UNIVERSITI PUTRA MALAYSIA
REZA AFSHAR HOSSEINABADI
FK 2009 107
CRASH DEFORMATION SIMULATION OF TUBULAR STRUCTURE TO DETERMINE AUTOMOTIVE CENTRE OF GRAVITY
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Crash Deformation Simulation of Tubular Structure to Determine Automotive
Centre of Gravity
By
REZA AFSHAR HOSSEINABADI
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of
the Requirements for the Degree of Master of Science
September 2009
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DEDICATION
To my dear parents
and
lovely wife
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ABSTRACT
Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment
of the requirement for the degree of Master of Science
Crash Deformation Simulation of Tubular Structure to Determine Automotive
Centre of Gravity
By
REZA AFSHAR HOSSEINABADI
September 2009
Chairman: Aidy Ali, PhD
Faculty: Engineering
In this study, the effects of crush behaviour of tubular structures have been
investigated throughout simulation work. The axial crush was performed to predict
the behaviour of tubular structures in terms of displacement of centre of gravity
(COG) and mass moments of inertia (𝐼𝑦𝑦 𝑎𝑛𝑑 𝐼𝑥𝑧).
Crush simulation includes two sections; close and open cross-sections respectively.
In the case of close cross-sections, a displacement of COG of tubular structures with
various polygonal cross-sections is numerically investigated under axial crush using
program code of ANSYS/LS-DYNA. A subroutine is developed using this code to
calculate the COG of deformed shape, during and after crush condition. The effect of
wall thickness on displacement of COG is also investigated. Subsequently, a
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procedure to find real time COG of tubular structure during and after crush is
developed. Base on this procedure, a macro is added in the frame work of
ANSYS/LS-DYNA to study the deformation behaviour of tubular structure by the
accurate criteria of COG, 𝐼𝑦𝑦 𝑎𝑛𝑑 𝐼𝑥𝑧. Furthermore, the optimum number of edge of
polygonal cross-section to have a reasonable symmetric deformed shape during crush
is determined. It is found that the effect of number of polygonal edges on symmetric
deformation of COG becomes more prominent as wall thickness of tubular structure
decreases. The higher number of edges stabilizes the deformation shape.
To examine the open cross-sections, the tubular structures with various Cee-shaped
cross sections are numerically investigated. The subroutine used for the first section
is performed again. Yet, the effect of wall thickness was also studied. Subsequently,
the effect of opening angle of Cee becomes more prominent as the wall thickness of
the structure decreases. As the thickness increases, displacement of the COG in crush
direction almost stabilizes for all opening angle of Cee in the range of 100 −
900 degrees. Furthermore, variation of 𝐼𝑦𝑦 of structure with thicker wall for different
cases of applied mass is approximately identical. As a contribution to real
application, Cee-shaped cross-sections with higher wall thicknesses can be used in
the form of frame structures in automotive industry in order to reduce the overall
weight of the structure and therefore, to save more energy.
The study is the continue by incorporating a developed subroutine that added in the
pre-processing module, in the frame work of ANSYS, distribution of the extra mass
according to specific assigned COG and calculation the first bending and torsional
natural frequencies of the simplified model in order to maximize these frequencies
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with final mass constraint was successfully investigated. It was found that adding the
extra mass symmetrically about longitudinal axes of Body In White (BIW), higher
values for first bending and torsional natural frequency is achieved.
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ABSTRAK
Abstrack tesis yang dikemukakan kepada Senat Universiti Putra Malaysia
sebagai memenuhi keperluan untuk ijazah Master of Sains
Simulasi Deformasi Remuk Struktur Berongga Bagi Penentuan Pusat Graviti
Automotif
Oleh
REZA AFSHAR HOSSEINABADI
September 2009
Pengerusi: Aidy Ali, PhD
Fakulti: Kejuruteraan
Didalam kajian ini, kesan sifat remukkan struktur berongga dikaji dengan
menggunakan kaedah simulasi. Remukkan arah menegak dijalankan bagi menjangka
anjakan pusat gravity (COG) dan momen inersia (𝐼𝑦𝑦 𝑎𝑛𝑑 𝐼𝑥𝑧).
