Glass Armour and Shaped Charge Jets

115 mm shaped charges were fired at a constant built-in standoffs of 3 caliber against on both sides with steel plate covered glass targets from 0° to 60° NATO angles. The residual jet tip velocities and the disturbed jet regions have been analyzed from double flash X-ray pictures of the residual jet behind the target. Surprisingly under small angles the tip regions and under large angles the residual jet velocity regions have been more disturbed. This can be explained by the fact that under small angles the closure effect of glass is efficient but no more under large angles. But here the cover plates of the glass sandwich are effective as bulging armour. From the penetration time measurements, compared to the theoretical penetration potential, and together with the jet fan the jet velocities, which are no more perfectly penetrating can be defined. From this can be derived an induction time or how fast the armour will start to interfere with the passing jet.     

Predominance of Shaped Charge Diameter to Performance Quality Against Special Targets

Shaped charges with higher jet tip velocities result in more residual penetration behind special targets, as demonstrated by bulging and ERA sandwiches, compared to charges with lower jet tip velocities.     

Criteria for modeling the penetration by long rods impacting a semiinfinite target at a high velocity

Criteria for modeling the penetration by long rods during a hypervelocity impact are refined by replacing the impactor and target materials with softer materials and conducting experiments at lower velocities. the modeling material was modeling clay, for which strength parameters were obtained which determine the penetration process.Arzamas. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 4, pp. 108–113, July–August, 1992.     

高性能钢纤维增强混凝土的抗侵彻行为及数值模拟(英文)

采用大掺量超细工业废渣取代水泥,并掺加了天然河砂以及高弹、高强的玄武岩石子,制备了不同强度等级的高性能钢纤维增强混凝土材料。采用φ25mm弹道炮开展了初速度为500～850m/s的正侵彻实验,获得了弹丸着靶速度、最大侵彻深度、弹坑直径以及靶体破坏形态等实验参数,采用经典公式对侵彻深度进行了分析,同时采用非线性有限元方法对侵彻全过程进行了数值模拟。结果表明:侵彻深度随着材料强度等级的提高略有降低,粗集料的掺加有利于提高靶体的抗侵彻能力,随着纤维掺量的降低以及侵彻速度的提高,材料破坏程度明显加剧,数值模拟结果同试验结果吻合较好,侵彻深度的模拟结果与试验值的误差均在5%以内。     

Impact Response and Analysis of Several Silicon Carbides

Several hot-pressed and sintered SiC variants were impacted with tungsten-carbide (WC) spheres at velocities up to 1700 m/s. Ballistic response curves of areal density penetrated as a function of impact velocity were generated to compare ceramics for ballistic applications. Observed response curve features are shown to be similar to those observed for metal impacts. Ballistics penetration models that captured these features for metal targets were utilized to analyze the ceramic data. Visual examination of damage type and extent suggested that cavity expansion expressions for target resistance might help to quantify the strength of fully confined, damaged, comminuted ceramics. The experimental results, visual observations, and preliminary analysis using a ballistics penetration model are presented.     

Shaped Charge Optimization against ERA Targets

Shaped charges with different angles or/and different liner wall thicknesses have been tested against an explosive reactive armor sandwich. The reason was to find out if more robust shaped charges give more residual penetration against an ERA sandwich, compared to shaped charges with more penetration performance in RHA targets. It was thought, that the latter ones are more sensitive against disturbances. But the shaped charges with the higher perforation capability have typically higher jet tip velocities and this gives more residual penetration also against ERA targets. In other words the so‐called more robust charges gave less performance against the ERA sandwiches than the shaped charges which have higher performance in RHA targets.     

Interaction of a Metallic Jet with a Moving Target

Study of interaction of a high velocity jet with a moving target has been carried out on the basis of simplifying assumptions of constant velocity of the jet and the target plate. The theoretical model meets the boundary conditions of the problem and predicts satisfactorily the main features of the phenomenon and the trend in variation of parameters like depth of penetration, surface cut and total distance travelled by target during the time of interaction of complete length of the jet. Unlike jet penetration in a stationary target, the penetration in a target, accelerated by thin layer of explosive, has been found independent of density of the target. The penetration, however, has been found strongly dependent on the angle of impact and the ratio of jet and target velocities.     

