AN INTELLIGENT ENVIRONMENT FOR THE OCCUPANT SIMULATION AND
DEFORMABLE DUMMY DESIGN
A Dissertation Presented to
The Faculty of the
Fritz J. and Dolores H. Russ College of Engineering and Technology
Ohio University
In Partial Fulfillment
of the Requirement for the Degree
Doctor of Philosophy
by
Shr-Hung Chen
June 2003
OHIO UNIVERSITY LIBRARY 1u Acknowledgments
I would like to express my sincere gratitude and appreciation to my advisor, Dr.
Bhavin V. Mehta, whose breadth of experience and knowledge was paramount to the
operation and completion of this project. My sincere thanks to Dr. Bob Williams for his
invaluable guidance in this work as well.
I would also like to thank Dr. Jay Gunasekera, Dr. Gregory Kremer, Dr. Dusan
Soeinaz, Dr. Daniel Guilno for their advice, thoughtfulness throughout my research and
being the members of my dissertation committee.
Also, I would like to thank Prasad Petkar and Srikanth Patlu for their excellent
cooperation throughout this project.
Finally, I would like to dedicate this dissertation to my parents, my wife Chiu-I,
son Sudatta , daughter Sophia and sister for their continued support, encouragement and patience in the pursuance of my education. TABLE OF CONTENTS ... 1 ACKNOWLEDGMENTS------. --.---.----.-.----. ..--.-..---.------.---....------.- ...... -...... -. 111
TABLE OF CONTENTS.---*----p------.----.--.---...--.----.--.-.--.-.-.F---.------.-..------..----.-.----....-. iv
LIST OF FIGURES vii
LJ-STOF TABLE ...... X
CHAPTER 1 INTRODUCTION .-s-.--.------.----...-.-.--...----.---.------..------.----.--...----....---...-.1
1.1 General Remarks...... 1
1.2 Occupant Protection System.-.------.-.--.------.------*-.----.------. -----.*-. 2
1.3 Research Objective ------.- -. .------.-. . .- .------.---- ..------. --..- - - - -.---...---- .. 4
1.3.1 An Intelligent Environment of Occupant Simulation.--.---..--.---- 5
1.3.2 Deformable Dummy..--.-.. .--.----- .----.------.--..-.--*-.------. -.----.-.-.--. ----. 8
1.4 Aim and Concept ...... 9
CH'4I'TER 2 LJTERATURE REVIEW.-----I .---.------.----.-----.--.-.------.-.. -----.-.--.----.-.------.- 10
2.1 The Computer Simulation of Crashworthmess and Occupant
Protection .----.- -- -. -.-. . . -- -.-. ------.. ------.. --.----. *. -.- -- .--. -. --.----- .. ---.------10
2.1.1 The Literature About Airbags --.-.-----..----.-.------.-.--.----.----.-.-.-.--.-.---.---.10
2.1.2 The Literature about Seat belt and Seat --..--.---..-.--.-.-.------.-.--.---.----11
2.2 The Literature About Deformable Dummy .-. - - -.- -.---. - -. ------.. . ------.-. - -.-. - - 12
CHAPTER 3 THE VALIDATION OF COUPLED CODE---..-.---.-..----e-.------.--.--.-.-.---- 14
3.1 Introduction.--.--.---..------.---.-v--.-.------..--...----.-....-.-.--.-.-..-....--.-.----7-.-.-.--.-- 14
3.1.1 ATB (Articulated Total Body) Program ---.---F------.-----..---.--.....v---.-.----. 14
3.1.2 LS-DWA promam ...... 16
3.1.3 The Development of Coupled Code ------.---e--.-.--v-.----.--.*-----.-.----.--..--. 17 v 3.2 The Validation of Coupled Code ...... 18
3.2.1 The Cases Studies...... 19
3.2.2 Conclusion...... 23
C.KAPTER 4 THE DESIGN OF INTELLIGENT ENVIRONMENT FOR THE
~ccuI"4NTSIMULATION ...... 24
4.1 Introduction...... 24
4.2 Modeling Three Dimension Seatbelt and Seat Models ...... 25
4.2.1 Three Dimension seatbelt Models...... 25
4.2.2 Three Ix-nension Seat Models ...... 29
4.3 Modeling the Airbag...... 32
4.3.1 The Airbag Material ...... 32
4.3.2 The Airbag Modeling Design and Inflation Process...... 35
4.3.3 The Airbag Profile and Folding Patters Algorithm ...... 3 7
4.4 The User Interface for Occupant Silnulation ...... 40
CHAPTER 5 THE METHODOLOGY OF DEFORMABLE DUMMY ...... 42
5.1 Introd~ctio!?...... 42
5.2 The Methodology of Deformable D-Y ...... 43
5.3 The Modeling Design of Deformable Segment...... 44
5.3.1 Material Consideration...... 44
5.3.2 The Modeling of Deformable Head and Upper Torso Segment...... 47
5.3.3 The Modeling of Deformable Upper Legs Segments...... 51 vi CHAPTER 6 THE STUDY OF RIGID DUMMY WITH RESTRAINT SYSTEM
SIM.JLATION----*--.-...--.---.------...----.-..------.--.------.--.-.-.------.-----.--.--.-.---.-.-.--- 54
6.1 Introduction .----.-----.--.-F-.------.----..-.----.--.----e-----.------.----.-----.------.------54
6.2 Case Study --.--..----.--.---.---.*-.-.-.--.-.----.----..-.------..-.------.-----.-..--.--..--.---.--.--56
6.3 Discussion...... 67
CHAPTER 7 THE SIMULATION OF DUMMY WITH DEFORMABLE SEGMENTS
AND THE DUMMY WITH COMPLETE VEHICLE MODEL ---...-----.---74
7.1 The Study of Dummy with Deformable Segment in Crashworthiness
Simulation--. - - -.-. . ------.- -. -- -.- -..------.- - -.- -.------..- -. ------.- .-.-... . -...... 74
7.1.1 Case Study...... 75
7.1.2 c is cuss ion.----.------.-.---.--.--F------.7.------..--..-.----.-----..---...... --...---.-.------.- 80
7.2 The Study of Dummy with Complete Vehicle Model and Restraint
System Simulation--v-..------.-----.----..-.------.---.------..---..------.-----. 86
7.2.1 Case Study-..*--.--.-.-.--..------...--.----.------.-----.-..---.-.--.----.------..------.---..------87
7.2.2 Discussion.------.--.-----..?----.-..---.-.----.*--.---*-....------.--.-----.-----...-.--- -.------89
CHAPTER 8 SUMMARY AND CONCLUSIONS .------..--.YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY 94
8.1 Summary...... 94
8.2 Conclusion------.------.------..------. .----.-...--.--. .. -.--.-- -.-----.- ---.---..- .------97
8.3 Future Work ---.-.-----.----.-.------. ..---.------. ------.---.------..------.----.--.---.-- 99
CHAPTER 9 REFERENCES 101
ABSTRACT..* -.- - -.--. --. ---. - --- -.- -.-. . . . -. - -. . - -.-. --. ------.------.--. ------.-- -.- -.. ------.------.------106 vii LIST OF FIGURES
Figure 1. 1 The Crash Rate fh-n 1982 to 1994...... 1
Figure 1-2 The Fatal Crash by Vehicle Type ...... 1
Figure 1-3 The fatality-and-injury-reducing effectiveness in relation to different types
of crashes...... 3
Figure 1-4 The Research Structure of the Intelligent Environment for Occupant
Simulation...... 7
FikWre 3-1 Organization of ATB Program and files...... 15
Figure 3-2 The ATB dummy model ...... 16
Figure 3-3 ATB ball, plane and motion (simple problem) ...... 20
Figure 3-4 Plot of Z acceleration of the ball in ATB and the coupled code...... 20
Figure 3-5 ATB Dummy and seat model simulated in coupled Code...... 20
Figure 3-6 ATE3 dummy and seat model ...... 20
Figure 3-7 X acceleration of dunmy's upper torso in ATB and coupled code...... 21
Figure 3-8 ATB dummy. seat and motion with LS-DYNA seatbelt...... 21
Figure 3-9 X Acceleration of upper torso running in coupled code...... 21
Figure 3-10 ATB dummy, seat and Motion with LS-DYNAAirbag...... 22
Figure 3-1 1 Plot of X Acceleration of Upper Torso in Coupled Code...... 22
Figure 3-12 ATB dummy. seat and motion with LS-DYNA seatbelt and Airbag...... 22
Figure 3-13 X acceleration of upper torso in coupled code software...... 22
Figure 4- 1 Fo~~l-naterial stress-strain curve ...... 29
Figure 4-2 Orientation of fabric material directions relative...... 33
Figure 4-3 The multi-layer fabric material rmdel...... 33 ... Vlll Figure 4-4 Airbag initial pressure-time curve...... 36
Figure 4-10 The airbag fh-le of wer interface...... 4 1
Figure 4-1 1 The def~l-mablesegment frame of user interface...... 41
Figure 5-1 The Designing of Deformable Dummy...... 43
F~gure5-2 The Male ATE3 Rigid Dummy with Deformable Segment...... 43
Frgure 5-3 Spring and dashpot models for viscose-elasticity ...... 46
Figure 5-4 The X-Y view of head model ...... 47
Figure 5-5 The isometric view of head model...... 4 7
Figure 5-6 The X-Y view of upper torso model...... 49
Figure 5-7 The ism-ietric view of upper torso ...... 49
Figure 5-8 The X-Y View of Upper Legs Model...... 51
Figure 5-9 The so metric View of Upper Legs Model ...... 51
Figure 6-1 The deceleration on the different initial velocity simulation...... 58
Figure 6-2 The X velocity of rigid dummy lower torso (segment 1)...... 59
Figure 6-3 The deceleration on the different initial velocity simulation...... 60
Figure 6-4 The X velocity of rigid dummy lower torso segment (segment 1)...... 60
Figure 6-5 The X velocity of rigid dummy upper torso (segment 3)...... 67
Figure 6-6 The X velocity of rigid dummy lower torso (segment 1)...... 68 ix Figure 6-7 The X displacement of rigid dummy lower torso (segment 1)...--.-.-.--.-....-... 69
Figure 6-8 The X velocity of rigid dummy upper torso (segment 3).------.-.------.---.-----, 69
Figure 6-9 The X Velocity of Rigid Dummy Upper Torso Segment (Segment 3)-.------.70
Figure 6-10 The X-axis Velocity of Segment 3 (Wl: 1 inch wide; W2: 2 inch wide).--.71
Figure 6-1 1 The X-axis Velocity of Upper Torso Segment (with Airbag) ------.-.------.A- 72
Figure 6-12 The X-axis Velocity of Upper Torso Segment (without Airbag)----.------.-.--. 72
Figure 6- 13 The X-axis Velocity of Upper Torso Segment on Different Airbag
Folding patterns ------.--.------.------.--* ---.--.* .--.-----7------..-.--..---....--. .------.-. 73
Figure 7-1 The X-axis velocity of lower torso segment ------.-.------.------..------.-8 1
Figure 7-2 The X-axis velocity of upper torso segment ---.---.------.- ---.------..--..-.---.----... 8 1
Figure 7-3 The maximum principle stress on deformable segment----.---m----A--.-..-----.------. 82
Figure 7-4 The maximum principle stress on the bottom of seat-.---.------.---..-----..------..---., 83
Figure 7-5 The X-velocit~of upper torso segment..------.------7-----m------e---.-----.-.------. 84
Figure 7-6 The deformation of head segment .---.--.------.--.-.------..--.--.------..----.--.-..--..--.-. 85
Figure 7-7 The stress of head segment--.------s------.--.--.------.--.----.------.------.a--....-.--F.-.-.--. 85
Figure 7-8 The maximum principle Stress on the Bottom of Seat -.-.--.------.-----.--.------..-,85
Figure 7-9 The X-velocity of seat, upper torso and head Segments.----s----A-----.-.-s..--.----.-. 90
Figure 7-10 The 2-velocity of upper torso and head Segments.---.------..--.--..-.--.-..---.-.-, 9 1
Figure 7-1 1 The Stress on The SeatbeltF------.------.s------p---.------.-e--*--.---.--.---. 9 1
Figure 7- 12 The Stress on The Bottom Part of Seat ------.------.---.--.--.-.---....--.--- -..--.---.--...92
Figure 7-13 The stress on the deformable segment of the deformable dummy with X LIST OF TABLES
Table 4-1 The Mechanical Property of Material Nylon 6 ...... 25
Table 4-2 One Inch Wide Seatbelt Models ...... 27
Table 4-3 Two Inch Wide Seatbelt Models...... 28
Table 4-4 Two Different Mesh Density Complete Seat Model ...... 30
Table 4-5 The Flat Seat Model and Shell Seat Model ...... 31
Table 4-6 The Pllrbag Folding Line and Adjusting Mesh For Airbag Folding...... 3 8
Table 4-7 The FEM Mesh for Different types of hrbag Folding Pattern...... 40
Table 5-1 The Mechanical Property of Orthotropic Material ...... 45
Table 5-2 The Three Different Segment of Head Model ...... 48
Table 5-3 The Detailed Describe of Each Parts of Head Segment...... 49
Table 5-4 The Three Different Segments of Upper Torso Model...... 50
Table 5-5 The Detailed Describe of Each Parts of Upper Torso Segment...... 50
Table 5-6 The Four Different Segments of Upper Legs Model...... 52
Table 5-7 The Detailed Describe of Each Parts of Upper Legs Segments...... 53
Table 6- 1 The Boundary and Initial Condition for 6 Simulation Cases ...... 55
Table 6-2 The model and simulation result of Hyper I11 dummy...... 56
Table 6-3 The Model and Simulation Result of167 LB Male Dummy ...... 57
Table 6-4 The Model and Simulation Result of 120 LB Female Dummy...... 57
