Design Report
Client:
Prepared by: Society of Automotive Engineers (SAE) Saluki Baja Team 39
F13-60-Baja
Submitted: 4/17/14
Team Members:
Austin Lewandowski
Keegan Lohman
Steven Baldwin
Preston Mathis
Thang Tran
Kyle Koester
[AL] (PM)
[KL]
[SB]
[PM]
[TT]
[KK]
Technical Advisor:
James C. Mabry ME Department
F13-60-Baja
SOUTHERN ILLINOIS UNIVERSITY CARBONDALE
COLLEGE OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
ME 495A – SENIOR ENGINEERING DESIGN
SAE SALUKI BAJA FRAME DESIGN
F13-BAJA-60
DATE SUBMITTED: April 18, 2014
SUBMITTED TO: SALUKI ENGINEERING COMPANY
TEAM MEMBERS:
Austin Lewandowski ME
Preston Mathis ME
Keegan Lohman ME
Kyle Koester ME
Steven Baldwin ME
Thang Quang Tran ME
2
F13-60-Baja
Transmittal Letter
April 18, 2014
SAE Saluki Baja
Southern Illinois University
Mail Code 6603
Carbondale, IL 62901
Phone (309) 370-9774
Saluki.Baja@gmail.com
Society of Automotive Engineers
SAE International
400 Commonwealth Drive
Warrendale, PA 15096-0001 USA
SAE International,
The subsequent design report, along with necessary user instructions and a completed chassis are
being presented in response to the proposal to design and manufacture a chassis for the 2014
SAE Baja vehicle.
This newly designed frame incorporates extensive use of 3D modeling programs particular to
finite element analysis to ensure a structurally sound frame in the worst impact and rollover
cases. Much of the frame was designed with the intent of mass production in mind. Safety of the
driver was held as the paramount design criteria, with weight reduction being a close second.
This frame is ready to be mounted with all bracketing, paneling, and subsystem components. The
frame is capable of housing a 10 horsepower OHV Intek Briggs and Stratton engine, and Dana
Spicer H12 gearbox in addition to an independent suspension. If you have any questions
concerning this design review, please contact me by e-mail at austin27ski@gmail.com or by
phone at (309)370-9774 at a time that is convenient to you.
SAE Saluki Baja is proud to have designed, produced, and documented this assignment for you,
and appreciates looks forward to conducting more business with you in the future.
3
F13-60-Baja
Acknowledgements
We would like to show particular appreciation to these individuals and companies who have
contributed sponsorships, time, or help to our project:
Advanced Technology Services (ATS)
Dassault Systemes SolidWorks
Wick’s Aircraft Supply
Sandvik Coromant
Carbondale Rural King
Carbondale Lowes
SIU Department of Technology
SIUC Engineering Student Council
Dr. Tsuchin Chu
Caleb McGee
We would like to specially thank both Dr. Tsuchin Chu and Caleb McGee who offered a
significant amount of time in helping our team with the application of FEA to the frame.
4
F13-60-Baja
Table of Contents
Page
Table of Figures
7
Table of Tables
8
Executive Summary
9
I.
Introduction
10
Project Description
10
Definition and Differentiation
10
Functional Description
10
III.
Cost
14
IV.
Implementation Schedule
15
Conclusions and Recommendations
16
Subsystem Descriptions
17
Material Selection
17
II.
V.
VI.
Functional Description
17
Option Comparison
18
Conclusion/Remarks/Fault Analysis
19
Frame Design
VII.
19
Functional Description
19
Cockpit
20
Front End
21
Rear End
22
Fabrication
24
5
F13-60-Baja
VIII.
IX.
X.
XI.
XII.
