Interaction of a shaped-charge jet with moving reactive armor plates

The mechanisms of the stationary and nonstationary interaction between a metal shaped charge jet and the front reactive armor plate (moving toward the jet) and rear (moving behind the jet) reactive armor plate. The range of interaction parameters in which these mechanisms take place was determined. The interaction of the shaped-charge jet with the front plate is mainly stationary and leads to the wearing of the jet in the transverse direction (reduction in the diameter of the jet) and its deflection by a small angle. The interaction of the shaped-charge jet with the rear plate is mainly of a nonstationary discrete nature and forms unilateral transverse perturbations in the jet, which, developing, lead to its bending and subsequent destruction.     

Spaced Armor Effects on Shaped Charge Jet Penetration

Spaced armor has a simple structure and is easily produced with low cost. Previous authors calculated how a jet penetrates spaced armor; but, this study provides both a theoretical calculation method describing the interaction of a jet with spaced armor and experimental data which agree well with the theoretical values. The effects of several factors were explored using LS‐DYNA such as the distance between the first plate and the second plate as well as layer thickness on the interaction between the jet and the target. A method for simulating the protection afforded by spaced armor and supporting the design of spaced armor is presented.     

反应装甲冲击引爆试验研究

研究了HMX基钝感炸药的机械感度.根据测试结果初步确定了反应装甲的装药配方,最终装药配方由改变模拟反应装甲上、下板的材料和厚度以及穿甲弹与反应装甲法线的夹角,用反应起始装药的引爆效果确定.结果表明,钝感炸药的撞击感度、摩擦感度均随HMX粒度的减小而降低,随钝感剂含量的增加而降低;反应装甲的装药配方为HMX97%、钝感剂3%.从理论上分析了炸药粒度变化对机械感度影响的机理,以及在穿甲弹参数和速度一定的条件下,反应装甲装药结构对冲击引爆的影响.     

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.     

The importance of jet tip velocity for the performance of shaped charges against explosive reactive armor

It is shown, that the portion of a shaped charge jet that emerges from explosive reactive armor is longer or at least less disturbed if the jet tip velocity can be raised. Generally, the residual jet length largely depends on the ratio of the reaction time of the armor and the standoff of the shaped charge from the armor.     

Stopping Power of ERA Sandwiches as a Function of Explosive Layer Thickness or Plate Velocities

The stopping power rises in symmetric sandwiches with increasing explosive layer thickness, which is equivalent to higher plate velocities. Further the additional weight is a burden for add‐on armor. Therefore a study was made with very thin sandwich plates of 1 mm as more or less the minimum, what can be used in practice. The reduction effect is more reduced with thicker plates at constant explosive layer thickness. For the penetration reduction the product of plate thickness and plate velocity seems important, as a thumb rule.     

Dynamic Plate Thickness of ERA Sandwiches against Shaped Charge Jets

The equation for the dynamic plate thickness is derived as a function of standoff distance Z₀, jet tip velocity v_j0, cutoff velocity v_jc, plate velocities v_PI and NATO angle of the ERA sandwich. The dynamic thickness is presented as functions of the different parameters for the front plate – flying against the shaped charge jet – and the rear plate – flying with the shaped charge jet. But the dynamic thickness is only one of the reduction factors of ERA sandwiches.     

Spallation affected fracture pattern of a titanium alloy plate subjected to linear shaped charge jet penetration

In this paper, the commercial finite element code LS-DYNA is employed to simulate the process of a certain kind of a linear shaped charge jet penetrating into a TC4 (Ti–6Al–4V) titanium alloy plate of moderate thickness. The fracture profiles agree well with experimental observations, which confirms the validity of the code and the Johnson–Cook material model applied to describe the TC4 plate. The fracture pattern of the plate is drawn based on this comparison.     

Effectiveness Factors for Explosive Reactive Armour Systems

The space and mass effectiveness of explosive reactive armours (ERA) can be compared either with the penetration in a semi-infinite target of RHA, or with an inert ERA, respectively with a spaced plate arrangement. The paper gives a clear information of the two different definitions which are demonstrated by tests performed with a large and a small shaped charge, respectively with a KE round from type APDS-FS.     

