Comparative Analysis of Behaviour of Engineering Composite Materials & their effect on Automobile Bumper Design

ISSN 2393-8471
International Journal of Recent Research in Civil and Mechanical Engineering (IJRRCME)
Vol. 2, Issue 2, pp: (20-36), Month: October 2015 – March 2016, Available at: www.paperpublications.org
Page | 20
Paper Publications
Comparative Analysis of Behaviour of
Engineering Composite Materials & their effect
on Automobile Bumper Design
1
Ajaykumar D. Katore, 2
Prof. Sachin Jain
1,2
NRIIST Bhopal, Madhya Pradesh, India
Abstract: A good design of car bumper must provide safety for passengers and should have low weight. Different
countries have different performance standards for bumpers. Under the International safety regulations originally
developed as European standards and now adopted by most countries outside. After the impact on the bumper all the
control systems and signing system should be in working conditions. It must also withstand static and dynamic loads
without undue deflection or distortion. The given model is tested under frontal collision conditions and the
resultant deformation and stresses are determined using hyper works software. Automotive development cycles are
getting shorter by the day. With increasing competition in the marketplace, the OEM’s and suppliers main challenge is
to come up with time-efficient design solutions. The design should be such that, it ensures the passenger safety; the
design should be cost effective also. Researchers are trying to improve many of existing designs using novel approaches.
Bumpers are fixed on the front and on the back side of a car and serve as its protection. They reduce the effects of
collision with other cars and objects due to their large deformation zones. The bumpers are designed and shaped
in order to deform it and absorb the force (kinetic energy) during a collision. Many times there is conflicting
performance and cost requirements, this puts additional challenge with R&D units to come up with a number of
alternative design solutions in less time and cost compared to existing designs. These best solutions are best achieved in a
CAE environment using some of the modern CAD and FEM tools. Such tools are capable of effecting quick changes in
the design within virtual environment.
Keywords: Automotive bumpers, Bumper, Bumper analysis, Bumper design, Crash energy Absorption, Development of
bumper system. Passenger Safety.
1. INTRODUCTION
In automobiles a bumper is the front-most or rear-most part, ostensibly designed to allow the car to sustain an impact
without damage to the vehicle's safety systems. They are not capable of reducing injury to vehicle occupants in high-
speed impacts, but are increasingly being designed to mitigate injury to pedestrians struck by cars.
Effect of materials and their properties on bumper:
1.1Modulus of Elasticity:
Mechanical specifications of the isotropic and metallic materials are illustrated in Table to study the effect of elastic
modulus on bumper impact behavior, three mentioned alloys.

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Fig.1.1.1: Elements of Bumper
Metals with different modulus of elasticity are selected where they have equal yield strength. The impactor collides to the
bumper perpendicularly with 4 km/h velocity. The deflection was measured at the nodes located in the middle of the
bumper horizontally. Point of center of impact was assumed 445 mm above ground in this simulation according to the
low-velocity impact
Table 1.1: Material properties of the models of bumpers
Fig.1.1.2: Deflection Comparison
1.2Yield Strength:
The effect of yield strength on impact behavior is studied with three different specifications on aluminum alloys. All
phenomena are attributed to the yield strength of aluminum. For different aluminum bumpers, difference between vehicle
and impactor velocities after impact increases by increasing the yield strength. According to these figures, the velocity of
impactor is not reduced to zero. The major reason is plastic deformation that occurs in the bumper and holders.

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Table 1.2.1: Material properties for Aluminium and Steel material
Fig.1.2.1: Various aluminum bumper deflections.
Fig.1.2.2: Kinetic energy transfer in aluminum 2219-T31 bumper
Fig.1.2.3: Kinetic energy transfer in aluminum 2024-T86 bumper.

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Fig.1.2.4: Impact forces in aluminum bumpers.
2. EFFECT OF THICKNESS PARAMETER ON BUMPER
Different bumper beam thickness made of high-strength steel (Bare/EG-HF 80Y100T) with 584 MPa yield strength were
chosen to determine the effect of impact behavior.
Fig.2.1: Effect of thickness on bumper deflection.
Fig.2.2: Effect of thickness on impact force.
The separation point and the maximum deflection point take place with a delay in thicker bumper. The study of impact
forces on bumper with various thicknesses shows that the impact force enhances following increasing the bumper
thickness as illustrated in Fig. 2.2. So, the acceleration rate of the car increases very fast, since this force applies in short-
time interval. By investigation of kinetic-energy diagram, it is observed that more kinetic-energy transfer from impactor
to vehicle and less plastic strain energy dissipates with increasing the bumper thickness.

