Penetrator Length Research Articles

Estimation of terminal ballistics parameters for several 7.62×51 mm projectiles using numerical simulations

Six widely used 7.62 ×51 mm projectile types (M80, M61, P80/1, M80A1, M1158, and M993) were subjected to the analysis in this paper. Numerical simulations (Ansys Autodyn) of projectile impacts on hard steel targets were performed as part of this analysis. Projectiles had the same impact velocity (800 m/s). This allowed evaluation of the projectile’s design and material’s effect on its performance against a hard steel target. Validation of the numerical model and used materials was first performed, using available experimental data. A short description and Computer-Aided Design (CAD) model of projectiles is also given. Comparing the M1158 projectile to other AP projectiles taken into consideration, it was concluded that the former had a much deeper penetration depth into a hard steel target (Armox 500T). The projectile’s penetrating capability is greatly impacted by the material selection used for its component parts. Assuming all other factors remain constant, penetrators with higher density and harderness can achieve deeper penetration. Under the same conditions, an increase in penetrator length results in an increase in penetration depth. The absence of a gilding metal jacket in the projectile’s frontal ogive section can decrease energy required to remove the jacket during the penetration, hence increasing the projectile’s penetration capabilities.

분절형 텅스텐 관통자의 초고속 관통특성에 관한 연구

본 논문의 목적은 수직 또는 경사각에 대한 분절형 관통자의 관통특성을 규명하는 것이다. 분절형 관통자의 기하형상비(L/D)는 각 1.0, 0.5, 0.25 이다. 적용된 충격속도와 경사각도는 각 1.5, 2.0, 2.5 km/s 그리고 15°, 30°, 45° 이다. AUTODYN-3D code 가 분절형 관통자의 관통성능을 연구하기 위해 사용되었다. 결과는 강판에 대한 분절형 관통자의 관통성능이 해당 연속적 관통자보다 분명하게 높은 특성을 나타냈다. 2.0 km/s 의 충격 속도와 L/D 가 1 일 때, 분절형 관통자의 뛰어난 관통성능을 관찰 할 수 있다. 이 경우 분절형 관통자의 관통성능은 해당 연속적인 관통자보다 7 % 높았다. 이러한 경향은 표적체와 발사체 사이의 상호작용 때문이다. 상호작용의 정도는 표적체와 발사체의 상대속도와 입사각도, 분절형 관통자의 개수에 의존하고 있다. 따라서, 분절형 관통자의 관통 성능은 충격속도의 증가, 관통자의 개수 및 관통길이를 통해서 높일 수 있음이 확인되었다.

Theoretical considerations on the penetration of powdered metal jets

This paper explores some of the theoretical issues encountered when interpreting the penetration behavior of an oilwell perforating charge, whose jet forms from an unsintered powdered metal (PM) liner. Appropriate treatments of the jet's porous compressible nature fill the gap between classical “continuous” and “fully particulated” jet penetration models. Within certain constraints, increasing a penetrator's length (even if by distension) increases its hydrodynamic penetration depth, while reducing its impact pressure; and a porous penetrator penetrates deeper than a non-porous penetrator of the same density, length, and velocity. Dynamic target pressure considerations lead to the conclusion that highly distended, low-velocity, PM jets should penetrate moderate-strength geologic targets effectively. After demonstrating that initial transient shock pressures may be much higher than steady-state penetration pressures, we suggest that initial penetration rates may be higher than the steady-state rates. This, in conjunction with the well-known “residual penetration” phenomenon, indicates that a non-continuous jet's penetration may be strongly influenced by transient effects.

