Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest...

Project Title:Project Title: Evaluation of Fuel Tank Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests Drop Tests and ASTM Tensile Tests conducted by Southwest Research conducted by Southwest Research InstituteInstitute

Date:Date: December 13, 2004 December 13, 2004

Submitted To:Submitted To: Dr. Kennerly H. Dr. Kennerly H. Digges, MVFRIDigges, MVFRI

Mr. R. Rhoads Mr. R. Rhoads StephensonStephenson

Prepared By:Prepared By: Dr. Nabih E. Bedewi Dr. Nabih E. Bedewi

Progress Report Progress Report No. 3No. 3FinalFinal

OUTLINEOUTLINE Questions to be Answered by StudyQuestions to be Answered by Study

Review of SwRI TestsReview of SwRI Testso Types of Fuel Tanks TestedTypes of Fuel Tanks Testedo Drop TestsDrop Testso Material Coupon TestingMaterial Coupon Testing

Nonlinear Finite Element SimulationsNonlinear Finite Element Simulationso Model DevelopmentModel Developmento Assumptions Assumptions

OUTLINE (cont.)OUTLINE (cont.) Simulation of Plymouth Grand Voyager TankSimulation of Plymouth Grand Voyager Tank

o Model DevelopmentModel Developmento Simulation Results and Comparison to SwRI TestSimulation Results and Comparison to SwRI Testo Summary of Simulation ResultsSummary of Simulation Results

Comparison of Generic Shape TanksComparison of Generic Shape Tankso Rectangular Tank Simulation Results and Rectangular Tank Simulation Results and

Comparison to SwRI TestComparison to SwRI Testo Rectangular Tank with a NeckRectangular Tank with a Necko Small Rectangular TankSmall Rectangular Tanko Summary of Simulation ResultsSummary of Simulation Results

OUTLINE (cont.)OUTLINE (cont.) Simulation of Different Coupon TestsSimulation of Different Coupon Tests

o SwRI Simple Tensile TestSwRI Simple Tensile Testo Hydrostatic Pressure on a Curved CouponHydrostatic Pressure on a Curved Coupono Combined Loading on a Curved CouponCombined Loading on a Curved Coupon

Simulation of Plymouth Tank with Gasoline Simulation of Plymouth Tank with Gasoline PropertiesPropertieso Drop Test SimulationDrop Test Simulationo Side Impact SimulationSide Impact Simulation

Conclusions and Proposed Future ResearchConclusions and Proposed Future Researcho Further Simulation StudiesFurther Simulation Studieso Proposed Testing ProgramProposed Testing Program

Questions to be Questions to be Answered Answered

Is there an aging effect on the structural Is there an aging effect on the structural integrity of the plastic fuel tanks?integrity of the plastic fuel tanks?

If so, do the geometry of the tank, type of If so, do the geometry of the tank, type of plastic, and pinch off strength have an plastic, and pinch off strength have an influence on the structural integrity?influence on the structural integrity?

Are the tensile tests that were conducted by Are the tensile tests that were conducted by SwRI adequate to replicate the loads seen SwRI adequate to replicate the loads seen in the drop tests to assess the strength of in the drop tests to assess the strength of the pinch off?the pinch off?

What additional tests, if any, should be What additional tests, if any, should be carried out to complete the evaluation and carried out to complete the evaluation and make final conclusions?make final conclusions?

Resources UsedResources Used

SwRI final report was reviewed in detailSwRI final report was reviewed in detail

Emphasis was placed on test conditions, Emphasis was placed on test conditions, photographs of undamaged and damaged photographs of undamaged and damaged tanks, description of results and conclusionstanks, description of results and conclusions

Biokinetics reports I and II were also Biokinetics reports I and II were also reviewed to understand how different test reviewed to understand how different test regulations and standards address aging and regulations and standards address aging and fuel effects fuel effects

The following SAE papers were also obtained The following SAE papers were also obtained and reviewed in detail:and reviewed in detail:

Papers ReviewedPapers Reviewed Crash-Resistant Fuel Tanks for Crash-Resistant Fuel Tanks for

Helicopters and General Aviation Helicopters and General Aviation Aircraft, SAE740358, 1974Aircraft, SAE740358, 1974

Development of Plastic Fuel Tanks Using Development of Plastic Fuel Tanks Using Modified Multi-Layer Blow Molding, SAE Modified Multi-Layer Blow Molding, SAE 900636, 1990900636, 1990

