Effect of projectile nose shape,impact velocity and target thickness on the deformation behavior of layered plates

The present study is based on the experimental and numerical investigations of deformation behavior of layered aluminum plates of different thicknesses under the impact of flat, ogive and hemispherical nosed steel projectiles. Thin-layered plates arranged in various combinations were normally impacted at different velocities with the help of a pneumatic gun. Ballistic limit velocity and the residual velocity of the projectiles for each layered combination were obtained experimentally as well as from the finite element code, and these were compared with those of the single plates of equivalent thicknesses. For two layers, the residual velocity was comparable to that of the single plate, however, when the number of layers was increased the velocity drop was found to be higher in the case of the single plate. Ogive nosed projectile was found to be the most efficient penetrator of the layered target. Hemispherical nosed projectile required maximum energy for perforation. Deformation profiles of the target plates in the layered combinations were measured, and it was found that hemispherical nosed projectile caused highest plastic deformation of target plates. Numerical simulation of the problem was carried out using finite element code ABAQUS. Explicit solution technique of the code was used to analyze the perforation phenomenon. Results of the finite element analysis were compared with experiments and a good agreement between the two was found.     

Energy absorption during projectile perforation of thin steel plates and the kinetic energy of ejected fragments

This paper concerns energy absorption in thin (0.4 mm) steel plates during perforation by spherical projectiles of hardened steel, at impact velocities between 200 and 600 m s⁻¹. Absorbed energies have been obtained from measured incident and emergent projectile velocities. These tests were simulated using ABAQUS/Explicit, using the Johnson and Cook plasticity model. A strain rate-dependent, critical plastic strain fracture criterion was employed to model fracture. Good agreement is obtained between simulations and experiment and the model successfully captures the transitions in failure mode as projectile velocity increases. At velocities close to the ballistic limit, the plates fail by dishing and discing. As the incident velocity is increased, there are two transitions in failure mode, firstly to shear plugging and secondly to fragmentation and petalling. The simulations also show that, during the latter mode of failure, the kinetic energy of ejected debris is significant, and failure to include this contribution in the energy balance leads to a substantial over-estimate of the energy absorbed within the sheet. Information is also presented relating to the strain rates at which plastic deformation occurs within the sample under different conditions. These range up to about 10⁵ s⁻¹, with the corresponding strain rate hardening effect being quite substantial (factor of 2–3 increase in stress).     

The effect of projectile properties on target cratering

The effect of projectile properties on target cratering is evaluated for two basic target designs: a simple, half-space target and a half-space target protected by a shield. The comparison of unshielded and shielded target impacts is based on empirical evaluations and emphasizes the velocity range of 4–6 km/sec. A wider velocity range, 0–8 km/sec, is considered for evaluations of projectile property effects. This paper examines the effects of projectile strength, density, shape, size, velocity and particulation. It was observed that the presence of a shield amplifies the influence of projectile density, shape and size but mitigates the influence of projectile velocity. For shielded target impacts the properties of the projectile debris cloud behind the shield were used to predict the crater damage to the target.     

Normal perforation of reinforced concrete target by rigid projectile

An analytical model on the normal perforation of reinforced concrete slabs is constructed in the present paper. The effect of reinforcing bars is further hybridized in a general three-stage model consisting of initial crater, tunnelling and shear plugging. Besides three dimensionless numbers, i.e., the impact function I, the geometry function of projectile N and the dimensionless thickness of concrete target χ, which are employed to predict the ballistic performance of perforation of concrete slabs, the reinforcement ratio ρ_s of concrete (or area density) and the tensile strength f_s of reinforcing bars are considered as the other main factors influencing the perforation process. Simpler solutions of ballistic performances of normal perforation of reinforced concrete slabs are formulated in the present paper. Theoretical predictions agree well with individual published experimental data and have a higher degree of accuracy than the model suggested by Dancygier [Effect of reinforcement ratio on the resistance of reinforced concrete to hard projectile impact. Nucl Eng Des 1997;172:233–45].     

An analytical model for tumbling projectile perforation of thin aluminum plates

An analytical model for the perforation of thin aluminum targets by tumbling cylindrical projectiles was developed. The target material was considered to be rigid—perfectly plastic without strain hardening, while the projectile was treated as undeformable. The perforation process was experimentally found to consist of three stages: plugging, hole enlargement, and front petaling. Both conservation of energy and conservation of momentum laws were used for modeling the plugging stage, while a lower bound method was employed during the hole enlargement stage. The energy dissipated during the petaling stage consists of shearing fracture of the petal, localized plastic shear in a zone contiguous with the edges, the momentum of the petal and the bending energy of the petal. The analytical results provided generally good agreement with the corresponding experimental data in terms of the final velocity and final oblique angle of the projectile as well as the crater length of the target.     