Dwell and Interface Defeat on Borosilicate Glass

We have conducted impact experiments using gold long rods into borosilicate glass and the measured the penetration velocity as a function of impact velocity. At sufficiently low-impact velocities, the glass target resists penetration and there is dwell; dwell is observed to approximately 450 m/s for bare glass. If a copper buffer is placed over the glass to eliminate the impact shock, significant dwell can be seen at impact velocities as high as 890 m/s. These impact velocities correspond to Bernoulli stresses of approximately 2.0 and 7.6 GPa, respectively. The paper describes the experimental data, and summarizes the results and our findings.     

Visualization of Impact Damage in Ceramics Using the Edge-On Impact Technique

Projectile impact generates severe fragmentation in ceramics which propagates at high velocities and precedes the penetration of the projectile. The high-speed photographic technique of the Edge-On Impact (EOI) has been developed at the Ernst-Mach-Institute (EMI) in order to visualize dynamic fracture in brittle materials. In a typical EOI test the projectile hits one edge of a specimen and fracture propagation is observed during the first 20 us after impact by means of a Cranz-Schardin highspeed camera. EOI tests allow a characterization of different ceramics by the macroscopic fracture patterns, single crack velocities, and crack front velocities (damage velocities). The phenomenology of damage propagation in several ceramics and a ceramic-metal composite is discussed. The EOI technique is useful for the evaluation of damage models for brittle materials because it enables a direct comparison of model predictions to experimental data obtained during the impact process.     

聚能杆式弹丸侵彻水夹层复合靶相似律分析

为降低聚能杆式战斗部研制成本,缩短研制周期,采用量纲分析方法对聚能杆式弹丸的成型以及侵彻水夹层复合靶板的相似律进行了分析。结果表明,当模型和原型战斗部结构、炸高及起爆点位置满足几何相似条件,且模型所用材料和原型相同,装药的起爆方式也相同,那么聚能杆式弹丸的形成过程便相似。最终形成的弹丸的速度相等,弹体相似。侵彻复合靶板的过程表明,模型和原型实验中的聚能杆式弹丸在相应厚度的水层中的速度损失相等;速度衰减率之比等于模拟比的倒数;弹丸对复合靶板的侵彻深度遵循相似律准则。实验结果验证了理论分析所得结论的正确性。     

Penetration of double-layer targets with an outer ceramic layer and optimization of their structure

Analytical formulas for calculating the maximum velocity of penetration of doublelayer cermet and ceramic/organic-plastic targets are obtained taking into account the structural characteristics of the target and the physical and mechanical properties of the projectile and target materials. Using these formulas, the ballistic resistance of targets was studied and the possibility of optimizing their structure was shown. The results agree qualitatively with available experimental data. The optimal relative thickness of the ceramic layer which provides maximum penetration velocity was determined at areal densities of the target of 30–50 kg/m² for different substrate materials. It is found that these velocity values depend weakly on the areal density of the target and are mainly determined by the properties of the substrate material.     

Determining the strength of filled epoxy from ballistic experiments

This paper analyzes the results of experiments with impact of metal spherical impactors on cylindrical targets of epoxy (filled with Al₂O₃ microparticles and without the filler) performed in a ballistic range. Impact velocities were limited to a range of 0.6–1.1 km/sec since higher velocities led to complete destruction of the targets. Impacts at the velocities considered produced channels of an almost cylindrical shape with the impactor stuck at the end of the channel. The strength of filled epoxy is estimated using the previously established dependence of the channel depth on the impact energy, the ratio of the densities of the impactor and target materials, and the tensile strength of the target material. It is found that at a mass fraction of the filler equal to 0.4, the strength of the target increased by a factor of approximately 1.5–2. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 123–130, September–October, 2008.     