Study on Rubber Composite Armor Anti‐Shaped Charge Jet Penetration

The process of rubber composite armor anti‐shaped charge jet (SCJ) penetration was divided into four parts based on jet deformation that occurred when the SCJ penetrated the rubber composite armor. Results on the interference speed interval, interference frequency, and surplus penetration capability of the SCJ with the rubber composite armor were derived based on the stress wave and the Kelvin‐Helmholtz instability theory. The effects of rubber layer thickness and obliquity of the armor for the composite armor anti‐SCJ penetration were studied through theoretical, X‐ray, and depth of penetration experiments. The results showed that when the obliquity was at 60° and the rubber layer thickness was in the range of 3 mm to 3.5 mm, the rubber composite armor seriously disturbed the stability of the SCJ. Thus, the rubber composite armor was found to have the best protection capability under these specifications.     

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.     

Theoretical and Experimental Study on the Effects of Impact Angle on the Performance of Kevlar Woven Fabric Rubber Composite Armor against Shaped Charge Jet Impact

Kevlar woven fabric rubber composite armor (WFRCA) is a type of add‐on armor that usually consists of two steel plates with two Kevlar woven fabrics and a rubber layer in between. In this study, a theoretical model was developed to analyze the effect of the impact angles on the performance of the Kevlar WFRCA against the shaped charge jet impact. The calculation of the precursor length was discussed in detail. A series of X‐ray experiments were conducted to analyze the disturbance mechanism and precursor length of the Kevlar WFECA against the shaped charge jet under different impact angles. Theoretical and experimental analyses showed that the greater the impact angle, the higher the tip velocity of the precursor and the shorter the precursor length. A microscopic study of the edge of the Kevlar woven fabric, rubber, and steel plates after the shaped charge jet impact was also conducted to evaluate the structure and composition. Several broken Kevlar fibers were embedded in the steel plate and the moving jet. This phenomenon can be used to further investigate the disturbance mechanism of the Kevlar WFRCA against the shaped charge impact.     

Jet Penetration of Surrogate Steel-Explosive Systems

Predicting the jet initiation of an explosive that is covered and in intimate contact with an inert material, is sensitive to the history of the jet in both the cover and the explosive. If the penetration velocity in the cover is subsonic, the acceptor explosive experiences complex wave structures that are significantly different from the case where the penetration velocity is supersonic. The pressure history in the explosive may cause prompt initiation, desensitization, or delayed initiation. We have used transparent polymethylmethacrylate (PMMA) as a surrogate for the explosive, allowing us to experimentally visualize the transition between the subsonic penetration behavior in a steel cover and the quasi-steady supersonic penetration behavior in the PMMA. The wave histories in PMMA downstream from two steel covers of different thicknesses have been measured by streak and image intensifier cameras and by flash radiography simultaneously. These were augmented with pressure gauges to measure the pressure history for one of the thicknesses. These experimental results and subsequent analysis show how initiation of an explosive acceptor can occur at various distances from the interface, depending on the thickness of the cover plate.     

An atomization model for splash plate nozzles

A model for the atomization and spray formation by splash plate nozzles is presented. This model is based on the liquid sheet formation theory due to an oblique impingement of a liquid jet on a solid surface. The continuous liquid sheet formed by the jet impingement is replaced with a set of dispersed droplets. The initial droplet sizes and velocities are determined based on theoretically predicted liquid sheet thickness and velocity. A Lagrangian spray code is used to model the spray dynamics and droplet size distribution further downstream of the nozzle. Results of this model are confirmed by the experimental data on the droplet size distribution across the spray. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Dynamic Anticumulative Protection

The characteristics of dynamic protection whose anticumulative layer consists of two metal plates with an explosive layer between them are substantiated theoretically and experimentally. The dependences of the penetration depth of a jet upon passage though the anticumulative layer on the angle of their interaction and the thickness of the explosive layer are obtained.     