Table 6-5 The One Inch wide Seatbelts (LSDYNA, Time = 0)...... 62
Table 6-6 The Two Inch wide Seatbelts (LSDYNA, Time = 0)...... 62
Table 6-7 The Simulation Result of One Inch wide Seatbelts...... 63
Table 6-8 The Simulation Result of Two Inch wide Seatbelts...... 63 xi Table 6-9 The Rigid Dummy with 1 Inch wide Seatbelt and Airbag..-...---.--..-----....---..... 64
Table 6-10 The Result of Rigid Dummy with Seatbelt and Airbag -----.------..----.--...--..--65
Table 6-1 1 The Hyper 111 Rigid Dummy with Lap Belt and Four Different Pattern
Airbag .----.----..------.------..-*------.------.--.-.---.------.------...-.--.-.------..-.66
Table 7-1 The Initial Condition for the Group of Dummy with Deformable Segment.75
Table 7-2 The Model and Simulation Result of Dummy with Deformable Segment----76
Table 7-3 The Models of Rigd dummy only and Dummy with All Deformable
Segments..------*----.------...------.---.------*------.--.-.----.------77
Table 7-4 The Model of Dummy with Deformable Segment .-----.--.---.-..------.----.--.----...--.78
Table 7-5 The Simulation Result of All Ivlodels * ---.---.--...----..-.----.----.----.-.---..-.------..-.79
Fable 7-6 The FEM CAR Model of Chevrolet C2500 Pickup-----.-----.------.--...--..--...---..... 87
Table 7-7 The Simulation Result of Chevrolet C2500 Pickup FEM CAR Model
Only.-. .---. --..-. - -.------.--.-.------.------.---- - .--- - -.- --.--- --.- ---. - -.- -- * ------... - - 87
Table 7-8 The Model of Whole FEM Vehcle Model with Rigid Dummy 88
Table 7-9 The Result of Whole FEM Vehicle Model with Rigid Dummy 88
Table 7- 10 The Model of Whole FEM Car and Dummy with Deformable Segments .-89
Table 7-1 1 The Result of Complete FEM Car and Dummy with Deformable CHAPTER 1 INTRODUCTION
1.1 General Remarks
Motor vehicle crashes are the leading cause of death between the ages of 1 and 40
for Americans, claiming 49,000 lives and injuring about 4.5 million others each year [I].
Estimates of the total annual economic cost of accidents range fiom $125 billion to $358
billion [2]. According to the data fiom the U.S. Department of Transportation, the crash
death rate (the number of people killed per 100 million vehicle miles traveled) was 1.6 in
2000, compared to the crash death rate of 2.3 in 1986 years and 2.2 in 1990 [2]. The
crash death rate has dropped in the past 10 years [3] (Figure 1- 1 and 1-2) because car and restraint system designs provided crash protection.
Speeding. Alcohol Invdvernent, and Fallurs To Use Restrairds Among Drlvers Involved in Fatal Crashes by Vehicle TYPE,from 1900s to 2000s
Figure 1-1 The Crash Rate from 1982 to 1994 Figure 1-2 The Fatal Crash by Vehicle Type Crashworthiness simulation has been a major factor that has enabled automotive
manufacturers to achieve a 30 to 50% reduction in development time and costs over the
past five years. Moreover, today this technology is considered a mature and proven
design tool for the development of automotive structures and restraint system design.
Only minimal prototype testing is needed, usually at the end of the design phase, for the purpose of confirming the "simulation based design".
Considering the advances in the area of crashworthiness simulation, the role of destructive crash testing may be limited to the validation of computer simulation of crash tests in the future.
1.2 Occupant Protection System
Motorists rely on "occupant protection systems" such as safety belts and air bags to save lives and prevent injuries in the event of a crash. Overall, American drivers and passengers have markedly increased their use of safety belts and airbags during the last ten years. In 1995, more than 98 percent of all new cars sold were equipped with driver or dual (driver and passenger) air bag systems. By September 1998, all new passenger cars and light trucks required the installation of air bags and manual lap/shoulder belts.
Seatbelts provide good protection against occupant ejection in fatal crashes. According to U.S. Department of Transportation data in the 1997, it saved an estimated
10,750 lives in car crashes, and only 1% of restrained occupants were ejected, compared
to 40% of unrestrained ones. Three-point belt restraint systems are the most popular to
use in vehicle seat belt design.
Airbag was designed primarily to provide protection in frontal crashes. The
effectiveness of the airbag as a safety device in decreasing fatalities and reducing
morbidity was well established. Airbags reduced fatal injuries by 45-50% if the driver
was belted and by 8-13% if the driver was unbelted (Figure 1-3 [4]). Therefore, the air bag had been popular with motorist. It was used in combination with safety belts to provide "significant life-saving results."
Front "I Damage Area
Of;%+ I ;i:g m;;;mtie LISM~IIY~I Belt
Figure 1-3 The fatality-and-injury-reducing effectiveness in relation to different types of crashes 4
Seat belts and airbags have considerably reduced the number of injuries from traffic accidents; however, both have their limitations. The seat belt reduces the motion of the body but leaves the head and neck unprotected, and airbags protect a front passenger in a frontal collision, but do not consider multidirectional forces or rear impact.
Good seat design could prevent the neck extension beyond the physiological range during rear-end car collisions. The consideration for seat design is how to prevent the hyperextension related injuries of the human upper torso and neck during a multidirectional impact. That included the head restraint system, seat angle, and soft seat material.
1.3 Research Objectives
The objective of this research is to create an intelligent environment for occupant simulation. The intelligent environment will include a database and a user interface.
The database consist of several newly created airbag, seatbelt, and seat models with several rigid dummies, and deformable dummy segments. The user could choose the components that they want from the database through the user interface and run the simulation instead of rebuilding each of the objects such as aircraft or automobile. The user also has the capability to add more objects in this database. 5 Another focus of this research is to develop a methodology to accommodate
deformable segments of dummies more easily in crash simulation studies. Currently, only rigid or non-deformable dummies are used in crash analysis. Initial models of deformable head and feet will be considered for this study. An approach to use the existing joint information and segment end positions from ATB will also be explored.
1.3.1 An Intelligent Environment of Occupant Simulation
Occupant simulation is engmeering analysis methods that uses rigd body dynamics and finite element methods to create mathematical models that describe the interaction of an occupant with the vehicle or aircraft interior during a crash simulation. This approach allows automobile, restraints systems, aircraft, and seat manufacturers to conduct optimization and conceptual parameter studies on the computer, whlch reduces the need for time consuming and costly physical tests.
Currently, the auto industry and the tier 11 suppliers perform rigid body dynamics using MADYMO (Mathematical Dynamic Models) or ATB (Articulated Total Body )
[24] and then simulate the occupant and the interior of an automobile using LS-DYNA and, or PAMCRASH. One of the objectives of this project was to couple the two software programs, ATB for rigid body dynamics and LS-DYNA for finite element 6 analysis. In most cases the models of the airbag, seat belt, and seat have to be recreated to perform a complete analysis, since LS-DYNA required one file containing data cards for analysis. The intelligent environment and user interface were created to help the designer conduct the simulation easier and faster and can analyze all the different combination available in our database of airbags, seat belts, and seat with the &fferent dummy configurations to get an optimum and safe interior. The environment lets the designer select different models and combines them into one ".k" file for LS-DYNA analysis. All the restraint systems and dummy models were separately created and tested under the new coupled software.
The project was funded by WPAFB (Biomechanics Lab). The project was divided into three sub-groups or components. Prasad Petkar, a graduate student at Ohio
University, was responsible for studying and creating the seat models. Srikanth Patlu, also a graduate student of Ohio University, was assigned the task of modeling the seat belt models (See Figure 1-4). Both Patlu and Petkar were working on their sub-sections as part of their master's thesis. Shr-Hung Chen, the author, was responsible for creating airbag models, the database whlch included seat, seat belt, airbag and dummy models, and developing an user interface to select the module from the database. The author 7
also developed a new methodology to accommodate defonnable (FEA) dummy
segments, and built into the database. All members of the group were responsible for validating the coupled ATB-LSDYNA code. The system which included user interface, ATB and LS-DYNA coupled code, and the database which have the restrainrs system model, rigid dummies and dummy with deformable segments was called intelligent environment for occupant simulation.
Seat systems oupled Code Validation: Airbag restraint systems, Model database User Interface
'Ihe Database and IntcWgcnt Ehnmmt oupled Code Validation: Occupant Simulation
W~ghtPatfernon Air Foxe Bass (WPAFB) ATB- LSDYNA Code Integration: LSTC
Figure 1-4 The Research Structure of the Intelligent Environment for Occupant Simulation
The software packages ATB (Articulated Total Body) and LS-DYNA (PC version) were coupled and integrated to provide researchers the capabilities of performing advance crash simulations in which one can include the dummy model from ATB and the seat belt, airbag, seat and other restraint system models from LS-DYNA. The coupled 8 code was supported by the WPAFB (ATB) and LSTC (LS-DYNA). Therefore, the
research was jointly undertaken by Wright Patterson &r Force Base (WPAFB) in Dayton,
OH and Livermore Software Technology Cooporation, CA (LSTC) with the Department
of Mechanical Engineering, Oho University, Athens OH.
1.3.2 Deformable Dummy
The deformable dummy was not widely used in crash simulations because of the
difficultly to model it and takes lot of CPU running time. By using the defomable
dummy in the occupant simulation, the researcher could study the details of the human body during the vehicle crash or side impact and provide information about stresses range
and deformation to the bones. Deformable Dummies can be used to predict bone injury
and fraclre during a crash. One other objective of this research was to create an
environment for deformable dummy segments using the available ATB information.
Currently, the crash simulation groups create deformable dummies of the whole human body and are relatively inaccurate, cumbrance to create and take a long time to analyze.
The new methodology introduced will let researchers create specific segment like the
skull, tibia, rib legs etc. and let them analyze these segments. 1-4 Aim and Concept
This research had the following main features:
+ The development and validation of the coupled code ATB and LS-DYNA.
+ The concept and design of deformable segment of dummy.
+ Modeling the 3-D airbag, seat belt, and seat model for the database of
intelligent environment.
