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Transcript of Project Report - Pritesh (1)
CRASHWORTHINESS OF FORD F250® TRUCK “ROLL OVER –INVERTED VEHICLE DROP TEST (SAE J996)”
by
Pritesh K ShahB.E. Mechanical Engineering, January 2003, Pune University, INDIA
A Project Report Submitted to the Faculty of Old Dominion University inPartial Fulfillment of the Requirement for the Degree of
MASTER OF ENGINEERINGin
DESIGN & MANUFACTURING
MECHANICAL ENGINEERING
OLD DOMINION UNIVERSITYAugust 2011
ME-11-0082
CRASHWORTHINESS OF FORD F250® TRUCK “ROLL OVER –INVERTED VEHICLE DROP TEST (SAE J996)”
by
Pritesh K ShahB.E. Mechanical Engineering, January 2003, Pune University, India
A Project Report Submitted to the Faculty of Old Dominion University inPartial Fulfillment of the Requirement for the Degree of
MASTER OF ENGINEERINGin
DESIGN & MANUFACTURING
MECHANICAL ENGINEERING
OLD DOMINION UNIVERSITYAugust 2011
Approved By:
___________________________ (Advisor)
___________________________
ABSTRACT
A finite element analysis of roof strength for Ford F250®® truck as per SAE J996
standard is performed using LS-DYNA®. A detailed finite element model was taken from
NCAC (National Crash Analysis Centre) at George Washington University Virginia.
NCAC is one of the prominent leaders in vehicle safety research. Efforts were taken to
subject the F250 FEM (finite element model) for roll over impact study with the
procedure suggested by SAE J996.
After running the F250 FEM for roll over, key areas for reduced impact on the
roof structure of the truck were addressed and were redesigned. Further, a detailed study
is carried out to compare the results between the original F250 model with the redesigned
model. A comparison chart was made to illustrate the reduced impact on the predefined
nodal points on the roof structure.
TABLE OF CONTENTS
CHAPTER 1........................................................................................................................7
INTRODUCTION...............................................................................................................7
1.1. United States standards applicable to rollover..........................................................8
CHAPTER 2......................................................................................................................11
CASE SETUP AND ANALYSIS......................................................................................11
2.1. F250 Model Environment.......................................................................................11
2.2. Frontal Impact Analysis..........................................................................................14
2.3. LS- DYNA simulation...........................................................................................15
2.4. Dummy Database...................................................................................................18
CHAPTER 3......................................................................................................................24
ROLLOVER – INVERTED VEHICLE DROP TEST......................................................24
3.1. Case setup...............................................................................................................24
3.2. Results of rollover impact of Ford F250® (SAE J 996)........................................27
3.2.1. Total Energies.....................................................................................................27
3.2.2. Roof intrusion/deflections........................................................................................28
3.3.3. Force V/s Deflection................................................................................................29
3.4. Redesign of Roof structure Ford F250®...............................................................30
3.5 Results: Redefined Roof Ford F250®....................................................................34
3.5.1. Total Energies..........................................................................................................34
3.5.2. Roof Intrusion/deflection.........................................................................................35
3.5.3. Force V/s Deflection................................................................................................36
3.6. Comparison.............................................................................................................37
CHAPTER 4......................................................................................................................39
CONCLUSIONS................................................................................................................39
REFERENCES..................................................................................................................40
LIST OF FIGURES
Figure 1 Highway rollover fatalaties...................................................................................7
Figure 2.1 NCAC FORD F250® Finite Element Model...................................................12