Simulasi remuk kesan hentaman ini dibahagikan kepada dua bahagian: tertutup dan
terbuka. Bagi kes tertutup, COG untuk struktur dengan polygonal keratin rentas
dikaji secara berangka. Menggunakan program kod ANSYS/LS-DYNA. Sebuah
pengatur caraan program di talis untuk mengukun COG bagi perubahan bentuk,
ketika dan selepas hentaman. Kesan ketebalan struktur berongga ini juga dikaji.
Seterusunya, kaedah mentukan COG secara seuanasa juda dibangunkan. Berasaskan
kaedah ini, makro ditambah didalam rangka ANSYS/LS-DYNA untuk mengkaji
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sifat deformasi tiub COG, 𝐼𝑦𝑦 𝑎𝑛𝑑 𝐼𝑥𝑧 . tambahan lagi, segi optimum poligonal
keratan rentas memiliki remukkan bentuk simetri. Di dalam kajian ini, didapati
jumlah segi poligonal adalah signifikan apabila ketebalan meningkat. Semakin tinggi
jumlah segi, semakin stabil keadaan remukkan.
Untuk mengkaji kes keratin rentas terbuka, tiub dengan beberapas bentuk Cee
terbuka diuji. Pengatucaraan yang sama untuk kes tertutup digunakan sekali lagi.
Kesan tebelatan juga dikaji. Kesan ketebales semakin jelas, anjakan COG disetuap
arah semakin stabil untuk setiap sudut 100 − 900 darjah. Tambahan lagi, variasi 𝐼𝑦𝑦
dengan beban yang seragan ditemui serupa. Sebagai sumbangan applikasi, bentuk
Cee dengan ketebalan tinggi boleh digunakan untuk struktur automotive bagi
mengurangkan berat seteterusnya tenaga.
Kejuan ini diteruskan dengan menanbahkan pengatucaraan didalam per proses
modul, didalam ANSYS, taburan lebihan beban mengikut keperluan spesifik COG,
dengan mengira lenturan dan puntiran frekuensi asli, didalam model yang diubah
suai, bagi memaksimumkan kekangan beban. Didapti, penanbahan beban secara
simetri di ats poksi memanjang di badan automotif, lenturan dan puntiran frekuensi
dicapai.
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ACKNOWLEDGEMENT
First and foremost I would like to express my deep gratefulness to my supervisor Dr.
Aidy Bin Ali for his support, encouragement and suggestions during the study and
preparation of this thesis. I truly appreciate the time he devoted in advising me and
showing me the proper directions to continue this research.
I would also like to express my gratitude towards my co-supervisor Professor Ir. Dr.
Barkawi Bin Sahari. I am grateful for his supervision, help, helpful advice and
knowledge that made an invaluable contribution to this dissertation. Many ideas
originate in our frequent discussion and his constant support and patience have been
of invaluable help.
I wish to express my special thanks and appreciation to my beloved parents, my wife
and specially my dear uncle Isa for their unconditional supports and good cheer.
Last but not least the deepest appreciation goes to my very close friends, Amirreza
and Ayyoub for their contentious support and encouragement. Another thank goes
for Guru for the translation of abstract into Malay language.
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APROVAL
I certify that a thesis Examination Committee has met on 8 September 2009 to
conduct the final examination of Reza Afshar Hosseinabadi on his thesis entitled
“Crash Deformation Simulation of Tubular Structure to Determine Automotive
Centre of Gravity” in accordance with Universities and University Colleges Act 1971
and Constitiuation of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998.
The Committee recommends that the candidate be awarded the Master of Science.
