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Simulation of IIHS Roof Strength Analysis on Toyota Corolla Chassis

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Simulation of IIHS Roof Strength Analysis
on Toyota Corolla Chassis
ME 65100: ADVANCED FINITE ELEMENTS METHOD
MASTER OF SCIENCE (MECHANICAL ENGINEERING)
SUBMITTED BY
HARSHAL DHAMADE
VIGHNESH SHETTY
TEJESH DUBE
DEPARTMENT OF MECHANICAL ENGINEERING
INDIANA UNIVERSITY-PURDUE UNIVERSITY INDIANAPOLIS
FALL 2018
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ABSTRACT
Amongst the types of crashes encountered, a rollover on the side or turning turtle can
have grievous consequences for the occupants. In this project, FMVSS 216 standards
were studied in order to carry out a quasi-static load test experimentation on Toyota
Corolla BIW. An explicit solver was used in LS Dyna to solve the set up and IIHS rating
system was studied by comparing the strength – to – weight ratio (SWR) of vehicle with
plate displacement.
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TABLE OF CONTENTS
1. Introduction
a. Crashworthiness
b. Crash rules and regulations in USA
c. New Car Assessment Program (NCAP)
2. Types of crash tests
a. Front Impact Overview
b. Side Impact Overview
3. Roof Crush
a. Testing Procedure
b. Result Calculation
4. Methodology
a. Model Creation
b. Finite Element Modeling
c. Contact Modeling
d. Material Modeling
5. Boundary Conditions
a. Constraints
b. Loading
c. Convergence criterion and Energy Plots
6. LS Dyna Model Simulation Results
a. Testing results and SWR Calculation
b. Results obtained from the model
i. A,B,C pillar stress contours
ii. Roof and roof cross member plastic strain
iii. Maximum Reaction Force
iv. SWR for current model
7. Conclusion
8. Future Scope
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1. INTRODUCTION
[IRJET] The greatest challenges faced by the automotive industry are been to provide
safer vehicles with high fuel efficiency at competitive cost. [1] Automotive design with
economy, safety and aesthetics has been a great challenge to design engineers. But
along with these advantages of light weight, more fuel efficiency and corrosion
resistance, safety is very important criteria for vehicle manufacturers, as vehicle
rollover crashes are frequent accidents worldwide. [4] Vehicle rollover crashes are
causing many fatalities like severe neck, head and spine injuries around the world.
Therefore, passenger safety is an important concern in the automotive industry, and
this is gradually growing every year. [3]
a) Crashworthiness
Automotive Vehicle Safety Standards Earlier, in February 2009, the IIHS (Insurance
Institute of Highway Safety) announced a new rating system based around roof crush
testing. The rating is must to ensure the safety of the passengers during rollover
accident of car. Although their procedure is like that of FMVSS 216 (Federal Motor
Vehicle Safety Standards), which is the American safety standards used for roof
crushing test.[6] The requirement of this test set up is to earn the highest rating of 4.0
times the vehicle's weight. The rating is 4, specified by both IIHS and FMVSS to
increase the safety of the passengers. This paper overview the IIHS test procedure and
present data from both the FMVSS 216 and IIHS test protocols. Readers of this paper
will gain a much broader understanding of roof crush testing and the impact it will
have on future vehicle designs.
Fig 1. Testing Procedure
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Roof Crush Resistance Test A rectangular block measuring 30 inches wide and
72 inches long is used to apply the load on car roof with 1.5 times the unloaded
vehicle weight with different angle inclination to rectangular block as indicated
in below figure. And the moving distance of roof structure must be less than
127mm or 5 inches as per FMVSS standards.
b) Crash rules and Regulations in USA
[BSsimulia] The National Highway Traffic Safety Administration (NHTSA) mandates
the use of certain test procedures to determine automobile roof crush resistance.