Figure 3 Ford F250® with frontal impact with a rigid barrier (no dummy) @ 35 mph....14
Figure 4 Different stages of simulation for frontal impact (no dummy) @35mph...........17
Figure 5 Hybrid III 50th percentile rigid Fe dummy.........................................................18
Figure 6 Positioned Hybrid III dummy.............................................................................19
Figure 7 Ford F250® with frontal impact with 50th percentile Hybrid III dummy @ 35
mph....................................................................................................................................23
Figure 8 Different stages of deflection of roof Ford F250® (SAE J 996).........................26
Figure 9 Total Energies plot for Ford F250® FEM...........................................................27
Figure 10 Roof displacement V/s Time plot for Ford F250® FEM..................................28
Figure 11 Wall force V/s Displacement plot for original F250 FEM................................29
Figure 12 Support plate finite element model...................................................................30
Figure 13 Different stages of deflection of redesigned roof Ford F250® (SAE J996).....33
Figure 14 Total Energies plot for redesigned roof F250 FEM..........................................34
Figure 15 Roof displacement V/s Time plot for redesigned roof F250 FEM...................35
Figure 16 Wall force V/s Displacement plot for redesigned roof F250 FEM...................36
Figure 17 Comparison of deflection for original and redesigned roof F250 FEM............37
Figure 18 Comparison of Wall Force V/s Displacement for original and redesigned roof
of F250 FEM......................................................................................................................38
NOMENCLATURE
FEM – Finite Element Model
FMVSS – Federal Motor Vehicle Safety Standards
SAE – Society of Automotive Engineers
NHTSA – National Highway Traffic Safety Administration
NCAC – National Crash Analysis Centre
ms- Milliseconds
N- Newton (Force)
DOE – Design of experiment
CHAPTER 1
INTRODUCTION
Every year more than 10,000 people die in rollover crashes. Rollover crashes
constitute to a meager 2 percent of all collisions and yet account for 24 percent of
passenger fatalities. Rollovers are one of the most dangerous forms of vehicle crashes
because of the high occurrence of occupants catastrophic head injuries and fatalities.
Figure 1 Highway rollover fatalaties
In 2007, the National Highway Traffic Safety Administration (NHTSA) made it
mandatory that all vehicles to be equipped with electronic stability control (ESC). By the
2008 model year, ESC was standard on 65 percent of passenger cars, 96 percent of SUVs
and only 11 percent of pickups. The ESC technology helps minimize skidding, as well as
maintains control when drivers swerve. ESC senses when a driver may lose control and
automatically applies brakes to individual wheels (Outer front wheel to counter over steer
or inner rear wheel to counter under steer) to help stabilize the vehicle and avoid a
rollover [6].
Considerable research has been undertaken over the years to differentiate rollover
according to severity and to develop a standard rollover test. In most cases the studies
are applicable to passenger cars. However, many of the principles are generally
applicable to all vehicles. In recent years, the increase in rollover casualties from the
growing population of pickups and SUV’s has emphasized the need to examine these
vehicles as separate classes.
1.1. United States standards applicable to rollover
The following FMVSS (Federal Motor Vehicle Safety Standards) are practiced in
application of rollover safety features. [1]
Interior Protection -FMVSS 201
Glazing Materials -FMVSS 205
Door Locks and Retention - FMVSS 206
Occupant Crash Protection - FMVSS 208
Windshield Mounting - FMVSS212
Side Impact Protection - FMVSS 214
Roof Crush Resistance - FMVSS 216
Fuel System Integrity - FMVSS 301 [1]
Rollover crashes have been differentiated by a large number of parameters that
may influence rollover outcomes. Examples of such parameters are the terrain
topography, roadway grade, curvature and vehicle type. Further, a basis for selecting test
procedures and relating compliance with these procedures to real world benefits is vitally
needed.
The problem of assessing countermeasures in rollover is perplexed by the lack of
dummies and test procedures to study rollover. There is no rollover test dummy which
has been validated in a manner similar to the Hybrid III in frontal crashes, or the SID in
side impacts.
As mentioned earlier many aspects contribute to the occurrence of rollover
crashes. Rollover occurrences are mainly related to the vehicle type, unsafe and
irresponsible driving behaviors such as hard steering maneuvers, bad road design, etc.
Certain class of vehicles, such as Sport Utility Vehicle (SUV) and pickup trucks, are
more prone to rollover than other classes of vehicles. Most vehicles do not have adequate
roof strength during a rollover.
