EHTC 2008 in Strasbourg

2nd European HyperWorks Technology Conference

Strasbourg September 30th – October 1st, 2008

Mine explosion and blast effect on vehicleanalysis of the potential damages on passengers

Romuald FALLET

CONTEXTCONTEXT

All over the world, All over the world, guerrilla methods are more and more used. guerrilla methods are more and more used.

Today, terrorist attacks can affect both military and civilian vToday, terrorist attacks can affect both military and civilian vehiclesehicles

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For these specific applications, numerical simulations can be usFor these specific applications, numerical simulations can be useful to eful to

estimate damages created by a mine explosion, and to improve surestimate damages created by a mine explosion, and to improve survivability vivability

of occupants.of occupants.

Numerical Simulation of a mine Numerical Simulation of a mine

explosion under a civil vehicleexplosion under a civil vehicle

The RADIOSS model takes into account :

– Arbitrary Lagrange Euler (ALE) method for Fluid and Explosive [JWL] Modeling

– Fluid Structure Interaction (FSI) between

vehicle and blast wave (interface type 18)

– Deformable Structure of vehicle

– HYBRID III dummies to estimate damages

caused by the blast wave

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Explosion of a buried landmine of 6 Kg of TNT under the Explosion of a buried landmine of 6 Kg of TNT under the

front wheel of a civil pick upfront wheel of a civil pick up

Landmine 6kg of TNT

Problems raised by this kind of applicationsProblems raised by this kind of applications

Distortions and deletions of the structure during

exploding solicitation ���� Impossibility to manage a fluid

mesh coincident to the structure mesh.

Interest of the Fluid Structure Interaction (FSI) Interest of the Fluid Structure Interaction (FSI)

interface TYPE 18 :interface TYPE 18 :

• Lagrangian structure and Eulerian fluid meshes are not linked

Inherent difficulties due to the interface TYPE 18Inherent difficulties due to the interface TYPE 18

• Determination of the good stiffness of interface

• Required finely of fluid mesh to get a good precision in the FSI

Numerical Simulation of a mine Numerical Simulation of a mine

explosion under a civil vehicleexplosion under a civil vehicle

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Eulerian Mesh

Lagrangian mesh

Fluid / structure interfaceFluid / structure interface

Previous studies have showed that the relation below can be used to estimate

the interface stiffness.

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This equation permits:

– To be freed from an analysis of sensitivity at each new study

– To have a good evaluation of every studied cases

Gap

ScK

⋅⋅=

2ρ

ρ : Fluid density

C : wave celerity

S : Shell Section of the structure parts

Gap : interface gap

Air is modeled as a perfect gas by Mie Gruneisen hydrodynamic law,

where pressure is given by the equation of state :

With

γγγγ =1.4 :

C0 = 0

C1 = C2 = C3 = 0

C4 = C5 = (γγγγ – 1) = 0.4

E0 = 0.25

Fluids Meshing and ModelingFluids Meshing and Modeling

Explosive part and AIR volume around vehicle are meshed with Explosive part and AIR volume around vehicle are meshed with

BRICK elements. BRICK elements.

Fluid Parts are set up with Arbitrary Lagrange Euler (ALE) formuFluid Parts are set up with Arbitrary Lagrange Euler (ALE) formulationlation

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( )ECCCCCCP µµµµ 54321032 +++++=

10

−=ρ

ρµ

Mine ModelingMine Modeling

� The mine shape has been defined as described in the “AEP-55 NATO/PfP UNCLASSIFIED /

Procedures for evaluating the protection level of logistic and Procedures for evaluating the protection level of logistic and light armored vehicleslight armored vehicles”

� The mine is modeled by a cylinder with an equivalent

mass of TNT (6 Kg).

� The TNT behavior is managed by Jones Wilkins Lee material Law [JWL] in which the Equation Of State of Pressure is calculated by the following equation:

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H= 80 mmΦ Φ Φ Φ = 250 mm

TNTTNT

Air blast Parameters versus distance for Air blast Parameters versus distance for

TNT Hemispherical Surface BurstTNT Hemispherical Surface Burst

Pressure wave and celerity of the blast are Pressure wave and celerity of the blast are

correlated with TM 5 correlated with TM 5 –– 1300 1300 ““Structures to Structures to

resist the effects of accidental explosionsresist the effects of accidental explosions””

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Blast wave shape in free field Blast wave shape in free field

Calculation of the Reduce distance Calculation of the Reduce distance

R (m.kgR (m.kg--1/3)1/3)

Mine ModelingMine Modeling

Blast simulation of the mine in semi free fieldBlast simulation of the mine in semi free field

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Rigid groundRigid ground

MineMine

DummyDummy

An Hybrid III dummy is set on seat to simulate driver behavior aAn Hybrid III dummy is set on seat to simulate driver behavior and to nd to

estimate body damages.estimate body damages.