Development of High Capacity Plastic Development of High Capacity Plastic Fuel Tanks for Trucks, SAE921513, 1992Fuel Tanks for Trucks, SAE921513, 1992

Comparative Life Cycle Assessment of Comparative Life Cycle Assessment of Plastic and Steel Vehicle Fuel Tanks, Plastic and Steel Vehicle Fuel Tanks, SAE982224, 1998SAE982224, 1998

Simulation Studies of Sloshing in a Simulation Studies of Sloshing in a Fuel Tank, SAE2002-01-0574, 2002Fuel Tank, SAE2002-01-0574, 2002

Structural and Material Features Structural and Material Features that Influence Emissions from that Influence Emissions from Thermoplastic Multilayer Fuel Thermoplastic Multilayer Fuel Tanks, SAE2003-01-1121, 2003Tanks, SAE2003-01-1121, 2003

Low Permeation Technologies for Low Permeation Technologies for Plastic Fuel Tanks, SAE2003-01-Plastic Fuel Tanks, SAE2003-01-0790, 20030790, 2003

Papers ReviewedPapers Reviewed

Review of SwRI TestsReview of SwRI TestsThe following information is extracted directly from The following information is extracted directly from

the SwRI test reportthe SwRI test report

Jeep Grand CherokeeTypical of some SUV tanks mounted behind the rear axle

Types of Fuel TanksTypes of Fuel TanksRECTANGULAR

* The Saturn tank tested is also rectangular but smaller and with thinner profile

Plymouth Grand VoyagerTypical of tanks with a narrow shape mounted inside the frame

rail and in front of the rear axle or rear suspension

RECTANGULAR WITH A NECK

Types of Fuel TanksTypes of Fuel Tanks

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.

Drop TestDrop Test

DROP TEST SETUP

SwRI’s Department of Fire Technology’s Test Facility, located in

San Antonio, Texas

Drop TestDrop Test

Drop TestDrop TestRECTANGULAR TANK

PRE AND POST IMPACT

Leakage of Conditioned Plymouth Plastic Fuel Tank After Severe Drop

RECTANGULAR TANK WITH A NECKPRE-POST IMPACT

Drop TestDrop Test

TENSILE TEST

ASTM D 638-00, “Standard Test Method for Tensile Properties of Plastics”

Typical Tensile TestSpecimen Coupon

Thickest Region at Pinch-OffLocation

Material TestingMaterial Testing

Voyager

Cherokee

Typical Tensile Test Setup

As these coupons were extracted from the fuel tanks, the pinch-off location in each wasperpendicular 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 Axial Load Per Unit Width Versus Displacement Diagram


Nonlinear Finite Element Nonlinear Finite Element SimulationsSimulations

Model Development and AssumptionsModel Development and Assumptions

Model DevelopmentModel Development

Several finite element models were initially Several finite element models were initially analyzed for different geometry tanks of analyzed for different geometry tanks of both plastic and steel composition to both plastic and steel composition to understand the behavior and assess the understand the behavior and assess the importance of the fluid/structure interactionimportance of the fluid/structure interaction

Some of the tank models existed already in Some of the tank models existed already in public domain vehicle models developed for public domain vehicle models developed for NHTSA while others were developed NHTSA while others were developed specifically for this study, as outlined laterspecifically for this study, as outlined later

Simulation BackgroundSimulation BackgroundTank Models Analyzed Tank Models Analyzed InitiallyInitially

Chevy C-2500 Truck Toyota RAV 4

Ford Econoline Ford Taurus

Effect of WaterEffect of Water

Simulation with no Water in the Tank (i.e. mass Simulation with no Water in the Tank (i.e. mass of water included but not the fluid-structure of water included but not the fluid-structure interaction)interaction)

Deformation at impact point is accurate, but bulging of tank Deformation at impact point is accurate, but bulging of tank and stress buildup in non-impact points is not representedand stress buildup in non-impact points is not represented

Modeling Water in the Modeling Water in the TankTank

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

Modeling Water in the Modeling Water in the TankTank

Simulation with water effectsSimulation with water effects

Deformation at impact point is accurate as well as Deformation at impact point is accurate as well as bulging of tank and stress buildup in non-impact pointsbulging of tank and stress buildup in non-impact points

Model DevelopmentModel Development This numerical model contains high-end simulation tools which This numerical model contains high-end simulation tools which

are sophisticated and require specialized expertise to develop are sophisticated and require specialized expertise to develop and useand use