The quasi-static roof crush test mandated by the FMVSS 216 subjects the vehicle
to a maximum force significantly less severe than would be applied to the vehicle during
a multiple rollover. The Society of Automotive Engineers (SAE) recommended practice
J996, Inverted Drop Test, is also a test of rollover crashworthiness, and was developed by
SAE in the late 1960s. Since it is a more severe test, numerous engineers prefer it to the
quasi-static FMVSS 216 test.
The SAE J996 test was designed, “…to obtain as closely as possible deformation
of a vehicle roof or roll bar structure which occurs in a vehicle rollover.” In this test, the
vehicle is inverted, given a roll angle, pitch angle, and drop height that are representative
of the assumed loading at rollover. The angles present ensure that the majority of
potential energy is transferred directly to the A-pillar structure. This standard does not
specify any crush measurement methodology, permanent or dynamic [7].
The project focuses on the roof strength of the Ford F250® in event of a rollover
by testing the FEM using the “Inverted Vehicle Drop Test Procedure – SAE J996.”
CHAPTER 2
CASE SETUP AND ANALYSIS
2.1. F250 Model Environment
A Finite Element Model (FEM) of Ford F250® was used from the National Crash
Analysis Centre (NCAC) [2]. NCAC at The George Washington University's Virginia
Campus is one of the nation's leading authorities in automotive and highway safety
research.
The finite element model of a 2006 Ford F250® pick-up truck was developed at
the NCAC for the National Highway Traffic Safety Administration (NHTSA). The Ford
F250® truck is a multi-purpose pickup truck. The vehicle obtained by the NCAC is an
Extended-Cab, with a wheel base of 3610 mm (142.12 inches) and a maximum width of
2030mm (79.92 inches). The F250 has a total kerb weight of 3016 kilograms (6072.2 lbs)
with a 5.4 litre V8 engine. The pickup truck has a 5 speed manual transmission with a
four wheel drive configuration. However, several other models exist, such as higher
engine capacity, automatic transmission and drive configuration, with no change in the
general geometry.
Figure 2.1 NCAC FORD F250® Finite Element Model
The model consists of 871 parts with 738165 nodes made up of 726759 elements.
The following table illustrates different type of elements constituting the total number of
elements.
Table 1 Types of elements in Ford F250® FEM
Shell element Beam element Solid element
698501 2353 25905
Specifically, the properties of each component are defined by a set of material cards
with four types of materials being used in the model. Each of the components is
subdivided into either shell elements, beam elements or hexahedron elements.
Two types of shell elements are used in the finite element model, viz. quadrilateral
shell elements and triangular shell elements. The formulation of both types of shell
elements used is based on Belytschko-Tsay theory. Table 2.1 enlists the material models
used in LS- DYNA® along with the number of components.
Table 2 LS-DYNA material models
Material type number
Material Type No. of Components
7 Blatz–Ko Rubber 18
S02 Damper Viscous 4
1 Elastic 70
57 Low Density Foam 12
9 Null 48
24 Piecewise Linear Plasticity 598
20 Rigid 106
100 Spotweld 1
S01 Spring Elastic 5
S04 Spring Non Linear Elastic 5
6 Viscoelastic 4
2.2. Frontal Impact Analysis
The F250 FEM (finite element model) was subjected to a frontal impact study with
the parameters suggested by Federal Motor Vehicle Safety Standard (FMVSS) 208 which
states
35 mph (56kph) into fixed barrier.
50th percentile Hybrid III adult male dummy in front seat.
Initially a full frontal impact without the dummy was simulated to check the accuracy
of the model from the NCAC reports. After successful model verification a 50 th percentile
Hybrid III dummy was defined in the vehicle model and the interaction of dummy with
the vehicle environment & the injury values were analyzed.
Figure 3 Ford F250® with frontal impact with a rigid barrier (no dummy) @ 35 mph
2.3. LS- DYNA simulationThe simulation was run for 150 milliseconds of simulation time with a time step
of 9.00 E-07. The total computational time required for the run was around 32 hours. The
simulation is done using a rigid barrier.