Empirical equations for the perforation of mild steel plates

The experimental results for the perforation energy of mild steel plate struck by flat-ended, non-deforming, cylindrical penetrators have been correlated using the principles of dimensional analysis. A correlation is presented for long penetrators. It is shown that for short penetrators a different response of the target is observed and that, at present, there are insufficient published data to produce a unifying correlation.     

Perforation of metallic plates struck by a blunt projectile with a soft nose

The present paper constructs a rigid–plastic model to assess the effect of a soft nose on the perforation of metallic plates struck by a stubby projectile. A low-density nose-cabin-column, i.e., an assembly of seeker and guidance/control unit, is installed in the front of a real missile. It usually acts as an energy absorber and buffer in the perforation of metallic plates and notably affects the terminal results of projectile. The problem is equivalent to a blunt rigid projectile with a soft nose perforating a circular metallic plate. Effects of transverse shear, bending and membrane deformations on the perforation process are included in a rigid–plastic analysis. Especially the effect of an ahead structural response, induced by the soft nose impacting the target plate, is considered in the model. Analytical formulae for the ballistic performance are obtained for a range of plate thicknesses, which agree well with available experimental results.     

弹体头部形状对碳纤维层合板抗冲击性能影响实验研究

为研究弹体头部形状对碳纤维层合板抗冲击性能的影响,利用一级气炮发射卵形头弹、半球形头弹和平头弹,对2 mm厚碳纤维层合板进行了冲击实验。利用公式拟合处理实验数据,揭示弹体头部形状对靶板弹道极限与能量吸收的影响,并且分析靶板冲击损伤形貌及机理特征。研究结果表明:平头弹弹道极限最高,半球形头弹次之,卵形头弹最低。弹体在低速度冲击时,弹体头部形状对靶板能量吸收率的影响更为显著。平头弹冲击时,靶板迎弹面受到均匀分布的环向剪切力,纤维同时被剪切,基体发生大面积剪切破坏。半球形头弹冲击时,靶板迎弹面受到非均匀分布的剪切力和挤压作用,纤维发生剪切断裂和拉伸断裂,基体发生剪切破坏和挤压破碎。卵形头弹冲击时,纤维发生单一的拉伸断裂,而基体则发生挤压破碎。弹体头部形状对靶板损伤的影响主要集中在迎弹面和中部纤维层。     

On the influence of constitutive relation in projectile impact of steel plates

In this paper the influence of constitutive relation has been studied in numerical simulations of the perforation of 12-mm thick Weldox 460 E steel plates impacted by blunt-nosed projectiles in the sub-ordinance velocity regime. A modified version of the well-known and much used constitutive relation proposed by Johnson-Cook and both the bcc- and hcp-version of the Zerilli-Armstrong constitutive relation were combined with the Johnson-Cook fracture criterion. These models were implemented as user-defined material models in the non-linear finite element code LS-DYNA. Identification procedures have been proposed, and the different models were calibrated and validated for the target material using available experimental data obtained from tensile tests where the effects of strain rate, temperature and stress triaxiality were taken into account. Perforation tests carried out in a compressed gas gun on 12-mm-thick circular Weldox 460 E steel plates were then used as base in a validation study of plate perforation using LS-DYNA and the proposed constitutive relations. The numerical study indicated that the physical mechanisms during perforation can be qualitatively well predicted by all constitutive relations, but quantitatively more severe differences appear. The reasons for this are discussed in some detail. It was concluded that for practical applications, the Johnson-Cook constitutive relation and fracture criterion seems to be a good choice for this particular problem and excellent agreement with the experimental results of projectile impact on steel plates were obtained under the conditions investigated.     