Development of such a simulation model was challenging because Development of such a simulation model was challenging because there are no systematic tools available for creating and setting-up there are no systematic tools available for creating and setting-up the coupling between the conventional finite element and the the coupling between the conventional finite element and the mesh-free (SPH) model, requiring extra attention and significant mesh-free (SPH) model, requiring extra attention and significant amounts of effort and timeamounts of effort and time

Several initial simulations were conducted to improve and Several initial simulations were conducted to improve and optimize the robustness, efficiency and accuracy of the model. optimize the robustness, efficiency and accuracy of the model. Some of the parameters that were investigated included: particle Some of the parameters that were investigated included: particle density, smoothing length, viscosity coefficient, and material density, smoothing length, viscosity coefficient, and material parametersparameters

Preliminary simulations were performed to ensure that the fluid Preliminary simulations were performed to ensure that the fluid (water) is at equilibrium prior to impact, and the final state was (water) is at equilibrium prior to impact, and the final state was used as the initial state for the drop test simulationsused as the initial state for the drop test simulations

Model DevelopmentModel Development Initial simulation results using the material data extracted Initial simulation results using the material data extracted

from the coupon tests performed by SwRI showed from the coupon tests performed by SwRI showed significantly more deformation compared with the drop significantly more deformation compared with the drop test results. After a literature survey on High Density Poly-test results. After a literature survey on High Density Poly-Ethylene fuel tank material properties a more accurate Ethylene fuel tank material properties a more accurate material data set was used which gave closer results to the material data set was used which gave closer results to the drop testsdrop tests

Since the pinch-off region played an important role in the Since the pinch-off region played an important role in the behavior of the fuel tank, extra attention was given to behavior of the fuel tank, extra attention was given to model this area. To represent the exact cross-section and model this area. To represent the exact cross-section and stiffness properties, five sets of beam elements were used stiffness properties, five sets of beam elements were used around the tank. This technique is selected also to monitor around the tank. This technique is selected also to monitor the forces in this regionthe forces in this region

Tanks were filled with water up to 74% capacity of the total volume

Modeling the Pinch-offModeling 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.

Material model and properties used for Poly-Ethylene plastic

o Piecewise Linear Plasticity Constitutive Modelo Density: 0.95E-9 Tons/mm3

o Elastic Modulus: 1200 N/mm2

o Poisson’s Ratio: 0.3o Yield Stress: 30 N/mm2

o Tangent Modulus: 12 N/mm2

o Cowper and Symonds strain rate effects with C=90 and P=4.5

Material model and properties for water

o Elastic Fluid (using SPH)o Density: 0.996E-9 Tons/mm3

o Poisson’s Ratio: 0.5o Bulk Modulus: 2250 N/mm2

Material Properties of Material Properties of the Modelthe Model

Simulation of Plymouth Simulation of Plymouth Grand Voyager TankGrand Voyager Tank

Model Development and Comparison with SwRI Model Development and Comparison with SwRI Drop TestDrop Test

Extraction of Tank Extraction of Tank GeometryGeometry

Digitized Voyager (Caravan) Digitized Voyager (Caravan) TankTank

Grand Voyager TankGrand Voyager TankFINITE ELEMENT MODEL OF THE TANK

The total weight of the tank is 73 kg of which 56 kg is the water weight

COUPLED FINITE ELEMENT AND MESHLESS MODEL

Grand Voyager TankGrand Voyager Tank

Various views of front side

COUPLED FINITE ELEMENT AND MESHLESS MODEL


Various views of back side

DETAILED PINCH-OFF REGION


DETAILED PINCH-OFF REGION


Three rows of beam elements parallel to pinch-off joint

Two rows of beam elements perpendicular to pinch-off joint

Force measurement

direction

Force measurement

direction

MODEL DETAILS


Number of Parts 11

Number of Shell Elements 16,876

Number of Beam Elements 1,717

Number of Nodes 16,572

Number of SPH Particles 124,198

Final Simulation Time 0.1 sec.

