Finite Element Analysis of the Effect of Flyer Plate

Finite Element Analysis of the Effect of Flyer

Plate Impacts on Rod Projectiles and

Shaped Charges

G.W.J. McIntoshDRDC Valcartier

Defence R&D Canada – ValcartierTechnical Memorandum

DRDC Valcartier TM 2003-373March 2004

Finite Element Analysis of the Effect of Flyer Plate Impacts on Rod Projectiles and Shaped Charges

Grant W.J. McIntosh DRDC Valcartier

Defence R & D Canada - Valcartier

Technical Memorandum

DRDC Valcartier TM 2003-373

March 2004

Author

Grant W.J. McIntosh

Approved by

Michel Szymczak

Head, Weapons Effects Section

© Her Majesty the Queen as represented by the Minister of National Defence, 2004

© Sa majesté la reine, représentée par le ministre de la Défense nationale, 2004

DRDC Valcartier TM 2003-373 i

Abstract

Numerical simulations were undertaken using LS-DYNA to investigate flyer plates as possible hard kill countermeasures against kinetic energy threats (tungsten rods at high velocity) and chemical energy threats such as shaped charge warheads. The results indicate that flyer plates can disrupt small 25-mm APFSDS-like projectiles effectively. Long 120-mm rods are much harder to disrupt and the various flyer plate combinations surveyed did not work. For shaped charge jets, distortion of the liner by flyer plate impact of the warhead and subsequent lack of jet formation is possible but there remains a non-negligible mass that impacts the armour of a light armoured vehicle.

Résumé

On a effectué des simulations numériques avec LS-DYNA pour déterminer si des plaques projetées étaient efficaces comme contre-mesures contre les menaces à énergie cinétique (flèche en tungstène à haute vitesse) et à énergie chimique comme les ogives à charge creuse. Les résultats démontrent que les plaques sont efficaces contre une petite flèche comme un projectile de 25 mm APFSDS. Les flèches de 120 mm sont beaucoup plus difficiles à arrêter. En effet, les plaques n’ont pas reussi à le faire dans les scénarios étudiés. Pour les charges creuses, une distorsion du cône causée par l’impact d’une plaque projetée et l’interruption de la formation du jet est possible, mais il reste une masse considérable qui frappe le blindage d’un véhicule blindé léger.

ii DRDC Valcartier TM 2003-373

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DRDC Valcartier TM 2003-373 iii

Executive summary For many armed forces, including Canada’s, geopolitical realities have changed the operational requirements for armoured vehicles. The ability to rapidly deploy anywhere in the world has become very important and to do so, an air transportable fighting vehicle is needed. In practice, this means a light armoured vehicle (LAV) weight of around 20 tons versus around 55 tons for a main battle tank, the weight difference due mainly to lighter armour. At the same time, more sophisticated anti-vehicle weapons are being developed. The aim of the present study is to examine flyer plates as hard-kill mechanisms applicable to active protection systems for a LAV. The study emphasizes the terminal ballistics aspects, i.e. the interaction between the threat and countermeasure. Numerical simulations were undertaken using LS-DYNA to ascertain whether or not flyer plate impacts are possibly useful as hard kill countermeasures against kinetic energy threats (tungsten rods at high velocity) and chemical energy threats such as shaped charge jets warheads. The results indicate that flyer plates can disrupt small 25-mm APFSDS projectiles effectively. Long 120-mm rods are much harder to disrupt and the various flyer plate combinations surveyed did not work. For shaped charge jets, distortion of the liner by flyer plate impact of the warhead and subsequent lack of jet formation is possible but there remains a non-negligible mass that impacts the armour of a light armoured vehicle

McIntosh, Grant.W.J. 2004. Finite Element Analysis of the Effect of Flyer Plate Impacts on Rod Projectiles and Shaped Charges DRDC Valcartier TM 2003-373

iv DRDC Valcartier TM 2003-373

Sommaire

Au sein de nombreuses forces armées, y compris celles du Canada, les réalités géopolitiques ont changé les conditions opérationnelles pour les véhicules blindés. La capacité de se déployer rapidement n'importe où dans le monde est devenue très importante et pour ce faire, il est nécessaire d’avoir un véhicule de combat transportable par avion. En pratique, cela represente un poids pour un véhicule blindé léger (VBL) d'environ 20 tonnes en comparaison avec d’environ 55 tonnes pour un char d’assaut, la différence étant principalement attribuable à un blindage plus léger. En même temps, des armes antivéhicules plus sophistiquées sont mises au point. Le but de la présente étude est d'examiner des plaques projetées comme mécanismes applicables aux systèmes de protection active pour des VBL. L'étude souligne les aspects d’interception de balistique terminale, c.-à-d. l'interaction entre la menace et les contre-mesures.

On a effectué des simulations numériques avec LS-DYNA pour déterminer si des plaques projetées étaient efficaces comme contre-mesures contre les menaces à énergie cinétique (flèche en tungstène à haute vitesse) et à énergie chimique comme les ogives à charge creuse. Les résultats démontrent que les plaques sont efficaces contre une petite flèche comme un projectile de 25 mm APFSDS. Les flèches de 120 mm sont beaucoup plus difficiles à arrêter. En effet, les plaques n’ont pas reussi à le faire dans les scénarios étudiés. Pour les charges creuses, une distorsion du cône causée par l’impact d’une plaque projetée et l’interruption de la formation du jet est possible, mais il reste une masse considérable qui frappe le blindage d’un véhicule blindé léger..

.

McIntosh, Grant.W.J. 2004. Finite Element Analysis of the Effect of Flyer Plate Impacts on Rod Projectiles and Shaped Charges DRDC Valcartier TM 2003-373

DRDC Valcartier TM 2003-373 v

Table of contents

Abstract................................................................................................................... i

Executive summary................................................................................................ iii

Sommaire .............................................................................................................. iv

Table of contents.....................................................................................................v

List of figures ........................................................................................................ vi

1. Introduction ........................................................................................................1

2. Numerical Simulations.........................................................................................2

3. Short Rod Impact Results.....................................................................................6

4. Long Rod Impact Results.....................................................................................7

5. Protection against Shaped Charge Attacks.............................................................9

6. Conclusions ...................................................................................................... 10

7. References........................................................................................................ 11

List of symbols/abbreviations/acronyms/initialisms ................................................. 12

Distribution list ..................................................................................................... 14

vi DRDC Valcartier TM 2003-373

List of figures

Figure 1. Rod geometry for the short rod...................................................................3

Figure 2. SC liner deformation 70 microseconds after contact (explosive and container not illustrated) ..................................................................................................9

DRDC Valcartier TM 2003-373 vii

List of tables

Table I. Steel (RHA) properties................................................................................3

Table II. Tungsten properties ...................................................................................4

Table III. Titanium properties ..................................................................................4

Table IV. Alumina ceramic properties ......................................................................4

Table V. Aluminum properties.................................................................................5

Table VI. Impacts at 0 degrees.................................................................................6

Table VII. Impacts at 30 degrees ..............................................................................6

Table VIII. Impacts at 30 degrees.............................................................................6

Table IX. Impacts at 0 degrees.................................................................................7

Table X. Impacts at 30 degrees ................................................................................7

Table XI. Impacts at 60 degrees ...............................................................................7

viii DRDC Valcartier TM 2003-373

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1

1. Introduction For many armed forces, including Canada’s, geopolitical realities have changed the operational requirements for armoured vehicles. The ability to rapidly deploy anywhere in the world has become very important and to do so, an air transportable fighting vehicle is needed. In practice, this means a light armoured vehicle (LAV) weight of around 20 tons versus around 60 tons for a main battle tank, the weight difference due mainly to lighter armour. At the same time, more sophisticated anti-vehicle weapons are being developed. The aim of the present study is to examine flyer plates as mechanisms applicable to active protection systems for a LAV. The study emphasizes the terminal ballistics aspects, i.e. the interaction between the threat and countermeasure. This work is part of a larger study of possible protection systems for light armoured vehicles (Ref. 1). It is also an extension of previous work on the present countermeasures (Ref. 2). The work was performed under project 12fh, Investigation of Advanced Protection Systems for LAVs between January 2002 and October 2003.

2 DRDC Valcartier TM 2003-373

2. Numerical Simulations

Numerical simulations of various scenarios were undertaken using the hydrodynamic finite-element program LS-DYNA. Full three-dimensional finite element studies were done for three possible threats: a short rod (9.67 cm) APFSDS penetrator, a long rod (52.56 cm) penetrator and a shaped charge (81-mm BRL). As hard-kill mechanisms, mainly flyer plates of various materials, thicknesses and velocities (speeds and angle of attacks) were studied. The rods were meshed across their faces and then with evenly spaced slices along their respective lengths. The element geometry is shown in Figure 1 for the short rod (50 longitudinal slices). The long rod uses a scaled-up version of the same cross-sectional mesh but with 150 longitudinal slices. The flyer plates were 15 cm by 15 cm by various thicknesses with an overall face mesh of 40 x 40 but with finer meshing in the center as, in general, the interaction between a rod and a flyer took place near the center of a plate. The mesh through the thickness of a plate was uniform and the number of elements increased with increasing thickness. Preliminary simulations of plate acceleration using layers of Detasheet (a flexible sheet explosive made of PETN and plastic binders) yielded flyer plate velocities that were subsequently used in best-case scenarios. 5-mm of explosive can accelerate a 5-mm thick steel plate to a velocity around 800 m/s and a 15-mm thick steel plate to 500 m/s. A much thicker explosive, 15 mm, can accelerate a 5-mm steel plate to 1200m/s. Thus, the flyer plates were launched (with no deformation i.e. flat) at velocities of 800 or 1200 m/s at angles of 0, 30 or 60 degrees between the plate normal and the rod velocity.

DRDC Valcartier TM 2003-373 3

Figure 1. Rod geometry for the short rod.

The rods were modeled using an elastic -plastic material model for typical tungsten. The same type of model also described the material properties of the flyer plates for generic rolled homogeneous armour (RHA) steel or titanium. Alumina (98% maximum density) was modeled using the Johnson-Holmquist ceramic model. The various material properties used are shown in Tables I-V.

Table I. Steel (RHA) properties

PARAMETER VALUE Density 7.85 g/cm3 Young’s modulus 1.975 Mbar Poisson’s ratio 0.33 Yield strength 0.0132 Mbar Tangent hardening modulus 0.0181 Hardening parameter 1.0 Failure Strain 1.0


Table II. Tungsten properties

PARAMETER VALUE

Density 17.7 g/cm3 Young’s modulus 3.24 Mbar Poisson’s ratio 0.303 Yield strength 0.0674 Mbar Tangent hardening modulus 0.00405 Hardening parameter 1.0 Failure Strain 2.0

Table III. Titanium properties

PARAMETER VALUE


Table IV. Alumina ceramic properties

PARAMETER VALUE

Density 3.8 g/cm3 Shear modulus 0.90160 Intact strength (normalized) 0.93 Fractured strength (normalized) 0.31 Strength parameter (strain rate dependence)

0.0

Pressure exponent for intact strength 0.6 Pressure exponent for fractured strength

0.6

Reference strain rate 1. Tensile strength 0.002 Maximum fractured strength (normalized)

0.

