Investigation On The Anti-penetration Properties And Mechanism Of Steel-Tube-Confined Concrete Targets

Concrete is widely used in protective structure like shielding layer and protective wall. Confined concrete has obvious advantages in anti-projectile performance than ordinary concrete. Research on the anti-penetration performance and mechanism of confined concrete which includes penetration test, numerical simulation and theoretical analysis was conducted in this paper to make up the severe shortage of present research. This study provides a reference for the design and application of protective structure such as shielding layer and protective wall and has important academic value and military significance. The main work of this paper can be summarized as follows:1. The penetration test that small diameter steel tube confined concrete targets impacted by 12.7mm hard core bullet was carried out in this paper to study the influence of impact eccentric distance, impact velocity, steel tube diameter and thickness on the anti-penetration performance of the targets and the anti-penetration performance against multiple-impact. The results show that: the target concrete exhibit cracked-comminuted response mode under penetration; penetration depth increases lightly with eccentricity and steel tube is easy to become buckling and tearing with a large impact eccentric distance; the larger the impact velocity, the penetration depth increases more obviously; targets show better anti-penetration performance with a smaller diameter or thicker steel tube, but invalid protection is easy to happen when diameter is too small and the penetration depth not decreases obviously with a more thicker steel tube which is not economical; the penetration depth of the steel tube confined concrete targets in this paper reduced 20% than the semi-infinite target; small steel tube targets can effectively resist 3 strikes and show better performance than semi-infinite targets in ultimate penetration depth and damage area.2. Based on penetration tests, numerical simulation about the anti-penetration mechanism was conducted by using ANSYS/LS-DYNA. The results show that: with the projectile invading, target concrete damage can be divided into crater-forming stage and tunnel penetration stage; the stress region of the target concrete in the early extends downward in a same hemispherical shape like the semi-infinite target, and last extends like a approximate plane wave due to the constraint of steel tube; the stress of steel tube decreases from up to down which respond synchronously with concrete, the unit circumferential stress is much higher than radial stress and the constraint function is maximized when projectile reach the same position for a given cross section; targets can be taken as semi-infinite when the ratio of target diameter to projectile diameter is larger than 31.9 for the projectile used in this paper with a velocity about 820m/s.3. Realizing the fact that the existing penetration depth formulas based on rigid projectile penetrating semi-infinite concrete targets are not applicable to forecast the penetration depth of steel tube confined concrete target, a new formula to predict the penetration depth of steel tube confined concrete target under the impact of hard core bullet was proposed based on Forrestal penetration depth model and characteristics of penetration tests. The calculations of this new formula are in good agreement with both the test results in this paper and other reference.All the work in this paper shows that steel tube confined concrete targets have excellent anti-projectile performance under both single and multiple impact, specifically in effective damage area and penetration depth reducing. But a lot of factors, not only the anti-projectile performance, should be taken into account to make an optimal design, such as economic factors.