Study and Investigate the Impact Behaviour of Automotive Bumper Beam under Crashes

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15 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Study and Investigate the Impact Behaviour of
Automotive Bumper Beam under Crashes

M.Balaji
S.Hari hara sudhan
,

Computer Aided Design

Alagappa chettiar college of Engineering and Technology, karaikudi

India

Affiliated to Anna University

1
balaji.mech33@gmail.com








Mechanical Engineering Department (W/S)

Alagappa chettiar college of Engineering and Technology, karaikudi

India







2

hari.mech.be@gmail.com



Ab
s
tract


T
he
Bumper beam is one of the key structures of
Automobile for absorbing energy of collisions during crashes. A
good design of this part of automotives must prepare for the safety of
passengers; m
eanwhile, should have low weight. Simpler Designs of
commercial front bumper beam are chosen in this study for
modelling and analysis the impact behaviour. In order to avoid
series of destructive test for a new vehicle to be performed the
necessity of econ
omical design using finite element is performed in
this study. Parameters like materials, shape and thickness are
considered for carrying out analysis with the help of Hypermesh 9.0
and LS
-
DYNA software. In this work an attempt to present such
commercially

used designs and analyzes it to compare the impact
behaviour of each design
.



Keywords


Impact, Collisions, FEA, Bumper Beam, Energy
Absorption

I.

I
NTRODUCTION

The Bumper is one of the most important parts of a car, found at
the rear
-
most and front
-
most parts. It helps the vehicle sustain
tremendous impact while preventing the safety systems from
being damaged. However, it can reduce the injury of passengers
espe
cially during high
-
speed impacts. It can somehow lessen the
injury that pedestrians can suffer after being hit by a car. The use
of bumpers in a car is a legal requirement in most jurisdictions. It
is important to abide by this rule so as not to cause bad
outcomes
in case accidents happen. An international RCAR working group
has developed test procedures to assess how well a vehicle’s
bumper system protects the vehicle from damage in low speed
impacts.

Damage in these tests closely replicates the damage pa
tterns
observed in real world low speed crashes and addresses three
components of bumper performance:

1. Geometry


vehicle bumpers need to be positioned at
common heights from the ground and extend laterally to the
corners in order to properly engage other vehicles in low
speed crashes.

2. Stability


vehicle bumpers need to be tall and wide enough
to re
main engaged with the bumpers of other vehicles despite
vehicle motion due to loading, braking, etc.

3
. Energy
-
absorption


vehicle bumpers should absorb low
speed crash energy without damage to other parts of the
vehicle.


II.

L
ITERATURE REVIEW

(i)
Javad Mar
zbanrad. et al, Masoud Alijanpour et. al, Mahdi
Saeid Kiasat.

et al.

investigated
the most important parameters
including material, thickness, shape and impact condition for
design and analysis of an automotive front bumper beam to
improve the crashworthin
ess design in low
-
velocity impact.

The simulation of original bumper under condition impact is
according to the low
-
speed standard of automotives stated in
E.C.E. United Nations Agreement, Regulation no. 42, 1994.
The bumper beam analysis is accomplished f
or composite and
aluminum material to compare the weight and impact
behavior. The strength in elastic mode is investigated with
energy absorption and impact force in maximum deflection
situation.

The time history of the calculated parameters is
showed in g
raphs for comparison. Furthermore, beside the
above
-
mentioned benefits, some more advantages like easy
manufacturing due to simple shape without
-
ribs, economical
aspects by utilizing low
-
cost composite material and reducing
weight with respect to others ca
n be achieved by SMC
material.

(ii)
M.M. Davoodi. et al., S.M. Sapuan. et. al., D. Ahmad. et
al., A. Aidy. et al., A. Khalina et al., Mehdi Jonoobi. et al.

focused on selecting the best geometrical bumper beam
concept to fulfill the safety parameters of the defined product
design specification (PDS). The mechanical properties of
developed hybrid composite material were considered in
different bumper beam conc
epts with the same frontal
curvature, thickness, and overall dimensions. The low
-
speed
impact test was simulated under the same conditions in
Abaqus V16R9 software. Six weighted criteria, which were
deflection, strain energy, mass, cost, easy manufacturing
, and
the rib possibility were
analysed to form an evaluation matrix.