Using Visual Basic to design a program to combine the airbag, seat belt, and
seat modeling data with different dummy types to run the simulation under
ATB and LS-DYNA coupling sofhvare packages. CHAPTER 2 LITERATURE REVIEW
2.1 The Computer Simulation of Crashworthiness and Occupant Protection
In recent years, CAE (Computer Aided Engineering) has become very popular for the effective development of many industrial fields. In the crashworthiness and occupant protection area, the CAE technology was used in analyzing full vehicle impact or representing the relationshp of the vehicle and the dummy. Gupta [6] developed the full finite element model of the 199 1 Ford Taurus, 1995 Chevrolet Lumina, and 1994
Dodge Intrepid for offset frontal impact crash simulation. Guha [7] tried to combine
LS-DYNA and MADYMO software packages in order to propose design changes to the vehlcle, based on the occupant injury and vehicle deformation predictions. Zhang [9] combined two different programs (ADAMS and NASTRAN) to analyze the kinematicsldynamic (ADAMS) and stress problem (NASTRAN) for the crashworthiness analysis.
2.1.1 The Literature About Airbags
Finite element techniques have been applied to the simulation of airbag behavior on this approach; the airbag deforms realistically when penetrated and generates bag inertia forces. Moreover, bag material properties can be incorporated in a direct way. Euler 11 discretization was used by Heijden [8] to simulate the gas blow forces for the gas inside the airbag. Nieboer [lo] and Brujis [ll] designed the model of the air bag by finite element formulation, which allows the determination of topological characteristics of the air bag and its contact with the impacting object with greater accuracy at any time during the simulation.
Patrick [12] studied how to reduce injuries when the air bag was deployed which occurred when the occupant was struck by a small but rapidly moving portion of the bag.
Even if this effect does not result in critical injuries, it can cause skin abrasions or eye injuries. Horsch [13] and Wehner [14] emphasized developing an improved understanding of near-position dnver loading by an inflating air bag using both a mid-size male Hybrid I11 dummy and physiological surrogates. Wang 1151 focused on the air bag mathematical models by thermodynamics theory ( the gas inflow, outflow, and the associated pressure-volume-temperature relationship), not just the uniform pressure assumption, in which the gas pressure and temperature remain uniform in the space inside the air bag. 2.1.2 The Literature about Seat belt and Seat
In 1972, Levine and Campbell El73 studied the data of accidents in North Carolina from 1966 to 1968. Their analysis of the data indicated that seat belts decreased the incidence of serious injury by over 57%. Deng 1161 tried to model the seat belt restraint system to prelct the occupant impact response based on dynamic principals. Freeman and Bacon [18] describe a spatial measurement system that was used to monitor dummy trajectories during the test and made the comparison between the Hybrid I1 and I11 dummy with respect to seat belt position.
In 1969, IOhlberg 1191 examined the automotive crash injury research data to determine whether injury exposure could be related to seat deformation. He found statistically significant reductions in injury frequency in cases where seat deformation occurred. In 1976, Severy [20] studied a new seat design of seat. The prototype of this design used sheet metal in place of the plastic membrane. It was installed in RSV test article and impacted at 40 mph by a production vehicle. The new design was maintained in ths test and the energy absorbers controlled the rebound motion of the unrestrained dummy reasonably well. 2.2 The Literature About Deformable Dummy
A human finite element model, which has bio-fidelity in geometry and characteristics, can be useful for evaluation of crash safety of a vehicle and design of new occupant restraint devices. Numerical models of crash dummies such as Hybrid 111 have been developed and used for crash test simulation, but most of the dummy models are set to rigid type during the simulation. Tamura and Furusu [21] develop the FEM deformable leg model for crash simulation. This model can show a detailed stress range of a leg that can show the highest stress during the crash simulation. Cesari [22] focused on how to create the FEM shoulder model for studying the damage of the human shoulder during side impact. Beaugonin 1231 combined the rigid component (bone) and deformable (foot ligament, angle ligament and Achlles tendon) part to build the FEM foot model for the simulation of the ankle dorsiflexion response during an impact loading.
The advantage of combining models saves the CPU time while obtaining the desired data. 14 CHAPTER 3 THE VALIDATION OF COUPLED CODE
3.1 Introduction
ATB is a rigid body dynamics program and LS-DYNA is a finite element analysis software for occupant simulation. The ATE3 and LS-DYNA coupled code could provide a single simulation tool with the advantage of each individual program. ATB could provide the database of dummy modeling (GEBOD) but has limited restraint system model capabilities such as airbag and complete seat model. LS-DYNA is a powerful finite element analysis program with many specialized restraint element including belts and the material for airbag modeling. With the coupled sofhvare, the user could take the
ATB's dummy model to the LS-DYNA, design the airbag, the seat belt, and the seat system and perform a detailed analysis of the occupant with the restraint system in an automobile or aircraft.
3.1.1 ATB (Articulated Total Body) Program
The Articulated Total Body (ATB) model is a three-dimensional coupled rigid body simulation program developed by the U.S. Air Force. It is the recognized standard for simulating the dynamic response of a rigid body system to applied forces. The body properties for occupants are produced by the GEBOD (Generator of Body Data) program based upon sex, height, and weight. The information about the dummy model
(GEBOD), vehicle description, and motion information is organized in the form of cards in the ATB input file (.ah) (see Figure 3- 1) [24].
Csmp%le ATI! lnp~thk r.!am outps hbtw npid with A-H Card6 and OUW
Figure 3-1 Organization of ATB program and files
GEBOD (Generator of Body Data) was designed specifically to provide the body data needed by the ATB program for human body dynamic simulations. The data provided can be used by other similar programs and in applications where the body link and mass properties are needed. GEBOD will generate the body segment and joint 16 properties (see Figure 3-2) [24] for Hybrid I1 dummy, Hybrid I11 dummy and any size male or female based on their height and weight. It also provides child data based on age, height, and weight.
Figure 3-2 The ATB dummy model
3.1.2 LS-DYNA Program
LS-DYNA is an explicit finite element program for the analysis of the non-linear dynamic response of three-dimensional structures. The program is owned and developed by Livennore Software Technology Corporation (LSTC) based in Livermore, California.
It incorporates a number of advanced features including fully automated contact handling and error checking, thermal modeling, adaptive meshing, coupled structure/fluid 17 modeling, bi-material elements, multiple airbag inflate models, integrated 2-D and 3-D modeling, and multiple local coordinate systems.
LS-DYNA is widely used by the automotive and aviation industry. It has nearly
100 constitutive models to simulate a whole range of engineering materials from steels to composites and soft foams to concrete. The code has an extensive element library including membrane, thin shell, thck shell, and solid formulations. Special features in the code include automatic contact algorithms, airbag inflation, and seat belt elements.
3.1.3 The Development of Coupled Code
LS-DYNA is a general purpose, explicit, finite element program used to analyze the nonlinear dynamic response of three-dimensional structures. It can predict how a prototype will respond to real-world events, thus minimizing the time spent in design and money spent on experimental testing. The ATB (Articulated Total Body) is used for predicting gross human body response in various dynamic environments. It was primarily designed to evaluate the three-dimensional dynamic response of a system of bodies when subjected to a dynamic environment consisting of applied forces and interactive contact forces. However, ATB has a limited restraint system, such as airbag, seat and FEM modeling capabilities, and LS-DYNA has dificulty creating a rigid human 18 dummy for the occupant simulation. Therefore, the coupled code with ATB and
1,s-DYNA has advantages fiom both ATB and LS-DYNA. The ATB and LS-DYNA coupled code could run the simulation by taking rigid dummies code and GEBOD database fiom ATB program and FEM model (such as airbag, seat, belt or complete FEM vehicle model) from LS-DYNA.
3.2 The Validation of Coupled Code
Validation of the coupled code developed in the project was done in order to validate future simulations and results obtained using coupled code. The quantitative evaluation consisted of comparing the acceleration data of the various dummy segments generated by the coupled code (rigid body output file) with the corresponding data sets generated by the ATB program.
Five separate cases were modeled and analyzed to compare the results and validate the coupled code. ATB and coupled software output data files were used to generate the plots of acceleration of the dummy's upper torso segment. The upper torso, being the most critical part of the human body that houses various vital organs, was chosen for the analysis. X acceleration was analyzed as the vehicle motion has only X translation degrees [28]. The five cases are as follows: Case 1 ATB ball, plane, and motion (simple problem)
Case 2 ATB dummy, seat, and motion with no seat belt
Case 3 ATB dummy, seat, and motion with LS-DYNA seat belt
Case 4 ATB dummy, seat, and motion with LS-DYNA airbag
Case 5 ATB dummy, seat, and motion with LS-DYNA belt and airbag
3.2.1 The Cases Studies
The purpose of Case 1 and Case 2 was to compare the results between running in
ATB software only and coupled code software. These two cases only included ATB rlgid body and motion only without any finite element part, such as seat belt or airbag.
Case 3, Case 4, and Case 5 were an ATB rigid dummy with LS-DYNA finite element components. These three cases were only running under coupled code software. The
ATB was the rigid body simulation program. The simulation of ATB software only considered the rigid component without any finite element part.
Case 1 was the simple rigid ball and plane problem where both ball and plane were modeled in ATB and the simulation was running in the coupled code using ATB input file
(.ain). The results showing Z acceleration of the ball, when the simulation is run using
ATB and also using the coupled code, is plotted in Figure 3-3. The plot is shown that 20 results from ATB and coupled software match almost exactly (Figure 3-4).
Figure 3-3 ATB ball, plane and motion Figure 3-4 Z acceleration in ATB and the coupled code
Case 2 was the ATE3 rigid dummy, rigid seat, and motion without any FEM component running in the coupled code and ATB software only. Figure 3-5 is shown the human dummy and seat modeled in ATB while the simulation is run using the coupled code with ATB input file. Figure 3-6 is shown the same model run in ATE3 at the same time-step (220 msec.). Figure 3-7 is shown a comparison of X acceleration of the upper torso of the dummy in ATB alone and coupled code. The results match almost exactly.
Figure 3-5 The simulation of case2 in coupled code Figure 3-6 The simulation of case2 in ATB 2 1
CASE 2 : X Acceleration
.01
Time (Sec.) Figure 3-7 X acceleration of dummy's upper torso in ATB and coupled code
Case 3 was an ATB rigid dummy, rigid seat and motion with LS-DYNA seat belt
(finite element belt) running in the coupled code software. Figure 3-8 is shown the ATB dummy and seat with LS-DYNA seat belt when the simulation is run in coupled code.
Figure 3-9 is shown X acceleration of upper torso of the dummy only in coupled code software.
Figure 3-8 The simulation of case3 in coupled code Figure 3-9 upper
Case 4 was an ATB rigid dummy, rigid seat and motion with LS-DYNA airbag
(finite element airbag model) running in the coupled code software. The airbag model 22 was modified by the LS-DYNA example (simple airbag model) [23] in order to run the
validation. Figure 3-10 is shown the ATB dummy and seat model, and the LS-DYNA
airbag model. The X acceleration of upper torso of the dummy in coupled software was
shown in Figure 3- 11.
Figure 3-10 The simulation of case4 in coupled code Figure 3-11 Plot of X Acceleration of Upper Torso
Case 5 was an ATB motion, rigid dummy and seat with LS-DYNA belt and airbag
(finite element airbag and seat belt model) running in the coupled code software. Figure
3-12 is shown the ATB dummy and seat mode with LS-DYNA airbag and belt mode.
The X acceleration of upper torso of the dummy in coupled software was shown in
Figure 3-13.
Figure 3-12 The simulation of case5 in coupled code Figure 3-1 3 X acceleration of upper torso 3.2.2 Conclusion
Five different cases were analyzed to compare the results and validate the integration of the two codes (See Appendix A). For the validation, both ATB and coupled code were used. From the first two cases, the results were found to be within acceptable limits. The other three cases (case 4, 5 and 6) have to be compared with experimental data to validate the accuracy of the coupled code because the ATB cannot analyze models with airbags. The experimental validation was done by WPAFB and found to be acceptable. CHAPTER 4 THE DESIGN OF INTELLIGENT
ENVIRONMENT FOR THE OCCUPANT SIMULATION
4.1 Introduction
The finite element (FEM) simulations have become a very efficient tool in crashworthiness design. By evaluating simulation results, an improved design can be obtained by changing a set of design parameters. Ths design approach may not always lead to the "best" design, since design objectives are often in conflict. The intelligent environment for occupant simulation could help researchers run their simulation much easier and faster.