Number of Processors 4

Computation Time 15 hrs

ELEMENT PRESSURE

Simulation of Grand Voyager Tank Simulation of Grand Voyager Tank Drop TestDrop Test

DEFORMATION-SLOSHING


IMPACT REACTION FORCE ON THE GROUND AT POINT OF IMPACT


INTERNAL PRESSURE ON TANK WALL AT SELECTED ELEMENT


The next series of slides The next series of slides show the results of the show the results of the

forces as measured by the forces as measured by the five sets of beam elements; five sets of beam elements; i.e. the forces observed at i.e. the forces observed at

the pinch-off region the pinch-off region during the impact during the impact

PINCH-OFF EVALUATION BEAM SET-I

Beam Element Data of Grand Beam Element Data of Grand Voyager TankVoyager Tank

Notice red spot (high loads) at the neck area

Click mouse on image to repeat

COMPARISON WITH SwRI DROP TEST: FAILURE OCCURRED IN HIGH LOAD NECK AREA AS PREDICTED BY THE MODEL



Region with maximum force

PINCH-OFF EVALUATION BEAM SET-II


PINCH-OFF EVALUATION BEAM SET-III


PINCH-OFF EVALUATION BEAM SET-IV


PINCH-OFF EVALUATION BEAM SET-V


MAXIMUM AXIAL FORCES FOUND AT DIFFERENT BEAMELEMENTS AT THE PINCH-OFF REGION


Peak force in perpendicular direction approx. 3,500 N (780 LB)

Summary of Simulation Summary of Simulation ResultsResults

Plymouth Grand Voyager TankPlymouth Grand Voyager Tank The FE analysis predicted the maximum loads at The FE analysis predicted the maximum loads at

the same location where the pinch-off region the same location where the pinch-off region ruptured in the test ruptured in the test

As expected, the maximum force occurred in the As expected, the maximum force occurred in the tank neck area since the cross section of the tank is tank neck area since the cross section of the tank is narrower leading to increased water pressure and narrower leading to increased water pressure and larger buckling loadlarger buckling load

The maximum force predicted is perpendicular to The maximum force predicted is perpendicular to the pinch off joint and is approximately 780 LB (this the pinch off joint and is approximately 780 LB (this is 40% higher than the force that failed the is 40% higher than the force that failed the specimens in the tensile tests performed by SwRI) specimens in the tensile tests performed by SwRI)

The peak force occurred at about 0.02 sec hence The peak force occurred at about 0.02 sec hence the strain rate effect is important (SwRI tensile test the strain rate effect is important (SwRI tensile test peaked in 1.2 min) peaked in 1.2 min)

Comparison of Generic Comparison of Generic Shape TanksShape Tanks

Generic Tank Generic Tank SimulationsSimulations

The purpose of this set of simulations is to investigate The purpose of this set of simulations is to investigate the effect of tank geometry on the forces generated at the effect of tank geometry on the forces generated at the joint the joint

The following three tanks were modeled:The following three tanks were modeled:o Rectangular tank of similar size as the Voyager tank without Rectangular tank of similar size as the Voyager tank without

neck (this represents the class of tanks such as the Jeep Grand neck (this represents the class of tanks such as the Jeep Grand Cherokee)Cherokee)

o Same size as above tank but with a neck section (this Same size as above tank but with a neck section (this represents the class of tanks such as the Plymouth Grand represents the class of tanks such as the Plymouth Grand Voyager)Voyager)

o Rectangular tank with smaller dimensions than first tank (this Rectangular tank with smaller dimensions than first tank (this represents the class of tanks such as the Saturn)represents the class of tanks such as the Saturn)

In all cases the thickness of the tank walls and the material properties were kept the same as the Voyager model

MODEL DETAILS

Number of Parts 10

Number of Shell Elements 18,049

Number of Beam Elements 1,680

Number of Nodes 18,051

Number of SPH Particles 102,259

Final Simulation Time 0.2 sec.

Number of Processors 6

Computation Time 28 hrs

Generic Tank ModelGeneric Tank Model

Weight:• Rectangular baseline tank: 75 kg of which 56 kg is water• Rectangular tank with neck: 75 kg of which 56 kg is water• Rectangular small tank: 48 kg of which 33 kg is water

Rectangular Tank Rectangular Tank (Baseline)(Baseline)




Peak tensile (+ve) forces

(red contours) occur at or near

the impact point

FAILURE IN SwRI JEEP CHEROKEE TEST


Rectangular Tank with a Rectangular Tank with a NeckNeck



Small Rectangular TankSmall Rectangular Tank

Maximum Force Maximum Force ComparisonsComparisons

Tank with Neck

Baseline

Smaller Tank

Tank with neck (Grand Voyager type)

Baseline rectangular tank (Jeep Cherokee type)

Small rectangular tank (Saturn type)


