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Progress Report No. 3 Final

Progress Report No. 3 Final. Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest Research Institute Date: December 13, 2004 Submitted To: Dr. Kennerly H. Digges, MVFRI Mr. R. Rhoads Stephenson Prepared By: Dr. Nabih E. Bedewi. OUTLINE.

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Progress Report No. 3 Final

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  1. Progress Report No. 3 Final Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest Research InstituteDate: December 13, 2004Submitted To: Dr. Kennerly H. Digges, MVFRI Mr. R. Rhoads StephensonPrepared By: Dr. Nabih E. Bedewi

  2. OUTLINE • Questions to be Answered by Study • Review of SwRI Tests • Types of Fuel Tanks Tested • Drop Tests • Material Coupon Testing • Nonlinear Finite Element Simulations • Model Development • Assumptions

  3. OUTLINE (cont.) • Simulation of Plymouth Grand Voyager Tank • Model Development • Simulation Results and Comparison to SwRI Test • Summary of Simulation Results • Comparison of Generic Shape Tanks • Rectangular Tank Simulation Results and Comparison to SwRI Test • Rectangular Tank with a Neck • Small Rectangular Tank • Summary of Simulation Results

  4. OUTLINE (cont.) • Simulation of Different Coupon Tests • SwRI Simple Tensile Test • Hydrostatic Pressure on a Curved Coupon • Combined Loading on a Curved Coupon • Simulation of Plymouth Tank with Gasoline Properties • Drop Test Simulation • Side Impact Simulation • Conclusions and Proposed Future Research • Further Simulation Studies • Proposed Testing Program

  5. Questions to be Answered • Is there an aging effect on the structural integrity of the plastic fuel tanks? • If so, do the geometry of the tank, type of plastic, and pinch off strength have an influence on the structural integrity? • Are the tensile tests that were conducted by SwRI adequate to replicate the loads seen in the drop tests to assess the strength of the pinch off? • What additional tests, if any, should be carried out to complete the evaluation and make final conclusions?

  6. Resources Used SwRI final report was reviewed in detail Emphasis was placed on test conditions, photographs of undamaged and damaged tanks, description of results and conclusions Biokinetics reports I and II were also reviewed to understand how different test regulations and standards address aging and fuel effects The following SAE papers were also obtained and reviewed in detail:

  7. Papers Reviewed • Crash-Resistant Fuel Tanks for Helicopters and General Aviation Aircraft, SAE740358, 1974 • Development of Plastic Fuel Tanks Using Modified Multi-Layer Blow Molding, SAE 900636, 1990 • Development of High Capacity Plastic Fuel Tanks for Trucks, SAE921513, 1992 • Comparative Life Cycle Assessment of Plastic and Steel Vehicle Fuel Tanks, SAE982224, 1998

  8. Papers Reviewed • Simulation Studies of Sloshing in a Fuel Tank, SAE2002-01-0574, 2002 • Structural and Material Features that Influence Emissions from Thermoplastic Multilayer Fuel Tanks, SAE2003-01-1121, 2003 • Low Permeation Technologies for Plastic Fuel Tanks, SAE2003-01-0790, 2003

  9. Review of SwRI Tests The following information is extracted directly from the SwRI test report

  10. Types of Fuel Tanks RECTANGULAR Jeep Grand Cherokee Typical of some SUV tanks mounted behind the rear axle * The Saturn tank tested is also rectangular but smaller and with thinner profile

  11. Types of Fuel Tanks RECTANGULAR WITH A NECK Plymouth Grand Voyager Typical of tanks with a narrow shape mounted inside the frame rail and in front of the rear axle or rear suspension

  12. Drop Test Accordance with U.S. DOT 49 CFR 393.67, Section E “Drop Test”. The Section E “Drop Test” of the referenced standard states that the fuel tanks shall be filled with a quantity of water having a weight equal to the weight of the maximum fuel load of the tank. The fuel tank is filled then dropped from a 30 ft elevation to assess the durability of the fuel tanks and measure the leak rate. After filling the fuel tank with a quantity of water having a weight equal to the weight of the maximum fuel load and selecting the vulnerable point of impact, the fuel tank was then positioned and strapped to the drop apparatus before being hoisted.

  13. Drop Test DROP TEST SETUP SwRI’s Department of Fire Technology’s Test Facility, located in San Antonio, Texas

  14. Drop Test RECTANGULAR TANK PRE AND POST IMPACT

  15. Drop Test RECTANGULAR TANK WITH A NECK PRE-POST IMPACT Leakage of Conditioned Plymouth Plastic Fuel Tank After Severe Drop

  16. Material Testing TENSILE TEST Voyager Cherokee Thickest Region at Pinch-Off Location Typical Tensile Test Specimen Coupon ASTM D 638-00, “Standard Test Method for Tensile Properties of Plastics”

  17. Material Testing As these coupons were extracted from the fuel tanks, the pinch-off location in each was perpendicular to the long-axis of the specimen parent material. The overall length of the specimen coupons depended on the location of extraction and ranged from 6 in. to 9 in. in length. The thickness of the specimen coupons varied as well, ranging from 0.2 in. to 0.5 in. For all specimen coupons, the thickest region was at the pinch-off location. Typical Tensile Test Setup

  18. Material Testing Typical Axial Load Per Unit Width Versus Displacement Diagram

  19. Nonlinear Finite Element Simulations Model Development and Assumptions

  20. Model Development • Several finite element models were initially analyzed for different geometry tanks of both plastic and steel composition to understand the behavior and assess the importance of the fluid/structure interaction • Some of the tank models existed already in public domain vehicle models developed for NHTSA while others were developed specifically for this study, as outlined later