NHTSA roof strength standard, FMVSS 216 seeks to reduce the risk of death and
serious injuries in rollover crashes. [1] In the test the force-deflection behavior of the
roof structure is measured by quasi-statically pressing a precisely positioned rigid
plate against the automobile. In geometrical approach the geometry of roof and its
supporting members i.e. A pillar, B pillar etc. must change. [2] [371] As part of the
design process, the test is often simulated analytically.
There are different standards and testing procedure depending on the vehicle type and
governing bodies around the globe, some them are mentioned below. [2] [371]
1. Controlled Rollover Impact System (CRIS) : A fixture holding the vehicle is
mounted on a semi-tractor and trailer. The fixture can be adjusted to drop the
vehicle a given height giving it a defined vertical velocity.
2. Jordan Rollover System (JRS) : This test is attained by mounting a vehicle on
an axis that permits it to roll and be dropped. Fig. 3 and 4 shows the actual
laboratory test and FE test model. As the vehicle is rotated by means of
pneumatic system, a roadway segment is run underneath, and the vehicle is
dropped so that its roof strikes the road as it would in an actual rollover.
3. Federation of Motor Vehicle Safety Standards No.216 (FMVSS 216) : It specifies
a quasi-static test procedure that measures the force required to push a metal
plate into the roof at a constant rate. It requires a reaction force equal to 1.5
times the weight of the vehicle be reached within 5 inches or 127mm of plate
displacement. This is commonly referred as the Strength to Weight Ratio (SWR).
The standard applied to vehicles like vans and light trucks with a GVWR (Gross
Vehicle Weight Rating) of 2,722 kilograms (6,000 pounds) or less. The new
standard also broadens the scope of covered vehicles to include those up to
GVWR of 4,536 kilograms (10,000 pounds).
4. The Insurance Institute of Highway Safety (IIHS) has developed its own rollover
crashworthiness rating. The IIHS specified for a GOOD rating in their program
will be Strength to Weight Ratio (SWR) of 4.0 in a one-sided platen test condition
like the existing FMVSS 216 test procedure. For an ACCEPTABLE rating, the
minimum SWR is 3.25 and MARGINAL rating value is 2.5. Anything lower than
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that is rated as POOR as shown in fig.8 This rating system is based on the
institute research showing that occupants in rollover crashes benefit from
stronger roofs.
c) New Car Assessment Program (NCAP)
[BSsimulia] For roof crush simulation, a force is applied quasi-statically to the side of
the forward edge of the vehicle roof structure through a large rigid block. The chassis
frame and the car’s sills are constrained to a rigid horizontal surface. The force applied
to the block and the displacement of the block are recorded throughout the test to
characterize the roof crush resistance. [1] Accurate and efficient finite element
modeling of the roof crush resistance test can facilitate the design of safer automobiles
as well as reduce development and testing costs.
In Explicit the central difference time integration rule is used to advance the solution.
The conditional stability of this approach requires the use of small-time increments.
It can, therefore, be computationally impractical for the modeling of quasi-static
events in their natural time scale. Event acceleration techniques must be employed to
obtain an economical solution. [3] [abaqus] As the event is accelerated, however,
inertial forces may become dominant. The goal is to model the process in the shortest
time period in which inertial forces remain insignificant.
Two methods to obtain an economical quasi-static solution with an explicit dynamic
procedure are [4]
 to increase the loading rates and to perform mass scaling. In which the duration
of the event is reduced artificially by increasing the rate at which the load is
applied.
 in the second method the material density is increased artificially, which leads
to an increase of the stable time increment.
Both methods are used at the same time for the present analysis.
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2. TYPES OF CRASH TESTS
1) Frontal Impact Overview [crash safety overview]
This standard specifies performance requirements for the protection of vehicle
occupants in crashes. The purpose of this standard is to reduce the number of deaths
of vehicle occupants, and the severity of injuries, by specifying vehicle
crashworthiness requirements in terms of forces and accelerations measured on
anthropomorphic dummies in test crashes, and by specifying equipment requirements
for active and passive restraint systems.