Generic Shape TanksGeneric Shape Tanks The FE analysis predicted the maximum The FE analysis predicted the maximum

loads near the same location where the loads near the same location where the pinch-off region ruptured in both the pinch-off region ruptured in both the rectangular (Cherokee) and tank with neck rectangular (Cherokee) and tank with neck (Voyager) tests (Voyager) tests

The addition of a neck section in a The addition of a neck section in a rectangular tank, keeping everything else rectangular tank, keeping everything else similar, increases the forces in the pinch-off similar, increases the forces in the pinch-off region by 50%region by 50%

Reducing the rectangular tank overall Reducing the rectangular tank overall dimensions and mass by 30%, dimensions and mass by 30%, keeping keeping everything else similar, reduces the forces everything else similar, reduces the forces in the pinch-off region by 10%in the pinch-off region by 10%

Summary of Simulation Summary of Simulation Results (cont.)Results (cont.)

Generic Shape TanksGeneric Shape Tanks

The Cherokee pinch-off contact area is 30% of the Voyager pinch-The Cherokee pinch-off contact area is 30% of the Voyager pinch-off contact area, therefore for the same amount of force:off contact area, therefore for the same amount of force:

o the stress in the Cherokee joint would be three times higherthe stress in the Cherokee joint would be three times highero the strength of the Cherokee joint would be a third of the Voyager’s the strength of the Cherokee joint would be a third of the Voyager’s

Since we did not receive the tested tanks from SwRI we cannot Since we did not receive the tested tanks from SwRI we cannot make similar conclusions about the Saturn Tank. However, if the make similar conclusions about the Saturn Tank. However, if the contact patch area is somewhere in between the Cherokee and contact patch area is somewhere in between the Cherokee and Voyager’s, then from the results of the generic tank simulations, Voyager’s, then from the results of the generic tank simulations, the stress in the Saturn joint would be 20% lower than the the stress in the Saturn joint would be 20% lower than the Cherokee’s.Cherokee’s.

Voyager pinch-off contact patch

Cherokee pinch-off contact patch

Simulation of DifferentSimulation of DifferentCoupon TestsCoupon Tests

Model Development and Comparison with SwRI Model Development and Comparison with SwRI Coupon TestsCoupon Tests

The next series of slides The next series of slides show results of three show results of three simulation cases for simulation cases for

different coupon tests that different coupon tests that were developed to try and were developed to try and

force a failure in the force a failure in the pinch-off area. The first pinch-off area. The first

scenario is the SwRI scenario is the SwRI tensile test.tensile test.

Simulation of Coupon TestsSimulation of Coupon Tests

Specimen FE model based on Voyager tank properties used in all

three cases

TOP VIEW

Applied Force

Applied Force

Click on image to see animation

Simulation of Coupon Simulation of Coupon TestsTestsCASE I - SIMPLE TENSILE TEST

EFFECTIVE STRESS



PLASTIC STRAIN



Simulation of Coupon Simulation of Coupon TestsTestsCASE II - HYDROSTATIC PRESSURE TEST

uniform pressure

Reaction force

Reaction force

GEOMETRY EXTRACTIONSimulation used to obtain curved geometry of Specimen

Simulation of Coupon Simulation of Coupon TestsTests


CASE II - HYDROSTATIC PRESSURE TEST

PRESSURE BOUNDARY CONDITIONhighest stresses and strains not at joint



CASE II - HYDROSTATIC PRESSURE TEST

Simulation of Coupon Simulation of Coupon TestsTestsCASE III – SPECIMEN WRAPPED AROUND PIPE

Fixed Pipe with

frictionless surface

Applied forceApplied force

USING CYLINDERhighest stresses and strains not at joint



CASE III – SPECIMEN WRAPPED AROUND PIPE


Coupon TestsCoupon Tests A simple tensile test such as the one performed by A simple tensile test such as the one performed by

SwRI is not representative because in the drop test SwRI is not representative because in the drop test the pinch-off joint is subjected to a bidirectional the pinch-off joint is subjected to a bidirectional force along, and perpendicular to, the jointforce along, and perpendicular to, the joint

Applying a hydrostatic force on a curved specimen Applying a hydrostatic force on a curved specimen is more representative of the drop test scenario is more representative of the drop test scenario because the primary loads are generated by the because the primary loads are generated by the water pressurewater pressure

This is not a simple test to perform and therefore This is not a simple test to perform and therefore an alternative is to place the specimen on a curved an alternative is to place the specimen on a curved low friction device (pipe) and applying a tensile low friction device (pipe) and applying a tensile force at the endsforce at the ends

Summary of Simulation Summary of Simulation Results (cont.)Results (cont.)