Members of the Examination Committee are as follows:
Chairman, PhD
Dr. Mohd Khairol Anuar Mohd Arifin
Department of Mechanical and Manufacturing Engineering
Faculty of Engineering
Universiti Putra Malaysia
(Chairman)
Examiner 1, PhD
Associate professor Datin Dr. Napsiah bt. Ismail
Department of Mechanical and Manufacturing Engineering
Faculty of Engineering
Universiti Putra Malaysia
(Internal Examiner)
Examiner 2, PhD
Associate professor Dr. Tang Sai Hong
Department of Mechanical and Manufacturing Engineering
Faculty of Engineering
Universiti Putra Malaysia
(Internal Examiner)
External Examiner, PhD
Associate professor Dr. Shahrum Abdullah
Department of mechanics and material
Faculty of engineering
University Kebangsaan Malaysia
(External Examiner)
BUJANG KIM HUAT, PhD
Professor and Deputy Dean
School Of Graduate Studies
University Putra Malaysia
Date:
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This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted
as fulfillment of the requirement for the degree of Master of Science. The members of
the Supervisory Committee were as follows:
Aidy Bin Ali, PhD
Senior Lecturer
Department of Mechanical and Manufacturing Engineering
Faculty of Engineering
Universiti Putra Malaysia
(Chairman)
Barkawi Bin Sahari, PhD
Professor
Institue Advanced Technology
Universiti Putra Malaysia
(Member)
HASANAH MOHD GHAZALI, PhD
Professor and Dean
School Of Graduate Studies
University Putra Malaysia
Date: 16 November 2009
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DECLARATION
I hereby declare that the thesis is based on my original work except for quotations and
citations which have been fully acknowledged. I also declare that it has not been
previously or concurrently submitted for any other degree at UPM or other institutions.
REZA AFSHAR HOSSEINABADI
Date: 23 November 2009
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TABLE OF CONTENTS
Page
DEDICATION ii
ABSTRACT iii
ABSTRAK vi
ACKNOWLEDGEMENT viii
APROVAL ix
DECLARATION xi
LIST OF TABLES xvi
LIST OF FIGURES xvii
LIST OF ABBREVIATIONS xxiv
1 INTRODUCTION 1
1.1. Introduction 1
1.2. Research Problem 2
1.3. Research Objectives 3
1.4. Scope of the Study 4
1.5. The Layout of this Thesis 4
2 LITERATURE REVIEW 6
2.1 Introduction 6
2.2 Previous Works on Crushing of Tubular Structures 6
2.2.1 Experimental and Theoretical Method 7
2.2.2 FEM and Experimental Method 10
2.3 Centre of Mass, centre of gravity and geometric centre 20
2.3.1 Centre of Mass (COM) 20
2.3.2 Application of COM 21
2.3.3 COM calculation of discrete system 21
2.3.4 COM calculation of continuous systems 22
2.3.5 COM and centroid 23
2.3.6 COM and symmetry 23
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2.3.7 COM of composite objects 24
2.3.8 Geometric centre (centroid) 25
2.3.9 Centre of Gravity (COG) 25
2.3.10 COG for a System of n Particles 27
2.3.11 COG of lines, areas and volumes 29
2.4 Experimental methods of determining COG 30
2.4.1 Pendulum test method 30
2.4.2 Frequency Response Function (FRF) method 30
2.5 Inertia properties of a structure 31
2.5.1 Why inertia properties are needed 31
2.6 COG and weight distribution 31
2.7 Body in white of an automotive 32
2.7.1 Unitized and frame constructions 33
2.7.2 Space frame technology 38
2.7.3 BIW and COG 39
2.8 Static analysis of body structure 41
2.8.1 Modal analysis 42
2.8.2 Natural frequency 42
2.8.3 FEA eigensystems 45
2.8.4 Methods of solution 47
2.9 Mode shapes of a structure 48
2.9.1 Introduction 48
2.9.2 Modal analysis of automotive body by FEM 49
2.10 Discussion 55
3 METHODOLOGY 58
3.1 Introduction 58
3.2 Numerical simulation of xial crush of tubular structure 61
3.2.1 The Finite Element Method - Analysis Stages 61
3.2.2 FEM commercial package 63
3.3 Pre-processing 63
3.3.1 Modelling 63
3.3.2 Meshing 66
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3.3.3 Material properties 67