Cutting and Coping
27
Bending
28
Welding
29
Finite Element Analysis
30
Functional Description
30
Loads
30
Meshing
31
Boundary Conditions
31
Conclusions/Remarks
32
Cost and Schedule
33
Fault Analysis
33
Global Considerations
33
Appendices
34
Vendor List
34
Derivations
34
Spreadsheet Calculations
43
Completed Product
45
References
46
6
F13-60-Baja
Table of Figures
Page
Page
F.1
Block Diagram
12
F.20
Image a and b show finished
welds for the frame
29
F.2
Strength vs. Density Plot
17
F.21
Display of meshing convergence
for SolidWorks
31
F.3
Basic 3-D model of frame
20
F.22
Front of Frame with FEA boundary
conditions
32
F.4
Side-view of wireframe
21
F.23
Right side of Frame with FEA
boundary conditions
32
F.5
Drawing of front-end with dimensions
21
F.24
Rollover with FEA boundary
conditions
32
F.6
Rear view drawing of wireframe
22
F.25
FEA deflection of right-side trailing
arm pivot point
34
F.7
Upper right-side view of 3-D finished
frame
23
F.26
FEA stresses of right-side trailing
arm pivot point
35
F.8
Right-side view of finished frame
23
F.27
Rear-end stresses in FEA
35
F.9
Angled left-side view of 3-D frame
23
F.28
Rear-end deformation in FEA
36
F.10 Engineering drawing of angled cope
24
F.29
Rollover FEA simulation with stress
with 22 mph impact
36
F.11
Engineering drawing of right angle cope
25
F.30
Rollover FEA simulation with
displacement
37
F.12
Engineering drawing of bent member with
dimensions
25
F.31
Rollover FEA simulation with stress
38
F.13 Sample 1 to 1 drawing
26
F.32
Frontal Impact displacement FEA
data
39
F.14
Sample 1 to 1 drawing with tubing on top
26
F.33
Frontal Impact FEA data fixed frame
39
F.15
Sample 1 to 1 drawing of roll-hoop
26
F.34
Trailing arm pivot point stresses in
FEA
40
F.16
Image of coping frame
27
F.35
Frontal impact extreme case in FEA
41
F.17
Image of rear-end setup
28
F.36
Displacement of frontal impact
showing safety
42
F.18 Image showing side of cockpit
28
F.37
Displacement of frontal impact in
direction of force
42
F.19 Image of tig welding in progress
29
7
F13-60-Baja
Table of Tables
Page
Page
T.1
Major design criteria for frame
13
T.6
Design criteria pertaining
to FEA
33
T.2
Costs of needed materials
14
T.7
Used material properties
with considered materials
43
15
T.8
Calculations based on
Newton's 2nd Law
43
T.3 Time schedule of process
T.4
Properties of considered steel alloys
18
T.9
Researched typical
impact forces
44
T.5
Mesh convergence chart for SolidWorks
31
T.10
FEA impact parameters
and calculations
44
8
F13-60-Baja
Executive Summary
This report reflects the results of F13-60-Baja’s design efforts imposed on the 2014 SAE Saluki
Baja Frame. The frame design focused on weight reduction, durability, cost, and
manufacturability with the constraint of accommodating a geometry of a previous suspension
design. The SAE Saluki Baja vehicle met all regulations and specifications set in the SAE Series
Rules. [1]. An SAE Baja frame includes the following subsections: roll cage, front end, and rear
end. All structural elements were fabricated using AISI 4130 Chromoly steel tubing. The team
created a 3-D assembly of the frame by using Autodesk Inventor Professional software. In
addition, SolidWorks Finite Element Analysis (FEA) was applied to ensure the safety and
strength of the design while minimizing weight. The frame is a mere 29.25 inches wide, 73
inches long, and weighs in at 80 pounds. This frame is structurally sound and can withstand very
harsh impact loading up to eight times the force of gravity (8G’s) in a collision. This project was
a breakthrough for the team in terms of creating a frame that was lighter, stronger, and smaller
than previous chassis. Overall the project cost $647.05. The project began January 6, 2014, and
was completed by March 1, 2014.
9
F13-60-Baja
I. Introduction
The Society of Automotive Engineers (SAE) hosts an annual international collegiate design
competition in which engineering students design, and build off-road vehicles in competition
against universities from all over the world. These off-road vehicle must be developed within
strict guidelines set forth by the Society of Automotive Engineers. Furthermore, Baja vehicles
are built for the purpose of mass production as a recreational vehicle for sale to the general
public in the amount of 4000 units per year [1]. Therefore, teams must produce a vehicle that
satisfies the manufacturability purposes while still maintaining a high level of safety. The
ultimate goal of this project is to build a frame that holds safety, durability, and
manufacturability paramount while remaining as lightweight as possible.
II.
Project Description
Definition and Differentiation
The definition of the SAE Saluki Baja chassis can be described as the body of the car. The frame
is what all control, drive, suspension, safety, and accessory parts are affixed allowing the vehicle
to become functional. The cockpit support (CS) structure has overhead roll bars and side impact
members that form a shell around the driver, and since rollovers are relatively common at
competitions, these structural members become extremely important for the safety of the driver.
The rear end frame (REF) supports the cockpit, and provides a mounting location for the rear
suspension, engine, and transmission. The front end frame (FEF) holds brackets for the front
suspension, steering, and vehicle controls. Using principles of Finite Element Analysis, a more
efficient design could be conducted by allowing thinner walled tubing in low stress areas,
allowing the frame to be lighter. Having a lighter frame increases vehicle acceleration, and
additionally allows for more responsive handling. The overall increase in performance by
reducing weight makes this particular frame design desirable to any potential competitor, or
recreational user.