This chapter will represent the restraint system model designs and user interface design of intelligent environment for the occupant simulation. The intelligent environment for occupant simulation includes coupled code, database and the user interface. The database could provide the researcher several different airbag, seatbelt, seat, and dummy models and improve the simulation much easier and faster. Also, the researchers could add their own models to this database. The user interface could help the researcher use this database more conveniently. 4.2 Modeling Three Dimension Seatbelt and Seat Models
The seat belt model was created by Srikanth Patlu [29] (a graduate student at Ohio
University), and the complete seat model which includes seat cushion, seat back and head
restraint was created by Prasad N. Petkar, [30] also a graduate student at Ohio University.
All of the seat and seatbelt models were modified by the author and put into the database.
4.2.1 Three Dimension Seatbelt Models
Seat belts provide the good protection against occupant ejection in fatal crashes.
The most widely used seat belt type is the three point seat belt (laplshoulder belts).
Some race car or aircraft used five points seat belt to protect the driver or pilot. In this research, the database of seatbelts was developed in order to determine the most effective belt model for frontal crashes. The different seatbelt models were shoulder belt, lap belt, three points belt and five points belts. The material of seatbelt is Nylon 6 Polymer, and
Table (Table 4-1) shows its mechanical property. The material type which was used in
LS-DYNA was "FABRIC".
Table 4-1 The Mechanical Property of Material Nylon 6
Nylon 6 :Mechanical Property Density Tensile Strength, Elongation @. break Flexural Modulus Flexural Yield Ultimate Strength /t- 0.0408 lblin 1 10900 psi 1 60 % / 392000 psi / 14500 psi 26
The widths of seatbelts was one inch and two inch in this database. The seabelt
models of one inch wide (Table 4-2) were created by Srikanth Patlu, and used in the
coupled code validation. The two inch seatbelt models (Table 4-3), which are generally
used in the automobile industry, were created by the author. There are four different
designing of seatbelt model: lap belt only, shoulder belt only, 3 points belt and 5 points
belt. The 3 points belt is used in the car driver or front seat passenger, and 5 points belt
is used in race car dnver or aircraft pilot. The lap belt only and shoulder belt only were
derived from 3 points belt. The lap belt is used in the airplane passenger or some car passengers, and shoulder belt only is used in the velxcle back seat passenger. These four types seatbelt model are widely use in the automobile or aircraft industry, and built into the database of this research. Table 4-2 One Inch Wide Seatbelt Models
Lap Belt Only Shoulder Belt Only A $
Three Points Belt Five Points Belt Table 4-3 Two Inch Wide Seatbelt Models
Lap Belt Only Shoulder Belt Only
Three Points Belt Five Points Belt -- 4.2.2 Three Dimension Seat Models
A good seat design could prevent the neck extension beyond the physiological range during rear-end car collisions. The consideration of seat design is how to prevent the hyperextension related injuries of the human upper torso and neck during a multidirectional impact. The complete seat model consisted of five parts: seat cushion, seat back, left pine, right pine, and head restraint.
Material for an automobile seat is an important part in the occupant protection of the rear impact stituation. One of the main requirements of the seat material is the energy absorption capacity. The material used for the seat cushion is "low-density foam"
(LS-DYNA material model). The material is hgh-energy absorption efficiency, light weight and moldability. The stress-strain cure of foam material shows in Figure 4-1.
1 Foam Material StressIStrain Curve
O.WE+OO ].WE-01 2.WE-01 3.00E-01 4.00E-01 5.00E-01 6.WE-01 7.WE-01 8.00E-01 9.WE-01 I.WE+M Strain
Figure 4-1 Foam material stress-strain curve 3 0
The seat models which were built into this database were four different types.
There are low density mesh complete seat model, high density mesh complete seat model,
flat seat model and shell seat model. The low mesh density complete seat model was
created by Prasad N. Petkar, and the author modified it to be the high mesh density
complete seat model (see Table 4-4). The high mesh density complete seat model will take much CPU running time, but it could provide more detailed information, such as seat
deformation, stress or strain to the user.
Table 4-4 Two Different Mesh Density Complete Seat Model
High Density Mesh Complete Seat Low Density Mesh Complete Seat Shell Element No.: 300 Shell Element No.: 138 Solid Element No.: 10240 Solid Element No.: 2277 Total Element No. :10540 Total Element No.: 24 15 The flat seat model and shell seat model (see Table 4-5) were created by the author in order to run the simple simulation more efficiently. The flat seat model retains foam material as its seat cushion, back, and head support, but the shape is simple and low mesh density. The shell seat model is shell element only, and the material of the seat cushion, seat back and head support is rigid. Both models were designed to run the simulation which did not need to study the detailed status about the seat model during the simulation.
Table 4-5 The Flat Seat Model and Shell Seat Model
The Flat Seat Model The Shell Seat Model Shell Element No.: 208 Shell Element No.: 424 Solid Element No. : 672 Solid Element No.: 0 I Total Element No.: 880 Total Element No.: 424 4.3 Modeling the Airbag
In this study, the airbag material, inflation process, and airbag folding algorithm will be considered. This included modeling of the fabric behavior for the airbag material. An inflator model was added to determine the mass and energy flow rate into the airbag from the inflator. Then, the airbag folding algorithms were developed to fold
FEM meshes of unfolded airbags into their initial folded geometry. The folding algorithm is embedded in the LS-INGRID mesh generator code.
4.3.1 The Airbag Material
A feature of fabrics is that it has almost no bending strength and compressive loads immediately result in buckling plus an inability to develop compressive stresses [36].
The airbag fabric model is based on orthotropic elastic material model which can be used in conjunction with several shell elements in LS-DYNA (type 34 material). The shell element could be represented by a multilayered laminate. To allow for an arbitrary orientation of the finite elements within the mesh, each ply in the fabric may have a unique orientation angle (P) which measures the offset angle (8) from some reference determined by the angle (y),defined for each element as shown in Figure 4-2. A multi-layered shell representation that can be used for airbag fabric modeling is shown in 33 Figure 4-3. The angle ,B could be defined at each integration point through the laminate thickness.
Figure 4-2 Orientation of fabric material directions relative
Figure 4-3 The multi-layer fabric material model 34
For the fabric material mode, we need to transform the stress tensor a and the rate of deformation tensor 2 into the material coordinate system denoted by the subscript L. Then, the stress will be updated in the material coordinates by [32]:
And then
- 1 Q Q12 0 0 0 -dl,-
A022 Q12 Q22 0 0 0 d22 A~Ln+1'2 = dol2 + 0 0 Q,, 0 0 dl, At (Eq. 4-2)
A023 O O O Q55 d23
AOld - O O O Q66--d314L
The Q,. will be defined as following equations: (Eq. 4-3)
Because of the symmetry properties: v2,= v,, -E22 (Eq. 4-4) El1
The idealized model produces a zero modulus for compressive strains and piecewise linear modulus for tensile strains. The zero compressive modulus simulates the inability of the fibers to carry compressive stress and the piecewise tensile modulus simulates the initial slack in the fabric [27]. 35
4.3.2 The Airbag Modeling Design and Inflation Process
A simplified gas model based on assuming uniform thermodynamic properties
(pressure, density, temperature and internal energy) throughout the airbag was coupled to the airbag structure. The keyword "*AIRBAG in LS-DYNA functions by defining thennodynamic behavior of the gas flow into the airbag as well as a reference configuration for the fully inflated bags [33].
"Gamma Law Gas Equation of State" was used in airbag simulation to determine the pressure in the airbag. This equation followed from the thermodynamic considerations of adiabatic expansion of an idea gas [33]. Ths equation is
p =(y-1)pe (Eq. 4-5) where p is the pressure, p is the density, e is the specific internal energy of the gas, c, is heat capacity at constant pressure, c, is the heat capacity at constant volume and y is the ratio of the specific heats:
y = -'' (Eq. 4-6) C,
The time rate of change of mass flowing into the bag is given as:
The inflow mass flow rate is give by the load curve "initial pressure - time curve" 36 (see Figure 4-4) [34].
AIRBAG INITIAL PRESSURE I
TTME (Sec) !
Figure 4-4 Airbag initial pressure-time curve [34]
The above equations provide the model which considered the mass flow due to the vents and leakage through the bag.
There were two types of contact option used in the airbag inflation process in
LS-DYNA. The "*CONTACTAIRBAG-SINGLE-SURFACE" was used in between airbag surface, and ""CONTACT -ENTITY? was used in between airbag surface and dummy. 4.3.3 The Airbag Profile and Folding Patters Algorithm
The profile of deflated airbag is created by MSC-PATRAN. The diameter is 28 inch and its thickness is 0.013 in [26]. The airbag (see Figure 4-5) will be inflated to an approximate volume of 366 1.44 in3 at a pressure of 0.58 psi. The FEM model simulated the airbag with 15 16 membrane quad elements.
Figure 4-5 The profile of deflated airbag model
For the airbag folding process, the flat surfaces are meshed with respect to the defined folding lines. A regular fold is also achieved when also the nodes on both sides of this line are on a parallel to the folding line, as shown in Table 4-6. The airbag folding algorithm was created by INGRID mesh generator. The INGRID allows for the following necessary attributes for airbag analysis: determination of surface normal, 38 initialization of orthotropic angles, and creating models with triangular or quadrilateral elements of elements of roughly uniform size to maximize the time step increment and sear the gap between two "pancake" bag model (see Figure 4-6) [35].
Table 4-6 The Airbag Folding Line and Adjusting Mesh For Airbag Folding
Fold 1 I
Airbag folding line Effect of adjusting mesh for airbag folding -- must closed by "seal"
Figure 4-6 The INGFUD sear fbnction
In ths study, are four different types of airbag folding pattern algorithms were created and built into the restraint database. Figure 4-7 showed the airbag folding pattern algorithms and Table 4-7 presents the FEM mesh of the airbag folding pattern.
AIRBAG MODEL I 7 1
Figure 4-7 The Airbag Folding Pattern Algorithms 40 Table 4-7 The FEM Mesh for Different types of Airbag Folding Pattern
--,..* :----_..- r. - --- - A .-. ., - 1. -
z 1
.->---.---.7.-:7.---- T:-- T:-- - .. ,a'- ~z:ig&~-~.&-~>/&L.-.L---* --.._._.*- -=+*:==+=--:~+~,- -. _-.--- - =.= .--.. - .- - . . ,- - .--7r$s------r+ ,, ,*;-> -,-.. ------%---~ 4, \--;-I---- -. ,.*/25- -- h*. &'T~-L.~- #.+? .-9".. \%?,- -%+ .r.*..;. .,:..--;.= l.L.;--< -==- &.+?<--- --.T".-." ~ C __ ..~ "Ly:trp- ...... - - - -. ------. -..- . z;77--z>-=--s ---.-:=+<=+- --::-7- -L ,a.= $*+
1 1
4.4 The User Interface for Occupant Simulation
The user interface was programmed in Visual Basic and included the database for the seat belt, seat, airbag, and dummy, which was created in ths research. The user can easily combine any component in this database to run the simulation in the coupled code and add new FEM model, rigid dummy, or deformable dummy and add new objects to this database for future work. For example, the user can choose the favorite component in the main form of the crash modeling environment (see Figure 4-8) and then take the dummy and restraint system model from different frame (see Figure 4-9, 4-10, 4-11).