High-velocity impact loading of thick GFRP blocks

In previous depth of penetration experiments with tungsten long rod projectiles was found that the ballistic resistance of a relatively thick - up to the penetrator length - glass fibre reinforced plastic block grows with increasing penetration depth. This penetration behaviour significantly differs from that of other inert armour materials. Until now, no significant difference between unconfined and totally confined GFRP configurations has been found. Newest experiments with up to semi-infinite thick GFRP blocks show a change in the penetration process: For thicknesses significantly higher than the penetrator length the protective power may saturate. During the late penetration phase the shortening and deceleration of the projectile induce a change of penetration mechanism from erosion to rigid body penetration. Additionally, the projectile may break into several individually tumbling parts. Reflected tension waves and, probably, pyrolysis effects may cause increasing precursory damage. These effects together are likely to explain the reduction of the ballistic resistance increase during the late penetration phase. Based on these experimental results the published working hypothesis on the governing mechanism of the GFRP penetration behaviour had to be completed. A new approach based on a hyperbolic tangent function seems to satisfactorily describe the observed thickness dependent phenomena.

A computational study of the influence of thermal softening on ballistic penetration in metals

A two-dimensional axisymmetric computational study of the penetration of a tungsten heavy alloy (WHA) rod into a 6061-T6 aluminum target has been performed using a Lagrangian formulation. Adaptive remeshing has been used to alleviate the problem of excessive distortion of elements which occurs during large deformation studies (such as ballistic penetration). Strain hardening, strain-rate hardening and thermal softening in both the penetrator and target materials are taken into full consideration. The computed depth of penetration (DOP), residual penetrator length and maximum crater diameter match very well the experimental results reported by Yadav and Ravichandran (Int. J. Impact Eng., Submitted for publication) for an impact velocity of 1100 m/s. Computer simulations reveal that in the absence of failure mechanisms (such as shear banding), introduction of thermal softening in the penetrator material decreases its depth of penetration in a metal target, when compared to a penetrator material which does not soften thermally. These results are in contrast to the recent work of Rosenberg and Dekel (Int. J. Impact Eng. 21 (1998) 283–296) and a plausible explanation for this discrepancy is presented.

Numerical simulations of low L/D rod aluminum into aluminum impacts compared to the tate cratering model

Summary Hydrocode numerical simulations have been made for 1100-0 aluminum rods into thick plates of the same material with parametric variations in the penetrator length to diameter ratio (L/D from 1/2–10) and impact velocity (1–6 km/s). The normalized penetration depth (P/L), primary penetration (P p /L), after-flow penetration (P a /L) and crater diameter (D c /D) were determined and compared with the results of the Tate penetration model and available test data. It was found that the hydrocode results agreed very well with the test data, but there was a trend for the Tate model to over-predict the after-flow penetration and crater diameter for low L/D values and high velocities. Correction factors that are a function of L/D and velocity have been found that, when applied to the Tate model penetration and diameter results, greatly improve the agreement with the test data and hydrocode calculations.

Eroded length model for yawed penetrators impacting finite thickness targets at normal and oblique incidence

Summary A simple expression is derived to estimate the residual length of a yawed, long-rod penetrator impacting finite thickness targets at both normal and oblique incidence. The unique feature of this model is a determination of the different penetration path through the plate which is not simply a line-of-sight thickness. The presence of yaw results in a penetration path which is determined by the magnitude and direction of the penetration velocity vector which is dependent upon the penetrator velocity component along that path. Hence, the material thickness penetrated through the finite target is an explicit, and variable, function of the impact geometry, (obliquity and yaw), impact velocity, and relative penetrator and target properties (densities and strengths). The eroded penetrator length is also dependent on both the penetration path angle and on the velocity component along that path and thus becomes an explicit function of these variables. Two simple expressions are derived to determine the eroded penetrator length and implications for deep target penetration degradation due to yaw are discussed.

The influence of experimental design on depth-of-penetration (DOP) test results and derived ballistic efficiencies

Experimental data for ceramic armor materials from two test methods, small-scale reverse ballistic tests and depth-of-penetration (DOP) tests, are reviewed and compared. Results from reverse ballistic tests can be used to estimate the length of rod erosion in the ceramic tiles of DOP tests. The outcome of a given DOP test can then be predicted by using recently published data bases on RHA penetration to determine the residual penetration into the steel back-up of the DOP test. Results of this methodology, compared to experimental DOP-test results, agree reasonably well for aluminum nitride and silicon carbide, even though scale sizes, impact velocities and experimental procedures varied considerably between investigators. The methodology was then applied to single-valued performance criteria for ceramic armor materials, for example, mass efficiency. This analysis demonstrates that in certain cases, test parameters, like the ratio of penetrator length to ceramic tile thickness, affect test results considerably more than differences between ceramic types. Thus, DOP tests must be properly designed and interpreted in order to assess correctly the ballistic performance of ceramics.