Fig 2. Types of Front Impact
This standard applies to passenger cars, multipurpose passenger vehicles, trucks, and
buses. In addition, Pressure vessels and explosive devices, applies to vessels designed
to contain a pressurized fluid or gas, and to explosive devices, for use in the above
types of motor vehicles as part of a system designed to provide protection to occupants
in the event of a crash.
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Fig 3. Test Configuration
Specified Test Parameters:






Work done in the system = (Average force on vehicle impacting the wall) + (Crush
+ Rebound of Vehicle)
Dissipation of Kinetic Energy into the Vehicle structure, by optimized
deformation for maximum energy absorption by the structural members and
away from the occupant.
The Energy Dissipation Rate is directly proportional to the Injury.
Deformation by optimizing the deformation mode by refining the parameters that
contribute to the axial crushing of the concerned structural members.
Maximizing the crush space.
Minimizing the intrusions in the members onto the occupant chamber, to avoid
occupant injury/fatality.
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2) Side Impact Overview
This standard specifies performance requirements for protection of occupants in side
impacts. The purpose of this standard is to reduce the risk of serious and fatal injury
to occupants of passenger cars, multipurpose passenger vehicles, trucks and buses
in side impacts by specifying strength requirements for side doors, limiting the forces,
deflections and accelerations measured on anthropomorphic dummies in test crashes,
and by other means.
This standard applies to passenger cars, and to multipurpose passenger vehicles,
trucks and buses with a gross vehicle weight rating (GVWR) of 4,536 kilograms (kg)
10,000 pounds (lb) or less, except for walk-in vans, or otherwise specified.
Fig 4. Structural criteria for side impact.
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3. ROOF CRUSH
1.
Actual Testing Procedure [IIHS Protocol] [7]
Roof strength evaluations consist of a quasi-static test conducted on a vehicle’s roof
in a manner like tests used to judge compliance with Federal Motor Vehicle Safety
Standard 216 (Office of the Federal Register, 2009). The main differences between the
procedure specified by the Insurance Institute for Highway Safety (IIHS) and that
specified by the US federal government are that the IIHS procedure:
● Specifies testing one side of a vehicle’s roof, does not include a headroom
criterion,
● Specifies testing to a given displacement instead of a given force level, and
● Specifies setting the vehicle’s pitch angle during testing based on the measured
on-road pitch angle.
An overall rating is assigned based on the peak strength-to-weight ratio (SWR)
measured within 127 mm of plate displacement.
 TEST VEHICLE SELECTION AND CURB WEIGHT MEASUREMENT
Curb weight values used for calculating SWR are based on IIHS measurements of a
vehicle, not the manufacturer’s specified curb weight. Test vehicle selection criteria is
provided in Appendix B.
Vehicle curb weight is measured with full fluid levels using scales manufactured by
Longacre Racing Products (Computer scales DX series 72634).
Fig 5. Testing Side View
 TEST VEHICLE PREPARATION
With the vehicle on a level surface, the on-road pitch angle at the front door sill is
measured on both sides of the vehicle. Unless the vehicle manufacturer requests
otherwise, roof racks and other nonstructural items that may be contacted during the
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test are left as installed from the factory. Any trim or other components are removed
if they interfere with supporting the vehicle along its rocker panels.
For vehicles with vertical pinch weld flanges on the bottom of the rocker panels, the
vehicle support system consists of one I-beam (HR A-36 W4X13) for each rocker panel.
Each I-beam has a clamping system incorporated on the top that is tightened against
the pinch weld flange to clamp the system in place.
Fig 6. Fixtures for testing.
 Testing
Roof strength evaluations are conducted on a quasi-static test system manufactured
by MGA Research Corporation (Figure 3). The system consists of an upright assembly
and attached loading head that can be fixed at varying heights from the ground as
well as at pitch angles ranging from -5 to +5 degrees to accommodate testing on the
driver or passenger side. The roll angle is permanently fixed at 25 degrees.
