SAFIR2010 Interim Seminar Impact Tests (IMPACT) and Structures under Soft Impact (SUSI) Kim Calonius, Ilkka Hakola, Simo Hostikka, Juha Kuutti, Auli Lastunen, Hannu Martikainen, Arja Saarenheimo, Ari Silde VTT Markku Tuomala TUT Ari Kankkunen HUT
Projects IMPACT and SUSI Experimental testing of deformable and hard missile impacts against concrete structures is carried out in the IMPACT project Numerical models and methods for impact analyses are developed and verified based on the tests in the SUSI project
IMPACT, General Overview Impact test results are needed in developing and verifying analytical and numerical methods for designing protective barrier structures. The IMPACT test facility has been built to investigate impacts of deformable and hard missiles on reinforced concrete target structures. The facility is designed for medium scale tests with a target width of 2 m, a missile mass of about 50 kg and impact velocity in the range from 60-180 m/s.
IMPACT, General Overview, Apparatus Debris shedding m = 0-100 kg (missile) + 50 kg (piston) v = 60 m/s - 200 m/s Pressure missile + piston accumulator p = 5-25 bar 0.5m m v Target wall (2 by 2 m) Back pipes Kick back frame L 2 = 13.5 m Acceleration tube L 1 = 12 m Piston catcher
IMPACT, General Overview, Phases of Project The IMPACT testing apparatus has been designed and built in 2003 and 2004 The first preliminary tests were conducted on 4.11.2004 At the beginning the target was a hanging wall made of steel and concrete and the missile was shot from inside the acceleration tube Next the target was supported on bedrock with four supporting pipes and anchoring bolts In 2006 the missile was installed and shot on top of the acceleration tube In 2007 the new supporting frame and force measuring plate were constructed for shooting deformable and hard missiles on reinforced concrete and pre-stressed concrete structures with bending and shear reinforcement
IMPACT, General Overview, Apparatus Impact apparatus
IMPACT, General Overview, Force plate Second version of force plate
IMPACT, General Overview, Measurements The sensors used in IMPACT tests: 1. Transducers to measure wall deflections 2. Strain gauges glued on the reinforcement to measure strains 3. Strain gauges on the surface of the concrete wall to measure strains 4. Force transducers behind the force plate 5. Strain gauges in the support beams to measure impact forces 6. Strain gauges glued on back pipes to measure support reactions 7. High speed cameras to obtain video of impact incident 8. Laser sensors to measure the speed of the missile 9. Accelerometer at the back of the missile to measure the deceleration of missile 10. Pressure sensor to measure air pressure near the target during impact The data from sensors is gathered using a sampling frequency of 100 khz. The measuring system includes anti-aliasing filtering capability and simultaneous measurements
IMPACT, General Overview, Measurements Deflection transducers
IMPACT, General Overview, Missiles The missiles used in tests have been made of steel pipe, aluminium pipe or thin-walled steel ventilation tube The missile can be filled with water or light concrete The first tests were made using steel missiles and shot from inside the acceleration tube 3D missiles composed of Al-pipe and wing necessitate shooting on top of the acceleration tube. Other missile types, Al-pipe and steel pipe missiles, are shot similarly
IMPACT, General Overview, Missiles Spirally seamed ventilation tube, shot from inside of the acceleration tube
IMPACT, General Overview, Missiles Aluminium pipe missile placed on rails on top of the acceleration tube
IMPACT, General Overview, Missiles 3D-missile with a wing on top of the acceleration tube