Coupon TestsCoupon Tests The results of the simulations clearly show that the The results of the simulations clearly show that the

latter provides the same type of load distribution latter provides the same type of load distribution as the hydrostatic case and the stress builds up as the hydrostatic case and the stress builds up more at the jointmore at the joint

However, all three cases were not able to generate However, all three cases were not able to generate a higher stress at the joint than the parent a higher stress at the joint than the parent material. material.

It is not clear at this point that there exists a It is not clear at this point that there exists a simple coupon test that can generate the load simple coupon test that can generate the load conditions to fail the pinch-off jointsconditions to fail the pinch-off joints

The models have a limitation in that they do not The models have a limitation in that they do not represent any micro-cracks in the joint which represent any micro-cracks in the joint which would initiate an early failure when testedwould initiate an early failure when tested

Simulation of Plymouth Simulation of Plymouth Tank with Gasoline Tank with Gasoline

PropertiesProperties

Simulations with Simulations with GasolineGasoline

The purpose of this set of simulations is to The purpose of this set of simulations is to investigate the effect of the gasoline investigate the effect of the gasoline properties on the behavior of the tanks as properties on the behavior of the tanks as compared to the water properties compared to the water properties

The following two scenarios were modeled:The following two scenarios were modeled:o Plymouth Grand Voyager Tank filled 100% with Plymouth Grand Voyager Tank filled 100% with

gasoline and dropped from a height of 30 feet gasoline and dropped from a height of 30 feet similar to the SwRI drop tests.similar to the SwRI drop tests.

o Same tank and fuel as above except the tank is Same tank and fuel as above except the tank is positioned horizontally and is impacted by a rigid positioned horizontally and is impacted by a rigid wall traveling at 13.4 m/s (same speed as the wall traveling at 13.4 m/s (same speed as the impacting tank in a free fall from 30 feet); i.e. impacting tank in a free fall from 30 feet); i.e. gravity is perpendicular to the impact direction.gravity is perpendicular to the impact direction.

Gasoline Filled Plymouth Gasoline Filled Plymouth TankTank

Vertical Drop

Vertical Drop


Side Impact


Force ComparisonsForce Comparisons

Forces Parallel to Joint

Tank filled with water (74% full)Vertical Drop

Tank filled with gasoline (100% full)Vertical Drop

Tank filled with gasoline (100% full)Side Impact

Force ComparisonsForce Comparisons

Tank filled with water (74% full)Vertical Drop

Tank filled with gasoline (100% full)Vertical Drop

Tank filled with gasoline (100% full)Side Impact

Forces Perpendicular to Joint


Gasoline Filled TanksGasoline Filled Tanks The behavior of the tanks when filled with gasoline and The behavior of the tanks when filled with gasoline and

dropped from 30 feet or impacted horizontally did not show dropped from 30 feet or impacted horizontally did not show any difference in the crush behavior or the maximum any difference in the crush behavior or the maximum measured loads (this is perhaps only the case when the tank measured loads (this is perhaps only the case when the tank is filled up to 100% of volume since the effect of gravity on is filled up to 100% of volume since the effect of gravity on the initial state of the fluid and void does not play a role).the initial state of the fluid and void does not play a role).

The behavior of the tanks when filled with gasoline and The behavior of the tanks when filled with gasoline and dropped from 30 feet did not show any change in terms of dropped from 30 feet did not show any change in terms of the the overall tank deformationoverall tank deformation and the and the locationlocation of the of the maximum pinch-off area forces when compared to the water maximum pinch-off area forces when compared to the water filled tanks dropped from 30 feet.filled tanks dropped from 30 feet.

However, the force-time history comparison shows an However, the force-time history comparison shows an increase for the gasoline tanks in the second peak by about increase for the gasoline tanks in the second peak by about 30% and an increase in the total pulse duration by about 30% and an increase in the total pulse duration by about 36% (since the crush behavior is the same in both cases then 36% (since the crush behavior is the same in both cases then this implies an increase in energy; viz. the area under the this implies an increase in energy; viz. the area under the force-deflection curve, of 36%).force-deflection curve, of 36%).