Numerical modeling of gas-jet wiping process

The proposed study focuses on the numerical modeling of the gas-jet wiping process, which is used to control the coating thickness applied on a solid substrate in various industrial processes. In the galvanization of steel strips, a turbulent slot jet is used to wipe the coating film dragged by a moving steel substrate after dipping in a liquid zinc bath. In the present study a numerical modeling approach of the process is presented using the VOF method for multiphase flows coupled with LES turbulence modeling. Simulations are carried out with three different codes, namely Fluent, OpenFOAM and the research code Thetis. A set of wiping conditions is selected to match a laboratory experiment on a dedicated setup, comparing the numerical results with the experimental data. In a case where the experimental value of the final to initial film thickness is 0.22, Fluent and OpenFOAM overestimate it predicting 0.36 and 0.31 respectively, while Thetis with 0.13 underestimates it. Thetis predicts the closest value to the experiments for the wave amplitude and OpenFOAM for the wavelength. A discussion of the observed differences in the results points out the best modeling practices for the jet wiping process.     

On the inconsistency of the asymmetric-sandwich gurney formula when used to model thin plate propulsion

The asymmetric sandwich Gurney formula is used extensively worldwide during explosive reactive armor and shaped-charge war-head design, in either its original form^(1,2) or its extended form used to model implosion configurations^(3–5). It is therefore very important to realize that calculations may contradict physical observations when the formula is used to calculate the velocity of thin plates having mass which is smaller than half the explosive mass per unit area. This inconsistency between calculation and experimental results is explained as resulting from the failure of the assumption made in deriving all the Gurney formulas that the velocity distribution of the explosive products is a linear function of the expansion coordinate.     

The Use of the [H<Subscript>2</Subscript>O–CO<Subscript>2</Subscript>] Arbitrary Decomposition Assumption to Predict the Performance of Condensed High Explosives

The plate dent test is one of the simplest tools for fast determination of the detonation pressure. The test is based on the observation that the detonation pressure correlates with the depth of the dent produced by a detonating explosive on a metal witness plate. The present study is aimed at developing a model for estimating the dent depth, which is used not only to obtain the detonation pressure, but also to evaluate the brisance relative to a reference explosive. It is shown that the experimental dent depth values for CHNO and CHNOClF explosives can be successfully reproduced by a model based on few parameters, namely: loading density, number of moles of gaseous detonation products per gram of the explosive, and average molecular weight of the gaseous products, where the number of moles and the mean molecular weight of the gaseous products are calculated according to the [H₂O–CO₂] arbitrary decomposition assumption. Furthermore, the predicted values of the dent depth and the Kamlet–Jacobs method are used to estimate the detonation pressure for 37 explosives. The results show that the pressures obtained on the basis of the dent depth values are in better agreement with experimental/thermochemical code data than the predictions of the Kamlet–Jacobs method.     

An Analytical Extension of the Critical Energy Criterion Used to Predict Bare Explosive Response to Jet Attack

Predicting explosive response to jet attack is difficult due to the complex nature of the projectile. The shock duration term in the critical energy(Ec) criterion developed by Walker and Wasley for plate impact is modified for application to round-nosed rods which appear to simulate jet attack. Experimental data on explosive initiation threshold in the cases of plate or rod impacts, LS DYNA2D simulations and data obtained with the new criterion are in good agreement.     

Technique for delaying splashing in jet wiping process

The current study presents an experimental investigation of a technique for delaying the occurrence of splashing in jet wiping process by means of a side jet. Gas jet wiping is a hydrodynamic method of controlling the film thickness applied on a substrate in coating processes. It consists of a turbulent slot jet impinging on a moving surface coated with a liquid film. The process is limited by splashing; a rather violent film instability which is characterized by the ejection of droplets from the runback flow and results in the detachment of the film from the substrate. In the present study an additional side jet is used close to the main wiping jet in order to stabilize the runback flow and avoid splashing. The mean film thickness after wiping is measured using a light absorption method and the results are compared for the single jet wiping and two jet configuration. It is shown that the use of the side jet allows for stronger wiping, resulting in lower values of the final film thickness which cannot be achieved with a single jet.