  21. Simulation Background Tank Models Analyzed Initially Chevy C-2500 Truck Toyota RAV 4 Ford Econoline Ford Taurus

  22. Effect of Water Simulation with no Water in the Tank (i.e. mass of water included but not the fluid-structure interaction) Deformation at impact point is accurate, but bulging of tank and stress buildup in non-impact points is not represented

  23. Modeling Water in the Tank A new method based on mesh-free elements (SPH) in LS-DYNA was used to model the fluid-structure interaction in the tank

  24. Modeling Water in the Tank Simulation with water effects Deformation at impact point is accurate as well as bulging of tank and stress buildup in non-impact points

  25. Modeling Water in the Tank Simulation with water effects Deformation at impact point is accurate as well as bulging of tank and stress buildup in non-impact points

  26. Model Development • This numerical model contains high-end simulation tools which are sophisticated and require specialized expertise to develop and use • Development of such a simulation model was challenging because there are no systematic tools available for creating and setting-up the coupling between the conventional finite element and the mesh-free (SPH) model, requiring extra attention and significant amounts of effort and time • Several initial simulations were conducted to improve and optimize the robustness, efficiency and accuracy of the model. Some of the parameters that were investigated included: particle density, smoothing length, viscosity coefficient, and material parameters • Preliminary simulations were performed to ensure that the fluid (water) is at equilibrium prior to impact, and the final state was used as the initial state for the drop test simulations

  27. Model Development • Initial simulation results using the material data extracted from the coupon tests performed by SwRI showed significantly more deformation compared with the drop test results. After a literature survey on High Density Poly-Ethylene fuel tank material properties a more accurate material data set was used which gave closer results to the drop tests • Since the pinch-off region played an important role in the behavior of the fuel tank, extra attention was given to model this area. To represent the exact cross-section and stiffness properties, five sets of beam elements were used around the tank. This technique is selected also to monitor the forces in this region • Tanks were filled with water up to 74% capacity of the total volume

  28. Modeling the Pinch-off To model the pinch-off regions, equivalent beam cross-sections were used with geometry properties extracted from the specimen pictures. Circular beams were modeled all around the tank with 11.684 mm and 13.208 mm radii. An average value of 0.4 in (10 mm) is used across the whole tank as the thickness value, where the thickness changes between 0.2 in and 0.5 in.

  29. Material Properties of the Model • Material model and properties used for Poly-Ethylene plastic • Piecewise Linear Plasticity Constitutive Model • Density: 0.95E-9 Tons/mm3 • Elastic Modulus: 1200 N/mm2 • Poisson’s Ratio: 0.3 • Yield Stress: 30 N/mm2 • Tangent Modulus: 12 N/mm2 • Cowper and Symonds strain rate effects with C=90 and P=4.5 • Material model and properties for water • Elastic Fluid (using SPH) • Density: 0.996E-9 Tons/mm3 • Poisson’s Ratio: 0.5 • Bulk Modulus: 2250 N/mm2

  30. Simulation of Plymouth Grand Voyager Tank Model Development and Comparison with SwRI Drop Test

  31. Extraction of Tank Geometry Digitized Voyager (Caravan) Tank

  32. Grand Voyager Tank FINITE ELEMENT MODEL OF THE TANK The total weight of the tank is 73 kg of which 56 kg is the water weight

  33. Grand Voyager Tank COUPLED FINITE ELEMENT AND MESHLESS MODEL Various views of front side

  34. Grand Voyager Tank COUPLED FINITE ELEMENT AND MESHLESS MODEL Various views of back side

  35. Grand Voyager Tank DETAILED PINCH-OFF REGION

  36. Grand Voyager Tank DETAILED PINCH-OFF REGION Force measurement direction Force measurement direction Three rows of beam elements parallel to pinch-off joint Two rows of beam elements perpendicular to pinch-off joint

  37. Grand Voyager Tank MODEL DETAILS

  38. Simulation of Grand Voyager Tank Drop Test ELEMENT PRESSURE

  39. Simulation of Grand Voyager Tank Drop Test DEFORMATION-SLOSHING

  40. Simulation of Grand Voyager Tank Drop Test DEFORMATION-SLOSHING

  41. Simulation of Grand Voyager Tank Drop Test IMPACT REACTION FORCE ON THE GROUND AT POINT OF IMPACT

  42. Simulation of Grand Voyager Tank Drop Test INTERNAL PRESSURE ON TANK WALL AT SELECTED ELEMENT

  43. The next series of slides show the results of the forces as measured by the five sets of beam elements; i.e. the forces observed at the pinch-off region during the impact

  44. Click mouse on image to repeat Notice red spot (high loads) at the neck area Beam Element Data of Grand Voyager Tank PINCH-OFF EVALUATION BEAM SET-I

  45. Beam Element Data of Grand Voyager Tank COMPARISON WITH SwRI DROP TEST: FAILURE OCCURRED IN HIGH LOAD NECK AREA AS PREDICTED BY THE MODEL

  46. Beam Element Data of Grand Voyager Tank Region with maximum force

  47. Beam Element Data of Grand Voyager Tank PINCH-OFF EVALUATION BEAM SET-II

  48. Beam Element Data of Grand Voyager Tank

  49. Beam Element Data of Grand Voyager Tank PINCH-OFF EVALUATION BEAM SET-III

  50. Beam Element Data of Grand Voyager Tank

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