Conclusions and Conclusions and Proposed Future Proposed Future

ResearchResearch

ConclusionsConclusions At impact the dynamics of the water sloshing causes the At impact the dynamics of the water sloshing causes the

water to continue to move down, and since it is an water to continue to move down, and since it is an incompressible fluid the tank has to expandincompressible fluid the tank has to expand

The FE analysis predicted the maximum loads at the The FE analysis predicted the maximum loads at the same location where the pinch-off region ruptured in same location where the pinch-off region ruptured in both tests (neck area in the Voyager and lower edge in both tests (neck area in the Voyager and lower edge in Cherokee) Cherokee)

A tank with a thin stiff neck, such as the Voyager tank, A tank with a thin stiff neck, such as the Voyager tank, cannot expand in the neck area leading to increased cannot expand in the neck area leading to increased water pressure and therefore large stresses develop at water pressure and therefore large stresses develop at the jointsthe joints

The addition of a neck section in a rectangular tank, The addition of a neck section in a rectangular tank, keeping everything else similar, increases the forces in keeping everything else similar, increases the forces in the pinch-off region by 50%the pinch-off region by 50%

The maximum force predicted in the Voyager simulation is The maximum force predicted in the Voyager simulation is perpendicular to the pinch off joint and is approximately perpendicular to the pinch off joint and is approximately 780 LB (this is 40% higher than the force that failed the 780 LB (this is 40% higher than the force that failed the specimens in the tensile tests performed by SwRI) specimens in the tensile tests performed by SwRI)

The Jeep Cherokee carries the most amount of fuel of all The Jeep Cherokee carries the most amount of fuel of all tanks tested, yet the pinch-off area has the thinnest cross-tanks tested, yet the pinch-off area has the thinnest cross-section (i.e. higher dynamic loads due to water weight and section (i.e. higher dynamic loads due to water weight and higher stresses due to smaller cross section area)higher stresses due to smaller cross section area)

The stress in the Saturn joint is estimated to be 20% lower The stress in the Saturn joint is estimated to be 20% lower than the Cherokee’s.than the Cherokee’s.

The pinch-off contact area is very important and has a The pinch-off contact area is very important and has a significant effect on the ability of the joint to withstand the significant effect on the ability of the joint to withstand the impact loads (the size of the Cherokee pinch-off contact impact loads (the size of the Cherokee pinch-off contact area is 30% of the Voyager pinch-off contact area)area is 30% of the Voyager pinch-off contact area)

Conclusions (cont.)Conclusions (cont.)

In all cases the peak force occurred at about 0.02 sec hence the In all cases the peak force occurred at about 0.02 sec hence the strain rate effect is important (SwRI tensile test peaked in 1.2 strain rate effect is important (SwRI tensile test peaked in 1.2 min) min)

A simple tensile test such as the one performed by SwRI is not A simple tensile test such as the one performed by SwRI is not representative because in the drop test the pinch-off joint is representative because in the drop test the pinch-off joint is subjected to a bidirectional force along, and perpendicular to, subjected to a bidirectional force along, and perpendicular to, the jointthe joint

It is not clear at this point that there exists a simple coupon test It is not clear at this point that there exists a simple coupon test that can generate the load conditions to fail the pinch-off jointsthat can generate the load conditions to fail the pinch-off joints

The models have a limitation in that they do not represent any The models have a limitation in that they do not represent any micro-cracks in the joint which would initiate an early failure micro-cracks in the joint which would initiate an early failure when testedwhen tested

While a tank filled with water up to 74% volume does represent While a tank filled with water up to 74% volume does represent the general crush behavior of the tank when compared to a tank the general crush behavior of the tank when compared to a tank filled with gasoline up to 100% volume, the maximum forces filled with gasoline up to 100% volume, the maximum forces generated at the pinch-off area could be as much as 10% lower generated at the pinch-off area could be as much as 10% lower and the total pulse duration as much as 36% lessand the total pulse duration as much as 36% less

Conclusions (cont.)Conclusions (cont.)

The following two questions may need to be The following two questions may need to be addressed with further simulation studies:addressed with further simulation studies:

o The drop test carried out by SwRI is certainly The drop test carried out by SwRI is certainly representative of a vehicle impact condition, however, representative of a vehicle impact condition, however, given that the loads that were generated with a given that the loads that were generated with a gasoline filled tank are more aggressive than those gasoline filled tank are more aggressive than those generated by the water filled tank, generated by the water filled tank, should the drop should the drop height or the amount of water be modified to reflect height or the amount of water be modified to reflect these changes for a possible future standard test?these changes for a possible future standard test?

o Is there some other combination of coupon samples and Is there some other combination of coupon samples and test configurations that could place the right amount test configurations that could place the right amount and direction of load on the joint to fail it such that a and direction of load on the joint to fail it such that a standard test could exist for testing tank joints? standard test could exist for testing tank joints?