'The selected models can be exported to a data deck by clicking on "Run ATB-LSDYNA
Coupled Code" button. If the user wants to study the result of rigid dummy only 4 1 without any FEM component, he can choose coupled code or ATB software package to finish the analysis from the main form. The ATB analysis is fast but crude, while the
LSDYNA analysis can take a long time but is mode accurate compared to ATB. The purpose of the user interface is trylng to make occupant simulation faster and easier.
wwy------, km re--: z3z--- 1 ' -"?a 1 sut mYl .-. - - - -- I . . ------> -rWEPRMc>-- --FmM
- - . .- - ---. . .- - -- - : r- sur EL1 RU / L _ - .. ; w- I rvl I
-Dm,.*-*--- LT I I-. ; - - .. -. ------I
Figure 4-8 The main form of user interface Figure 4-9 The dummy frame of user interface
Figure 4-1 0 The airbag frame of user interface Figure 4-1 1 The deformable segment frame 42 CHAPTER 5 THE METHODOLOGY OF DEFORMABLE DUMMY
5.1 Introduction
In occupant safety analysis, numerical simulations of crash events provide a valuable tool for the automotive engneer. The realistic models of the occupant or the dummy as the surrogate in the development process are of particular interest.
Commonly, dummy models based on the dynamics of linkages of rigid bodies are used to predict the behavior of the crash victim. These models are based on data of the victim, its environment, and the crash conditions. Validated data sets for the different types can make the modeling of a crash event very efficient. A significant shortcoming of such an approach, however, is the need to provide experimental force deflection data as input for the contact models.
The deforrnable dummy could provide the data of the stress range and the body deformation and help the researcher to realize the details of human injury during crash.
However, the deformable dummy is not easy to create and takes lot of CPU running time.
The idea of thts research is to try and find a new methodology to create the deformable segment easily and quickly by using available GEBOD information from ATB. 5.2 The Methodology of Deformable Dummy
The ATB software could provide the dummy joint and rigid body dynamic information, and LS-DYNA could support the FEM deformable segment creation.
The new idea is to combine the joint information from ATB software and FEM segment model from LS-DYNA, which will provide a new method to create a deformable segment model more easily and quickly.
There is an example shown in Figure 5-1 and 5-2. The blue ellipse was modified by the original ATB male rigid dummy. The blue ellipse was a small rigid ellipse which moved together with ATB rigid dummy head segment. The red ellipse was created by
LS-DYNA and it is a finite element deformable ellipse. After combining the red and blue ellipse, the red ellipse has the same movement as the blue ellipse. This methodology will provide a much simpler and easier way to create a deformable segment.
Figure 5-1 The Designing of Deformable Dummy Figure 5-2 The iso-view of Deformable Dummy 44 5.3 The Modeling Design of Deformable Segment
In this study, the deforrnable segments focused on the head, upper torso and upper legs. The material considerations of the deforrnable segment are orthotropic elastic and visco-elastic material. The orthotropic elastic material simulated bone behavior and the visco-elastic material simulated muscle behavior. In this study, the deformable segment did not create very detailed modeling. The head model was modified from the head model of LSTC Hybrid I11 dummy. The upper torso model and upper legs models were modified from the upper torso model of ATB Hybrid I11 rigid dummy [24]. All of the deformable segments combine several different parts, materials, and properties. The
LS-DYNA rigid shell element constrained to the ATB rigid dummy in order to move together with the ATB dummy segment. The solid element part used LS-DYNA node constrained code "Constained-Extra-Nodes-Set" constrained to shell element part and used "Contact~Tied~Surface~to~Surface~Title~Offset"between different solid element parts.
5.3.1 Material Consideration
Although the bone is known to behave orthotropically [36] and is strain rate dependent, these properties were accounted for using material type 2
(Mat-Orthotropic -Elastic) LS-DYNA material code. In orthotropic materials, there is 45
no interaction between the normal stresses a,, a,, o, and the shear strains 6, , 6, ,
E,,, . Then, the Compliance Matrix takes the form:
(Ps. Ex,Ey, Ez are three drfSerent Young B Modulus, vp, v,, vv are Poisson B Ratio and G,,
G, (7, are Shear Modulus) -
where -=-,VyZ "w ",- "n --=-"" "'x (Eq. 5-2) Ey E, E, Ex ' Ex Ey
The mechanical property of orthotropic material is shown on Table 5-1 1371.
Table 5- 1 The Mechanical Property of Orthotropic Material
Orthotropic Elastic Material
Elastic Modulus (E) E, = 2.466E6 (psi) E b= 1.668E6 (psi) Ec = 1.668E6 (psi)
Shear Modulus (G) G, = 4.786E5 (psi) Gb= 5.221E5 (psi) Gc = 4.786E5 (psi)
The visco-elastic material was used to simulate muscle and skin behavior in this 46 study. That is the material type 6 LS-DYNA material code [36]. The visco-elasticity describes a material which exhibits a combination of viscous and elastic behavior simultaneously. It can appear to be either solid or liquid, depending on whether the dominant property is elastic or viscous. A common approach to modeling visco-elastic behavior is by means of combining elements representing ideal elastic and viscous behavior. The usual method of doing this is using a spring and dashpot analogy. The spring represents ideal properties and the dashpot, ideal viscous properties. The simplest combinations are to put the two elements in a series and in parallel. This combination was so called Maxwell element and the Kelvin or Voigt element. These are illustrated in Figure 5-3 below.
Maxwell Element Kelvin-Voigt Element
Figure 5-3 Spring and dashpot models for visco-elasticity 47
The shear relaxation behavior is described below: (Go: Short-time shear modulus; G, :
Long-time shear modulus; P : Decay constant)
G(t) = G, + (Go - ~,)e-~' (Eq. 5-3)
v A Jaumann rate formulation is used: (o,is the prime denotes the deviatoric part of the
stress rate; Dijis the strain rate)
v t 0, = 2j0G(t - r)D; (r)dr (Eq. 5-4)
5.3.2 The Modeling of Deformable Head and Upper Torso Segment
The head segment and upper torso consisted of three different parts. There are one rigid shell element part and two deformable solid elements parts. The rigid shell element part was constrained to the ATB rigid dummy segment.
Head Segment Model
The head segment was modified from the LSTC Hybrid I11 dummy (see Figure 5-4, 5-5).
Figure 5-4 The X-Y view of head model Figure 5-5 The Iso-Mew of head model 48
Each part of head segment model is shown in Table 5-2. The black segment was rigid shell element and constrained with segment number five (head segment) of the ATB rigid dummy. The properties of white and gray segments were solid elements. The total element number, which included shell and solid elements, was 2336.
Table 5-2 The Three Different Segment of Head Model
Table (Table 5-3) shows the element number, material type, element property of each part of the deformable head segment. Table 5-3 The Detailed Describe of Each Parts of Head Segment
HEAD SEGMENT; Total Element No.: 2336 C I I 1 I Segment LS-DYNA Element Element Material Type Color PART No. No. Property Black 103000 1 4 16 Shell Element Rigd
/ White 1 1030002 1 1040 1 Solid Element 1 Orthotropic Elastic 1 I Gray ) 1030003 / 880 1 Solid Element / Viscose Elastic I
@per Torso Segment Model
The upper torso segment was modified from the ATB Hybrid I11 rigid dummy (see
Figure 5-6 and 5-7).
Figure 5-6 The X-Y view of upper torso model Figure 5-7 The Iso-View of upper torso
The detailed model is shown in Table 5-4. The black segment was rigid shell element
and constrained with the segment number three (upper torso segment) of ATB rigid
dummy. The properties of white and gray segments were solid element. The total
element number, which included shell and solid element, was 3300. 50 Table 5-4 The Three Different Segments of Upper Torso Model
Table 5-5 shows the element number, material type and element property of each part of the deformable upper torso segment.
Table 5-5 The Detailed Describe of Each Parts of Upper Torso Segment
UPPER TORSO SEGMENT; Total Element No.: 3300
Segment LS-DYNA Element Element Material Type
Color PART No. No. Property
Black 105000 1 416 Shell Element Rigid
White 1050002 1040 Solid Element Orthotropic Elastic
Gray 1050003 880 Solid Element Viscose Elastic 5.3.3 The Modeling of Deformable Upper Legs Segments
The upper legs segments consisted of four different parts. There was one rigid
shell element part and three deformable solid elements parts. The rigid shell element
part was constrained to ATB rigid dummy segment. The other three solid element parts
were of deformable material and contacted to rigid shell element part.
The upper legs segments were modified from the ATB Hybrid I11 dummy (see
Figure 5-8, 5-9).
Figure 5-8 The X-Y View of Upper Legs Model Figure 5-9 The Iso-View of Upper Legs Model
The detailed model is shown in Table 5-6. The red segment was rigid shell element, and constrained with segment number six and nine of ATB rigid dummy. The pink segment is rigid solid segment which was move together with red shell segment The total element number, which included shell and solid element, was 2640. Table 5-6 The Four Different Segments of Upper Legs Model
r I I
Table 5-7 shows the element number, material type and element property of each part of the deformable upper legs segment. Table 5-7 The Detailed Describe of Each Parts of Upper Legs Segments I UPPER LEGS SEGMENT; Total Element No.: 2640 I ! Right Upper Leg Segment (From Part No, 1060001 to 1060004) / Segment LS-DYNA / Element I Element I Material Type I Color / Part No. 1 No. Property 1 1060001 220 Shell Element Rigid
Dark Yellow 1 1060002 2 16 Solid Element Orthotropic Elastic 1 Dark Blue 1 1060003 1 684 1 Solid Element Orthotropic Elastic
I Dark Pink 1 1060004 1 200 1 Solid Element I Viscose Elastic
Left Upper Leg Segment porn Part No, 1090001 to 1090004)
Segment LS-DYNA Element Element Material Type Color PART No. No. Property
Red 1090001 220 Shell Element Rigid
Light Yellow 1090002 2 16 Shell Element Orthotropic Elastic
Light Blue 1090003 684 Solid Element Orthotropic Elastic
Light Pink 1090004 200 Solid Element Viscose Elastic CHAPTER 6 THE STUDY OF RIGID DUMMY WITH
RESTRAINT SYSTEM SIMULATION
6.1 Introduction
In this research, ATB rigid dummy was used with the restraint systems such as airbag, seatbelt and seat model to create six simulations. The six cases were:
1. The simulation of Hyper 111, male and female rigid dummy.
2. Different initial velocity with the same deceleration.
3. Different initial velocity with different deceleration. All movements were
stopped as the same time (0.15 sec).
4. The Hyper I11 dummy with different types of seatbelt. The initial velocity was
45 mph (792 idsec) and stopped as 0.15 sec.
5. The Hyper I11 dummy with airbag in the same boundary condition. . The initial
velocity was 45 mph (792 idsec) and stopped as 0.15 sec.
6. The Hyper 111 dummy with four different types of airbag folding patterns. .
The initial velocity was 45 mph (792 idsec) and stopped as 0.15 sec.
The first three cases are to validate the intelligent environment for occupant simulation. The coupled code validation of thls chapter is to run the simulation with complete intelligent environment system. It is different from previous work. The
fourth case is to get the best design of seatbelt model and width in the occupant
simulation. The fifth case is to study the influence of airbag in the simulation. The
sixth case is to compare the result of different airbag folding pattern. Table 6-1 shows
the dummy type, restraint system type, and motion condition for all cases in ths group of
simulations.