Functional Description
The frame was designed using Autodesk Inventor Professional modeling software along with
guidelines from the SAE Series Rules. In addition, FEA was applied using 4130 Chromoly to
ensure the safety and strength of the design. The weight of the frame after construction is 80
pounds. FEA test scenarios showed that the frame can survive and protect a driver during an 8G
front impact, 3G side impact and 5G roll over situation. The cost for the fabrication is 855
dollars, so the frame is relatively cost efficient for manufacturing.
The project was divided into two main portions. The first portion was the design process and the
last half of the project was the fabrication process. In the design process, there are three
subsystems including material selection, frame design, and FEA.
10
F13-60-Baja
The material selection is the first step of the design process. The purpose of material selection is
to evaluate candidate materials in order to achieve the best combination of price, safety, and
meeting performance requirements. Based on material selection requirements of SAE, AISI 4130
Chromoly steel tubing of various circular cross sections was chosen out of all steel and
aluminum alloys to be the most suitable material for the frame.
The frame design process focused on safety, durability, manufacturability, and weight. It
consisted of designs for the primary sections including the cockpit, front end, and rear end. A
three dimensional (3-D) model of the frame with exact dimensions for frame members was
created using Autodesk Inventor Professional software.
Finite Element Analysis is a numerical analysis technique for finding approximate solutions to a
physical problem defined in a finite region or domain by using computer software. In this
project, Dassault Systemes SolidWorks was used to analyze critical failure points, increase
quality of design, ensure the safety and achieve weight reduction goals.
The interaction between design subsystems is shown in Figure 1. First the frame was modeled as
a wireframe sketch (shown in Figure 4, 5, and 6). From here the material selection process took
over to define the material. With the geometry and materials specified, FEA could now begin.
With loads and supports defined; the software shows stresses and strains in the frame. If a
member’s strength is greater than the Von Mises stress by a desired factor or safety, its size
could be reduced. However, if the results are not desirable, the engineer cycles back to correct
the flaws of the original design whether in the original sketching phase or by changing the
material cross section. This cycle may be repeated until a satisfactory frame, that exceeds design
specifications, is developed.
11
F13-60-Baja
Figure 1: The above figure shows the approach of team F-13-60-Baja in the design of the 2014
Baja frame.
The design process of the frame was broken down into specific components, and each task was
delegated to a team. Dependencies assured that each team had to work together throughout the
entire process to meet all design goals.
12
F13-60-Baja
Table 1: The above table shows the major criteria that was considered for the frame.
F13-60-Baja Frame Design Criteria
Displacement (in)
Expected Achieved Allowable/Achieved
Overall Weight
(lbs)
Maximum
Width (in.)
Maximum
Length (in.)
Maximum
Height (in.)
Side impact (G
force)
Rear impact (G
Force
Front impact (G
force)
Top impact (G
force)
Axial Stress (psi)
Allowed/Achieved
100
80
-
-
32
29.25
-
-
80
73
-
-
48
46.25
-
-
3
11
6/0.1
106,022/61,701
4
11
12/0.88
106,022/46,995
8
46
12/0.6
106,022/99,421
5
32
6/7.88
106,022/300,000
13
F13-60-Baja
III. Cost
Table 2: The table below shows a breakdown of the costs associated with
the materials used in constructing the frame.
Item
Line
1
2
3
4
5
6
1
Description: Completed Roll Cage Tubes Only
Material:
Part Name
Material
1.25"x.065"
4130 Chrome Moly
1"x.065
4130 Chrome Moly
1"x.035
4130 Chrome Moly
Argon
Welder gas
ER70S-2 Tig Rod
1/16"
ER70S-2 Tig Rod
3/32"
on Frame Subsystem Form A
Density
14
Unit
Amount
Feet
28.9
Feet
36.9
Feet
36.7
tanks
3
packages
3
packages
4
Weight
0.00
0.00
0.00
0.00
1.00
1.00
$/Unit
$3.52
$3.45
$3.52
$70.00
$11.17
$11.33
Subtotal:
Cost
$101.73
$127.31
$129.18
$210.00
$33.51
$45.32
$647.05
F13-60-Baja
IV.
Implementation Schedule
Table 3: This table shows the amount of time required to complete
each task with fabricating and finishing the frame.