3.3.4 Applying boundary conditions 71
3.4 Processing 75
3.4.1 Computational Processing 75
3.5 Post-processing 76
3.5.1 Reading the result and implementing the
subroutine 76
3.6 Implementing COG auto generation subroutine 77
3.7 Methodology of COG auto adjust 78
3.8 Pre-processing 79
3.8.1 Modeling 79
3.8.2 Meshing 80
3.8.3 Material Properties 81
3.8.4 Applying Boundary Conditions 82
3.9 Implementing subroutine 82
3.9.1 Step 1: Obtain the COG and total mass of the
initial model 84
3.9.2 Step 2: Define desired COG on X-direction (the
model is symmetric about X-axis) 85
3.9.3 Step 3: Define Co-ordination of extra mass
(according to the centrioad of the extra mass) 85
3.9.4 Step 4: Obtain the value of extra mass on X-axis
and the COG of new model on Y-axis 86
3.9.5 Step 5: Overlap added parts with the initial
model 87
3.9.6 Step 6: Define material properties of added parts,
meshing the new model (consisting of the initial
model and the added parts) 88
3.9.7 Step 7: Apply boundary conditions and solve 88
3.10 Processing 88
3.10.1 Computational Processing 88
3.11 Discussion 88
4 RESULTS AND DISCUSSION 90
4.1 Introduction 90
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4.2 Result of axial crushing of tubular structure with various
polygonal cross-sections 90
4.2.1 Reading result in each increment of time 90
4.2.2 Verification of simulation work 92
4.2.3 Displacement of COG in every computational
condition 108
4.2.4 Calculation of mass moments of inertia 111
4.2.5 Displacement of COG by different wall thickness 112
4.3 Conclusions of axial crush of tubular structure with
different polygonal cross-sections 113
4.4 Result of axial crushing of tubular structure with various
Cee-shaped cross-sections 114
4.4.1 Reading result in each increment of time 114
4.4.2 Deformed shapes of tubular structures 115
4.4.3 Displacement of COG in every computational
condition 118
4.4.4 Calculation of mass moments of inertia 123
4.5 Conclusions of axial crush of tubular structure with
different Cee-shaped cross-sections 129
4.6 Results of applying COG auto adjust subroutine in order to
find the desired COG and calculation of first bending and
torsion natural frequencies. 129
4.7 Parameters used for second subroutine 134
4.7.1 Extra mass 135
4.7.2 COG on Y-axis 135
4.7.3 First bending natural frequency 138
4.7.4 First torsional natural frequency 138
5 CONCLUSIONS AND RECOMMENDATIONS 140
5.1 Conclusions 140
5.2 Recommendations for further work 141
REFRENCES 142
APPENDICES 150
BIODATA OF STUDENT 163
LIST OF PUBLICATIONS 164
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LIST OF TABLES
Table Page
2.1 ID number and properties of candidate material [63]. 54
2.2 Optimized first bending frequencies [64]. 55
3.1 Material Properties of tubular structures with normal polygonal
cross-sections [65]. 68
3.2 Material Properties of tubular structures with normal polygonal
cross-sections [65]. 69
3.3 Material Properties of shell structure of simplified BIW. 81
4.1 Comapring simulated results with predicted model and errors in the
case of tubular structure with thickness of 1.5 mm. 104
4.2 Comapring simulated results with predicted model and errors in the
case of tubular structure with thickness of 2.5 mm. 104
4.3 COG properties and first bending and torsional natural frequencies
of initial model. 130
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LIST OF FIGURES
Figure Page
2.1 A typical load-displacement trace for PVC square tube under
quasi-static compression [13]. 7
2.2 Elastic buckling modes of thin PVC square tubes with (a) t/d =
0.034, l/d =3 and (b) l/d = 4 [13]. 8
2.3 Load-displacement curve [31]. 9
2.4 Crush deformation by different number of corners with different
wall thicknesses [34]. 11
2.5 Effect of crush strength versus number of corners and thicknesses
[34]. 11