Table 6-1 The Boundary and Initial Condition for 6 Simulation Cases rCASE No. Dummy Type Restraint Sys tern Motion Type Hvper 111 Dummv Low Mesh Complete Seat htial Vel.= 45 MPH CASE 1 167 1b Male Dummv 1 inch wide 3 Points Belt Vel.=O at 0.15 Sec. 120 Ib Female Du- Airbag Low Mesh Complete Seat Initial EL= 25, 35, CASE 2 Hyper 111 Dummy 1 inch wide Lap Belt 45,55,65 MPH Airbag Same Deceleration Low Mesh Complete Seat Initial El.= 25, 35, CASE 3 Hyper I11 Dummy 1 inch wide Lap Belt 45,55,65 MPH Airbag Low Mesh Complete Seat Initial Vel.= 45 MPH CASE 4 Hyper I11 Dummy 8 Diflkrent fipes ofBelts Vel.=O at 0.15 Sec. Airbag Low Mesh Complete Seat Initial Vel.= 45 MPH CASE 5 Hyper I11 Dummy 4 Types of 1 inch wide Belts Vel.=O at 0.15 Sec. WithAir bag Low Mesh Complete Seat Initial Vel.= 45 MPH CASE 6 Hyper 111 Dummy 1 inch wide Lap Belt Vel.=O at 0.15 Sec. 4 Folding Patterns Airbag 6.2 Case Study
Case I: The Simulation of Hyper III, Male and Female Rigid Dummy
The ATE3 program could create the Hyper I11 dummy, female and male very easily by using GEBOD database. In this case, the simulations are rigid dummies with one inch wide, 3 points seatbelt, airbag and seat. The initial velocity is 45 mph (792 inlsec) and the motion was stopped at 0.15 sec. The rigid dummies were created by ATB program. There are Hyper I11 dummy, 167 LB male dummy, and 120 LB female dummy. The total segment numbers of Hyper I11 dummy are 17, and the segment numbers of the male dummy and female dummy are 15. Table 6-2 shows the model and simulation result of Hyper I11 dummy simulation.
Table 6-2 The model and simulation result of Hyper 111 dummy
LSQYNA LSOYNA TlME=O
Ftlngr tnnls LSDYNA LSDYNA 5 7 Table 6-3 shows the model and simulation result of 167 LB male dummy simulation.
Table 6-3 The Model and Simulation Result ofl67 LB Male Dummy
LS-DYNA LSOYNA TIME = 0 TIME = 0 k:, , L" k
-. LSOYNA 9.908etDO4 _ TIME = 0.16135 8.917c4OB4. 7.526r*OB4 - 6.936rlW4 5.94sc+Oe4 - 4.95421084 -
2.972~+084. 1.98Lr*W4.
0.WacMOB
Table 6-4 shows the model and simulation result of 120 LB female dummy simulation.
Table 6-4 The Model and Simulation Result of 120 LB Female Dummy
LS-DYNA LSOYNA TIME = 0 TIME = 0
'.. '\ . . L i.
LS-DYNA C7ase 2: Dzferent initial velocify with the ,same deceleration.
This case is the simulations of Hyper I11 rigid dummy with 1 inch wide lap belt, airbag, and seat. The simulations were five different initial velocities at 25 mph (440 in/sec), 35 mph (616 idsee), 45 mph (792 idsec), 55 mph (968 idsec) and 65 mph (1144 idsec). All the motion was stopped by the same deceleration (see Figure 6-1).
DECELERATION
Figure 6-1 The deceleration on the different initial velocity simulation.
Figure 6-2 shows the result of X-axis displacement and velocity of rigid dummy lower torso segment (segment 1). VELOCITY (SEGMENT I)
+ 35 MPH -45 MPH ++ 55 MPH
'-0I
I TIME (SEC) I
Figure 6-2 The X velocity of rigid dummy lower torso (segment 1)
Case 3: Drflerent initial velocity with d@erent deceleration. All movements were
stopped as the same time (0.15 sec).
In this case, the Hyper I11 rigid dummy was chosen in the simulations. The restraint system includes 1 inch wide lap belt, airbag and seat. The initial velocities were 25
MPH, 35 MPH, 45 MPH, 55 mph and 65 MPH. Case 2 set the deceleration to be constant and this case (case 3) consider the stopped time of motion to be constant. The value of decelerations were different (see Figure 6-3) in each initial velocity in order to make the velocity to be zero at 0.15 sec. Figure 6-4 shows the result of X-axis velocity and velocity of rigid dummy lower torso segment (segment 1). DECELERATION
1 TIME (SEC) 1 Figure 6-3 The deceleration on the different initial velocity simulation.
I THE VELOCITY OF LOWER TORSO SEGMENT (SEGMENT 1)
-t VELOCITY 25 MPH +VELOCITY 35 MPH --A- VELOCITY 45 MPH *VELOCITY 55 MPH
Figure 6-4 The X velocity of rigid dummy lower torso segment (segment 1) 61
Cuse 4: The Hyper 111 dunzmy with dzflerent types ofseutbelt. The initial velocity was
35 mplz (792 ihec) and stopped as 0.15 sec.
The purpose of this case is focused on the influence of different types of seatbelts.
There are 4 different models of seatbelts (3 points, 5 points, lap belt only and shoulder belt only) and 2 different widths (linch and 2 inch) in the database of intelligent
environment for occupant simulation. The initial velocity was 45 mph and the motion was stopped at 0.15 sec, and the rigid dummy was Hyper I11 dummy. Table 6-5 shows the model of dummy with 1 inch wide seatbelt and Table 6-6 shows the model of dummy with 2 inch wide seatbelt. The simulation results are shown in following Table 6-7 and
Table 6-8. Table 6-7 is the result of 1 inch wide seatbelt model and Table 6-8 is the 2 inch seatbelt model. Table 6-5 The One Inch wide Seatbelts (LSDYNA, Time = 0)
Width = 1 inch; 3 points belt Width = 1 inch; 5 points belt
Width = 1 inch; lap belt Width = 1 inch; shoulder belt - -
Table 6-6 The Two Inch wide Seatbelts (LSDYNA, Time = 0)
L" L
Width = 2 inch; 3 points belt Width = 2 inch; 5 points belt
Width = 2 inch: lau belt Width = 2 inch: shoulder belt Tab'e 6-7 The Simulation Result of One Inch wide Seatbelts
LS-OYNA Mnac WP LS-DYNA Mngc LNcls TIME = 0.102 TIME = 0.160 CMtmmo~ 1.26ZerW7. 2.46SerWs _ Ethsth. Slmsc lrm] 1.136crD67. 1.972e+11(11~2.zf8e*m6 -! lJJ10erO07 - 2zLk 1.725r+C1!~6 - 7.572et096 1.473~+006- 6.310e*106- 1.232ctW6. 5.Ot8et106. 9.85Bc.W5.
7.39tetOOS~ ,&;;;I ,&;;;I 2.524~+WS_ 4.9m+w5. I.262ctW6- t ?.65e+005~ 0.01111rt0110 .I 0.OOOerWo Width = I inch; 3 points belt Width = 1 inch; 5 points belt
Fhge L-1% LS-DYNA Fringe kin ~:z~~~~TIMECommrc . d0.160 4.733et006. *lh*." I"*] 4.747r1005 - 3.786clWs- 4.152..0@5- 4.2-+w6 - 1 3.313ctP16 - 3.56&*085_ Z.%?eraos- 2.840et006_ t367e1006- 2.373trQa5 _ 1.W3H006 l.7aZktm. 1.42Or*006~ l.l@lrW. 9.466c.w5 54*w4. 4.73kt005 _ O.O(lbtOO0 - I -ii 0.000~*000_ I Width = 1 inch; lap belt Width = 1 inch; shoulder belt 64
Case 5: The Hyper III dummy with airbug in the same boundary condition. . The initial
velocity was 15 rnph (792 inhec) and stopped as 0.15 sec
This case tried to study the difference between dummy with airbag during the crashworthiness simulation. The simulation is Hyper I11 rigid dummy with four different 1 inch wide seatbelts, seat, and with airbag in order to compare the previous case (case 4) of the dummy with seatbelt but without airbag. The initial velocity is 45 mph and the motion was stopped at 0.15 sec. Table 6-9 shows the model of dummy with airbag, and Table 6-10 shows the simulation results.
Table 6-9 The Rigid Dummy with 1 Inch wide Seatbelt and Airbag
3 Point Seatbelt with Airbag 5 Point Seatbelt with Airbag *9- c"T-
Lap Seatbelt with Airbag Shoulder Seatbelt with Airbag 1 65 Table 6-10 The Result of Rigid Dummy with Seatbelt and Airbag
- I I LS-DYNA
3 Point Seatbelt with Airbag 5 Point Seatbelt with Airbag
LS-DYNA Ftinge Levels Fringe LMIS TllllE=0.16 9.961er084 C* 01 MoWrrstms~ 8.B74ct181- 8.965ct004. 7.88&+884 - 7.969e+004 1- 1 6.902cMO4 - 6.S73et004 - 1 5.977ctoo4 - i 5.916eWl4 - 4.93iki004 - 4.981ct004 - 3.984~+004 3.944ctOO4 - ' 2.%8c+@04 - 2.988c+O04. 1.972cr004 - 1.992C+OM _ S.850eto03. 9.961c+003 - L" k" 0.000ctM0 Lap Seatbelt with Airbag Shoulder Seatbelt with Airbag
C'hse 6: The Hyper 111 dummy with four dzferent types of airbag foldingpatterns. . The
initial velocity was 45 mph (792 idsec) and stopped as 0.15 sec.
The influence of airbag folding during the crashworthiness simulation will be the focus in this case. The simulation is Hyper 111 rigid dummy with 1 inch wide lap belt only, seat, and four types of folding airbags. The initial velocity was 45 MPH, and the motion was stopped at 0.15 sec. Table 6-1 1 shows the model of the rigid dummy with
four different types of airbag folding patterns.
6.3 Discussion
In first case, was to compare the difference among three different rigid dummies.
Figure 6-5 and Figure 6-6 show the X-axis velocity comparison of rigid dummy upper torso (segment 3) and lower torso (segment 1). According to the Figures 6-5 and 6-6, the X-Velocity of segment 1 and 3 are close among these three models especially the rigid dummy of male and female. The vibration of Hyper I11 dummy is lugher than the other two models because the Hyper 111 dummy had 17 segments and the male and female dummy only had 15 segments. .
RIGID DUMMY UPPER TORSO (SEGMENT 3) X VELOCITY
Figure 6-5 The X velocity of rigid dummy upper torso (segment 3) 68
RIGID DUMMY LOWER TORSO (SEGMENT 1) X VELOCITY
-0 1
Figure 6-6 The X velocity of rigid dummy lower torso (segment 1)
In second case, we study the interaction between rigid dummy and restraint system with different initial velocity and the same deceleration. Figures 6-7 and 6-8 shows the results of X-axis displacement and velocity of rigid dummy upper torso segment
(segment 3). AccorQng to Figure 6-8, the curve of X axis velocity of segment 3 are similar. The slope of all curve is much close because the same deceleration. DISPLACEMENT (SEGMENT 1)
-+ 25 MPH -+35 MPH +45 MPH +55 MPH
I TIME iSEC)
Figure 6-7 The X1)displacement of rigid dummy lower torso (segment
VELOCITY (SEGMENT 3)
TIME (SEC)
Figure 6-8 The X velocity of rigid dummy upper torso (segment 3) 70
Case 3, this simulation is similar to case 2 but the deceleration was different for all models. The initial velocities of all models are hfferent but all motion stopped at 0.15 sec. Therefore, the slope of velocity curve of all models was much different (see
Figures 6-9).
THE VELOCITY OF UPPER TORSO SEGMENT (SEGMENT 3)
-+- 35 MPH -45 MPH +- 55 MPH
Figure 6-9 The X Velocity of Rigid Dummy Upper Torso Segment (Segment 3)
Case 4, there were 2 different widths and 4 different types of belts to be compared.
Table 6-6, it is shown that the 5 points belt design is the best design for a human dummy during the simulation, as it could hold the dummy much steadier than other belt designs.
According to Table 6-7, all designs with 2 inch belt widths could hold the dummy steady, proving that wider belts were better. According to Figure 6-10, the curves of 1 inch 5 7 1 points belt and 2 inch 4 points belt are much similar because the 5 points belt design is the best design to hold the dummy steady. The width of the belt will have greatly effect the re~lt.