IMPACT, General Overview, Concrete walls The first campaign was conducted using reinforced concrete slabs with dimensions 2 by 2.2 m and thickness of 150 mm with bending reinforcement and shear reinforcement in some cases. Target in series 1
IMPACT, General Overview, Concrete walls The second concrete wall test campaign was made with prestressed concrete walls with a thickness of 250 mm. Pre-stressing was carried out using post tensioning bars (Dywidag bars without injection). In some tests shear reinforcement with T-bars was introduced. Target in series 2
SUSI, Numerical analyses overview Post-analyses of the two presented tests (642: dry and 644: wet): FEM analysis using Abaqus/Explicit FEM analysis using LS-Dyna (Dry test 642) Simplified two degree of freedom model Load functions used in the models are calculated using Riera s method: F( t) V ( t) P ( x) ( x) V ( t) c M P ( x) c uncrushed 2 F(t) is impact force V(t) is missile velocity M uncrushed is uncrushed section mass (x) is missile mass distribution P c (x) is missile crushing force
Aluminium missiles in the studied tests Dry missile m=51.5 kg V=109 m/s Wet missile m=50.9 kg (inc. 28 kg water) V=105 m/s
Displacement sensor locations in dry and wet tests Dmax 2000 D1-WET D1-DRY 2100 Wall thickness 150 mm, reinforcement ratio 0.67%
Abaqus/Explicit finite element models 1) Wall shell element model 2) Wall and supporting frame shell and beam model Loading area Reinforcement modelled with rebar layers
Solid element model (LS-Dyna) Wall modelled with 130122 solid elements Rebars modelled with beam elements Loading area
Material properties for concrete Stress-strain curve for concrete 10-0,01-0,008-0,006-0,004-0,002 0 0,002 0,004 0,006 0-10 Stress (MPa) -20-30 -40-50 -60 Strain (mm/mm) Material models used are concrete damaged plasticity model in Abaqus/Explicit and Winfrith model in LS-Dyna
Material properties for reinforcement steel 1000 900 800 Smeared stress to take into account the surrounding concrete Stress (MPa) 700 600 500 400 300 A500HW MAT_1_6 200 100 0 0 0,02 0,04 0,06 0,08 0,1 Strain (mm/mm) Experimentally measured stress-strain curve
Simplified 2 degree of freedom model for wall deformation Separate degrees of freedom for bending and shear deformations Modelled with two mass-spring elements Shear cone
Two degree of freedom model for shear deformable plate Spring behavior Shear behavior Bending behavior
Calculated and measured wall displacements of Test 642 (Locations D1 and Dmax) 0.08 0.07 Test 642, wall deflection measured D1 Abaqus shell D1 Deflection [m] 0.06 0.05 0.04 0.03 0.02 Abaqus shell Dmax Abaqus shell+beam D1 Abaqus shell+beam Dmax LS-Dyna D1 0.01 0-0.01 0 0.02 0.04 0.06 0.08 0.1 0.12 Time [s] LS-Dyna Dmax TDOF Dmax
Calculated and measured wall displacements of Test 644 (Locations D1 and Dmax) Test 644, wall deflection Deflection [m] 0.1 0.09 0.08 0.07 0.06 0.05 0.04 measured D1 Abaqus shell Dmax TDOF Dmax Abaqus shell D1 0.03 0.02 0.01 0 0 0.02 0.04 0.06 0.08 0.1 0.12 Time [s] Abaqus shell+beam Dmax Abaqus shell+beam D1
3.E+06 Calculated and measured impact forces of Tests 642 and 644 Test 642 and 644 forces load 642 2.E+06 2.E+06 1.E+06 Load functions calculated using Riera s method back pipes 642 Abaqus shell+beam 642 force [N] 5.E+05 load 644 0.E+00 0 0.01 0.02 0.03 0.04 0.05 0.06 back pipes 644-5.E+05-1.E+06 time [s] Abaqus shell+beam 644
SUSI, Studies of liquid spreading in impact 20 wet IMPACT tests have been carried out and analyzed in the test campaign Liquid spreading and its effect on impact loads have been studied using different missiles and targets
STUDY OF LIQUID DISPERSAL OBJECTIVES Liquid dispersal is studied in order to: Support IMPACT-tests with respect to liquid-filled missiles. Measure, analyze and document the liquid dispersal during the IMPACT-tests. Choose and validate a numerical simulation tool for the simulation on liquid dispersal and, ultimately, fires resulting from aircraft impact.