In addition, selected concept can be strengthened by adding
reinforced ribs or increasing the thickness

of the bumper beam
to comply with the defined PDS
.


III.

R
EGULATIONS OF BUMPER

STANDARD
S

The United States National Highway Traffic Safety
Administration (NHTSA) issued the very first regulation
applicable to the use of car bumpers in the country in 1971. It
was called Exterior Protection, which was part of the Federal
Motor Vehicle Safety S
tandard No. 215. The Bumper is one
of the most important parts of a car, found at the rear
-
most
and front
-
most parts. It helps the vehicle sustain tremendous
impact while preventing the safety systems from being
damaged. However, it can reduce the injury o
f passengers
especially during high
-
speed impacts. It can somehow lessen
the injury that pedestrians can suffer after being hit by a car.
The RCAR Bumper Test encourages vehicle manufacturers to
produce effective bumper systems that feature tall energy
abs
orbing beams and crash boxes that are fitted at common
heights and can effectively protect the vehicle in low speed
crashes. The bumper systems should also have wide beams
that protect the corners of the vehicle in low speed crashes.

In the opinion of RCAR
, good vehicle bumper beams
should:



be fitted to both the front and rear of vehicles



be replaceable without cutting or welding



be positioned to fully engage with the front and rear
bumper barriers



be torsion
-
resistant to carry eccentric loads without
t
wisting



absorb energy and restrict damage to the bumper system
only



be attached to the body via energy absorbing structures
that are inexpensive to repair or replace



be stable during impacts to prevent underride and
override



prevent damage to structura
l, welded or bonded and other
expensive parts



extend laterally to protect vehicle corner

IV.

MECHANICS AND MODELL
ING

It is important in the study of impacts to distinguish between
the two different types of impacts that occur, elastic and
plastic impacts. In an elastic impact a negligible amount of
energy is lost between the two impacting bodies, for example,
the collisi
on of two billiard balls. A plastic impact involves a
significant amount of energy dissipated in the collision. An
impact between two vehicles or between one vehicle and a
rigid body, where the vehicles crumple on impact, is an
example of an elasto
-
plastic

impact. The impacting
phenomenon between an impactor and the front bumper
under
collisions
could be very complicated, since transient and
nonlinear analyses are involved. But, in designing the front
bumper, automobile manufacturers insist that the bumper
system should not have any material crash or failure.
Therefore, up to that point, the total energy is conserved
throughout the impact duration.
Some simpler conceptual
designs are made according to Bumper standards and
Dimensions referred from RCAR bumper

test,



National Highway Traffic Safety A
dministration

laboratory
Test procedures. Thickness is considered as variable
parameter and other dimensions are designed under allowable
sizes.

Sheet metal Design is involved for

designing

Bumper
Beams
as shown in

fig 1,2,3,4.
Using Catia

V5 R11

the models are
designed
. Bumper is designed as per the Standard
s

followed.



Fig 1: Simple hat profile
Fig 2: Double Hat profile


Fig 3: Oblique profile


Fig 4: Closed Hat profile

Simpler Designs Profiles of Bumper

beams
are

taken

into
study and
Modelled

Using Catia v5 r11
. Variable Parameters
like Shape, thickness can be modified from this basic Design
in future for analysis and Improvement. Options like Bends,
Punch,
and Rib

are used to create the model.

These mod
els are
analysed for the Energy absorption behaviour and
categorise
the results to compare among the other designs.


V.

FINITE ELEMENT MODE
LLING

There was a general approach for all the aforementioned
models, i.e. with different material, shape and thickness

created in LS_DYNA. The CAD data of the bumper structure
was imported and the surfaces were created and meshed.
Since the average thickness of bumper was much smaller than
the other dimensions of the part, the best element for meshing
was the shell elemen
t. Hypermesh is used to mesh the model
and to give all the inputs and load conditions that can be
directly exported to LS
-
DYNA.