Table 3 LS-DYNA simulation parameters
Version LS- DYNA_971
Revision 7600.1224
Precision Single (I4R4)
Feature SMP
OS level Linux
Number of processors 8
Total elapsed time 32 hours
Simulation time 150 milliseconds
The truck model comes in contact with the barrier at roughly about 5
milliseconds; the front hood starts to deform at 20 milliseconds. Maximum crush occurs
at 110 milliseconds. Figure below shows different stages of deformation of truck during
the simulation time.
Simulation results for Ford F250® with frontal impact with a rigid barrier (no dummy) @ 35 mph
(a) @ 24ms
(b) @ 40 ms
(c) @ 70 ms
(d) @ 150 ms
Figure 4 Different stages of simulation for frontal impact (no dummy) @35mph
2.4. Dummy Database
The Hybrid III is the most widely applied dummy for frontal impact. The series
includes a 5th percentile female, a 50th percentile male, and a 95th percentile male. The 50th
percentile is a five feet six inch dummy model with a weight of 170lbs, for the analysis
the 50th percentile male dummy is used. The details of the dummy can be found in the
LS-DYNA ftp site [5] which includes the calibration tests, positioning details, post
processing, Part ID details and the transformation details. The dummy model used in the
analysis is shown below.
Figure 5 Hybrid III 50th percentile rigid Fe dummy
The dummy model is imported in LS-DYNA® and positioned in the driver seat of
the vehicle via H point operations. By doing this we can get the responses of the dummy
and the interactions with vehicle environment along with the injury values.
The figure below shows the final positioned dummy on the vehicle’s driver seat.
Contacts are defined with the help of contact ids obtained from the report from LS-
DYNA®.
Figure 6 Positioned Hybrid III dummy
Since all LSTC (Livermore Software Technology Corporation) dummies use the
mm‐ms‐kg‐kN unit system, we use the following conversion to convert to mm-s-tonne
unit system.
Figure 2-6 Transform keyword file
LS-DYNA simulation for Ford F250® with frontal impact with Hybrid III 50 th
percentile dummy @ 35 mph
The simulation was run for 150 milliseconds of simulation time with a time step
of 9.00 E-07. The total computational time required for the run was around 32 hours 29
minutes. The truck model comes in contact with the barrier at roughly about 5
milliseconds; the front hood starts to deform at 20 milliseconds. Maximum crush
occurred at 110 milliseconds. Figure below shows different stages of deformation of
truck during the simulation time.
Table 4 LS-DYNA simulation parameters
Version LS- DYNA_971
Revision 7600.1224
Precision Single (I4R4)
Feature SMP
OS level Linux
Number of processors 8
Total elapsed time 32 hours 29 minutes
Simulation time 150 milliseconds
(a) @ 24ms
(b) @ 40 ms
(c) @ 70 ms
(d) @ 150 ms
Figure 7 Ford F250® with frontal impact with 50th percentile Hybrid III dummy @ 35 mph
CHAPTER 3
ROLLOVER – INVERTED VEHICLE DROP TEST
3.1. Case setup
For rollover - inverted vehicle drop test as per SAE J996 the Ford F250® truck
was inverted with a roll angle defined at 25° and a pitch angle defined at 5°.A rigid plate
for impact was defined and the drop height was set at 12 inches (300mm) . Computation
time was reduced by giving an initial velocity to the vehicle and was brought right above
the rigid plate. The initial velocity was defined in LS-DYNA input deck via
*INITIAL_VELOCITY_GENERATION.