Homogenized penetration calculations

A model was developed which describes the penetration of a target composed of multiple discrete elements in terms of the penetration of an equivalent single-element target of identical thickness. To achieve this aim, the effective density and target resistance terms for the equivalent target have been homogenized from the densities and target resistances of the individual discrete elements composing the original target. Though the current model may be employed to treat a target's internal air gaps in the homogenization process, the current model does nothing special to address target considerations, such as obliquity, confinement, length-to-diameter (L/D) effects, etc. Rather, the model was intentionally restricted to flat-plate-type target elements being impacted at normal incidence, to focus upon the homogenization technique itself. To avoid the need to transform the shape or velocities of the bodies in question, only techniques which strictly preserved length and time dimensions were considered. Several homogenization schemes were examined and compared to the corresponding multi-element penetration calculation. It was determined that a straightforward volume averaging of target properties is usually not sufficient to effectively simulate a multi-element target. Other techniques presented here seem to do a better job at predicting residual penetrator length and velocity, respectively.

The relation between the penetration capability of long rods and their length to diameter ratio

Summary Recent experimental studies, on the penetration of long rods into semi-infinite steel targets, reveal some features which cannot be predicted by the conventional 1-D penetration model of Alekseevskii and Tate. This paper presents experimental results together with 2-D simulations which were performed in order to investigate this discrepancy. Specifically we are interested in the question of whether the normalized penetration curve— P/L ( P is penetration depth, L is penetrator length)—is dependent on penetrator's length to diameter ratio in the range of L/D = 10–40. Both experimental and simulation results show a decrease of about 15% between P/L values for L/D = 10 and 20 rods as well as for L/D = 20 and 30. These, rather large, differences are discussed in terms of material parameters which are resonsible for the discrepancy between the 1-D model and both experiment and simulation. Moreover, we have simulated the penetration of long rods having zero yield strength. Our results show that for large aspect ratios ( L/D > 30) these weaker rods penetrate more than those with their full yield strength. This crossover phenomenon is both counterintuitive as well as opposed to the predictions of the 1-D model for this combination of rod-target materials.

Observations concerning the penetration mechanics of tubular hypervelocity penetrators

The work reported here concerns the penetration mechanics of hypervelocity tubular penetrators. The results of analytical modeling, hydrocode calculations and terminal ballistic tests of the normal impact and penetration of hypervelocity tubular projectiles are compared. A steady-state penetration process with constant penetration velocity is observed in many cases. The penetration efficiency (penetration depth per consumed penetrator length) in a steady-state process is dependent on the ratio of inner to outer tube diameter, on the ratio of tube material to target material density and on impact velocity. For normal impact, penetration efficiency is generally at least as high as that of a solid rod with equal length, equal outer diameter, equal mass and equal velocity.

2-D computer simulations of segmented penetrators impacting semi-infinite steel targets

It has been shown that penetrator efficiency, i.e. the ratio of penetration to penetrator length ( P/L), increases as the ratio of the penetrator length to diameter decreases ( L/D). This suggests a long rod penetrator divided in several smaller length segments separated at a distance should improve performance when performance is measured in terms of total penetration. Numerical simulations are presented examining the performance of A. C. Charters' 7 segment 18 g kinetic energy penetrator at normal impact against a semi-infinite T4340 steel target. The two dimensional simulations compare the effects of the spacers used in Charters' penetrator with a similar penetrator without spacers; compare the performance of equivalent mass and diameter and equivalent mass and length monolithic penetrators to that of their segmented counterpart at velocities of 3.0, 3.4 and 4.0 km/s; examine the effects on performance of spacing-to-diameter ratio; and examine the use of penetration efficiency as a measure of the performance of segmented penetrators.