IMPACT TEST ANALYSIS OF AUTOMOBILE
CRASHBOX
A PROJECT REPORT
Submitted in partial fulfilment for the award of the degree of
Bachelor of Technology
in
Mechanical Engineering
by
ARSH THAKUR – 18BME0657
DARSHIT AGRAWAL – 18BME0323
SESHENDRA KALYAN PEPAKAYALA – 18BME0332
School of Mechanical Engineering
APRIL,2022
TABLE OF CONTENTS
Table of Contents
School of Mechanical Engineering _______________________________________________ 1
DECLARATION BY THE CANDIDATE ___________________ Ошибка! Закладка не определена.
BONAFIDE CERTIFICATE ____________________________ Ошибка! Закладка не определена.
ACKNOWLEDGEMENT _____________________________ Ошибка! Закладка не определена.
EXECUTIVE SUMMARY __________________________________________________________ 3
LIST OF TABLES ________________________________________________________________ 4
LIST OF FIGURES _______________________________________________________________ 5
LIST OF SYMBOLS AND ABBREVIATIONS _______________ Ошибка! Закладка не определена.
1.
INTRODUCTION AND LITERATURE REVIEW ______________________________________ 6
1.1.Background __________________________________________________________ 6
1.2.Problem Statement ____________________________________________________ 7
1.3.Motivation __________________________________________________________ 7
1.4.Challenges Faced _____________________________________________________ 8
1.5.Approach ____________________________________________________________ 8
1.6.Literature Review ________________________ Ошибка! Закладка не определена.
1.7.Knowledge Gained from Literature Review _________________________________ 9
1.8.Gaps in Research _____________________________________________________ 10
1.9.Aim and Objective____________________________________________________ 11
2.
METHODOLOGY AND EXPERIMENTAL WORK _________________________________ 12
2.1Design Approach _____________________________________________________ 12
2.2Process flow _________________________________________________________ 13
2.3Material ____________________________________________________________ 14
2.4Analysis Procedure____________________________________________________ 16
2.5Structures ___________________________________________________________ 17
3.
Results and discussion ___________________________________________________ 21
4.
Conclusion _____________________________________________________________ 28
EXECUTIVE SUMMARY
In the growing automotive world, manufacturers compete to fabricate the best-in-class product
with no compromise with durability and safety of vehicle. One such element of car is crash box
which makes our vehicle safe and durable. Crash box is a passive safety system which is
intended to absorb kinetic energy in case of impact at low velocity frontal crash and
maintaining the vehicle deceleration in a safer limit, so as to minimizing the chance of injury of
the passenger’s during collision. This crash box is installed between the bumper and the side
member of the vehicle chassis. During crash the crash, the crash box should deform preceding
to surrounding parts by absorbing maximum energy so that there is minimum service cost after
the crash. In order to develop durable and safer vehicles, crashworthiness of automobiles has
become a crucial parameter. This paper aims to provide a comprehensive study of crash box
and to develop an optimized crash box which can absorb the maximum impact energy and is
having minimum peak force.
Keywords: Crash Box, LS Dyna, Origami Structure, Re Entrant Structure, Transition Structure
LIST OF TABLES
Table 1: Literature Review ______________ Ошибка! Закладка не определена.
Table 2: Material properties of Steel and Aluminum ______________________14
Table 3 : Dimensional Range ________________________________________16
Table 4: Re-entrant Crash-Box Results _________________________________25
Table 5: Modified Square Crash-Box Results ____________________________25
Table 6: Protruding Crash-Box Results ________________________________26
Table 7: Origami Crash-Box Results __________________________________26
Table 8:Crush Force Efficiency ______________________________________26
LIST OF FIGURES
Figure 1: Process Flow Chart ________________________________________13
Figure 2: True Stress vs Plastic Strain curve of Structural Steel _____________15
Figure 3: True Stress vs Plastic Strain curve of Al6061 ____________________15