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The 50th percentile ATD represents the average male of populatioThe 50th percentile ATD represents the average male of population between 1970s n between 1970s

and 1980s with the following figures: and 1980s with the following figures:

�� length (standing position): 1.72 m length (standing position): 1.72 m

�� weight: 78 kg weight: 78 kg

�� erect sitting height: 0.88 m erect sitting height: 0.88 m

Mine explosion SimulationMine explosion Simulation

Damages caused by the mine explosion under front wheel Damages caused by the mine explosion under front wheel

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[6 Kg of TNT]

Mine explosion SimulationMine explosion Simulation

Blast effect on the front part of the car structure. Blast effect on the front part of the car structure.

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Mine explosion SimulationMine explosion Simulation

Blast effect on the front part of the car structure. Blast effect on the front part of the car structure.

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Mine explosion SimulationMine explosion Simulation

Damages caused by the mine explosion: a hole is created in the uDamages caused by the mine explosion: a hole is created in the under nder

structure parts by the blast structure parts by the blast �������� The blast penetrates in the vehicle The blast penetrates in the vehicle

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In the firsts millisecond of the explosion, Legs are broken

Important structural damages are noticed on the lower parts of the vehicle

Mine explosion SimulationMine explosion Simulation

To estimate damages on driver body, the AEPTo estimate damages on driver body, the AEP--55 NATO can be used.55 NATO can be used.

For examples, Pelvis acceleration or contact forces between feetFor examples, Pelvis acceleration or contact forces between feet and and

under structure can be plotted.under structure can be plotted.

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average vertical acceleration on driver [filtered at 500 Hz]

-30

-20

-10

0

10

20

30

40

50

60

0 5 10 15 20 25

Time in ms

Ac

ce

lera

tio

n in

g

Pelvis accelerationPelvis acceleration

Lower Tibia Load CellLower Tibia Load Cell

In this case tolerance value of 5.4 In this case tolerance value of 5.4 kNkN is is

reached at 3 ms.reached at 3 ms.

Mine explosion SimulationMine explosion Simulation

Pressure measured at the head level of dummyPressure measured at the head level of dummy

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Pressure time history in vehicle

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Time in ms

Pre

ss

ure

in

MP

a

Sound level above 140 dB

Pressure level MPa

Protection designProtection design

In case of important damages, simulation can be used to design In case of important damages, simulation can be used to design and and

test shield to reinforce vehicle structure test shield to reinforce vehicle structure �������� Armor plates can be added Armor plates can be added

under vehicle to avoid blast penetration in car.under vehicle to avoid blast penetration in car.

Here, a plane steel armor plate is tested :Here, a plane steel armor plate is tested :

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A quarter of FE Model is used for simulation

Rigid vehicle

Steel Armor plate

Cylindrical mine (6 Kg of TNT)

Protection designProtection design

Pressure level on steel armor plate. Pressure level on steel armor plate.

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armor plate

Rigid part on top

Air

Mine : 6 Kg of TNT

Blast absorber to limit accelerationBlast absorber to limit acceleration

In case of important acceleration level on passenger, energy In case of important acceleration level on passenger, energy

absorbers can be mounted under seat to limit acceleration peak.absorbers can be mounted under seat to limit acceleration peak.

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seat energy absorber

ConclusionsConclusions

� This methodology is adapted to study that kind of phenomena or This methodology is adapted to study that kind of phenomena or

cases where blast is generated by an explosion far from vehicle.cases where blast is generated by an explosion far from vehicle.

��Sensitivity studies can be easily performed to improve vehicle Sensitivity studies can be easily performed to improve vehicle

design or to prepare a tests campaigndesign or to prepare a tests campaign

�� This methodology can be applied to other explosion cases : This methodology can be applied to other explosion cases :

-- Explosion of hydrogen tank to evaluated damages on persons Explosion of hydrogen tank to evaluated damages on persons

around detonation pointaround detonation point

-- Luggage explosion in plane or trainLuggage explosion in plane or train

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