Analytical modeling for the ballistic perforation of planar plain-woven fabric target by projectile

This paper presents an analytical model to calculate decrease of kinetic energy and residual velocity of projectile penetrating targets composed of multi-layered planar plain-woven fabrics. Based on the energy conservation law, the absorbed kinetic energy of projectile equals to kinetic energy and strain energy of planar fabric in impact-deformed region if deformation of projectile and heat generated by interaction between projectile and target are neglected. Then the decrease of kinetic energy and residual velocity of projectile after the projectile perforating multi-layered planar fabric targets could be calculated. Owing to fibers in fabric are under a high strain rate state when fabric targets being perforated by a high velocity projectile, the mechanical properties of the two kinds of fibers, Twaron^® and Kuralon^®, respectively, at strain rate from 1.0×10⁻² to 1.5×10³ s⁻¹, are used to calculate the residual velocity of projectile. It is shown that the mechanical properties of fibers at high strain rate should be adopted in modeling rate-sensitivity materials. Prediction of the residual velocities and energy absorbed by the multi-layered planar fabrics show good agreement with experimental data. Compared with other models on the same subject, the perforating time in this model can be estimated from the time during which certain strain at a given strain rate is generated. This method of time estimation is feasible in pure theoretical modeling when the perforation time cannot be obtained from experiments or related empirical equations.     

Elastic buckling strength of corroded steel plates

Corrosion makes structures more vulnerable to buckling and yielding failures. It is common practice to assume a uniform thickness reduction for general corrosion. To estimate the remaining strength of corroded structures, typically a much higher level of accuracy is required, since the actual corroded structures have irregular surfaces. Elastic buckling of simply supported rectangular corroded plates are studied with one- and both-sided irregular surfaces. Eigenvalue analysis by using finite element method (FEM) is employed for computing Euler stress. The influence of various geometric and corrosion characteristics are investigated and it is found that the aspect ratio of the plate, the average thickness diminution, the standard deviation of thickness diminution and the amount of corrosion loss have influence on the reduction of buckling strength of the corroded plates. Buckling strength of one- and both-sided corroded plates are the same. In plates with low value of aspect ratio, reduction of buckling strength is negligible. Reduction of buckling strength is more prominent in plates with higher aspect ratio. Reduction of buckling strength is very sensitive to the amount of corrosion loss; the higher the amount of corrosion loss, the more reduction of buckling strength. Reduction of buckling strength is less sensitive to the standard deviation of thickness diminution.     

不同头部形状的PC弹丸撞击LF6铝板实验研究

该文介绍不同头型聚碳酸脂(PC)弹丸撞击LF6铝靶板的动力学响应实验,给出弹靶作用过程中靶体的响应历程,以及过靶后弹体与靶板的变形图像,实验结果表明穿靶机制主要两种:扩孔冲塞型和尖端冲塞后撕裂翻转型。     

The effect of impact velocity and target thickness on ballistic performance of layered plates using Taguchi method

This paper presents the effect of test parameters such as Impact velocity, configuration and target thickness on ballistic performance of weldox steel plates against 7.62 mm APM2 projectile using Taguchi method. Trials were planned using an L 18 orthogonal array with 18 combinations of test variables to assess the influence of various factors. Numerical simulations have been carried out using Ansys Autodyn code with the above three process variables. Failure mechanisms of target plates of various single and multi-layered configurations were also discussed. Most portion of the kinetic energy of the projectile was expended in plastic deformation of the target material before perforation due to better bending stiffness of the target plate. Results showed that target thickness and impact velocity were the significant variables on residual velocity. Layer configuration was found to be insignificant relating to ballistic performance. Significant interaction is observed between impact velocity and target thickness from interaction plots. Simulated and experimental results showed good agreement with each other.     

分层对TC4钛合金板抗平头弹撞击失效特性的影响

使用Abaqus/Explicit有限元分析软件,开展平头弹撞击不同厚度双层TC4钛合金板数值模拟,研究双层TC4钛合金板撞击失效特性与失效模式随厚度变化规律及机理.通过对比撞击试验与仿真结果,验证数值模型和参数的有效性.在此基础上与等厚度单层TC4钛合金板的抗侵彻性能进行对比,结果表明,对于12.68 mm直径的平头...     

弹体侵彻混凝土数值模拟失效指标研究

摘要: 利用单个立方体单元压缩和拉伸数值模拟揭示了HJC混凝土模型的抗压,抗拉和损伤特性,将该模型用于模拟Hanchak侵彻试验,采用最大主应变,等效塑性应变和最大拉静水力三种失效模式后得到的残余弹速和靶板破坏现象与试验结果对比后,最大主应变和拉静水失效得到的弹体残余速度误差比等效塑性应变失效要小,等效塑性应变失效得到的靶板表面破坏现象与实验结果也相差较大。 关键词：HJC混凝土模型;数值模拟;失效指标;弹体侵彻;混凝土板