2.6 Different bulge height [39]. 14
2.7 Simulated and experiment of crush [17]. 15
2.8 Comparison of simulation and experimental of force-displacement
[17]. 16
2.9 Comparison between crush load–displacement of empty and foam-
filled [28]. 17
2.10 Interaction effect in foam-filled tube [28]. 18
2.11 and experimental crash pattern and crash load-displacement curve
of empty tube [29]. 19
2.12 A comparison between crash load-displacement of empty and
foam-filled tubes [27]. 20
2.13 COM of a system consisting of two masses [46]. 22
2.14 The COM and geometric centroid share the symmetries of the
object [46]. 24
2.15 COM of composite system [45]. 24
2.16 Geometric centre of triangle. 25
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2.17 System of n particles [47]. 27
2.18 System of n particles (rotated 90 about x axis) [47]. 29
2.19 A sample BIW [50]. 33
2.20 (a) body-over-frame and frame structure. (b) unibody structure
[51]. 33
2.21 A unibody of automotive structure [51]. 34
2.22 Half-ton 2002 Dodge Ram pickup truck [52]. 34
2.23 BIW of Honda Acura MDX 2007 and different possible impact
situation [53]. 35
2.24 Different construction of BIW of Honda Acura MDX 2007 [53]. 35
2.25 Cross-section used in side construction [53]. 36
2.26 Cross-section used in rear construction [53]. 37
2.27 Distributed load pattern in the case of frontal impact in frontal
construction [53]. 37
2.28 Cross-sections used in frame construction [53]. 38
2.29 Modern space frame of a vehicle construction [55]. 39
2.30 BIW and different attached part of automotive body [55]. 40
2.31 The developed front platform with developed of side and center
member assembly front floor [39]. 41
2.32 Spring-Mass system and free body diagram [56]. 43
2.33 Tacoma Narrows bridge disaster [59]. 48
2.34 Modal analysis of a automotive body [59]. 49
2.35 Modal analysis of automotive body by FEM [60]. 51
2.36 Average of first torsional and first bending frequencies
maximization results from topology optimization (a) and sizing
optimization (b) [61]. 52
2.37 Mode density of BIW [62]. 53
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2.38 First bending frequency maximization results: (a) 1% added mass
(b) 3% added mass [64]. 55
3.1 Overall project flowchart of COG auto generation. 59
3.2 Overall project flowchart of COG auto mass adjust. 60
3.3 Procedure of implementing COG auto generation, during and after
crush deformation of tubular structure in ANSYS. 62
3.4 Various polygonal cross-sections. 64
3.5 Various Cee-shaped cross-sections. 66
3.6 Shell 163 geometry [65]. 67
3.7 Stress-strain curve of material with polygonal cross-section. 68
3.8 Stress-strain curve of material with Cee-shaped cross-section. 70
3.9 Procedure of defining model behaviour in ANSYS. 71
3.10 Two components used for simulation of crush and boundary
conditions, in the case of regular polygonal cross-sections. 72
3.11 Geometric modeling and boundary conditions of regular polygonal
cross sections. 73
3.12 Two components used for simulation of crush and boundary
conditions, in the case of Cee-shaped cross-sections. 74
3.13 Geometric modeling and boundary conditions of Cee-shaped cross
sections. 75
3.14 Selecting the specific substep and reading the results. 76
3.15 Calling the subroutine through ANSYS command line. 77
3.16 Procedure of subroutine to calculate the COG of deformed shape of
tubular structure. 78
3.17 Procedure of implementing COG auto adjust subroutine in the
finite element model of tubular structure. 79
3.18 Shell structure of BIW developed in Solidworks. 80
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3.19 Shell 63 geometry [66]. 81
3.20 Applying boundary conditions on BIW to obtain first bending and
torsional natural frequency. 82
3.21 Regions for adding the mass according to desired COG. 83
3.22 Procedure of COG auto adjusts subroutine of tubular structures. 84