Figure 4: Analysis Setup ____________________________________________17
Figure 5: Modified Square Crash-Box _________________________________17
Figure 6: Protruding Design _________________________________________18
Figure 7: Re-entrant Crash Box ______________________________________19
Figure 8: Origami Crash Box ________________________________________20
Figure 9: Energy Absorption Comparison ______________________________21
Figure 10: Peak Crushing Force Comparison ___________________________22
Figure 11: Mean Crushing Force Comparison ___________________________23
Figure 12: Displacement Comparison _________________________________23
Figure 13: Specific Energy Absorption _________________________________24
Figure 14:Crush Force Efficiency _____________________________________24
CHAPTER 1
1. INTRODUCTION AND LITERATURE REVIEW
In this chapter an attempt has been done to optimize the efficiency of the crash box by exploring
different structural geometries and comparing different materials. The crash box is to designed to
absorb the kinetic energy during the frontal impact at low speeds and to avoid large structural
damage to the chassis. The significance of the crash box is to cut down the re-pair cost of the
vehicle due to the collision. The efficiency of the crash box has been conducted according to the
Research Council for Automotive Repairs (RCAR) regulations which is 16kmph to minimize the
repair costs.
1.1. Background
In the 21st century every consumer is aware about the importance of safety, thus it is must for
every manufacturer to make the vehicle as safe as possible and crash box plays a major role in
that area.
Crash box is a passive safety element which is part of the crashworthy system and its role is to
reduce the severity of frontal impacts that affect passengers or key vehicle elements.
It is located in between the bumper and first side member of the vehicle so whenever the vehicle
crashes the impact is absorbed by the bumper and crash box only.
During the collision the kinetic energy of the vehicle is converted to the strain energy of the
crash box.
Crash box ensures that the vehicle deaccelerates in a safer limit and also the impact on the
vehicle chassis is minimum, thus ensuring the safety and durability of the vehicle.it also helps in
reducing the repair cost as most of the damage is absorbed by the crash box.
The crash box comes in various structures and geometries and their crashworthiness is
determined by the parameters such as peak crushing force and energy absorption.
1.2. Problem Statement
Safety of automobiles is very important to reduce the occurrence of vehicle accidents and its
consequences. Safety of an automobiles is determined by the vehicle’s crashworthiness.
Crash box plays a predominant roll in crashworthiness of a vehicle in a crash test at lowspeed frontal impact. The crash box absorbs the impact due to the crash and ensures the
safety of the other components and minimizes the repair cost.
The crash box is assembled in-between the bumper and side member of the vehicle chassis.
The crash box should play a sacrificial role as it needs to deform prior to the other parts of
the vehicle. The extensive research on improving the crashworthiness of crash box were
focused on simple structural geometries.
The aim of this research is to explore the different geometries and to do a comprehensive
study of various complex geometries, their performance with structural steel and aluminum
6061 materials with respect to various parameters such as “peak crushing force”, “energy
absorption”, “mean crushing force” and “crush force efficiency”.
1.3. Motivation
Designs of automobiles are changing with emerging demands of several aesthetic features and
efficient design based on geometry. There is a rising demand to improve the crash worthiness of
an automobile.
The development of new structural geometries and crash analysis techniques have enabled us to
analyse the crashworthiness of the components. One of the parameters of the improving the
crashworthiness is the structural geometry.
The key parameter of the crash box is to absorb the maximum amount of kinetic energy and
deform prior to all other components in a low-speed frontal crash. The main motivation of this
project is to enhance the crashworthiness of the crash box by iterating the structural geometry
which can absorb maximum kinetic energy and get deformed at the earliest.
1.4. Challenges Faced
TIME:

The analysis of complex structures takes days to process the Results.
Multiple Thickness structure:

We have restricted our design and analysis to single thin wall structures as we used Shell
command to analyze our crash box structures in Ls Dyna.
User-Friendliness:

The analysis setup is too complex.

Extracting the results is tough.

Multitasking is not supported.
1.5. Approach
Our approach is fairly simple, it starts with very common steps like gathering data and setting up
our goals. Gathering data is very important and must step as it updates us about the current trends
in the market. We read research papers, articles, watched videos etc. to gather as much info as
possible. Our next step was to organize the given data by extracting information from that data as
well as arranging it from newest to oldest to get an exact idea of what progress took place and
what are the gaps in research. In our case, we found that most of the research is done on simple
designs, and whatever research is done on complex models is not compared with these simple
designs. The next step was to clearly define our aim and set up objectives to achieve these goals.
This also involves determining the evaluation parameters and software to be used for designing
and analyzing the crash box.
We opted for a design approach that involves designing simple as well as complex geometries
and analyzing them with different materials to get until we get the best results. We used
SOLIDWORKS software for designing and LS DYNA software for analyzing the crash box and
recording results. We started with a simple design and analyzed it and generated results. Based
on these results we iterated the model and did so till we achieve our desired results and at last,
compared the best designs of the crash box with each other. We also validated our results by
comparing them with other research work from a reputed journal.
1.6. Knowledge Gained from Literature Review

Crash-box is the predominant automotive parts for energy dispersion and absorption.

Its role is to get crushed by absorbing crash energy preceding to surrounding parts so
that the damage of the main chassis body is minimized and passengers are not harm.

The structure must be able to absorb the kinetic energy, mainly through permanent
distortion and deaccelerate the automobile in its safer limits.

Crash boxes are commonly made from thin-walled tubes with a square or rectangular
profile, are assembled between the bumper and chassis of car.

The reason for using thin-walled structures is because they have relatively stable and
predictable deformation patterns, least manufacturing costs.

An ideal crash box must fulfill the following requirements: a low peak force, i.e., the
reaction force during the crushing process and a high specific energy absorption,
defined as the total energy absorption divided by total mass of crash-box, to absorbe
as much kinetic energy as possible.

The design factors which effect the crashworthiness of crash box is its material,
dimensions, design of the crash box, manufacturing process used, discontinuities
present in the structure, shape of the box, taper angle if any etc.

The evaluation parameters for evaluation of the crashworthiness are the overall
energy absorbed, the peak crushing force, compressive displacement of crash-box, the
mean crushing force in crushing process of crash-box.

1.7.
Gaps in Research
No combined study of complex and simple structure
o Although many papers are published related to simple and complex
geometries but not many papers are available which collectively studies both
simple as well as complex designs.

No comprehensive study is available comparing different material and design.

Impactor is not properly defined

Studies are restricted to single parameters only.
o A very few studies are done which evaluates crash-box using multiple
parameters. Most of them are comparing either crushing forces or energy
absorbed.

No proper study is done to find out the effect of manufacturing process on crash-box
performance
1.8.
Aim and Objective
The project aims to do a comprehensive study on various designs of crash box and determine the
most optimized crash box amongst them.
We will be designing multiple structural geometries which starts from simple structures such as
rectangle, hexagonal to complex structural geometries such as origami, re-entrant structure and
transitions. We have used solid works software for designing various structures and geometries
of crash box and analysed them using LS DYNA software.
The crashworthiness of the crash box depends on the parameters such as peak crushing force,
maximum displacement and maximum energy absorption which was determined by crashing the
crash box to the impactor at low speed. The project is purely simulation based and is done in
online mode over a span of three months. This project can serve as a guide to crash analysis if
crash box as it includes simple structural geometries to complex models of crash box.
The objective of our study is to provide a comprehensive study on the passive safety system of
vehicles i.e., crash box and to come up with an optimized design of crash box. This study is
essential because it improves the safety and durability of our vehicle.
The project provides an overview of crashworthiness of various crash box models and aims to
develop an optimized crash box to improve the safety and durability of vehicle.

To design various crash box models and geometries.

To evaluate parameters like maximum peak force and energy absorbed using LS DYNA
software.