Further Simulation Further Simulation StudiesStudies

The simulation study clearly shows that there are unique The simulation study clearly shows that there are unique features in each of the tanks tested that some broad features in each of the tanks tested that some broad conclusions about tank design and testing could be drawn.conclusions about tank design and testing could be drawn.

While the analysis could explain why certain tank designs have While the analysis could explain why certain tank designs have higher loads, and therefore would require thicker tank walls higher loads, and therefore would require thicker tank walls and larger pinch-off contact patch sizes, it did not answer the and larger pinch-off contact patch sizes, it did not answer the question as to why the conditioned tanks failed while the new question as to why the conditioned tanks failed while the new ones did not.ones did not.

It is obvious that exposure to fuel may have some degrading It is obvious that exposure to fuel may have some degrading effect on the structural strength of joints. However, the effect on the structural strength of joints. However, the results of the simulations also showed that there are some results of the simulations also showed that there are some design considerations which could be addressed to reduce the design considerations which could be addressed to reduce the loads and to strengthen the joints.loads and to strengthen the joints.

It is believed from the analysis that the tanks tested were It is believed from the analysis that the tanks tested were subjected to loads at the borderline of the joint strengths. subjected to loads at the borderline of the joint strengths. Therefore, more statistically significant tests should be Therefore, more statistically significant tests should be performed. performed.

Proposed Testing Proposed Testing ProgramProgram

It is proposed to run a set of drop tests to: (a) provide the It is proposed to run a set of drop tests to: (a) provide the necessary validation of the FE models, (b) include sufficient necessary validation of the FE models, (b) include sufficient statistical significance to get meaningful results, and (c) statistical significance to get meaningful results, and (c) understand the contribution of fuel exposure in the pinch off understand the contribution of fuel exposure in the pinch off area by testing new tanks that have been exposed to fuel for a area by testing new tanks that have been exposed to fuel for a period of at least 72 hours. The latter is a requirement in a period of at least 72 hours. The latter is a requirement in a number of fuel tank compliance tests including ECE and military number of fuel tank compliance tests including ECE and military test procedures.test procedures.

The proposed program would include the following 46 drop The proposed program would include the following 46 drop tests:tests:

Test 1:Test 1: Custom made clear tank to visualize water slosh and tank bulging effectsCustom made clear tank to visualize water slosh and tank bulging effectsTests 2-6:Tests 2-6: 1998 Saturn Twin Cam 4 Dr1998 Saturn Twin Cam 4 Dr New tanks (not exposed to fuel)New tanks (not exposed to fuel)Tests 7-11:Tests 7-11: 1998 Saturn Twin Cam 4 Dr1998 Saturn Twin Cam 4 Dr New tanks (filled w/ fuel for 72 hrs)New tanks (filled w/ fuel for 72 hrs)Tests 12-16:Tests 12-16: 1998 Saturn Twin Cam 4 Dr1998 Saturn Twin Cam 4 Dr Reconditioned tanksReconditioned tanksTests 17-21:Tests 17-21: 1998 Plymouth Grand Voyager1998 Plymouth Grand Voyager New tanks (not exposed to fuel)New tanks (not exposed to fuel)Tests 22-26:Tests 22-26: 1998 Plymouth Grand Voyager1998 Plymouth Grand Voyager New tanks (filled w/ fuel for 72 hrs)New tanks (filled w/ fuel for 72 hrs)Tests 27-31:Tests 27-31: 1998 Plymouth Grand Voyager1998 Plymouth Grand Voyager Reconditioned tanksReconditioned tanksTests 32-36:Tests 32-36: 1998 Jeep Grand Cherokee1998 Jeep Grand Cherokee New tanks (not exposed to fuel)New tanks (not exposed to fuel)Tests 37-41:Tests 37-41: 1998 Jeep Grand Cherokee1998 Jeep Grand Cherokee New tanks (filled w/ fuel for 72 hrs)New tanks (filled w/ fuel for 72 hrs)Tests 42-46:Tests 42-46: 1998 Jeep Grand Cherokee1998 Jeep Grand Cherokee Reconditioned tanksReconditioned tanks

Proposed Testing Program Proposed Testing Program (cont.)(cont.)

The EndThe End

Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest...

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Transcript of Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest...