2009 Insensitive Munitions and Energetic Materials Technology Symposium, Tucson, Arizona11-14 May 2009

Modeling Fragmentation Performance of Insensitive Explosive Fragmentation Munitions

V. M. Gold and Y. Wu U.S. Army RDECOM-ARDEC Picatinny, New Jersey

Acknowledgments

US Army ARDEC:

Dr. E. L. BakerMr. A. J. MockMr. W. J. PoulosMr. W. Ramos Mr. P. J. SamuelsMr. L. SotskyMr. T. Wu

Polytechnic Institute of New York:

Professor L. I. Stiel

Outline

• Introduction: Overview of the PAFRAG (Picatinny Arsenal FRAGmentation) Modeling Methodology

• Modeling Fragmentation Performance of Insensitive Explosive Fragmentation Munitions

• Summary

CALE PAFRAG CASRED/ALGRID

CALE

Dynamic high-strain high strain rate

continuum analyses

PAFRAG – Picatinny Arsenal

Fragmentation code

Fragmentation modeling

CASRED/ALGRID

Lethality Codes

Model the effectiveness of the

munition

PAFRAG Modeling Lethality Modeling

PAFRAG Modeling Methodology

Fragmentation Arena TestingExpensive

Inexpensive

Z-data

Stress Release WaveFracture

Region UnderPlastic Expansion

Region StressRelieved

A2

B2

B2

A2

B1

A1A1B1

2/1

0

m

eNmN

VrPx F

2/1

02

302

1 x

Average circumferential fragment length:

Average fragment mass:

Fragment size distribution:

Natural Fragmentation: PAFRAG-MOTT Model

Based on MottBased on Mott’’s theory of breaks theory of break--up of cylindrical up of cylindrical ““ringring--bombsbombs””

is a statistical parameter and can be determined from fragmentation test data

Final munitions require arena testing

PAFRAG ExperimentationPAFRAG Experimentation

High Speed PhotographyHigh Speed Photography

Sawdust Fragment RecoverySawdust Fragment Recovery

N=N(m)

Fragment velocities Surface cracking

Celotex™ Rear Fragment RecoveryCelotex™ Rear Fragment Recovery

NR =NR (m)

Orthogonal X-rays

PAFRAG experimentation is adjusted according to specific project/customer needs

gives

Flash RadiographyFlash Radiography

0 2 4 6 8 10 12 14 16 18 20 22 24 26Time, sec

1

2

3

4

5

6

7

8

9

10

V/V 0

V/V0=3.1

V/V0=6.2

V/V0=1.8

Axial cracking starts

Detonation products break through and appear on the surface

V/V0 vs Time and High Speed Photography

“Average” Fragmentation Time

0 30 60 90 120 150 180

, degrees

0

50

100

150

200

Num

ber o

f fra

gmen

ts

0.0 0.6 1.2 1.8

Fragment mass m, grams

0

500

1000

1500

Num

ber o

f fra

gmen

ts, N

Explosive

Hardened steel shellR

z

Steel fragments

R

z

v

CALE

Predicts Lethality

Predicts number of fragment distributions

PAFRAG Modeling Methodology for Lethality Assessments

Sawdust fragment recovery test data

PAFRAG modeling and experimentation

Predicts mass and velocity flow field

Z-data

PAFRAG

V/V0=3, t=49sec

FuzeV/V0=3, t=40sec

R

z

v

Steel FragmentsBooster

Main ChargeNose Front Mount and Front Retainer

Charge A

Charge B

Fragmenting Shell

FuzeExplosive

CALE-PAFRAG Modeling

Charge A

Charge B

Given: Fragmentation performance of Charge AFind: Fragmentation performance of Charge B

0 2 4 6 8 10 12 14 16 18 20Fragment mass m, grains

0.2

0.4

0.6

0.8

1.0

1.2

Num

ber o

f fra

gmen

ts, N

/N0

COMP-B, Arena Test Data, AverageCOMP-B, Sawdust Test Data, 346COMP-B, Sawdust Test Data, 347COMP-B, PAFRAG Analyses fitted to test data, =54.4HBU-88B, PAFRAG Analyses fitted to test data, =51.0PAX-25, PAFRAG Analyses fitted to test data, =40.0

9%

32%

Cumulative number of fragments versus fragment mass, Charge A

decreases with brisance decreases

Comp-BHBU-88B

PAX-25

Parameter

versus explosive detonation Chapman-Jouguet (CJ) pressure

17 19 21 23 25 27 29 31PCJ, GPa

35

40

45

50

55

60

Charge A, PAFRAG Analyses fitted to dataCharge A, =(PCJ)Charge B, PAFRAG Analyses fitted to dataCharge B, assumed =(PCJ)Charge B, estimated

PAX-25

PBXN-9

Comp-B

HBU-88

TNT, =44.88

PAX-3,=55.65

GUDN/TNT (45/55)=44.38

IMX-101, =44.03

Comp-B, =55.85

from test data(PCJ ) assumed

Cumulative number of fragments versus fragment mass, Charge B

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Fragment mass m, grains

0.1

0.3

0.5

0.7

0.9

1.1

1.3

Cum

ulat

ive

num

ber o

f fra

gmen

ts, N

/N0 PBXN-9, Arena Test Data, Average

PBXN-9, PAFRAG Analyses fitted to test data, =56.0Comp-B, PAFRAG Analyses, =55.85PAX-3, PAFRAG Analyses, =55.65TNT, PAFRAG Analyses, =44.88GUDN/TNT (45/55), PAFRAG Analyses, =44.38IMX-101, PAFRAG Analyses, =44.03

PCJ decreases,

decreases, fragmentation performance degrades

PBXN-9Comp-B

PAX-3 GUDN/TNT (45/55)

TNT IMX-101

Fragment velocities versus theta for varying explosive compositions, Charge B

0 20 40 60 80 100 120 140 160 180, degrees

0.00

0.05

0.10

0.15

0.20

0.25

Vel

ocity

, V, c

m/

sec

PBXN-9, Arena Test DataPBXN-9, PAFRAG Analyses, Cell Data, t=40sec, V/V0=3PBXN-9, PAFRAG Analyses, Momentum Average, t=40sec, V/V0=3Comp-B, PAFRAG Analyses, Momentum Average, t=45sec, V/V0=3PAX-3, PAFRAG Analyses, Momentum Average, t=48sec, V/V0=3TNT, PAFRAG Analyses, Momentum Average, t=52sec, V/V0=3GUDN/TNT (45/55), PAFRAG Analyses, Momentum Average, t=49sec, V/V0=3IMX-101, PAFRAG Analyses, Momentum Average, t=52sec, V/V0=3

Fragment velocities decrease

Summary

New modeling methodology for assessing performance of IM munitions developed

Employing IM explosives with low brisance properties and low Chapman-Jouguet (CJ) pressures leads to decreases in the fragment numbers and velocities

Based on the experimental data available to-date, an approximately linear relationship between the -parameter and the Chapman-Jouguet (CJ) detonation pressures is observed

To maintain lethality requirements, explosive fragmentation munitions with IM formulations requires employing high fragmentation steel alloys, or controlled/preformed fragmentation techniques, or a combination of thereof

Back-up slides