Investigation On The Mechanism And Trajectory Of Projectile Penetrating/Perforating Reinforced Concrete Target

The research on penetration / perforation of reinforced concrete targets can provide the necessary theoretical support for effective damage effect of earth penetrating weapons and effective protection capability of reinforced concrete structures.In this paper,based on the relevant research achievements of plain concrete targets,the mechanism and trajectory of projectile penetrating / perforating reinforced concrete target were researched using the methods of experimental comparison,theoretical modeling and computational analysis.(1)The meticulous contrast experiments considering the reinforcement effects were conducted and comparatively analyzed.The reinforcements provide indirect penetration resistance by restricting the whole concrete with bonding effect,and also provide direct penetration resistance by the collision with projectile.The shallow layer of reinforcements can reduce the depth of crater,and the impact position and reinforcing method also affect the penetration resistance of projectile.The mechanism of projectile penetrating / perforating reinforced concrete target was given through summarizing the influences of reinforcements.(2)By treating reinforced concrete as a composite uniform material,the reinforcement ratio was introduced into the constitutive equation through toughness,and the cavity expansion theory of reinforced concrete was modified and deduced to reflect the influence of reinforcement ratio on indirect resistance.The crater depth model considering the mass of projectile,the initial velocity and the embedment depth of first reinforcement layer was established based on the regression analysis of experimental data.Combined the theory and model together,the calculation accuracy of penetration depth and overload were improved.(3)By treating reinforced concrete as a combined structural material,combined with the analysis of reinforcement dynamic response,projectile impact position and interaction with two reinforcement layers,the relatively complete penetration resistance model of rigid projectile penetrating reinforced concrete target was established,which can reflect the influences of relative impact position and reinforcement configuration details on penetration depth and overload(pulse-like peak raising).The proportion of indirect and direct penetration resistance is depending on the initial conditions,and the penetration depth decreases with the increasement of reinforcement ratio.The small diameter reinforcing target with the same reinforcement ratio is usually more effective in protection,and when the projectile diameter / mesh size >2,the differences of penetration depth caused by different impact positions can be ignored.(4)The existing empirical formulas were collected and comparatively analyzed.The modified Forrestal semi-empirical penetration calculation formula and the modified Chen perforation calculation formula were established,which considered the influences of reinforcements on crater depth,cone-shaped plug,indirect and direct resistance.The upper and lower limit of penetration depth / residual velocity caused by different impact positions can be quickly obtained without iteration calculation.The average penetration depth / residual velocity of the small diameter reinforcing target with the same reinforcement ratio is relatively low.As the ratio of projectile diameter to reinforcement mesh size increasing,the differences between the upper and lower limit of penetration depth / residual velocity are significantly reduced.(5)The free surface effect model of reinforced concrete targets was established by introducing the embedment depth of first / last reinforcement layer.The collision analysis model was established through the dispersion,coordinate transformation and dynamic response analysis of reinforcements.Based on the differential area force law and reinforced concrete cavity expansion theory,the trajectory prediction program of rigid projectile penetrating / perforating finite thickness reinforced concrete target was compiled.The first reinforcement layer can weaken the free surface effect,and the direct collision of reinforcements on projectile can aggravate or suppress the trajectory deflection.The trajectory and motion parameters tend to be complicated when adding reinforcements in target.The main factors affecting trajectory,such as initial velocity, position of mass center,inclination / attack angle,impact position,projectile size and reinforcing mode,were discussed and analyzed.Especially for the condition that the mass and moment of inertia are small,the reinforcement ratio is high,the reinforcement diameter and strength are big and the density of reinforcement configuration is large,the reinforcements can introduce randomness into the regularity of penetration / perforation trajectory due to the direct collision.