Hugoniot elastic limit (HEL) 0.0279 Pressure component of HEL 0.0146 Energy conversion fraction 1.0 Plastic strain to fracture 0.01 Plastic strain to fracture exponent 1.0 Bulk modulus 1.3095 Second order elastic constant 0. Third order elastic constant 0. Failure strain 1.0


Table V. Aluminum properties

PARAMETER VALUE



3. Short Rod Impact Results A 9.67-cm long, 0.838962-cm diameter right circular cylindrical tungsten rod was launched at 1400 m/s for an initial kinetic energy of 0.090313 MJ against plates at various angles, thicknesses and materials. The base armour was 150-mm x 150-mm x 15-mm RHA. Residual velocities and energies are reported for the rod only if it perforates this backing. The results are summarized in Tables VI-VII.

Table VI. Impacts at 0 degrees

FLYER CONSTRUCTION FLYER VELOCITY (M/S) RESIDUAL ENERGY (MJ) RESIDUAL VELOCITY

(M/S)

15-mm Ti 1200 0.028568 839 15-mm RHA 1200 0.022435 792.2 15-mm SiC/5-mm RHA 1200 0.039772 1094 15-mm Al2O3/5-mm RHA 1200 0.046024 1169.1

Table VII. Impacts at 30 degrees


(M/S)

15-mm Ti 1200 Did not perforate 0 10-mm Ti 1200 Did not perforate 0 10-mm RHA 1200 Did not perforate 0 5-mm RHA 1200 0.04333 243.84 5-mm Ti 1200 0.059556 354.39

Additional simulations were performed with 5-mm thick aluminum base armour. All other conditions remained the same for a 30-degree impact angle. These results are summarized in Table VIII.

Table VIII. Impacts at 30 degrees

FLYER CONSTRUCTION FLYER VELOCITY (M/S) RESIDUAL ENERGY (MJ) RESIDUAL VELOCITY (M/S)

15-mm Ti 1200 0.06209 1171. 10-mm Ti 1200 0.06314 1175. 10-mm RHA 1200 0.04995 1099. 5-mm RHA 1200 0.06777 1207. 5-mm Ti 1200 0.07878 1307.


4. Long Rod Impact Results A 52.56-cm long, 2.414-cm diameter right circular cylindrical tungsten rod was launched at 1500 m/s and with a kinetic energy of 4.6679 MJ against plates at various angles, thicknesses and materials as well as impact velocities. The base armour was 150-mm x 150-mm x 15-mm RHA. Again, residual velocities and energies are reported below in Tables IX-XI for the rod only if it perforates this backing.

Table IX. Impacts at 0 degrees


(M/S)

15-mm Ti 1200 4.4046 1453.0 15-mm Ti 800 4.3930 1456.1 15-mm RHA 1200 4.3747 1453.0 15-mm RHA 800 4.3439 1447.9 15-mm Al2O3/5mmRHA 1200 4.2617 1446.6

Table X. Impacts at 30 degrees


(M/S)

15-mm Ti 1200 4.2895 1439.0 15-mm Ti 800 4.2738 1447.9 10-mm Ti 1200 4.3737 1452.8 5-mm Ti 1200 4.4244 1461.3 15-mm RHA 1200 4.1153 1410.8 15-mm RHA 800 4.1893 1421.3 10-mm RHA 1200 4.2983 1442.2 5-mm RHA 1200 4.3915 1455.9 15-mm Al2O3/5mm RHA 1200 4.1179 1416.3

Table XI. Impacts at 60 degrees


(M/S)

15-mm Ti 1200 3.7970 1338.5 15-mm Ti 800 4.0083 1340.5 15-mm RHA 1200 3.7654 1350.3 15-mm RHA 800 3.7392 1348.9 15-mm Al2O3/5mm RHA 1200 4.2099 1420.5

A plate size 300 mm x 300 mm was tried for 15-mm thick RHA at 800 m/s for 30 degrees angle of impact. In this case, the residual energy was 3.9622MJ and the residual velocity was 1381.2 m/s. (versus 4.1893 MJ and 1421.3 m/s for a 150mm by 150 mm plate). The difference is not really due to the plate mass difference. Rather, it is due to the longer interaction between the tail of the rod and the plate.