Model of the penetration of a metal barrier by a rod projectile with an angle of attack

A relatively simple dynamic model is proposed for calculating parameters characterizing the penetration of a barrier by a rod projectile with an angle of attack. Together with the factors examined in the case of axisymmetric penetration within the framework of the well-known Alekseevskii-Tate scheme, the model considers the action of transverse forces and rotation of the rod. Calculations of the penetration of steel barriers by tungsten projectiles with a relative length of 12.8–17.4 at collision velocities of 1800–2100 m/sec along a normal to the surface showed good agreement with experimental data for angles of attack from 0 to 68°.All-Union Scientific Research Institute of Experimental Physics, 607200 Aramas-16. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 3, pp. 104–109, May–June, 1995.     

Penetration Cutoff Velocities of Shaped Charge Jets

The maximum depth of penetration, P_max, of a shaped charge jet can theoretically be calculated from 5 quantities for the purely continuous, or for the initially continuous and then particulated, or for the fully particulated penetrating jet. These quantities are the distance Z₀ of the target plate from the virtual origin, the value of γ (i.e. the square root of the ratio of target to jet density), the jet tip velocity v_j,0 the efficient residual velocity v_j,min, and the particulation time t_p. Instead of calculating the individual values of v_j,min for the individual depths of penetration P_exp at various standoff distances, this quantity can quite simply be read from the standoff diagram by means of the penetration cutoff lines- a so-called Standoff/Cutoff-diagram -, using the experimentally determined depth of penetration P_exp. The penetration cutoff lines are lines which start at the virtual origin and which represent the ideal increment in depth of penetration per jet velocity interval in the standoff diagram, the abscissas of this line corresponding to the jet tip velocities. The methods are demonstrated and explained, using the results of three firings with one type of shaped charge as an example. The shots were made at 6, 12, and 24 calibers standoff distance, and the cratering history was also determined in these trials.     

Failure and fragmentation of ceramic target with varying geometric configuration under ballistic impact

The failure and fragmentation of monolithic bare alumina 99.5% ceramic target and energy dissipation of steel 4340 projectile have been studied in a series of ballistic experiments carried out, with the incidence velocities in a range, 122–290 m/s. The velocity drop and energy dissipation increased with incidence velocity for 10 mm thick target with damage zone extended upon the whole area of rear face at higher velocities. The ballistic results obtained with the 10 mm thick target have been compared with the ballistic performance of the 5 mm thick target used in a previous study to explore the effects of target thickness on the failure mechanism. A model for the residual velocity of projectile after perforation of the single layered ceramic target has been developed based on the Lambert Jonas model by using the experimental data available for 5 mm and 10 mm thick alumina 99.5% target against 10.9 mm projectile. The residual velocities and damage patterns were reproduced with a reasonable amount of accuracy by a three-dimensional finite element model developed on commercial ABAQUS/CAE. The effect of obliquity and projectile diameter to target thickness ratio (D/T) on ballistic performance has been determined by the numerical simulation model with impact velocity in a range of 300–500 m/s. A spatial variation of ejected fragments velocity at different time steps was plotted to develop a velocity profile for the ceramic fragments coming out of the target. A semi-empirical model has been proposed for residual velocity after perforation of a monolithic ceramic target, relating to the incidence velocity and projectile diameter to target thickness ratio. The monolithic ceramic targets have been investigated for a comparative assessment of energy dissipation by the ceramic layer to eventually design an efficient front layer of a ceramic based composite armour in future studies.     

Particle Deposition in Wakes: Inertial and Coulombic Effects on Capture By Single and Multiple Spheres in Line

Ten-micrometer dioctylphthalate droplets tagged with sodium fluorescein were collected on six metal spheres, 0.6 cm in diameter and arranged in a line parallel to the axis of flow. The particles carried negative charge in the range 0.9–1.7 × 10^?5 stC while the collectors were charged positively in the range 8.0–23.0 stC. The carrier stream velocities used were 600, 1200, 1500, 1800, and 2400 cm/s and spacings between targets of two through six diameters center-to-center were tested. Collection efficiencies for each target were determined by measuring the number of deposited particles, and the particle concentration in the air stream using fluorometric techniques.