4.1 Selecting the specific substep and reading the results. 91
4.2 Calling the subroutine through ANSYS command line. 91
4.3 Deformed shapes of tubular structure with octagonal cross section
for thickness of 1 mm. 92
4.4 Displacement of COG vs. time during the crush of tubular structure
with octagonal cross section for thickness of 1 mm. 93
4.5 Mass moment of inertia vs. time during the crush of tubular
structure with octagonal cross section for thickness of 1 mm. 94
4.6 Deformed shapes of tubular structure with octagonal cross section
for thickness of 2 mm. 95
4.7 Displacement of COG vs. time during the crush of tubular structure
with octagonal cross section for thickness of 2 mm. 96
4.8 Mass moment of inertia vs. time during the crush of tubular
structure with octagonal cross section for thickness of 2 mm. 97
4.9 Deformed shapes of tubular structure with octagonal cross section
for thickness of 3 mm. 98
4.10 Displacement of COG vs. time during the crush of tubular structure
with octagonal cross section for thickness of 3 mm. 99
4.11 Mass moment of inertia vs. time during the crush of tubular
structure with octagonal cross section for thickness of 3 mm. 100
4.12 Displacement of COG vs. time during the crush of tubular structure
with octagonal cross section for thicknesses of 1, 2 and 3 mm. 101
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4.13 Deformed shapes of tubular structure with octagonal cross section
for thickness of 1.5 mm. 102
4.14 Deformed shapes of tubular structure with octagonal cross section
for thickness of 2.5 mm. 103
4.15 Displacement of COG vs. time during the crush of tubular structure
with octagonal cross section for thicknesses of 1.5 and 2.5 mm and
comparison with the predicted model. 105
4.16 Deformation shapes (initial, 100 ms and 150 ms after crush), initial
wall thickness: (a) 1 mm; (b) 2 mm; (c) 3 mm. 106
4.17 The effects of increasing the number of corners and thickness on
behaviour of deformed shapes at 150 ms after crush. 107
4.18 Displacement of COG for various cross-sections with thickness=1
mm. 108
4.19 Displacement of COG for various cross-sections with thickness=2
mm. 109
4.20 Displacement of COG for various cross-sections with thickness=3
mm. 110
4.21 Mass moments of inertia about COG for various polygonal cross-
sections with different thicknesses. 112
4.22 Displacement of COG for various cross-sections with different
thicknesses. 113
4.23 Selecting the specific substep and reading the results. 115
4.24 Calling the subroutine through ANSYS command line. 115
4.25 Deformed shapes of different cross sections with thickness of 1
mm. 116
4.26 Deformed shapes of different cross sections with thickness of 2
mm. 116
4.27 Deformed shapes of different cross sections with thickness of 3
mm. 117
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4.28 Deformed shapes of different cross sections by applying 10 (1)
and 20 Kg (2) on the structure, (a) with thickness of 2 mm. (b) with
thickness of 3 mm. 118
4.29 Displacement of COG versus opening angle of Cee in the case of
applying 10 kg on the structure with thickness of 1 mm. 119
4.30 Displacement of COG versus opening angle of Cee in the case of
applying 10 kg on the structure with thickness of 2 mm. 120
4.31 Displacement of COG versus opening angle of Cee in the case of
applying 10 kg on the structure with thickness of 3 mm. 121
4.32 Displacement of COG versus opening angle of Cee in the case of
applying 10 kg on the structures with thicknesses of 1, 2 and 3mm. 122
4.33 Displacement of COG on Y axis versus opening angle of Cee with
thickness of 2 and 3 mm. 123
4.34 Variation the Mass moment of inertia about the COG by various
opening angle of Cee in the case of applying 10 kg on the structure
with thickness of 1 mm. 124
4.35 Variation the Mass moment of inertia about the COG by various