Four hydraulic actuators control the movement of the platen along two linear guides.
The entire system is mounted on a T-slot bed plate anchored to the floor of the test
facility.
Once the vehicle is positioned correctly, the rocker panel supports are clamped to the
two perpendicular I beams, and the beams are marked to allow confirmation that the
vehicle position is maintained during the test. For body-on-frame vehicles, the frame
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is supported to prevent the weight of the chassis from stressing the body at the body
mounts.
The roof is crushed to a minimum displacement of 127 mm at a nominal rate of 5
mm/second. Some tests are conducted to a greater displacement to collect additional
strength data for research purposes. Force data are recorded from five load cells
(Interface Inc. model 1220) attached to the loading platen.
Displacement data are recorded from four linear variable displacement transducers
(LVDTs) (MTS Temposonics model GH) integrated into the hydraulic actuators. Figure
4 shows the locations of the load cells and LVDTs on the loading platen.
(a)
(b)
Fig 7. (a) Roof Crush setup (b) Actual testing validation.
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4. METHODOLOGY
To simulate the roof crush in LS Dyna, the following approach is used from modeling
to analysis. Further sections describe the steps taken to model the roof crush along
with model details to calculate SWR for the BIW of Toyota Corolla.
Fig 8. Flowchart of the model.
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1) Model Creation
a) Hypermesh[thesis] [8/9]
Altair’s HyperMesh is a high-performance finite element pre- and postprocessor that is compatible with most widely used finite element solvers.
HyperMesh user-interface is easy to learn and supports many CAD geometry
and finite element model files, thus increasing interoperability and efficiency.
HyperMesh includes a sophisticated suite of easy-to-use tools to build and
edit models. For 2D and 3D model creation, users have access to a variety of
mesh generation panels besides HyperMesh powerful auto-meshing module.
Automatic mid-surface generation, a comprehensive laminate modeler and
morphing (to stretch existing FE meshes to new design geometries), and
creating surfaces from the existing mesh offer new levels of model
manipulation.
The surface auto-meshing module in HyperMesh is a robust tool for mesh
generation that provides users the ability to interactively adjust a variety of
mesh parameters for each surface or surface edge.
b) LS Dyna
[website] [10] LS-DYNA is a general-purpose finite element program capable
of simulating complex real-world problems. It is used by the automobile,
aerospace, construction, military, manufacturing, and bioengineering
industries. LS-DYNA is optimized for shared and distributed memory Unix,
Linux, and Windows based, platforms, and it is fully QA'd by LSTC. The
code's origins lie in highly nonlinear, transient dynamic finite element
analysis using explicit time integration.
"Nonlinear" means at least one (and sometimes all) of the following
complications:
Changing boundary conditions (such as contact between parts that
changes over time)
● Large deformations (for example the crumpling of sheet metal parts)
● Nonlinear materials that do not exhibit ideally elastic behavior (for
example thermoplastic polymers)
●
"Transient dynamic" means analyzing high speed, short duration events
where inertial forces are important. Typical uses include:
●
Automotive crash (deformation of chassis, airbag inflation, seat belt
tensioning)
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Explosions (underwater Naval mine, shaped charges)
● Manufacturing (sheet metal stamping)
As the model is solved using an Explicit solver, LS Dyna creates a perfect
environment for that in this project.
●
2) Finite Element Modeling
a) Geometry
i)
BIW
The BIW (Body in White) for Toyota Corolla 2012 model was taken from
CCAC (Center for Collision Safety and Analysis) FE model database.
The model was validated against several full‐scale crash tests. It is
expected to support current and future research related to occupant
risk and vehicle compatibility, as well as barrier crash evaluation,
research, and development efforts.