To analyze the crashworthiness of these models and determine the most optimized design
amongst them.
CHAPTER 2
2.0 METHODOLOGY AND EXPERIMENTAL
WORK
2.1
Design Approach
The aim of this paper is to study the crashworthiness of the crash box and to optimize the
design of the crash box.
To achieve this, we started with very basic geometries such as rectangular, cylindrical,
hexagonal, and then modified the structures by adding triggers in the design based on the
analysis. Later on, we have designed and analyzed unconventional designs also such as
re-entrant structure, origami and transition structure.
In this study we have analyzed the crash boxes developed above using both mild steel
and aluminum6061.We modified the structures in order to maximize the energy
absorption of the crash box and minimize the peak crushing force. We used
SOLIDWORKS software to design the crash boxes and for analysis and simulation we
used LS DYNA software.
2.2
Process flow
Figure 1: Process Flow Chart
The very first step to start our study is by clearly defining what problem we are tying to solve
and how can we solve the problem. This also involves setting up our aim and objectives along
with evaluation parameters.
After clarifying our goals and objectives next step is material study, we will decide what
potential material we can use for our study following which comes designing. We are using
SOLIDWORKS software to design geometries and do modelling.
The modelled design was then analysed using LS DYNA software by keeping the mesh as fine
as possible to get the best results and applying the constrains in such a way to achieve realistic
results. The designs are then evaluated and if required its parameters are iterated so as to get
optimized results. The results are validated and conclusion is stated.
2.3
Material
The materials used in this study is mild steel and aluminium 6061 whose properties are
listed below. The crash-box models are analysed using both materials to determine the
most crashworthy component.
Table 1: Material properties of Steel and Aluminum [17][18]
Property
Structural Steel
Aluminium 6061
2x105
72x103
0.3
0.33
7.85e-006
2.85e-006
Tensile Yield Strength
(MPa)
250
276
Tensile Ultimate Strength
(MPa)
460
310
Young's Modulus
(MPa)
Poisson's Ratio
Density (kg/mm³)
Crash-Box analysis is carried out in plastic range of stress strain curve which is shown
below.
Trur Stress(MPa)
True Stress vs Plastic Strain curve of Steel
500
450
400
350
300
250
200
150
100
50
0
0
0,05
0,1
0,15
0,2
0,25
0,3
Plastic strain
Figure 2: True Stress vs Plastic Strain curve of Structural Steel
True Stress vs Plastic Strain Curve of AL6061
400
True Stress (MPa)
350
300
250
200
150
100
50
0
0
0,01
0,02
0,03
0,04
0,05
Plastic Strain
Figure 3: True Stress vs Plastic Strain curve of Al6061
0,06
0,07
0,08
0,09
In this present study the structural geometry of the crash box is modelled using Solid
works software by restricting the dimensions to a certain range as shown in the table (2).
Table 2 : Dimensional Range
S
No.
Dimension
Min
value
(mm)
Max
value(mm)
1
Thickness
3
3
2
Length
60
90
3
Breadth
60
90
4
Height
165
165
5
Radius
70
90
2.4
Analysis Procedure
The FEA of the crash boxes is performed using LS DYNA software with fine mesh size
of 3mm and taking special care around discontinuities. An impactor was generated with
dimensions 160*160*10 mm3 with a density of 0.005kg/mm3 making it equivalent to a
commercial vehicle. The crash-box was modelled as shell and its lower nodes were fixed.
It was presumed that the impactor would be a rigid body. To replicate the mass of the
impacting device, a specific mass was allocated to the impactor, and the initial velocity
was imparted into the model by designating initial velocity condition to the impactor
nodes. Except for the vertical axis, which aligns with the impact direction, the affecting
mass was limited in all directions.
Impactor
Impactor Direction
Crash-Box
Figure 4: Analysis Setup
In the crush simulation, a general contact algorithm was used. Automatic node to surface
contact was defined among the impactor and the surface of the crash-box. Automatic
single surface contact was established on the column wall to prevent from infiltration
between each compression in the crash box walls during crush buckling process.
The strain hardening behaviour was incorporated in the form of the true stress – plastic
strain curve, which was modelled as piecewise linear plastic, and the material was