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3. EFFECT OF RIBS ON BUMPER
The ribs are strengthening plates of average thickness 4 mm, mainly placed along the vertical and horizontal direction of
bumper beam as shown in Fig.3.1, for preventing deflection of lateral surfaces and thus creating a rigid structure. To study
the effect of ribs on impact behavior, high-strength steel (Bare/EG-HF 80Y100T) with 584 MPa yield strength is chosen.
Fig.3.2 clearly shows how ribs can reduce deflections: 19% comparing conditions of bumper with-ribs and without-ribs.
As shown in this figure, this decrease is also noticeable in separation time of the without-ribbed bumper after a time of
0.054 s, due to lower rigidity of the structure.
Fig.3.1: Ribs in vertical and horizontal direction.
Fig.3.2: Deflections in two case studies of bumpers
Fig.3.3: Impact force in two case studies of bumpers.

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In addition, it is observed from Fig. 3.3 that ribbed bumper has a stronger impact force than un-ribbed one. Augmentation
of maximum impact force is 7%. This phenomenon increases the rigidity of the bumper structure and grows impact force.
Careful attention of the impact velocities represents that the ribs do not have an influence on vehicle and impactor
velocities. Here, it is comprehended that finding an un-ribbed structure with the same speed decelerating behavior as the
ribbed bumper is a very reasonable replacement solution and should be precisely focused due to the advantage of ease of
manufacturing, however; the ribs have an effect on impact behavior.
4. PASSENGER EFFECT
The presence of passengers on impact behavior with mentioned steel is investigated by considering the passenger’s
weight in the mass point elements. For simplification, the effect of distribution of passengers was ignored here. In fact, the
presence and absent of passengers investigated in this study as in the standards also recommend three passengers added to
driver. The impact force with and without passengers is calculated and shown in Fig. 4.1. It shows that the impact force is
increased up to 12% by existing passengers. So car’s kinetic energy decreases comparing with the case of without
passenger.
Fig.4.1: Impact force in two case studies of bumpers for passenger effect.
Fig.4.2: Deflections in two case studies of bumper.
5. INTRODUCTION TO FINITE ELEMENT METHOD
The finite element method (FEM), sometimes referred to as finite element analysis (FEA), is a computational technique
used to obtain approximate solutions of boundary value problems in engineering. Simply stated, a boundary value
problem is a mathematical problem in which one or more dependent variables must satisfy a differential equation
everywhere within a known domain of independent variables and satisfy specific conditions on the boundary of the
domain. The boundary conditions are the specified values of the field variables (or related variables such as derivatives)
on the boundaries of the field. Depending on the type of physical problem being analyzed, the field variables may include
physical displacement, temperature, heat flux, and fluid velocity to name only a few.

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5.1 A general procedure for finite element analysis:
1. Preprocessing:
The preprocessing step is, quite generally, described as defining the model and includes
 Define the geometric domain of the problem.
 Define the element type(s) to be used.
 Define the material properties of the elements.
 Define the geometric properties of the elements (length, area, and the like).
 Define the element connectivity’s (mesh the model).
 Define the physical constraints (boundary conditions).
 Define the loadings.
 The preprocessing (model definition) step is critical.
2. Solution:
During the solution phase, finite element software assembles the governing algebraic equations in matrix form and
computes the unknown values of the primary field variable(s). The computed values are then used by back substitution to
compute additional, derived variables, such as reaction forces, element stresses, and heat flow. As it is not uncommon for
a finite element model to be represented by tens of thousands of equations, special solution techniques are used to reduce
data storage requirements and computation time. For static, linear problems, a wave front solver, based on Gauss
elimination is commonly used.
3. Post-processing:
Analysis and evaluation of the solution results is referred to as post processing. Postprocessor software contains
sophisticated routines used for sorting, printing, and plotting selected results from a finite element solution. Examples of
operations that can be accomplished include-:
 Sort element stresses in order of magnitude.
 Check equilibrium.
 Calculate factors of safety.
 Plot deformed structural shape
 Animate dynamic model behavior.
 Produce color-coded temperature plots.
6. INTRODUCTION TO ANALYSIS
Analysis is done by selecting appropriate solver and carrying out the operations in various stages to obtain solution. The
analysis of bumper can be done by using explicit solvers like LS- Dyna, Abaqus, etc. whichever suitable. Particularly
analysis is carried out in three stages by performing various operations in software.
1. Stage-I
In this stage .igs file is imported to the meshing software like Hypermesh. The CAD data of the bumper structure is
imported and the surfaces were created and meshed. Since the average thickness of bumper is much smaller than the other
dimensions of the part, the best element for meshing is the shell element. Some various choices of impact elements can be
considered like implicit and explicit model. Here, nonlinear explicit impact modelling elements are used for analysis.