Actual Vehicle to Model Mass, Inertia, and CG Comparisons based
upon Data from Testing at SEAS, Inc
Fig 9. Actual vs FEA Model from CCAC.
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Crush Plate
Based on IIHS roof strength testing, the crush plate is designed with
762 x 1829 mm dimensions.
(a)
(b)
Fig 10. Crusher Plate (a) Geometry (b) FE model
b) Meshing
Computational vehicle models need to capture the deformation and
interaction of vehicle parts and subsystems occurring during impact. The
accuracy with which the crash behavior of a vehicle is simulated depends
on the quality of the computer aided design (CAD) data and its meshing.
The BIW and Plate assembly was meshed using HyperMesh by Altair. Holes
with a radius of more than 5 mm were meshed by surrounding it with
minimum six elements. Very small parts, like nut-bolts, also were removed
from the geometry, and then spot-welds were created in their places to
represent bolts, rivets, and welds.
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Fig 11. Meshed BIW
c) Mesh Quality Criteria
Some default quality criteria are available in HyperMesh, including the
following:
 Min Side Length: Length of the smallest side of an element.
 Max Side Length: Length of the largest side of an element.
 Aspect Ratio: Ratio of longest side to the shortest side of an element.
 Warpage: Deviation of an element or element face from being planar.
 Min/Max Quad Internal Angle: The minimum/maximum angle of a
quad element.
 Min/Max Tria Internal Angle: The minimum/maximum angle of a
triangle element.
 Percent of Triangular Elements: Ratio of the number of triangular
elements to the total number of elements.
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For quality criterion was prepared as listed in the table and it is maintained
throughout the meshing process. While meshing it was made sure that
minimum element size should not be less than 5 mm in order to maintain
the minimum time step of one micro second without using mass scaling.
Table 1. Mesh quality criteria values
No.
Quality Parameter
Allowable min/max
1
Minimum Side Length
5 mm
2
Maximum Side Length
20 mm
3
Maximum Aspect Ratio
5
4
Maximum Warpage Angle
20º
5
Minimum Quad Internal Angle
45º
6
Maximum Quad Internal Angle
135º
7
Minimum Tria Internal Angle
20º
8
Maximum Tria Internal Angle
120º
9
Percent of Triangular Elements
4.8%
d) Model Summary
The BIW and Plate were meshed using the mesh quality criteria as given in
the previous section in HyperMesh. The element and node information are
given in the table below and the element types used in the next section.
Table 2. Mesh attributes
Part
No. of Elements
Nodes. Of Nodes
BIW
960116
981187
Plate
21755
22080
Fig 12. Model overview
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e) Element Description
All shell elements include membrane, bending and shear deformation. The
default Belytschko-Tsay formulation is the most economical and is used in this
problem. For eg. Belytschko-Tsay membrane: (and fully integrated membrane):
appropriate for fabrics etc. where bending stiffness is negligible.





Huges-Liu
Belytschko-Tsay
C0 Triangular Shell
Belytschko-Tsay membrane
Fully Integrated Shell
Table 3. Element types and properties
Type of Element
Rigid Elements
Mass Elements
Bar Elements (1 D)
Weld Elements (1D)
Trias Elements (2D)
Quad Elements (2 D)
Property
Welds
Welds
Spot Welds
Welds
Surface
Surface
19
Number
107
30
5384
915
46641
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3) Contact Modeling
In crash analysis, the deformations can be very large and predetermination of
where and how contact will take place may be difficult or impossible. For this
reason, the automatic contact options are recommended as these contacts are nonoriented, meaning they can detect penetration coming from either side of a shell
element.
a) Types of Contacts
i)
ii)
Surface to Surface
This type of contact is defined between the plate and BIW at the B
pillar.
In
crash
analysis,
the
contact
type
*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE is a recommended
contact type since, in crash simulations, the orientation of parts
relative to each other cannot always be anticipated as the model
undergoes large deformations.