Analysis Procedure:

Explicit Dynamic Analysis Finite Element Program is used
to solve highly non
-
linear Transient Dynamic Probl
ems. LS
-
DYNA solver has Benefits of fastest explicit features than any
other explicit code in Market place. LS
-
DYNA is mostly
applicable for,



Crash worthiness Analysis



Manufacturing Process(Deep drawing, Hydro Forming,
Rolling, Extrusion etc)



Forming Proce
ss (Drop test, Contact test, Pendulum
Impact Test)

Materials
used

Young’s
modulus(b)
䝰a

Poisson’s
o慴楯(
𝛝

)


䑥Dsity
(ρ)

䭧/mm
3

Commercial
steel bare

207

0.3

7.8e
-
6

Aluminium
3105
-
H18

68.9

0.33

2.72e
-
6

PEP

1.2

0.4

0.9e
-
6


Table 1: Material
Properties used



The procedure for an explicit dynamic analysis is similar to
any other analysis that is available in the ANSYS program.
The three main steps are:



Build the model



Apply loads and obtain the solution



Review the results

When solving
Dynamic problems with Fem, it must be
remembered that we use FEM only for spatial Discretization
and the temporal time discretization is always using the FEM.
We divide the total response time into much smaller intervals
called time steps or increments. Th
e equilibrium equation and
the value of unknowns are determined at (t+At) based on
value of time t. Explicit methods are those in which the
information at time step n+1 can be obtained in terms of
previous time steps and there is no dependence on the curre
nt
time step.

Altair HyperMesh 9.0 includes many new features that can
improve and automate your CAE processes. It is Universal
Finite element pre
-
post processor software. This capability
allows for consistent modeling practices for 1D, 2D, and 3D
elements
.


The basic modeling process in HyperMesh, given a
mesh, involves the creation materials and properties followed
by the assignment of properties to elements or components.

VI.

PROCESSING


The impactor, as a steel structure, was modelled with rigid
solid impac
t elements according to precise dimensional
drawings from the E.C.E. Standard. Material type 20 (mat
-
rigid) is

assigned using Hypermesh 9.0 used for further
analysis in LS
-
DYNA
.

Fig. 5 shows the model of bumper
beam and the impactor.

Bumper beam is assign
ed as
deformable structure is so called “MAT type 24”
A
, Piecewise
Linear Isotropic model. A
s shown, the impactor collide to the
bu
mper beam in straight direction
and perpendicularly.



Fig 5 Bumper
beam and Impactor



Fig 6 Fixed Constraints

(I) Material properties:

Table 1: Material Properties used

(II) Loads and Constraints:

Usually in all finite element study constraints plays a major
role. Bumper

beam

is constrained at both the ends as shown in

fig 6. The impactor collides to the bumper perpendicularly
with 18.6 mm/msec velocity (based on LS
-
DYNA standard
units)

(III) Parameters considered:

Parameters like thickness, shape are varied for carrying out
the analysis with constant velocity.
Characte
ristics of
Impactor remain

constant
for all the cases
. Thickness varies
from 2mm to 4mm in the increasing order of 0.25 mm.

Hypermesh software is used to assign all loads and constraints
that will be used in LS
-
DYNA for analysis. Keyword file is
exported f
rom Hypermesh that is used in LS
-
DYNA solution
manager to solve and LS
-
DYNA Pre/Post processor to
produce results.

Case (i): Simple hat Profile is tested for impact behaviour for
varying thickness 2mm to 4mm
in the increasing order o
f 0.25
mm with three di
fferent materials viz., Steel, Aluminium,
PEP(Poly Ethylene Propylene)

Case (ii): Double hat Profile is tested for impact behaviour for
varying thickness 2mm to 4mm
in the increasing order o
f 0.25
mm with three different materials viz., Steel, Aluminium,
PEP
(
Poly Ethylene Propylene).

Bumper beam

Impactor

Fixed Constraints

Case (iii): Oblique hat Profile is tested for impact behaviour
for varying thickness 2mm to 4mm
in the increasing order o
f
0.25 mm

with three different materials viz., Steel, Aluminium,
PEP(Poly Ethylene Propylene).