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2. Stage-II
After meshing is completed we apply boundary conditions. These boundary conditions are the reference points for
calculating the results of analysis. In short we here go for the preparation of deck. Here we apply define and apply various
loads. Different load steps are created which are to be applied during analysis. Here surrounding effect is been taken into
consideration while applying loads. Elements are defined by their properties. Material properties such as density, modulus
of elasticity, Poisson’s ratio etc. is assigned to the elements. Here proper arrangements are made so that we can run the
analysis in solver software.
3. Stage-III
Meshed and boundary condition applied model is imported to the solver. Analysis process starts after applying run in the
solver software. Software first calculates the deflection with respect to the boundary conditions applied. Then on the basis
of deflection it calculates strain. Once the strain is calculated we know modulus of elasticity then we can calculate the
stress values. Results are viewed and accordingly modifications are suggested. Modifications are suggested according to
high stress regions obtained. If the stresses are beyond the permissible limits then changes such as change in material,
change in thickness of component or addition of ribs etc are made according to suitability.
7. TESTING METHODS
1. Full-Wrap Frontal Collision Test:-
Dummies are placed in both the driver's and passenger's seats and the vehicle is made to collide with a concrete barrier at
a rate of 55 km/h. Actual collisions of this type tend to occur at speeds lower than that of this test. The dummies are then
checked for injuries to the head, neck, chest and legs, the vehicle is checked for damage, and the results are used to
evaluate the degree of passenger protection in 5 levels.
Fig.7.1: Full- Wrap frontal collision test image
2. Offset Frontal Collision Test:
The dummies are placed in the driver's and front passenger's seats and the test vehicle is made to collide head-on with an
aluminum honeycomb, on the driver's side (at an offset of 40%). The dummies are checked for injuries to the head, neck,
chest and legs, the vehicle is checked for damage and deformation, and the results are used to evaluate the degree of
passenger protection in 5 levels.
Fig.7.2: Offset frontal collision test image

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3. Side Collision Test:-
Among the passenger injuries which occur in automobile collisions, side collisions cause the most damage next to frontal
collisions. In this test, a truck with a weight of 950 kg is made to collide at a speed of 55 km/h with the side of a stationary
test vehicle with a dummy in the driver's seat. The dummy is checked for injuries to the head, chest, abdomen, and waist,
and the results are used to evaluate the degree of passenger protection in 5 levels. 5
Fig.7.3: Side collision test image
8. IMPACT PRINCIPLE
An isometric view of impact layout is shown in Fig. 13.1 to study the impact principle on Bumper assembly.
Fig.8.1: Isometric view of Impact Layout
The impacting phenomenon between an impactor and the front bumper in a low-speed full crash 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. Since the impactor is assumed to be rigid and the bumper beam
is made of metallic material and shock absorber is a relatively low stiffness material, the distribution of the impact load is
irregular along the contact area and over the contact region of the bumper, the bumper beam subjected to the impact load
undergoes a constant deformation dmax. A principle of energy conservation in the elastic impact is used; the kinetic energy
before impact is conserved and converted to elastic energy and the kinetic energy of the impactor and the automobile at its
maximum deﬂection, i.e.,
Where mA is the mass of the impactor, mB the mass of vehicle, vA the velocity of the impactor before impact and v0 the
final velocity of the impactor and vehicle in maximum deflection point. Keq the equivalent impact stiffness of a bumper

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and is obtained by the relationship of displacement and reaction forces from beam analysis. An important consideration of
momentum is that it can be neither created nor destroyed. Thus, the momentum before an impact is equal to the
momentum after the impact. At the moment of its maximum deflection, a principle of momentum conservation before and
after impact can be expressed as follows:
From equations (1) and (2) the maximum deflection dmax is obtained as follows:
After separation point, energy and momentum conservation equations can be expressed as follows:
The Eq. (6) can be used to find the energy dissipated, ED, during an impact. This is found by subtracting the kinetic
energy of the two masses after impact, and the kinetic energy of the impactor before impact.
System formulation -:
Figure 8.2: One dimensional mass spring damper model.
The time-invariant mass spring damper model with n-degrees of freedom (DOF) shown in Figure 13.2 above can be
described in continuous time by a second order differential equation
Where m, c and k represents n * n mass, damping and stiffness matrices respectively. X is a n * 1 vector of displacements,
and and are both vectors of the same size with velocities and accelerations. The matrix b is the n *r input matrix
and f is an r * 1 vector of input excitations. By introducing the state vector X as the system can be written in the
first order matrix form as
Where are the time-invariant continuous time system matrices where N = 2n and M denotes the
number of outputs y. Multiplying (2) with and integrating yields
Equation (3) is the analytical solution to the continuous model.