The X Axis Velocity of Segment 3
Time I
Figure 6-10 The X-axis Velocity of Segment 3 (W1 1 rnchwide, W2 2 mch wide)
Case 5 studies the influence of the airbag far the human dummy during the simulation. The curves of X-axis velocity of upper torso segment (see Figure 6-1 1) are much smoother than the curves of models without the airbag (see Figure 6-12). The dummies did not have too much vibration when the dummy with the airbag. This means more safety for human dummy when it with airbag during the crashworthiness simulation. THE X-VELOCITY UPPER TORSO SEGMENT (WITH AIRBAG)
TIME
Figure 6-1 1 The X-axis Velocity of Upper Torso Segment (with Airbag)
THE X-VELOCITY OF UPPER TORSO SEGMENT (DUMMY WITHOUT AIRBAG)
TIME (set)
Figure 6-12 The X-axis Velocity of Upper Torso Segment (without Airbag) 73
Case 6, there were four different folding patterns design of airbag. The figure6-12 shows comparison of the X-Axis velocity of upper torso segment on different airbag folding patterns. From Figure 6-13 shows the curves of X-axis velocity were closed and could provide the information which the different folding pattern designs of airbag did not have much influence for human dummy during the simulation.
THE X-AXIS VELOCITY OF SEGMENT 3 ON FOUR DIFFERENT AIRBAG FOLDIh'G PATTERNS
1 TIME
Figure 6-13 The X-axis Velocity of Upper Torso Segment on Different Airbag Folding Patterns CHAPTER7 THE SIMULATION OF DUMMY WITH DEFORMABLE SEGMENTS AND THE DUMMY WITH COMPLETE VEHICLE MODEL
7.1 The Study of Dummy with Deformable Segment in Crashworthiness
Simulation
Although the rigid dummy could provide information of dummy motion to the researcher during the crashworthiness simulation, there were some limitations that the rigd dummy cannot support. The researcher could not read the stress and deformation from the rigid dummy; therefore, the deformable segment was created for solving the problem which the rigid dummy could not do. The users could choose any deformable segment to study, or they could take any combination of deformable segments for their research. They do not need to take a long time to create a whole FEM dummy, or take lot of CPU time to run the simulation. There were two different cases in this group of simulation. The two cases were:
1. The comparison of dummy motion between rigid dummy and dummy with
deformable segment (upper torso segment or head seapent)
2. The simulation results of rigid dummy with different combinations of
deformable segments, lap belt, and airbag. Table 7-1 shows the dummies and restraint system for this simulation group.
Table 7-1 The Initial Condition for the Group of Dummy with Deformable Segment
Restraint System: Low Mesh Complete Seat; I inch wide 3 Points Belt
- -- / CASE No. I Dummy Type / Restraint System 1 Hyper I11 Rigid Dummy Low Mesh Complete Seat;
CASE 1 Dummy with Deformable Upper Torso Segment 1 inch wide 3 Points Belt; I / Dummy with Deformable Head Segment I I Hyper I11 Rigid Dummy Low Mesh Complete Seat;
Dummy with Deformable Upper Torso Segment 1 inch wide 3 Points Belt;
CASE 2 Dummy with Deformable Head Segment Airbag
Dummy with Deformable Upper Legs Segments L Dummy with All Deformable Segments 7.1.1 Case Study
C,'ase I: The colnparison of dummy motion between rigid dummy and dummy with
deformuble segment (upper torso and heaq
The focus of ths case was to study the difference between the whole rigid dummy and rigid dummy with deforrnable segments. The Hyper I11 rigid dummy was considered in this case study. There were three models to make comparison. One was
rigid dummy only, and the second one was a rigid dummy with defonnable upper torso
segment. The thrd was a rigid dummy with a deformable head segment. All the models came with 1 inch wide lap belt only and low mesh complete seat model. The
initial velocity was 45 mph (792 idsec), and the motion stopped at 0.15 sec Table 7-2
shows the models and results in this case study.
Table 7-2 The Model and Simulation Result of Dummy with Deformable Segment - - The Model of Simulation The Result of Simulation
-*"-,,-- ,
- Rigd Dummy Only Rigid Dummy Only I
LSDYNA Fr)qe Lmls ~m~14G16002 -%-MI :::::::I 20Olet(lO4~ 2 01ctow 2 101~4004~ 1 75ht004 1 4OOr4004 1 050ctm4 i 7 802ctM3 _ t. 3dCIle+Ml3 0 BMc+~B-I The Rigid Dummy with Deformable The Rigid Dummy with Deformable - Upper Torso Segment Upper Torso Segment
LS-DYNA Flfwe Levels TlblEP0.16002 4 265etUO4. 3 839eM04.1 3 412ctil04 - 2 S86crOO4 2 65k*004~ 2.113ctOM 1 706~1004 2 I ZaOeteo4 8 531ct003 kx 4 *.s~oo3-1 =-&'"k0.000ctOW The Rigid Dummy with Deformable The Rigid Dummy with Deformable L.- Head Segment Head Segment 77 Cuse 2: The simulation result of rigid dummy with different combinations of deformable segment, lap belt, and airbag.
The focus of ths case was to make a comparison between a rigid dummy and dummy with any combination of deformable segments. The restraint systems of all models were airbag, lap belt only, and seat. The initial velocity was 45 MPH. There were five models to be considered in this case: Hyper I11 rigid dummy only, rigid dummy with deformable upper torso (segment 3), rigid dummy with deformable head segment
(segment 5), rigid dummy with deformable upper legs segment (segment 6 and 9), and rigid dummy with all deformable segments. Table 7-3 shows the model of Hyper I11 rigid dummy only and the dummy with all deformable segments.
Table 7-3 The Models of Rigid dummy only and Dummy with All Deformable Segments.
"--,-", l3--L?mv# 7-. . -. . 1 Table 7-4 shows the model of dummy with deformable segment upper torso, head or upper legs, and Table 7-5 shows the simulation result of all models.
Table 7-4 The Model of Dummy with Deformable Segment
- The Dummy with Deformable Upper Torso Segment LIYIYYIQm s4w"ym w. , 7,-. .
- The Dummy with Deformable Head Segment I%DWYtB).Rn -uwY.uI w. , -. .
-- The Dummy with Deformable Upper Legs Segments Table 7-5 The Simulation Result of All Models r LS-DY NA Fringe Levels LS-DYNA Fringe Lcwls TIME=O.l6 TIME4.16 9.84le+004 - Contours of Cootours of Etlgttue stws Emctive Stms' 8.857et004 - 7.873et004 -1 6.889et004 - 4.605~+004- 5.905e+084 - 4.118etO04 - 4.921erOtI4 - 3.432et004 - 3.937et084 - 2.746et804 - 2.952~+084- 2.059er004 - 1 1.373e4004 - F 6.864et003 - 0.000et000 - Rigid Dummy Only Deformable Upper Torso Segment C I Fringe Levels LSDYNA Fringe Levels LS-DYNA TlME=O.O67 TIME=O.lG 1.519et005 - Contours of 1.501e+005 - Contours of Effective Stm Effective Shaa 1.367et005 - 1.351e+005 - 1.215et005 - 1.201e+UU5 - I 1.063et005 - 1.Q51e+005 - 9.1 14et004 - 9.007~*004- 7.595~2004- 7.506e+004 - 6.076e4004 - 6.005e+004 - 4.557~4004- 4.604et804 - 3.038e4004 - 3.002e+004 .. 1.519e4004 - 1.501e+004 t 0.000et000 -I 0.800e+000 it- 1 Deformable Head Segment Deformable Upper Legs Segments
LS-DYNA Fringe Lcvels LS-DYNA Fringe L~ls 7.858e4004 - TIME=0.073 4.198e+004 - Contwn of 3.778et004 - 7.072et004 _ Effecttve Sbeea [v-m 3.358et004 6.286et004- - 2.938et004 - 5.501ct004 - 2.519et004 4.71 5~4004- - 2.099e4004 - 3.929er004- 1.679et004 3.143~4004- 2.357et004 - 1.259et004- 8 395et003 - 1.572cr004 - 4 198e+003 - 7.858ct003 - 0.000et000 - 0.80Qe4000 - I i.- Dummy with All Deformable Segments 7.1.2 Discussion
Case 1 studied the difference between the simulations of rigid dummy only and dummy with deformable segments. Figure 7-1 shows the X-axis velocity of segment 1, and Figure 7-2 is shown the X-axis velocity of segment 3. From Figure 7-1, all the curves of X-axis velocity are closed because all of the models in this case have the same initial velocity and deceleration. Therefore, the curves of Figure 7-1 are similar.
According to Figure 7-2 there were some differences among these three models, especially the rigid dummy. The results of the models of dummy with deformable upper torso segment and dummy with deformable head segment were closed because these models came with different element properties. The dummy model, rigid dummy only, was shell element only. The element properties of dummy with defonnable segments were the combination of shell ele~nentand solid element (deformable segments). THE X VELOCITY OF SEGMENT 1 +RIGID DUMMY ONLY tDUMMY WITH DEFORMABLE UPPER TORSO SEGMEM x DUMMY WITH DEFORMABLE HEAD SEGMENT
TIME
Figure 7- 1 The X-axis velocity of lower torso segment
THE X-VELOCITY OF UPPER TORSO SEGMENT +RIGID DLTMMY ONLY -+DUMMY WITH DEFORMABLE UPPER TORSO SEGMEm +DUMMY WlTH DEFORMABLE HEAD SEGMEM
Figure 7-2 The X-axis velocity of lower torso segment
The Figure 7-3 shows the maximum principal stress on the deformable segment (upper 82 torso and head segment) during the simulation. (RDF The rigid dummy only; DF-3:
The dummy with deformable upper torso segment; DF-5: The dummy with deformable head segment)
I THE MAX PRWS. STRESS ON DEFORMABLE SEGMENT I
0.000EtOO 2.OM)E-02 4.000E-02 6.OKIE-02 8.OCOE-02 1.000E-01 1.200E-01 1.4WE01 1.600E-01 TIME (set)
Figure 7-3 The maximum principal stress on deformable segment
The Figure7-4 shows the maximum principal stress on the seat (bottom part) during the simulation. (RDF The rigid dummy only; DF-3: The dummy with deformable upper torso segment; DF-5: The dummy with deformable head segment) 83
THE MAX. PRINS. STRESS ON SEAT (BOTTOM)
Figure 7-4 The maximum principal stress on the bottom of seat
From Figure 7-4 shows the rigid dummy caught the maximum stress on the bottom part of the seat. The initial motion of rigid dummy only is from ATB program only. The dummy with deformable segments combines the motion with ATB and LS-DYNA program, especially on the gravity influence.
In case 2 shows us the results for the dummy with different deformable segment combination. Figure 7-5 shows the X-velocity of segment 3. (Rigid: rigid dummy only;
DF3: dummy with deformable segment 3; DF5: dummy with deformable segment 5;
DF69: dummy with deformable segment 6 and 9; DF-ALL: dummy with all deformable segments) X-AXIS VELOCITY OF SEGMENT 5
I TIME
Figure 7-5 The X-velocity of upper torso segment.
The models of the dummy with deformable head segment and dummy with all deformable segments (see Figure 7-6 and 7-7) could not complete the whole simulation, and it stopped at 0.068 sec. The problem is the solid element of deformable head segment caught the negative volume when the head segment touches the airbag, because the skin material of the deformable head segment was soft. LS-DYNA Frlnae Lwels TIME=O.OB Contours d Effectfve Stress [vml
3.875et004 - 3.321e+004 - 2.768tt004 - 2.21 4e+004 - 1.661ttB04 -
Figure 7-6 The deformation-of head segment Figure 7-7 The stress of head segment
The curves of X-axis velocity of the other models looks much closed. Figure 7-8 shows the maximum principal stress of seat bottom part during the simulation.