Flyer plates with practical thicknesses (thinner) and lower velocities will not be able to stop this size of long rod kinetic energy penetrator. .


5. Protection against Shaped Charge Attacks Light passive armour alone cannot stop a shaped charge jet. It is therefore imperative to disrupt the charge before it detonates. To do this, a flyer plate impact was tried with an ignition of the shaped charge delayed until after significant disruption of the charge liner had occurred. For the shaped charge studied (81-mm BRL flying at 800 m/s), a 15-mm RHA flyer plate at 1000 m/s that strikes at 30 degrees, 70 microseconds or sooner before the ignition of the explosive charge can totally deform the liner and hence, remove the threat of a well-defined jet. This is illustrated in Figure 2. It does not eliminate other dangers as there is still a significant mass moving at the shaped charge launch velocity as well as a blast to defend against.

Figure 2. SC liner deformation 70 microseconds after contact (explosive and container not

illustrated)


6. Conclusions Protection of a light armoured vehicle against small projectiles is possible using a variety of techniques. The simulations indicate that, for straightforward practical flyer plates, only protection against the short rod penetrator can be achieved using flyer plates. Against a long rod projectile, nothing that was tried disrupted the long rods sufficiently to provide adequate protection. Against a shaped charge, distortion of the liner by a flyer plate before detonation can eliminate the jet threat. Whether or not a practical implementation of these protection systems can be achieved is open to discussion.


7. References

1. Bergeron, G., presentation to TAG 2f, DRDC-Valcartier, September 23, 2003 (private communication)

2. McIntosh, G., Szymczak, M., “Ballistic Protection Possibilities for a Light Armoured

Vehicle”, 20th Ballistics Symposium, Orlando, Florida, 23-27 September 2002

.


List of symbols/abbreviations/acronyms/initialisms

Al

Al2O3

APFSDS

BRL

KE

LAV

PETN

RHA

SC

Aluminum

Alumina (aluminum oxide)

Armour Piercing Fin Stabilized Discarding Sabot

Ballistics Research Laboratory (US)

Kinetic Energy

Light Armoured Vehicle

Pentaerythriol tetranitrate

Rolled Homogenous Armour (steel)

Shaped Charge


Distribution list

Internal Distribution


1 – Director General

3 – Document Library

1 – Dr. Grant McIntosh (author)

1 – Dr. Dennis Nandlall

1 – Ms. Manon Bolduc

1 – Dr. Amal Bouamoul

1 – H/WE

1 – Mr. Guy Bergeron

1 – Mr. Ghislain Pelletier

1– Dr. Jean Fortin


External Distribution


1 – DRDKIM (unbound copy)

1 – DRDC

1 – National Library of Canada

1 – Director Land Requirements 3 (DLR-3)

1 – Director Land Requirements 3-3 (DLR-3-3)

1 – Director Science and Technology (Land) 5 (DSTL-5)

dcd03e rev.(10-1999)

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3. TITLE (Its classification should be indicated by the appropriate abbreviation (S, C, R or U) Finite Element Analysis of the Effect of Flyer Plate Impacts on Rod Projectiles and Shaped Charges (U)

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Numerical simulations were undertaken using LSDYNA to investigate flyer plate impacts as possible hard kill countermeasures against kinetic energy threats (tungsten rods at high velocity) and chemical energy threats (shaped charge jets). The results indicate that small 25-mm APFSDS projectiles can be disrupted (eroded) effectively by flyer plates. Long 125-mm rods are much harder to disrupt and the various flyer plate combinations surveyed did not work. For shaped charge jets, distortion of the liner by flyer plate impact of the warhead and subsequent lack of jet formation is possible but there remains a non-negligible mass that impacts the armour of a light armoured vehicle.

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Finite Element Analysis of the Effect of Flyer Plate