Impact Loaded Structures

Impact Loaded Structures

Tuomo Kärnä & Arja Saarenheimo & Markku Tuomala

Copyright © VTT

VTT TECHNICAL RESEARCH CENTRE OF FINLAND

Impact Loaded Structures Impact Loaded Structures

Tuomo Kärnä (1), Arja Saarenheimo(1) & Markku Tuomala(3)

SAFIR Puoliväliseminaari 21.01.2005

v1 v2 v3

Numerical Studies

v

Experiments

(1) Technical Research Centre of Finland

(2) Tampere University of Technology

21.04.23 3Copyright © VTT


1. Objectives

• Adopt and verify numerical models to simulate an aircraft

impact against a nuclear power plant

• Make experiments to - measure impact forces

- study fracture mechanisms of a concrete wall

- study the shedding of depris

• Use the test data to verify the numerical methods adopted



2. Numerical studies of preliminary model tests

• axisymmetric Finite Element (FE) analyses • semiempirical and analytical methods

Geometry of a tube missile: d = 273 mm, t = 5 mm, L = 910 mm Material properties: Modulus of Elasticity 206 GPa, Poisson’s ratio 0.3

The effect of strain rate to the plastic flow:

is the equivalent plastic strain rate, is the effective yield stress and is the static yield stress, for structural steels D = 40 and p =5.

. ~

0

~.

01 ,

p

pl D

vL

d

M = 30 kg or 38 kg

v = 121 m/s



Assumed elasto-plastic stress-strain curve



Plastic deformations, m=32 kg

Plastic deformation



Axisymmetric crushing, wrinkle width

, where r is radius and h is wall thickness3

rhl

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0 0.001 0.002 0.003 0.004 0.005

Time (s)

Ra

dia

l dis

pla

ce

me

nt

(m)

Rad_in_41 kg

Rad_out_41kg

Rad_in_32kg

Rad_out_32kg

r = 134 mm, h = 5 mm => l = 35 mm

Measured r=24 mm



Axial displacement and velocity

-0.2

-0.18

-0.16

-0.14

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 0.001 0.002 0.003 0.004 0.005

Time (s)

Ax

ial d

isp

lac

em

en

t (m

)

Mass 41 kg

Mass 32 kg

Measured: L 17.5 cm

-20

0

20

40

60

80

100

120

0 0.001 0.002 0.003 0.004 0.005

Time (s)

Vel

oci

ty (

m/s

)

Mass 41kg

Mass 32 kg



Calculation of reaction forceRiera’s formula

2( ) ( ( )) ( ( ))( ( )) ,c mF t P x t m x t v t where Pc is the crushing load or buckling load of the missile body, m(x(t)) is the mass per unit length of missile (at time t in contact with the target) vm(x(t)) is the velocity if the undeformed (or uncrushed) part of the missile at time t.

Folding mechanism for steel pipe

2( ) ( ( )) ( ( ))( ( )) ,c mF t P x t m x t v t



Reaction force:FE analysis / Riera's formula

0

5

10

15

20

25

0 0.001 0.002 0.003 0.004

Time (s)

Fo

rce

(M

N)

FE_AXI M=41 kg FE_AXI M=32 kg

Riera M=30 kg sy=250 MPa



Predicted Reaction force during impactSimplified methods using different asumptions

M=30kg

0

0.5

1

1.5

2

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Time (s)

Re

ac

tio

n f

orc

e

(MN

)

Jones_pl Jones_vp Pc=sy*A Barr

1D_ipl 1D_hard Pc_J

Cylindrical missile, 30 kg

Yielding

Visoplastic approach Plastic analysis

Spring-mass models

Crushing load component



Predicted Velocity function during impact

M=30kg

-10

15

40

65

90

115

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Time (s)

Ve

loc

ity

(m

/s)

sy=250 MPa rate dep plastic Barr FE_AXI_32kg

Cylindrical missile, 30 kg



3. Apparatus for Experimental Simulations

Impact wall

Acceleration tube Missile+piston

m

v

Pressure accumulator p = 5 - 30 bar

L1 = 12 m L2 = 13.5 m

m = 0 kg -50 kg (Missile) + 35 kg (piston)v = 100 m/s - 250 m/s

1

23 4

Debris shedding

5

0.5 m



Pressure accumulator

Impact wall

Accelerationtube

Compliant support of counter reaction

Components of the Test ApparatusView at an underground space



Moving components of the facility

Piston moving inside the acceleration tube

Rail on the acceleration tube

Impact wall

Missile moving ouside the acceleration tube

Ris

to R

um

pu

ne

nT

IED

E 1

/20

05

, p

p.

8-9



Performance characteristics

Test 601

0

25

50

75

100

125

150

175

200

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured

Acceleration Free fly

Test 601

0

25

50

75

100

125

150

175

200

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured

Acceleration Free flyAcceleration Free fly

Test 603

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured


Test 603

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured


TEST 601

- Initial pressure 3.3 bar.

- Weigh of the piston 23 kg.

- No missile.

TEST 603

- Initial pressure 9.6 bar.

- Weigh of the piston 23 kg.

- No missile.

Comparisons between measured and predicted velocities:



Test 604

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured

Free flyAcceleration

Test 604

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured

Free flyAcceleration

Test 605

0

25

50

75

100

125

150

175

200

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured


Test 605

0

25

50

75

100

125

150

175

200

0 2 4 6 8 10 12 14 16 18

x (m)

v (m

/s)

Calculated

Measured

Acceleration Free flyAcceleration Free fly

TEST 604 - Initial pressure 17.5 bar. - Weigh of the piston 23 kg. - No missile.

TEST 605 - Initial pressure 8.4 bar. - Weigh of the piston 33.6 kg. - Missile 41 kg

Performance (Cont.)



Details / TEST 605

Performance (Cont.)

Missile ready to be launched

Missile after the impactTriggering the measurements



Summary of the performance characterisitics of the test apparatus

• Normal mode of operation - Missile, max 50 kg- Piston 35 kg- Inital pressures, max 25 bar- Impact velocity 100 - 200 m/s

• Enhanced mode of operation - Missile / piston, max 50 kg- Initial pressure, max 30 bar

- Impact velocity, max 250 m/s

Performance (Cont.)



4. Conclusions

• A FE code Abaqus Explicit has been adopted for impact simulations

• Simplified numerical methods are also used

• An experimental apparatus has been constructed and tested

• Preliminary results show similarities between the numerical

simulations and the tests

• The test programme will be continued in 2005 and further

numerical studies will be made using

- soft missiles

- reinforced concrete walls

Impact Loaded Structures

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