THE MA,Y. PRINS STRESS ON SEAT
Figure 7-8. The maximum principal Stress on the Bottom of Seat
From Figure 7-8, shows the stress on the seat for all models. The result did not change too much even for the rigid dummy only because all the models had airbag. 86
7.2 The Study of Dummy with Complete Vehicle Model and Restraint System
Simulation
The above chapter, chapter 6, provides the information about the simulation of a rigid dummy, and this chapter is going to study the simulation of a dummy with deformable segments. All of the above simulation models just simulated the dummy in the vehicle which had initial velocity and deceleration but could not provide detailed information about the dummy and vehcle. Another consideration is how to apply the database which was created for an intelligent environment for occupant simulation in this research into the real vehcle model. The two cases were:
1. The rigid dummy with complete car model
2. The dummy with deformable segments with a complete car model.
The FEM car model was downloaded from national crash analysis center (NCAC)
(see Table7-6) [38]. The model is a Chevrolet C2500 Pickup, and the total element number is 10500. The initial velocity was 62.6 mph, and it hit the rigid wall at 0.004 sec (see the results in Table 7-7). The consideration of the dummy with a complete car model is the restraint system with rigid dummy only or rigid dummy with deformable segments. Table 7-6 The FEM CAR Model of Chevrolet C2500 Pickup
LII-Ymm LIQIUrnIM . D vm.. I
Table 7-7 The Simulation Result of Chevrolet C2500 Pickup FEM CAR Model Only
7.2.1 Case Study
C'ase I: The rigid dummy with complete car model
The Hyper 111 rigid dummy with seat, seatbelt and airbag was applied to work with the whole FEM Chevrolet C2500 Pickup model for ths case study. The initial velocity of this sinlulation was 62.6 mph and hit the rigid wall after 0.004 sec. The total simulation time was 0.04 see, and it took 154 minutes CPU running time in the Compaq
SP 700 PC with two PI1 500 MHz CPUS. The following tables shows the model (Table 7-8) and simulation result (Table 7-9) for this case study.
Table 7-8 The Model of Whole FEM Vehicle Model with Rigid Dummy
Table 7-9 The Result of Whole FEM Vehicle Model with Rigid Dummy
Fringe Levels
3.249et007
Case 2: The dummy with deformable segment with complete car model.
This case studies the simulation results of dummy with deformable segments, restraint system, and whole FEM car model. The FEM car model was Chevrolet C2500
Pickup, and its initial velocity is 65.6 MPH. The boundary condition was the same as the above case, but the dummy is not rigid dummy only. It is the dummy with defonnable segments. The deformable segments are upper torso, head and upper legs.
The restraint system is a low mesh complete seat model, 1 inch wide lap belt and airbag 8 9 model. The total simulation time was 0.04 sec, and it took 447 minutes CPU running time in the Compaq SP 700 PC with two PI1 500 MHZ CPUS. The model (Table 7-10) and result (Table 7-1 1) of this simulation are shown below.
Table 7-10 The Model of Whole FEM Car and Dummy with Deformable Segments
Table 7-1 1 The Result of Complete FEM Car and Dummy with Deformable Segments
LSOYNA LEDYNA Fringe Levels Fringe Levels TIME=0.033 TIYE10.033 c~nlwmof 4.808etO07 - contwm of 4.808et007 Efiectlve Stms [vm] Ethctivs Stms [vml 4.327ct007 - 4.327et007] 3.847ct007 _ 3.847~+007- 3.366cr007 - 3.366et007 - 2.885erO07 - 2.885et007 - 2.404er007 - 2.404et007 - 1.923etU87 - 1.923erOO7 - 1.442erM17 - 1.442er007 - 9.617~+006- 4.808e+006 - 4.808et006 L O.OOOetOO0 - 0 000etOOO -
7.2.2 Discussion
There were two different cases in this group of simulation. The first case is a complete car model with Hyper I11 rigid dummy, and the second case is the complete car model with the dummy with all deformable segments. All models with the same car 90 model and restraint system have the same initial velocity and deceleration. The general purpose is to compare the results between these Qfferent models. The model of the dummy with all deformable segments stopped the simulation at 0.0033, because the head segment touched the airbag and the deformable head segment got the negative volume. Figure 7-9 shows the X-velocity of seat, upper torso, and head segments.
(ST-RG: The Seat Part of Rigid Dummy Model; ST-DF: The Seat Part of Dummy with
Deformable Segment Model; S3-RG: The Upper Torso Segment of Rrgid Dummy Model; ;
S3-DF: The Upper Torso Segment of Dummy wrth Deformable Segment Model; S5-RG:
The Head Segment of Rigid Dummy Model; S5-DF: The Head Segment of Dummy wrth
Deformable Segment Model) I THE X-VELOCITY OF SEAT, UPPER TORSO AND HEAD SEGMENTS I
--t ST-DF
Figure 7-9 The X-velocity of seat, upper torso and head Segments.
Figwe 7-10 shows the Z-velocity of seat, upper torso, and head segments.
THE &VELOCITY OF SEAT, UPPER TORSO AND HEAD SEGMENT
TIME
Figure 7-1 0 The Z-velocity of upper torso and head Segments. Figure 7-11 and 7-12 shows the stress on the seatbelt and bottom parts of the seat.
(Rigid: Rigid Dummy Car Model; DEF: Dummy with Deformable Segment Car Model)
THE STRESS ON THE SEATBLET
Figure 7-1 1 The Stress on The Seatbelt
THE STRESS ON BOTTOM PART OF SEAT
TIME
Figure 7-12 The Stress on The Bottom Part of Seat 93 Figure 7-13 shows the stress on the deformable segment of the defonnable dummy
with complete car model.
THE STRESS ON THE DEFORMABLE SEGMENTS
I TIME I
Figure 7-13 The stress on the deformable segment of the deformable dummy with complete car model
According to Figure 7-10, 7-11, 7-12 and 7-13, the results did not change too much between these two models, and the researcher could read the stress and deformation output from the simulation case of deformable dummy with complete car model. CHAPTER 8 SUMMARY AND CONCLUSIONS
8.1 Summary
The intelligent environment for occupant simulation and deformable dummy segments has been created in this research. The software packages ATB (Articulated
Total Body) and LS-DYNA were coupled and integrated to provide researchers the capabilities of performing advanced crash simulations in which one can include the dummy model from ATB and the seatbelt, airbag, seat, and other restraint system models from LS-DYNA. The user interface could help researchers by providing an intelligent environment for occupant simulation, select combination of models from the database, and create new models to add them into this database. The deformable dummy segment could enable the researcher to study the stress and deformation of some important dummy segments during the simulation, and do not need to create an entire FEM dummy, thus saving CPU running time, disk space, and improving accuracy.
In Chapter 1, motivation and the objective of the present study were described. It also described the idea of ATB program and LS-DYNA program coupled code and the advantages for this coupled code. The research for the creation of the restrained system database was also presented in this chapter. Chapter 2 presented the detailed literature 95
review. The needs for created the intelligent environment for occupant simulation and
the research for the whole FEM deformable dummy or FEM deforrnable segments were
described.
In Chapter 3, the five test cases were developed during the research to validate the
coupled code, and the test cases consisted of various combinations of dummy and
restraint systems. The output in term of acceleration of the dummy segment 3 (upper
torso segment) was compared with the already validated ATE3 program results, and the
results compared withn acceptable limits.
Chapter 4 showed how to create the model and material data of restraint system database, such as airbag, seatbelt, and seat. And Chapter 5 described the modeling and material property of deformable dummy segments such as head, upper torso, and upper legs.
Chapter 6 presented the results and discussion of rigid dummy with restraint system simulation. The objective was to study the interaction between the rigid dummy and restraint system during the motion. The first case is comparison of the differences among different types of dummies like Hyper 111, male, and female dummy. The second
and third case studied the motion of rigid dummy in the changeable velocity or 96 deceleration. The fourth case is to study the differences of the rigid dummy with different types of seatbelts. The fifth case presented the functions of airbag during the motion, and the sixth case studied an influence for the different folding patterns of the airbag. All the dummies in these six simulations were rigid dummies.
Chapter 7 described the simulation results and discussion for the dummy with deformable segments in the crashworthiness simulation. Another focus in the chapter was the simulation of dummy and restraint systems, which was provided in this database, with complete vehicle model, and made a comparison between rigid dummy and dummy with all deformable segments.
The general purpose for this simulation group of dummies with deformable segments was to compare the difference between rigid dummies and dummies with deformable segments during the occupant simulation. The first case compared the differences between a rigid dummy only and a dummy with deformable segments. The second case studied the situation of dummies with different combinations of deformable segments.
The focus of the dummy with the whole FEM vehicle model simulation was to study the situation of a database of an intelligent environment how to work with the whole 97
FEM car model. It also studied the difference of simulation results between the rigid
dummy and dummy with deformable segments in the same car model.
8.2 Conclusion
The work of ATB and LS-DYNA coupled code validation was done in Chapter 3,
and it was a group effort. Details can also be found in Patlu7s [29] and Petkar's, [30]
thesis.
1. The database with a user interface for occupant simulation was created by the author.
All of the restraint system models (airbag, seatbelt, and seat) were created using the
LS-DYNA program. The rigid dummy information was provided by ATB's
GEBOD program. The database provides 8 types of seatbelt models, 4 types of
seat models, 4 folding patterns of airbag models, and the 3 different rigid dummy
models (Hyper 111, Male, and Fernale). The user interface could help the user to
use the database and add new models into this database.
2. The general idea of a dummy with deformable segments was to design the
deformable segment which could move together with smaller ATB rigid dummy
segment. The deformable segment could use the joint data provided by ATB
program. This idea provided a new and faster way to create deformable segments. 98 In this research, the segment model of upper torso, head and upper legs was
considered. Each deformable dummy segment included three parts. The one
rigid shell element part moves with ATB rigid segments. The two solid element
parts were constrained with the rigid shell element part.
3. The rigid dummy simulation provided the information about the interaction of the
rigid dummy and restraint system. The first two cases focused on the motion
influence and the other cases considered the differences between the dummies with
different restraint system combinations. From the study of rigid dummy simulation
results, it is shown that the 2 inch wide belt is better than 1 inch wide belt for
holding a human dummy. If the seatbelt is used with an airbag, it makes the human
dummy steadier.
4. The first case of the simulation of dummy with deformable segment using a rigid
dummy is to validate the model of the dummy with deformable segments. The
rigid dummy is widely used in the industrial and research areas. It is easy to
control the boundary and initial condition for the occupant simulation. Case 2
could show the stress and deformation output of the deformable segment. From the
deformable skull analysis one can see the injury to the human face where the airbag is inflated.
5 The rigid dummy only and dummy with deformable segments could provide the
similar motion information in the dummy with complete vehicle simulation. The
rigid dummy could save CPU time for running the simulation. The deformable
dummy provides stress and deformation of deformable segment to the researcher,
which the rigid dummy could not support.
8.3 Future Work
1. To expand the data base by collecting more data and model information about the
seat, seatbelt, and airbag models which are used in the industry.
2. To modify the code of user interface to JAVA language, and the user could use the
intelligent environment for occupant simulation on the Internet. This would help
the researcher use this function without a high performance computer.
3. It could create more detailed models of deformable head, upper torso, upper legs
segments or other dummy segments. Although the more detailed model will cost
high density element mesh, it could provide mode detail information about the stress
and deformation. The new model could be an option to choose by the user.
4. The problem of ATB and LS-DYAN coupled code still has some minor problems. The function of "DEFORMABLE- TO-RIGIDAUTOMATIC" provided by
LS-DYNA program, it work in the general LS-DYNA code, would not work in the coupled code. If the problem could be fixed, the design of the defonnable dummy will be even easier in the future. CHAPTER 9 REFERENCES
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Mechanical Engineering
An Intelligent Environment for the Occupant Simulation and Deformable Dummy Design
( 106 PP)
Director of Dissertation: Dr. Bhavin V. Mehta
Occupant simulation is engineering analysis methods that use rigid body dynamics and finite element methods to create mathematical models that describe the interaction of an occupant with the vehicle or aircraft interior during a crash simulation.
The main goal for the research work is to create an intelligent environment for occupant simulation, and develop a new methodology to accommodate defomable segments of dummies more easily in crash simulation studies.
The intelligent environment will include a database and a user interface. The database consists of several newly created restraint system models with several rigid dummies, and deformable dummy segments. The user interface could help researchers by providing an inteIligent environment for occupant simulation, select combination of models from the database, and create new models to add them into this database. The tieformable dummy segment could enable the researcher to study the stress and