opening angle of Cee in the case of applying 10 kg on the structure
with thickness of 2 mm. 125
4.36 Variation the Mass moment of inertia about the COG by various
opening angle of Cee in the case of applying 10 kg on the structure
with thickness of 3 mm. 126
4.37 Variation the Mass moment of inertia about the COG by various
opening angle of Cee in the case of applying 10 kg on the
structures with thicknesses of 1, 2 and 3 mm. 127
4.38 Variation the Mass moment of inertia about the COG by various
opening angle of Cee in the case of applying 10 kg (1) and 20 kg
(2) on the structures with thicknesses of 2 and 3 mm. 128
4.39 Applied Boundary conditions to obtain the first bending and
torsional natural frequencies. 130
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4.40 Different position of the extra mass along X-axis. 131
4.41 Variation of first bending natural frequency by different position of
extra mass along Z-axis (XC=8.0 cm). 132
4.42 Variation of first torsional natural frequency by different position
of extra mass along Z-axis (XC=8.0 cm). 133
4.43 Different positions of the extra mass along Z-axis. 134
4.44 Variation of extra mass by displacing the COG along X-axis. 135
4.45 Variation of the COG along Y-axis by displacing the COG along X-
axis for different position of extra mass at X=80 cm (symmetric
about X-axis and at the middle of platform). 136
4.46 Variation of the COG along Y-axis by displacing the COG along X-
axis for different position of extra mass at X=80, 85, 90 and 95 cm
(symmetric about X-axis and at the middle of platform). 137
4.47 Variation of the first bending natural frequency by displacing the
COG along X-axis for different position of extra mass at
extra_mass=80 cm (symmetric about X-axis and at the middle of
platform). 138
4.48 Variation of the first torsional natural frequency by displacing the
COG along X-axis for different position of extra mass at
extra_mass=80 cm (symmetric about X-axis and at the middle of
platform). 139
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LIST OF ABBREVIATIONS
BIW Body In White
COG Centre Of Gravity
COM Centre Of Mass
CAE Computer Aided Engineering
FEM Finite Element Method
FE Finite Element
MDO Multi Design Optimization
APDL Ansys Parametric Design Language
NGV Natural Gas Vehicle
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CHAPTER 1
1 INTRODUCTION
1.1. Introduction
The performance of vehicle in the event of collision is one of the most prominent
areas that must be considered at the design stage. For instance a dangerous situation
resulting in injury of the occupants can occur if the deformation of vehicle body
members extends into the passenger compartment. To ensure adequate occupant
protection, the crash energy must be absorbed through a deformation of front-end of
automotive body structure.
All of the members, including the front-end and side members, particularly, play a
major role in absorbing crash energy. Therefore, rising up their energy absorption
efficiency is an important key point in improving the crashworthiness of the
vehicle’s front-end. The side members are generally structured as thin-walled
components which have square, rectangular or hat-shaped cross-sections. It is
generally curved positioned below the passenger compartment due to their positional
relationship with the suspensions and other parts. However its front portion needs to
be kept as straight as possible in order to make them capable to withstand greater
loads. It is evident that the ability of side members to absorb energy is efficiently
increased by proper design so that the collapse will be in predicted manner with
preventing their side walls collapse in bending. This type of collapse mode can be
engineered through several innovative techniques such as placing beading or
reinforcements at appropriate place along the side members.