For this model, the plate is defined as the MSID (Master) and the BIW
is defined as SSID (Slave) for the surface to surface contact. The values
for friction are given as below:
Table 4. Friction values
Type of Friction
Value
Static Coefficient of Friction
0.2
Dynamic Coefficient of Friction
0.2
Viscous Damping Coefficient
20%
Edge to Surface
In tied contact types, the slave nodes are constrained to move with the
master surface. At the beginning of the simulation, the nearest master
segment for each slave node is located based on an orthogonal
projection of the slave node to the master segment. If the slave node is
deemed close to the master segment based on established criteria, the
slave node is moved to the master surface. In this way, the initial
geometry may be slightly altered without invoking any stresses.
*CONTACT_TIED_SHELL_EDGE_TO_SURFACE_CONSTRAINED_OFFS
ET contact is given to all the spot welds in this model. For this type of
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contact, Spot weld beam elements (PBEAM) are taken as slave (SSID)
and corresponding surfaces. The contact thickness for slave and
master is given 0.9.
iii)
Single Surface
These contact types are the most widely used contact options in LSDYNA, especially for crashworthiness applications. With these types,
the slave surface is typically defined as a list of part ID’s. No master
surface is defined. Contact is considered between all the parts in the
slave list, including self-contact of each part. If the model is accurately
defined, these contact types are very reliable and accurate. However, if
there is a lot of interpenetrations in the initial configuration, energy
balances may show either a growth or decay of energy as the calculation
proceeds.
For
crash
analysis,
the
contact
type
*CONTACT_AUTOMATIC_SINGLE_SURFACE are used for contacts
between vehicle component on BIW. All components and BIW are
considered as Slave.
Table 5. Friction values
Type of Friction
Value
Static Coefficient of Friction
0.3
Dynamic Coefficient of Friction
0.3
Viscous Damping Coefficient
20%
b) Spot Welds
Rigid massless beam (spotweld) : Used for transmission of moments, shear
and normal forces.
Fig 13. Spot weld reduced models
Brittle failure of the spotweld occur when
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Spotweld failure due to plastic straining occurs when the effective nodal
plastic strain exceeds the input value. This option can model the tearing out
of a spotweld from the sheet metal due to plasticity in the material
surrounding the spotweld.
Contact type 8: nodes spotwelded to surface : Slave nodes are tied to the
masters until a failure criterion is reached. Thereafter they can slide on or
separate from the masters as in a type 5 contact surface. This type of surface
can be used to represent spot-welded or bolted connections.
Failure criterion:
Table 6. Element Information
Type of elements
Number of Elements
Rigid Weld
107
1D Welds
5384
PBeam
915
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4) Material Modeling
The types of Materials used for this model and their properties are defined in this
section.
i)
MAT_9 (Null Material) : For solid elements equations of state can be
called through this model to avoid deviatoric stress calculations. A
pressure cutoff may be specified to set a lower bound on the pressure.
This material model has been very useful when combined with the
reactive high explosive model where material strength is often
neglected. The null material should not be used to delete solid
elements. An optional viscous stress of the form
is computed for nonzero .
ii)
MAT_20 (Rigid Material): The rigid material type 20 provides a
convenient way of turning one or more parts comprised of beams,
shells, or solid elements into a rigid body. Approximating a deformable
body as rigid is a preferred modeling technique in many real-world
applications. For this model the plate is given MAT_20 material.
Two unique rigid part IDs may not share common nodes unless they
are merged together using the rigid body merge option. A rigid body
may be made up of disjoint finite element meshes, however. LS-DYNA
assumes this is the case since this is a common practice in setting up
tooling meshes in forming problems.
iii)
MAT_24 (Piecewise Linear Isotropic Plasticity) : The plasticity
treatment in this model is quite it includes strain rate effects and does
not use an equation of state. Deviatoric stresses are determined that
satisfy the yield function
For complete generality a table defining the yield stress versus plastic
strain may be defined for various levels of effective strain rate. All the
structural components of the chassis are given this material model.