considered to be isotropic.
2.5
Structures
a. Square with grooves and holes
Figure 5: Modified Square Crash-Box
The rectangle with grooves and hole’s structure is the modified design of a simple rectangular
crash box. The grooves on the lateral sides and holes on the edges acts as triggers and allows
controlled deformation of the crash box which results in lowering the peak crushing force and
maximizing the energy absorption during the impact.
b. Protruding design
Figure 6: Protruding Design
This is another modification of simple crash box. In this design, small protrusions are emerging
from the crash box, during an impact the inner wall gets deforms first resulting in piling of
protrusions which enables the crash box to absorb more energy.
c. Re-entrant Structure
Figure 7: Re-entrant Crash Box
Our aim is to design a structure which absorbs maximum impact of the collision with minimum
peak crushing force. One such structure is “Re-entrant structure” which is having negative
Poisson’s ratio. The structure tends to absorb more energy as compared to conventional
structures and its mesh like structure helps in reducing the peak and mean crushing force. The
basic repetitive shape is shown below.
D. Origami Structure
Figure 8: Origami Crash Box
Origami is basically a Japanese art form of folding paper; the application of this technique to the
crash box enables the thin-walled structure to have pre folded geometry which acts as crash
initiators and help the structure to possess controlled and uniform deformation easily with
minimal force while absorbing the impact from the crash.
Chapter 3
3.0 Results and discussion
The results of the FEA performed on various crash-boxes is summarized below in the form of
bar graph and tables. Evaluation parameters to check the crashworthiness of these crash-box is
“Energy Absorption”, “Peak Crushing Force”, “Mean Crushing Force” and “Specific Energy
Absorption”.
Energy Absorbtion
12 650 J
12 600 J
12 550 J
12 500 J
12 450 J
12 400 J
12 350 J
12 300 J
12 250 J
12 200 J
Rentrant
Square with grooves Protruding Rectangle
and holes
Mild Steel
Origami
Aluminium 6061
Figure 9: Energy Absorption Comparison
The main objective of a crash box is to absorb as much as impact energy as possible. Our
analysis shows that energy absorbed by steel as well as aluminum doesn’t exhibit any significant
difference except in case of origami structure.
Energy absorbed by square crash box with triggers is least whereas energy absorbed by “Reentrant” and “Protruding” structure is highest and almost identical whereas origami structure
stands around 12550J. Thus, according to energy absorption “Protruding” structure is slightly
better than “Re-entrant” structure, then comes “origami” and “square with triggers”.
Peak Crushing Force
450 KN
400 KN
350 KN
300 KN
250 KN
200 KN
150 KN
100 KN
50 KN
0 KN
Rentrant
Square with grooves Protruding Rectangle
and holes
Mild Steel
Origami
Aluminium 6061
Figure 10: Peak Crushing Force Comparison
Peak crushing force implies the highest force incurred in the crash box structure during the
momentum transfer. It is observed that peak crushing force required by steel is higher than that
of aluminium for all design except origami. From these results we can see infer those Aluminium
structures are better than steel as deformation would be done easily reducing the load on chassis
and other components.
Mean Crushing Force
400 KN
350 KN
300 KN
250 KN
200 KN
150 KN
100 KN
50 KN
0 KN
Rentrant
Square with grooves Protruding Rectangle
and holes
Mild Steel
Origami
Aluminium 6061
Figure 11: Mean Crushing Force Comparison
Mean crushing force also shows the same trend as peak crushing force, the crushing force
required to crumple crash box is more for steel material as compared to aluminium. It is highest
for square with grooves and holes crash box and lowest for origami aluminium crash-box.
Displacement
100 mm
90 mm
80 mm
70 mm
60 mm
50 mm
40 mm
30 mm
20 mm
10 mm
0 mm
Rentrant
Square with
grooves and holes
Mild Steel
Protruding
Rectangle
Origami
Aluminium 6061
Figure 12: Displacement Comparison
Displacement represents how much crash-box is crushed. More the displacement the less
potential is left for crash box to absorb. We can clearly figure out that displacement of
aluminium structures is more as compared to steel structures. Deformation in origami structure
is highest and it is lowest in square with triggers.