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Furthermore, it was found that aluminium columns are also connected to the vehicle
bumpers as a crush boxes to protect the passengers and the structure itself under
impact loading. The aluminium columns are used to absorb the initial kinetic energy
and keep the force level sufficiently low, so that lead to prevent from damage to the
front-end compartment. Generally, the energy absorption will take place by extensive
folding and bending collapse of the column wall. A specific characteristic of such a
deformation mechanism is obtained when the rate of energy dissipation is located
over the narrow zones, while the rest of the structure experiences a rigid body
motion. At present, an increased of interest on vehicle safety have led to a
comprehensive research [1] of the crash response of aluminium tubes from all
aspects, experimental, analytical and numerical means. In this study, the Finite
Element Method (FEM) was used to locate the centre of gravity (COG) of such
tubular structures during and after axial crush deformation in order to have an
accurate situation of deformed shape concerning the COG. Further more it will lead
to come out with proper criteria to decide on the behaviour of tubular structure in
term of deformation shape.
1.2. Research Problem
Thin-walled tubular structures are commonly used as the strengthening members in
an automotive Body In White (BIW). Many researchers [2-20] have paid
considerable attention on the crush behaviour of tubular structure for the past two
decades. There have been a lot of activities on dynamic crush of tubular structures
during recent years and most of them have been concerned with the energy absorbing
systems of vehicles [21-29].
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Assessing the general deformed shape of tubular structure during crush has been
performed based on visual observation. However, this deformation is accessible in
finite element simulation, having an accurate situation of deformed shape concerning
the COG of structure was the lack of studies. Hence having a subroutine in FEM will
help the researchers to obtain the inertia properties of arbitrary tubular shapes during
and after crush deformation, and evaluate the accuracy of phenomenon of deformed
shape of tubular structure during and after crush.
A number of automobile manufacturers have developed and produced all-aluminum
bodies as a means of weight reduction [67]. Hence, examining the deformation
behavior of various tubular structures made of aluminum by means of variation of
their COG during and after crush deformation will help to extend the application of
light materials for automotive BIW.
Furthermore, the correct location of COG is prominent for engineers in Computer
Aided Engineering (CAE) analysis, when it comes to vehicle yaw, moment and
rotation due to impact. Yet again, at design stage, mass in CAE model should be
evenly distributed in order to obtain the correct COG. For instance, by having some
extra parts in new designs such as adding fuel tanks in Natural Gas Vehicle (NGV),
having the correct COG is a very prominent issue.
1.3. Research Objectives
The objectives of the study are:
1. To develop an algorithm that can auto adjust the location of COG of
deformed shape, during and after crush.
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2. To simulate the real time location of COG of the tubular structure during and
after axial crush.
3. To develop a subroutine to distribute the extra mass according to specific
assigned COG and access the first bending and torsion natural frequencies of
the simplified model in order to maximize these frequencies with final mass
constraint.
1.4. Scope of the Study
The study involves finite element simulation of crushing the tubular structures with
different polygonal and open cross-sections, incorporating the subroutine integrated
to the post processing module, in the framework of ANSYS/LS-DYNA. The
experimental determination of COG location during deformation is not covered in
the scope. The verification of the developed modelled was carried out based on
analytical establish calculation.
1.5. The Layout of this Thesis
This thesis consists of five chapters including the introduction in Chapter 1, followed
by literature review on Chapter 2. The literature review is covered from the previous
works have been performed by many researchers on analysis of tubular structures
subjected to crushing using different approaches, including: experimental, theoretical
and FEM. The COG definition and different methods used in determining COG also
discussed in this chapter.
Chapter 3 discusses the methods used and finite element analysis procedure
involved. In addition the procedures of subroutines that added in the post-processing
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and pre-processing module of ANSYS/LS-DYNA code to calculate COG of
deformed shape and adjust the COG in specified location are also discussed. Chapter
4 presents the results and discussion of the results. Chapter 5 highlights the
contribution to new study, conclusions and recommendations for future work.
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