied and indicated to be proportional to the sharpness of projectile nose.Nevertheless,it has been demonstrated to be irrelevant to both concrete strength and impact velocity.Beyond the entrance phase at the front of the penetration trajectory,the results showed that the penetration in tunnel region can be approximately divided into three phases in terms of initial impact velocity.At the first phase,in which impact velocity ranges from 100m/s to 600m/s,the deceleration depended on initial impact velocity.For the second phase,when impact velocity locates in 600m/s-800m/s,the deceleration was constant and can be simplified as irrelevant to both initial and instantaneous velocity.When impact velocity ranges from 800m/s-1300m/s,the deceleration was related to instantaneous penetration velocity,and a target inertia term should be added to target resistance.A good agreement on penetration depth and penetration resistance was reached between the present equation and experimental data.Furthermore,for large projectiles,the correlation between penetration resistance and geometrical parameters of projectiles was analyzed in terms of numerical model,the results proposed that the penetration resistance acting on per unit area was irrelevant to both mass and length of projectiles,while negative correlation to the diameter of projectiles.Also the calculated results on DOP agreed well with experimental data.As for the mass abrasion of projectiles during high speed penetration into concrete targets,in this study,a semi-empirical model was developed based on Jones abrasion model,in which thermal melting of projectile materials generated by friction work was considered as the primary mechanism of mass loss.The tangential force between the target and projectile was considered as a Coulomb friction,a parametric analysis demonstrated that the friction coefficient was related to the relative strength and hardness of projectile and target materials.For large projectiles,a correction item of projectile diameter was introduced in the model.Furthermore,with the assumption that the shape of projectiles nose after penetration is still ogival,a predicted method on the change in nose shape was developed,and both the predicted mass loss and nose shape after penetration agreed well with experimental data.Based on Voronoi method,a meso-scale model of concrete was established with introducing the mortar and coarse aggregates,and the effect of meso-scale parameters on the deflection of trajectory.The results showed that the ratio of projectile diameter to aggregate diameter was the major factor in the deflection of trajectory,with increasing the value of the ratio,the deflection of trajectory will become less apparent.The structural stability of projectiles under asymmetric mass abrasion and heterogeneous resistance of mortar and aggregates was analyzed.The results indicated that the dangerous section located between the arc-shaped interface of the projectile body to about 4/9 from the warhead.Furthermore,the dynamic response of projectiles after the plastic hinge appeared was studied based on the theory of travelling plastic hinge.