An effective Coulombic attraction parameter K _Eeff , was defined to take into account non-Stokesian drag during particle collection at high velocities. This term was combined with an effective Stokes number to provide the empirical relation, for single spherical targets: η= 1.4[Stk _eff + (2K _Eeff )^1/2]. A model is presented to describe the concentration distribution of particles in the wakes of multiple spherical targets, in-line. This model is based on the lateral turbulent transport of particles into the wake between targets. A correlation between the particle deposition of any trailing target, normalized to that of the leading target, and the modified Graetz number, (n - l)^1/3(Gz)^?1, where n is the rank of the target in the series and Gz = 4(z/D)/Pe, enables one to predict deposition on trailing targets.     

Mechanics of penetration of ceramic targets

A model for the penetration of a ceramic target with the formation of an expanding conical hole is proposed that can be used to determine the apex angle of the cone knocked out from the target. The main cause of this fracture of ceramic targets is that the tensile strength of a ceramic material is much lower than its compressive strength. A method for calculating the maximum penetration velocity in a ceramic target without substrate was developed using the energy fracture criterion for ceramics. Two-dimensional numerical simulation of the impact of a steel projectile on a corundum plate showed satisfactory agreement between the calculated and experimental configurations of the resulting conical crack provided that the ratio between the compressive and tensile strengths corresponds to the recommendations of the developed model.     

Segmented Penetrators

This paper analyses the terminal ballistic performance of segmented rod penetrators in semi-infinite, spaced as well as reactive targets. The model scaled projectiles with a mass of about 10 g are launched by a light gas gun of caliber 30 mm at velocities up to 4 km/s. To keep the initial acceleration low enough, the junction between the first and the second stage of the gun was appropriately modified. The projectiles are composed of a series of tungsten alloy segments guided by a thin light metal tube. Between the segments with a L/D-ratio of one there are cylinders made of plastics or aluminium. Usually the space is in the order of one or two projectile diameters. The perforation power of such segmented rods is compared with two types of homogeneous projectiles of equal mass and velocity. One reference projectile has equal length but lower diameter, the other one has the same diameter but a lower length. Experiments against semi-inifite targets show an increase in penetration depth of about 20 %, compared with homogeneous projectiles of the same diameter. This advantage vanishes if the reference projectile has equal length. In the four-plate target as well as in the reactive armour, segmented rods are significantly less efficient due to their low stiffness and greater length.     

Fragment Generator

The design of a fragment generator and the determination of the hit density and of the velocity distribution are described in detail. From the correlation of the fragment hits on the target plate and the X-ray flash radiographs it is possible to ascertain the launch angles in the elevation and azimuth directions and, hence, also to determine the true distances the fragments have traveled from the point of detonation of the high explosive charge to the location where the radiograph was taken. In this manner, a precise determination of the velocities of the individual fragments can be made. In spite of the rather large scatter of the depths of penetration of the cube-shaped fragments in the mild-steel target plate, a correlation can be established between the impact velocity and the depth of penetration.     

Penetration depth of broadcast urea granules in puddled wetland rice soils

The efficiency of urea in wetland rice cultivation is known to be increased by placement below the soil surface. The penetration of broadcast urea into puddled soil might be a way to achieve placement of urea in soil. This paper combines an analysis of the free fall of urea granules in the atmosphere and a layer of water on the soil surface with measurements of granule penetration into puddled soils. The process of free fall can be described in terms of the height of fall in air, the depth of the water layer, and the terminal velocities and characteristic distances for free fall in air and water. The penetration depth of a particular granule with a particular velocity at the water/soil interface depends on the type of soil and its physical condition. Granule mass ranged from 0.1 to 0.5 g, granule velocity from 1 to 10 m s^–1, depth of the water layer from 0 to 30 mm and penetration depth from 0 to 35 mm. There is some indication that the penetration depth is proportional to the square root of the kinetic energy at the water/soil interface.