Specific Energy Absorbtion
40 000 J/Kg
35 000 J/Kg
30 000 J/Kg
25 000 J/Kg
20 000 J/Kg
15 000 J/Kg
10 000 J/Kg
5 000 J/Kg
0 J/Kg
Rentrant
Square with
grooves and holes
Mild Steel
Protruding
Rectangle
Origami
Aluminium
Figure 13: Specific Energy Absorption
Specific energy absorption is ratio of energy absorbed and the mass of the crash box, this helps
us to understand the energy absorption capability of the crash box. The specific energy
absorption of aluminium crash boxes is approximately double when compared to steel crash
boxes. It is observed specific energy absorption of the modifies square crash box is the maximum
of both steel and aluminium when compared respectively.
Crush Force Efficiency
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
Re-entrant Structure
Square with grooves and
holes Structure
Structural Steel
Protruding Structure
Aluminium
Figure 14:Crush Force Efficiency
Origami Structure
The crush force efficiency is the ratio of the mean crushing force and peak crushing force. The
closer to 1 is the better as it lowers deceleration on to the travellers at the early stage. The
triggered square structure of tops the list with CFE of 0.90 with structural steel material.
The results of individual structures are summarized below.
Table 3: Re-entrant Crash-Box Results
Re-entrant Structure
Parameters
Structural Steel
Aluminium 6061
Peak Crushing Force (KN)
387.08
316.49
Mean Crushing Force (KN)
232.50
220.16
Displacement (mm)
54.59
70.76
Energy Absorption (J)
12610.30
12613.6
Specific Energy Absorption (J/Kg)
7378.76
19958.23
Table 4: Modified Square Crash-Box Results
Square with grooves and holes Structure
Parameters
Structural Steel
Aluminium 6061
Peak Crushing Force (KN)
405.92
377.37
Mean Crushing Force (KN)
366.936
264.50
Displacement (mm)
46.176
46.89
Energy Absorption (J)
12360.2
12360.60
Specific Energy Absorption (J/Kg)
13405.86
36248.09
Table 5: Protruding Crash-Box Results
Protruding Structure
Parameters
Structural Steel
Aluminium 6061
Peak Crushing Force (KN)
380.558
370.20
Mean Crushing Force (KN)
159.17
152.44
Displacement (mm)
79.92
82.78
Energy Absorption (J)
12617.50
12619.00
Specific Energy Absorption (J/Kg)
7731.311
20927.03
Table 6: Origami Crash-Box Results
Origami Structure
Parameters
Structural Steel
Aluminium 6061
Peak Crushing Force (KN)
190.59
210.58
Mean Crushing Force (KN)
161.0
140.0
Displacement (mm)
78.28
89.79
Energy Absorption (J)
12620.70
12625.10
Specific Energy Absorption (J/Kg)
8644.31
23379.81
Table 7:Crush Force Efficiency
Crush Force Efficiency
Aluminium
Structural Steel
Re-entrant Structure
0.69
0.60
Square with grooves and holes
Structure
0.70
0.90
Protruding Structure
0.41
0.41
Origami Structure
0.64
0.84
Chapter 4
4.0 Conclusion
The paper successfully compares the crashworthiness of various crash box geometries as well as
their behavior as steel and aluminium structures. Crash boxes were evaluated based on Energy
Absorbed, peak and mean crushing force as well as their deformations.
It was noted in terms of material, that there is a significant difference in the specific energy
absorbed, the aluminium structures showed better results than steel and the peak crushing force
and mean crushing force of the steel structure were higher when compared to that of aluminium
structures.
Origami structure showed the optimum deformation and the energy absorbed by this structure is
equivalent to other crash-box structures for both steel and aluminium structure, also its peak and
mean crushing force is significantly lower than other structures, thus it can be concluded that
origami gives the best results so far.
It was observed that the performance of the protruding structure and re-entrant structure is almost
comparable and better than origami and square crash-box with triggers in terms energy
absorption, but the protruding structure has an edge over the re-entrant crash box as it deforms
uniformly throughout the impact.
Crashworthiness of a traditional crash box i.e., a square crash box with triggers is least compared
to other structures. It has absorbed the least amount of energy and had the highest peak and mean
crushing force and with the least deformation.
Thus, it can be concluded that more research is needed in the field of crash boxes and vehicle
safety.
CONTRIBUTION STATEMENT
Everyone has contributed equally in both designing, analysis and report making part the project.
Verified by
(Signature of the Guide)