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MAT_100 (Spot Weld) : This material model applies to beam element
type 9 for spot welds. These beam elements may be placed between any
two deformable shell surfaces and tied with type 7 constraint contact
which eliminates the need to have adjacent nodes at spot weld
locations. For our model, All the Spotwelds are given MAT_100.
Fig 14. Spot welds
Beam spot welds may be placed between rigid bodies and
rigid/deformable bodies by making the node on one end of the spot
weld a rigid body node which can be an extra node for the rigid body.
In the same way, rigid bodies may also be tied together with this spot
weld option.
v)

MAT_123 : An elasto-plastic material with an arbitrary stress versus
strain curve and arbitrary strain rate dependency can be defined with
this model. Another model, MAT_PIECEWISE_LINEAR_PLASTICITY, is
similar but lacks the enhanced failure criteria. Failure is based on
effective plastic strain, plastic thinning, the major principal in plane
strain component, or a minimum time step size.
Sub-assembly Material configurations : For the model, there are certain subassemblies which are defined with some of the material models explained above.
The assembly and their material properties are :
Roof and Side Panel Assembly - The material cards given to the BIW
components under roof assembly i.e. the A,B,C pillars and the roof are
MAT_24 – Steel.
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Table 7. Material properties for MAT_24
Property
Range
Density
7.85 – 7.89 x10-9 tonnes/mm3
Youngs Modulus
210 GPA
Poisson’s Ratio
0.3
Yield Strength
180 – 450 MPA
Tangent Modulus
5x103
Element Formulation (Belytschko Tsay)
2
Element surface thickness
0.52 – 2.21 mm
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5. BOUNDARY CONDITIONS
The boundary conditions i.e. constraints, velocities and convergence criterion
defined for this model are specified below:
1) Constraints (SPCs) : The single point constraints are basically fixing
DOF’s on the nodes of the model. For this model, all 6 DOFs are fixed along
the selected nodes as shown in the figure.
Fig 15. SPCs along the bottom of the BIW.
Along the bottom part of the chassis, the nodes are fixed according to the
IIHS testing station mounts.
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2) Loading : For loading the plate in downward direction, a local coordinate
system was set up for the plate and along negative Z direction of the plate
a boundary prescribed motion is given. A load curve is defined for the
motion as shown in the figure.
Fig 16. Load curve for Boundary prescribed motion
Fig 17. Plate initial loading.
3) Convergence Criteria and Energy Plots : The explicit solver for LS Dyna
was used to converge the solution. The test runs for around 100 ms till
127 mm deformation of the body by the plate. The maximum velocity was
given as 1270 mm/s as per the load curve. To help converge the solution,
the following convergence criteria were given,
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Time Step
End Time
Mass Scaling
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Table 8. Convergence criteria
4.42x10-7
100 ms
~ 5%
With the given parameters, a full model for BIW without any structural
components takes around 15 – 17 hours on a supercomputer. For quick
simulations, further the model was stripped down one containing only side panel
roof assembly along with the wind shield and other discarding the front end of
the chassis.
(a)
(b)
Fig 18. (a) Energy Plot (b) Crusher plate displacement plot
6. RESULTS
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1) Testing results and SWR Calculation : According to the IIHS testing criteria,
the main results to be calculated after the testing is done are the Fmax which is
maximum resultant force on the body at the point of contact and based on the
ratio of Fmax to the kerb weight of the vehicle SWR (Strength to Weight ratio) is
calculated.
Fig 19. IIHS SWR calculation
Fig 20. SWR vs Plate displacement
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2) Results obtained from the model : After the solution was converged, the
following results were calculated from the stripped-down model.
a)
A,B,C pillar stress contours : Along the roof and side panel assembly, the
part which undergoes maximum deformation are A, B and C pillars. The
stress contours around that region is shown in the figures.