Case (iv): Closed hat Profile is tested for impact behaviour for
varying thickness 2mm to 4mm
in the increasing order o
f 0.25
mm with three different materials viz., Steel, Aluminium, PEP
(Poly Ethylene Propylene).

VII.

RESULTS AND DISCUSSI
ON


The main criteri
on to be discussed is energy absorbing
behaviour of bumper beams during head
-
on collisions.
Analysis is carried out upto 20 millisecond. Results for
different
Designs

and
for varying
thickness are obtained and
compared to study the impact behaviour of beam
s

under study
.

Results for case (i) with thickness 2mm and steel material is
shown below. Similarly Results are obtained for different
thickness and materials.

Max.Displacement is measured at the
condition of Bumper Rebound i.e. the time at which the
impac
tor gets Rebound after hitting the bumper.

(I) Sample Results
:


Fig 7
: Nodal Displacement at Bumper rebound condition




Fig 8
:
Max. Nodal Displacement Plot over time




Fig 9
: Energy plot for Bumper system

(Simple hat profile
Steel material 2mm)








Fig 10
: Kinetic Energy plot (Impactor)




Fig
11
: Kinetic energy plot (bumper)

Impact behaviour of Bumper beam is analyzed based on
energy absorption of the beam and the displacement condition.

Fig
7

shows the Nodal Displacement at the bumper rebound
c
ondition.
fig 8 shows Max. Nodal displacement plot over the
period of time.
A good bumper should prevent the impact
energy getting transferred to the passengers
also with a
minimal thickness. Fig 9 shows the Energy plot for th
e
Bumper system includ
ing Bumpe
r and impactor. Fig 10, 11

shows the kinetic energy plot for Impactor and bumper
individually.

Similarly by increasing thickness and by varying
Materials results are plotted for comparison.


Analysis is to be carried out

for other cases

to find the
appropr
iate condition for the different designs based on
energy absorption behaviour and nodal displacement.



R
EFERENCES

[1]


JavadMarzbanrad , MasoudAlijanpour , MahdiSaeidKiasat
. Design
and analysis of an automotive bumper beam in low
-
speed frontal
crashes. Thin
-
Walled Structures 47 (2009) 902

911.

[2]

M.M. Davoodi, S.M. Sapuan , Ahmad , A. Aidy , A. Khalina , Mehdi
Jonoobi
. Concept selection of car bumper beam with developed hybri
d
bio
-
composite material. Materials and Design 32 (2011) 4857

4865.

[3]

M.M. Davoodi, S.M. Sapuan, D. Ahmad, Aidy Ali, A. Khalina, Mehdi
Jonoobi.

Mechanical properties of hybrid kenaf/glass reinforced epoxy
composite for passenger car bumper beam. Materials a
nd Design 31
(2010) 4927

4932.

[4]

M.M. Davoodi, S.M. Sapuan , R. Yunus
. Conceptual design of a
polymer composite automotive bumper energy absorber. Materials and
Design 29 (2008) 1447

1452.

[5]

A.R. Mortazavi Moghaddam, M. T. Ahmadian.

Design and Analysis of
an Automobile Bumper with the Capacity of Energy Release Using
GMT Materials. World Academy of Science, Engineering and
Technology 76 2011.

[6]

A. Hambali, S. M. Sapuan, N. Ismail, Y. Nukman.

Material selection of
polymeric composite
automotive bumper beam using analytical
hierarchy process.

J. Cent. South Univ. Technol. (2010) 17: 244−256.

[7]

HyperMesh V9.0 software package along with User Guide Manual


Altair Engineering India Ltd.

[8]

Bus Rollover Analysis with LS
-
DYNA.

CADFEM GmbH. Kadi
r
Elitok, FEA Engineer TEMSA A.S. Fatih Han Avci, FEA Engineer
TEMSA A.S.

[9]

RCAR Bumper Test, Issue 2.0. September 2010.

[10
] LS
-
DYNA Keyword user’s manual. July 2006 version 971.