A total of 10 nodes are defined to obtain the database history to monitor the
amount of roof intrusion. The nodes are defined via node set in the
DATABASE_HISTORY_NODE_SET. The averages of the 10 nodes are used to
calculate the amount of roof deflection. Figure 3.1 shows the deformation of the roof at
different stages of simulation
(a) @ 40 ms
(b) @ 75 ms
(c) @ 100 ms
(d) @ 120 ms
Figure 8 Different stages of deflection of roof Ford F250® (SAE J 996)
3.2. Results of rollover impact of Ford F250® (SAE J 996)
3.2.1. Total Energies
Figure 9 Total Energies plot for Ford F250® FEM
Figure 9 shows the global internal, kinetic & the total energies of the system. It
can be seen that at the start of the solution, the internal energy is zero and the kinetic
energy is equal to the total energy. When the F250 truck hits the rigid wall, the kinetic
energy of the system decreases and is converted to internal energy of the materials. The
kinetic energy and the internal energies meet at roughly 70 milliseconds, and the kinetic
energy continues to decrease whereas the internal energy continues to increase. The
sudden spike in the internal energy is due to the hourglass energy which occurs due to
under integration of elements. The roof structure being made up of very thin shell
elements excites the hourglass energy mode causing the internal energy to spike up.
3.2.2. Roof intrusion/deflections
Figure 10 Roof displacement V/s Time plot for Ford F250® FEM
Figure 10 shows the average nodal displacement for the rollover impact analysis of
Ford F250® truck. The maximum average displacement of the nodes is 267.64 mm,
which means the roof structure had intruded in the driver compartment by approximately
10 inches. The amount of roof intrusion has to be reduced to avoid any interface between
the driver and the roof structure to avoid catastrophic head injury or fatalities.
3.3.3. Force V/s Deflection
Figure 11 Wall force V/s Displacement plot for original F250 FEM
Figure 11 shows the Force V/s Displacement curve for the Ford F250® truck.
From the graph we can see that the truck experiences a maximum wall force of
approximately 35Kn and yields a total intrusion/deflection of roof structure by 265 mm.
3.4. Redesign of Roof structure Ford F250®
As seen above the F250 truck when subjected to a rollover impact gave a maximum
roof deflection of 267.64 mm. To make the car safer for rollover impact, the roof of the
vehicle had to be redesigned. This was done in three parts.
The roof material was changed from mild steel to ST 44 grade steel
A support plate was added between the A and the B pillar for roof support.
The thickness of the roof was changed from 0.8mm to 1.8mm
Figure 12 Support plate finite element model
Figure 3.5 shows the support plate used between the A and the B pillar to support
the deformation of the roof structure. The section is defined as Belytschko –Tsay shell
element [8]. The plate has a thickness of 2 mm with holes and slots similar to the
connection plate in the basic model. The plate is spot welded at 15 points to the roof rail
structure via spot weld beam sections and acts as an additional support to the roof rail.
The total increase in the mass of the roof by this redesign was in the tune of 45.15 lbs
(20.32 kgs) with the roof thickness change constituting to approximately 40 lbs.
(a) @ 55 ms
(b) @ 55 ms
(c) @ 100 ms
(d) @ 55 ms
Figure 13 Different stages of deflection of redesigned roof Ford F250® (SAE J996)
3.5 Results: Redefined Roof Ford F250®
3.5.1. Total Energies
Figure 14 Total Energies plot for redesigned roof F250 FEM
Figure 14 shows the global internal, kinetic & the total energies of the system. It can
be seen that at the start of the solution, the internal energy is zero and the kinetic energy
is equal to the total energy. When the truck hits the rigid wall, the kinetic energy of the
system decreases and is converted to internal energy of the materials. The kinetic energy
and the internal energies meet at roughly 50 milliseconds, and the kinetic energy
continues to decrease whereas the internal energy continues to increase. The internal and
kinetic energy should meet roughly at half the total energy and continue to stay at that
point without crossing for the rest of the analysis. The remaining energy, other than the
sum of kinetic & internal energies is the hour glass energy.
3.5.2. Roof Intrusion/deflection
Figure 15 Roof displacement V/s Time plot for redesigned roof F250 FEM
Figure 15 shows the average nodal displacement for the Redesigned Roof Ford
F250® truck. The maximum average displacement of the nodes is 193.73mm. There is a
significant reduction in the amount of roof displacement approximately 28 %( 73.91
mm).
