Impact Loaded Structures

1. Impact Loaded Structures Tuomo Kärnä & Arja Saarenheimo & Markku Tuomala

2. Numerical Studies Experiments v1 v2 v3 v SAFIR Puoliväliseminaari 21.01.2005 Impact Loaded Structures Tuomo Kärnä (1), Arja Saarenheimo(1) & Markku Tuomala(3) (1) Technical Research Centre of Finland (2) Tampere University of Technology

3. 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

4. d v L 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: M = 30 kg or 38 kg v = 121 m/s 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.

5. Assumed elasto-plastic stress-strain curve

6. Plastic deformations, m=32 kg Plastic deformation

7. Axisymmetric crushing, wrinkle width r = 134 mm, h = 5 mm => l = 35 mm Measured Dr=24 mm

8. Axial displacement and velocity Measured: DL 17.5 cm

9. Calculation of reaction forceRiera’s formula 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

10. Reaction force:FE analysis / Riera's formula

11. Cylindrical missile, 30 kg Spring-mass models Yielding Visoplastic approach Plastic analysis Crushing load component Predicted Reaction force during impactSimplified methods using different asumptions

12. Predicted Velocity function during impact Cylindrical missile, 30 kg

13. Debris shedding 5 m = 0 kg -50 kg (Missile) + 35 kg (piston) v = 100 m/s - 250 m/s Impact wall Pressure accumulator p = 5 - 30 bar Acceleration tube Missile+piston v 1 m 0.5 m 4 3 2 L2 = 13.5 m L1 = 12 m 3. Apparatus for Experimental Simulations

14. Impact wall Pressure accumulator Accelerationtube Compliant support of counter reaction Components of the Test ApparatusView at an underground space

15. Impact wall Rail on the acceleration tube Moving components of the facility Risto Rumpunen TIEDE 1/2005, pp. 8-9 Missile moving ouside the acceleration tube Piston moving inside the acceleration tube

16. Performance characteristics Comparisons between measured and predicted velocities: 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.

17. Performance (Cont.) 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

18. Performance (Cont.) Details / TEST 605 Missile after the impact Triggering the measurements Missile ready to be launched

19. Performance (Cont.) 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

20. 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