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9. BUMPER ASSEMBLY ANALYSIS
9.1 Original Model Analysis:
We are provided with bumper assembly as shown in fig.14.1 whose component thickness are listed in the table
Fig.9.1: Assembly of bumper system to be analyzed
Table no.9.1 part details-:
Sr. no. Part name Original model thickness
1 Front panel 01.60mm
2 Side panel 01.60mm
3 Bracket 04.00mm
4 Supporting Bracket 12.00mm
5 Chassis parts 10.00mm
9.2 Preprocessing:
The model consists of infinite number of points hence it should be discretized to some finite number of divisions on
which analysis is to be carried out. So we mesh this model to divide it into finite number of divisions called as nodes and
elements. We prefer 2d or shell mesh as the third dimension (thickness) of all the components is very small as compared
to other two dimensions (length and width) Mesh size is selected by convergence criteria. After meshing the model
appears as shown in fig.9.1 and 9.2 the meshed model is then checked for quality of mesh.
Fig.9.2.1: meshed model of bumper system assembly
(Front view)

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Fig.9.2.2: meshed model of bumper system assembly
(Rear view)
Once the meshing is done model is checked for quality and normal so that stress regions are properly defined after
analysis. After meshing materials of respective parts are assigned to them by their material properties such as modulus of
elasticity, poisons ratio, density of material, etc. . Here we are provided with Steel as a basic material whose properties
are described in table below.
Fig 9.2.3: ANSYS for Original Bummer
Table 9.2.1: Material properties of Steel
Material Modulus of elasticity Density Poisson ratio
Steel 210 kN/mm^2 7.86e^-6
kg/mm^3
0.29
This material is further classified as soft steel and hard steel and assigned to the components as shown in table 9.3

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Table 9.2.2: Assignment of Materials to components-:
Sr. no. Part name Material
1 Front panel Soft steel
2 Side panel Soft steel
3 Bracket Hard steel
4 Supporting Bracket Hard steel
5 Chassis parts Hard steel
6 Impactor Rigid
The values and curves of stress strain plots of both the material is as shown below.
Table 9.2.3: Soft steel stress strain curve data-:
STRESS (X) STRAIN (Y)
0.001 0.2
0.002 0.21
0.003 0.22
0.005 0.24
0.008 0.27
0.1 0.391
0.14 0.4
0.16 0.41
0.19 0.43
0.2 0.44
0.21 0.44
0.22 0.44
Table 9.2.4 Hard steel stress strain curve data-:
STRESS (X) STRAIN (Y)
0.001 0.342
0.002 0.344
0.003 0.345
0.005 0.35
0.007 0.358
0.011 0.36
0.1 0.39
0.12 0.41
0.15 0.43
0.18 0.47
0.2 0.49
0.21 0.49
0.22 0.49

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Fig.9.2.4: Comparison curve between hard and soft steel
Figure 14.1.1.3 shows the comparison curve of hard steel and soft steel through their nonlinear curves. Boundary
conditions are reference for problem solving in analysis. This deals with constraining (fixing) the model, application of
loads, giving proper contacts etc. . Here we are provided with the constrained conditions, mass of vehicle which is about
887kg and velocity of impact which is 10m/sec. bolt connections are given by beams and proper constraints are applied.
The constrained model appears as shown in fig. 9.2.3
Fig.9.2.5: Bumper assembly after preprocessing
The velocity is given to the impactor through proper contacts defined between bumper and impactor. The mass of vehicle
here is considered during impact conditions. Contacts are defined via elements as shown in fig. 14.1.1.5
Fig.9.2.6 Image of contacts in the model
9.3 Solution stage-:
After pre processing model is further send for analysis. Here we use LS- Dyna solver for analysis purpose which is an
explicit solver. Explicit refers to the numerical method used to represent and solve the time derivatives in the momentum
and energy equations. The following figure presents a graphical description of

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Explicit time integration. The displacement of node n2 at time level t+Δt is equal to known values of the displacement at
nodes n1, n2, and n3 at time level t. Systems of explicit algebraic equations are written for all the nodes in the mesh at
time level t+Δt. Each equation is solved in-turn for the unknown node point displacements. Explicit methods are
computational fast but are conditionally stable. The time step, Δt, must be less than a critical value or computational errors
will grow resulting in a bad solution. The time step must be less than the length of time it takes a signal traveling at the
speed of sound in the material to traverse the distance between the node points.
The results achieved by ANSYS for modified values
Fig.9.3.1: ANSYS for modified Bumper
9.4 Experimental Set up:
Testing ground the test area shall be large enough to accommodate the impactor (striker) propulsion system and to permit
after-impact displacement of the vehicle impacted and installation of the test equipment. The vehicle shall be placed on a
horizontal and level rigid smooth surface.
Fig. 9.4.1: Bumper and Fixture Assembly.