STUDY OF LIQUID DISPERSAL STATUS 20 wet IMPACT tests have been analyzed: 16 tests with cylindrical missiles 4 tests with 3D missiles Water mass 8... 68 kg Impact velocity 70... 177 m/s Impact against either steel plate or concrete wall Numerical simulations have been performed using Fire Dynamics Simulator software.
STUDY OF LIQUID DISPERSAL MAIN RESULTS FROM THE CYLINDRICAL MISSILES Liquid dispersal takes place mainly in the direction of wall tangent. Spreading angle about 0 10 from wall tangent. Direction is symmetrical. Initial speed of liquid is even 2.5 times the impact speed. The stable size of the droplets is small, and they slow down soon after the impact. Measurement from oil-coated plates on the floor shows arithmetic mean diameter of 200...300 µm.
STUDY OF LIQUID DISPERSAL MAIN RESULTS FROM THE 3D MISSILES Very asymmetric spreading. Effects of the missile geometry and structure are strong. Due to the wings, the vertical directions are more pronounced than horizontal. Spreading speed difficult to measure using the current methods that are based on cameras. Droplet sizes difficult to measure.
STUDY OF LIQUID DISPERSAL EXAMPLE OF RESULTS Droplet size distribution 0,3 Number fraction [-] 0,25 0,2 0,15 0,1 0,05 105 m/s, 3.5 m 105 m/s, 5.5 m 165 m/s, 3.5 m 165 m/s, 5.5 m 125 m/s, 3.7 m 125 m/s, 4.1 m 125 m/s, 5.1 m 125 m/s, 5.3 m 0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Size [mm]
STUDY OF LIQUID DISPERSAL NUMERICAL SIMULATIONS Fire Dynamics Simulator (FDS) Most widely used fire simulation software in the world. Based on CFD using Large Eddy Simulation (LES). Focus on the two-phase flow simulation Using Eulerian-Lagrangian method of droplet tracking For example: droplet trajectory is solved from ODE
STUDY OF LIQUID DISPERSAL VALIDATION OF NUMERICAL SIMULATIONS Velocity ratio V/Vi [-] 1 0.8 0.6 0.4 0.2 0 V impact = 125 m/s, V i,w ater = 250 m/s, m w ater = 37 kg Exp. 0 (up) Exp. 45 Exp. 90 Exp. 135 FDS5 FL=1000, drag red. FDS5 dm=300 FL=1000 0 0.5 1 1.5 2 Distance from missile [m] Validations on two scales Simulations of industrial nozzles Simulations of IMPACT tests Challenges High speed friction correlations numerical accuracy secondary breakups Drop-drop interactions Boundary conditions Direction Speed Size distribution
STUDY OF LIQUID DISPERSAL FEASIBILITY STUDY OF NUMERICAL SIMULATIONS Impact speed 125 m/s 37 l (25 kg) heptane C 7 H 16 Liquid speed 250 m/s Release time 10 s Release angle 0...15 deg Mean diameter 300 m 120 100 50 fluid cells Simulation time 15 s. Computation time 9.2 CPU h
IMPACT, Conclusions of experimental tests Impact facility is developed from year 2003, and has reached now mature status Capability of testing with various missiles and targets Repeatable tests can be carried out Most important measurements are the impact forces and target wall deformations First phase of the international test campaign is completed
SUSI, Conclusions of numerical simulations Simplified analytical methods and more detailed numerical models give consistent results and are in agreement with test results Calculation models predict displacements and rebar strains well The predicted frequency of elastic vibration after the first peak deflection is higher that that found in experiments The whole test setup needs to be modelled for more accurate predictions due to dynamic interactions of target and support structure Shell models are capable for predicting deflection due to soft missile impacts Material parameters for nonlinear concrete models need to be determined carefully 3D elements are needed for modelling local behaviour due to hard missile impact
SUSI, STUDY OF LIQUID DISPERSAL SUMMARY IMPACT-tests have provided useful and new information on the spreading of liquid from a high-speed impact. Numerical simulations need experimental information for validation specification of boundary conditions. The spray spreading simulations with FDS-program have been validated.
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