3.5.3. Force V/s Deflection
Figure 16 Wall force V/s Displacement plot for redesigned roof F250 FEM
The redesigned roof structure gives a maximum intrusion of 193mm for
approximately 25 Kn of wall force.
3.6. Comparison
Figure 17 Comparison of deflection for original and redesigned roof F250 FEM
Figure 17 shows the comparison of deflection for the basic model (Line B) and
the redesigned roof (Line A). From the graph we can see that at the end of 120 ms the
total deformation of roof for the redesigned roof F250 model was 194 mm as compared
to the original F250 model which has a roof deformation of 264 mm.
Figure 18 Comparison of Wall Force V/s Displacement for original and redesigned roof of F250 FEM
Figure 18 shows the wall force versus displacement for the original Ford F250®
and the redesigned roof FEM. From the graph we can see that the force acting upon the
roof has reduced from approximately 35 Kn to 25 Kn (28.57 %). The maximum
deflection of the roof has been minimized to the tune of 70mm
CHAPTER 4
CONCLUSIONS
The rollover impact test procedure as suggested by SAE J996 was performed on
finite element model of a Ford F250® truck and the redesigned roof of Ford F250® and the
results were compared. During the study of typical rollover, the goal is to achieve
minimum roof intrusion to avoid contact between the roof structure and the passenger
head to avoid and catastrophic head injuries or fatalities. The parameters that affect the
outcome of a rollover impact are stiffness and geometry of roof structure, A and B pillar
reinforcement, occupant restraint system characteristics and stiffness and properties of
interior components. With this model all of the above mentioned parameters can be
varied to have a DOE study for various rollover scenarios including varying velocities
and angle of impact.
To protect driver in the driver compartment following things should be
considered. Defining certain accident situations (standard accidents), providing a well-
defined safe zone space into which no structural elements penetrate during the collision
and during the structural deformation and damage, keeping the driver in the safe zone
space during the collision. In current regulation, driver safety is not adequately
considered so this issue needs to be addressed during specifying the rollover impact
regulations.
Most of the fatal injuries in the rollover impact are caused between the passenger
head and the roof structure so it is recommended that more importance should be given to
the stiffness, geometry and the area of impact locations. This developed LS-DYNA
model is not validated and it just gives the estimate of the roof structure intrusion. In
future by validating this model by incorporating a certified rollover test dummy actual
injury values in case of a rollover impact can be accurately predicted.
A detailed study can be performed to assess more severe test conditions to
develop complete strong regulations. Furthermore, various other occupant positions like
passenger side, rear side can be considered for study.
REFERENCES
[1] National Highway Traffic Safety Administration, "Federal Motor Vehicle Safety
Standards and Regulations," in Crashworthiness, ed. Washington, DC, 1999.
[2] National Crash Analysis Centre. (2007). Finite Element Model Archive.
Available: http://www.ncac.gwu.edu/vml/models.html
[3] Livermore Software Technology Corp. (2007). LS-DYNA Theory 2006.
Available: http://www.lstc.com/manuals.htm
[4] Livermore Software Technology Corp. (2007). Keyword 971 2 volumes
Available: http://www.lstc.com/manuals.htm
[5] Livermore Software Technology Corp. (2008). Index of /user/lstc-dummies.
Available: http://ftp.lstc.com/user/lstc-dummies/
[6] D. Shepardson, "Newer SUVs now safer than cars in a crash," in Detroit News,
ed. Detroit, 2011.
[7] P. D. Stephen A. Batzer, P.E. & Robert M. Hooker, "DYNAMIC ROOF CRUSH
INTRUSION IN INVERTED DROP TESTING."
[8] Belytschko & Tsay, "Explicit Algorithms for Nonlinear Dynamics of Shells","
vol. AMD-Vol.48, ASME, 209-231, 1981.
[9] K. Elitok, "Explicit Dynamic Analysis of Vehicle Roll-Over Crashworthiness
Using LS-DYNA ", Mechanical Engineering, Istanbul Technical University,
2006.