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a) The impactor shall be of rigid construction, the impact contour being of hardened steel.
b) The impacting surface shall conform to the diagram in the figure
c) The effective mass shall be equal to the mass corresponding to the “unladen weight" of the vehicle to be tested
Fig.9.4.2: Impactor.
d) With plane of the impactor vertical, the reference line shall be horizontal.
e) The first contact of the impactor with the vehicle shall be by the impact contour on the protective device.
f) The reference height is 445 mm.
10. CONCLUSION
From above analysis we come to the conclusion that the permissible strain values can be achieved by changing the
thickness of bumper components. Changing the thickness is one of the cost effective way to get the assembly in safety
zone as compared to others such as change in geometry or addition of ribs.
 From study we have calculate the permissible strain values by changing the thickness of bumper components.
 Changing the thickness is one of the cost effective way to get the assembly in safety zone as compared to others such
as change in geometry or addition of ribs.
 We have evaluated the permissible plastic strain values which will help in knowing energy absorption, thus making the
component assembly safe.
Sr. Part Name Size 1 ANSYS 1 Result Size 2 ANSYS 2 Results
1 Front panel 1.6 0.25 0.24 2 0.18 0.20
2 Side panel 1.6 0.07 0.08 1.6 0.12 0.13
3 Bracket 4 0.33 0.31 6 0.25 0.23
4 Supporting Bracket 12 0.20 0.21 12 0.26 0.22
5 Chassis 10 0.0 0.0 10 0.01 0.01

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 Increasing bumper thickness causes a rise in bumper rigidity increasing its strength. Consequently, it results in
reduction in strain values.
 Even by using material like Composite materials we can increase the energy absorption capacity of the bumper.
 Strain failure of composite material is (3.6/20) 1/5th
 Their density (970) is 1/9th to that of steel, but it’s not cost effective.
 For same strain the weight of bumper gets reduced to 44%
11. FUTURE SCOPE
 We have changed the thickness of components to get the strain values in permissible limits. Same can be achieved by
change of material with some superior properties like composite materials with optimum cost.
 By adding material we can increase the strength of the component.
 We can also go for the development of some composite materials which would have greater strength and less cost.
Same principle can be applied to increase strength of components in other applications.
 For example we can increase the thickness of leaf spring if it fails to give a strong support to absorb shocks. Addition
of ribs is also the other way to increase the stiffness of component to avoid the failure.
 Also we can add alloying elements in the material.
REFERENCES
[1] Javad Marzbanrad, Masoud Alijanpour, Mahdi Saeid Kiasat (2009), “Design and analysis of an automotive bumper
beam in low-speed frontal crashes” Science Direct paper pp.902-911.
[2] Liquan Mei and C.A. Thole (2007) “Data analysis for parallel car-crash simulation results and model optimization”
Science Direct paper pp. 329-337.
[3] Nader Abedrabbo and Robert Mayer (2009) “Crash response of advanced high-strength steel tubes: Experiment and
model” Science Direct paper pp.1044-1057
[4] F.Ince, H.S. Turkmen, Z. Mecitoglu, N. Uludag, I. Durgun, E. Altınok and H. Orenel (2011) “A numerical and
experimental study on the impact behaviour of box structures.” Science Direct paper pp.1736-1741
[5] Bryan C. Baker, Joseph M. Nolan, Brian O’Neill and Alexander P. Genetos (2007) “Crash compatibility between
cars and light trucks: Benefits of lowering front-end energy-absorbing structure in SUVs and pickups” Science
Direct paper pp.116-125
[6] Tso-Liang Tenga, Fwu-An Changb, Yung-Sheng Liuc and Cheng-Ping Peng (2007) “ Analysis of dynamic response
of vehicle occupant in frontal crash using multibody dynamics method” Science Direct paper pp.1724-1736
[7] O.G. Lademo, T. Berstad, M. Eriksson, T. Trylan, T. Furu, O.S. Hopperstad and M. Langseth (2007) “A model for
process-based crash simulation” Science Direct pp.376-388
[8] Jovan Obradovic, Simonetta Boria and Giovanni Belingardi (2011) “Lightweight design and crash analysis of
composite frontal impact energy absorbing structures.” Science Direct pp.423-430

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