Fig 21. Equivalent Stresses
Fig 22. Equivalent Stresses on the Pillars
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Fig 23. Maximum stresses along the roof and side panels
Fig 24. Equivalent Stresses on the Pillars
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a)
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Roof and roof cross member plastic strain : The equivalent plastic strains
are calculated along the roof cross members as the intrusions occur in that
region.
(a)
(b)
Fig 25. (a) Effective plastic strain along roof cross member
(b) Zoomed in image
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b)
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Maximum Reaction Force : The maximum reaction force is used to calculate
the SWR rating for the given model.
Fig 26. Maximum reaction force in N (newton)
c)
SWR for current model : For current model the SWR rating is calculated
using the relationship:
SWR = 1.5 * Fmax/m*g
SWR = 54997 *1.5/543.7*9.81
SWR = 6.87
Since the weight of reduced chassis is used the SWR is quite high than
usual. If we calculate it based on the above reaction forces and original BIW
weight it comes around 1.97 – 2 which is acceptable.
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2. CONCLUSION
The various statistical analyses in this project support the hypothesis that passenger
vehicles with a higher SWR in the roof crush test are likely to experience less vertical
roof intrusion in rollover crashes than vehicles with a lower SWR. This finding in
combination with IIHS’s previous research demonstrating a relationship between roof
intrusion and head, neck, or face injuries confirms a relationship between greater roof
strength and fewer injuries. This finding also supports the validity of SWR as a measure
of roof strength because it was found to be a statistically significant predictor of vertical
roof intrusion in real-world rollovers.
3. FUTURE SCOPE
The results of the analysis can be improved further by considering additional contact
interactions in the vehicle structure. The detailed model uses more complete contact
definitions with contact defined for the entire model rather than for the most critical
regions.
The model under consideration is based on a public domain FEA model and does not
represent an actual production vehicle. No information was available to verify the
material properties, shell thicknesses, spot weld spacing, and other details that must
be specified. These properties have a significant influence on the model behavior.
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4. REFERENCES
1) Roof Crush Analysis for Improving Occupant Safety, Sainath Arjun Waghmare, Prashant
D. Deshmukh, Swapnil S. Kulkarni, International Journal of Advanced
Engineering Research and Studies, Oct-Dec 2013, ISSN2249–8974.
2) Crash Safety Overview, NCAP.
3) Rollover and Roof Crush Analysis of Low-Floor Mass Transit Bus, Pankaj S.
Deshmukh, Thesis submitted to Dr Babasaheb Ambedkar Marathwada
University, 2002.
4) Automobile Roof Crush Analysis with Abaqus, Abaqus Technology Brief, April
2007, Simulia.
5) Roof Strength Testing and Real-World Roof Intrusion in Rollovers, Traffic Safety
Facts Research Note, National Highway Traffic Safety Administration, Aug 2010,
DOT HS 811 365.
6) Crashworthiness Evaluation Roof Strength Test Protocol (Version III), Insurance
Institute for Highway Safety, Jul 2016.
7) Electronic Code of Federation, FMVSS 208 Ocupant Crash Frontal Impact
Protection, 2018, link: www.ecfr.gov/cgi-bin/text-idx?node=se49.6.571_1208
8) Electronic Code of Federation, FMVSS 214 Side Impact Protection, 2018, link:
www.ecfr.gov/cgi-bin/textidx?SID=d4f7934ae1a2a7a6b5db134cd041add8&mc=true&node=se49.6.571_12
14&rgn=div8
9) Quasi-static Simulations using Implicit LS-Dyna, Satish Pathy, Thomas Borvall,
14th International LS-Dyna User’s Conference, June 2016.
10) Vehicle Roof Crush Modelling and Validation, Mingzhi Mao, E.C. Chirwa, T.
Chen, 5th European LS-Dyna User’s Conference.
11) LS-Dyna Keyword Manual.
12) LS-Dyna Theory Manual.
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