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
F13-60-Baja Frame Design Time Schedule
Activity
Time Required (hours)
Process Total
213.5
Material Selection Process Total
18.0
Research
14.0
Selection matricies
4.0
Finite Element Analysis Total
130.0
Design/Model Frame
96.0
Perform Analysis
24.0
Adjust Design from Analysis
10.0
Fabrication Total
65.5
Print 1:1 drawings for all subsystems
6.0
Cut RRH tubes
0.5
Bend RRH tubes
2.0
Cope RRH tubes
2.0
Construct Base Frame (BF) Jig
0.5
Cut BF tubes
0.5
Bend BF tubes
2.0
Cope BF tubes
2.0
Weld BF tubes
3.0
Construct Front End (FE) Jigs
1.0
Cut FE tubes
0.5
Cope FE tubes
3.0
Construct Rear End (RE) Jigs
0.5
Cut RE tubes
0.5
Bend RE tubes
2.0
Cope RE tubes
3.0
Weld RRH
3.0
Weld FE tubes
3.0
Weld RE tubes
4.0
Construct Cockpit Support (CS) Jigs
2.0
Cut CS tubes
0.5
Cope CS tubes
5.0
Weld CS and Overhead Members
8.0
Wire Brush and Prep Final Members for Welding
4.0
Remove metal jigs from CS
3.0
Finish Weld All Members
4.0
15
F13-60-Baja
V. Conclusions and Recommendations
The design allowed for all excess space to be eliminated. This frame offers optimal driver
comfort, safety and will accommodate all required equipment in the smallest possible package.
The design allowed for simplification of several other subsystem mounts, which in turn saved
valuable curb weight. It is also important to note that the chassis will handle normal operation
conditions with ease, but the Finite Element Analysis is only a theoretical calculator and does not
ensure that the frame will handle extreme impact load cases. As with any motor vehicle use,
there is an inherent danger/risk to the driver.
As mentioned previously, the frame design did save much space and weight, but proved to be
difficult for several FEA software packages to model. The complexity of the design only allowed
for a very low level analysis to take place. This frame is overbuilt in many places because of this
fact. If the frame were simplified, a more in depth analysis could be done to further reduce
excess member size while improving the structural integrity of the frame. Also, geometry of the
frame to meet the rear end suspension requirements made some difficult parts to fabricate.
Perhaps designing a new rear end geometry instead of building the chassis to fit the suspension
would be a better approach.
Before this design can be implemented, it is also important to remember the hazards associated
with the fabrication processes. With the cutting, coping, bending, and grinding there are always
the risk of flying material. Safety glasses, long pants, and close toed shoes should be worn at all
times. When using the vertical mill, it is essential to know how to operate the machine safely,
and look out for those around you. Tungsten inert gas (TIG) welding was a critical process used
throughout the construction, and steps to minimize ultra violet (UV) light exposure such as long
pants, long sleeve welding jacket, welding mask, and gloves are strongly encouraged.
16
F13-60-Baja
VI. Subsystem Descriptions
Material Selection
Functional Description
Material selection is the first step of the design process. The purpose of material selection is to
evaluate all candidate materials in order to achieve the best option considering price, and
meeting specific performance requirements. Based on material selection requirements of SAE,
AISI 4130 Chromoly steel tubing of various circular cross sections and wall thickness was
chosen out of all steel and aluminum alloys to be the most suitable material for the frame
because of its high yield strength, and strength/weight ratio.
The material selection includes translation, which expresses design requirements as constraints
and objectives. The concept of screening, which eliminates materials that do not meet
requirements by using constraints. Ranking is the process of choosing the best materials using
objectives. And finally the documentation, which collects information about the best materials is
possibly the most important part of the process. The step by step process is shown below.





Translation: Express design requirements as constraints and objectives.
Function: The frame is an interior skeleton of the off-road racing Baja vehicle.
Constraints: Must be strong so that the frame can survive a
Objective:
Minimize mass
 Minimize the cost
Free Variables: Choice of material
o Screening: Eliminate materials that cannot do the job by using constraints
o Ranking: Choose the best materials using objectives
o Minimize mass and cost:
Figure 2: The above figure shows a strength vs. density plot used in material selection. [2]
17
F13-60-Baja
Option Comparison
Materials may be selected by using material selection charts like that of Figure 2. Aluminum and
steel have been found to be two popular materials used in Baja frame designs. Aluminum alloys
are less stiff than steel, but they are lighter. However, by SAE rules for the 2014 season, only
steel tubing of at least 0.18% carbon content can be used for the primary roll cage. The material
chosen to construct the frame must meet certain safety specifications according to the 2014 SAE
Rulebook. These rules state that the primary roll cage “must be steel tubing with an outside
diameter of 1 inch and a wall thickness of 0.120 inch and a carbon content of at least 0.18%,” or
a greater bending stiffness and bending strength of circular steel tubing [3].
Yield Strength
AISI
MPA
1018
310
1030
345
1040
374
1050
427
1060
421
1095
500
4130
436
4140
655
4340
855
Tensile Strength, Density
Hardness
Ultimate (Mpa) Kg/m3
g/cc
USD/Ton
450
7.87
73
700
525
7.8
80
1500
595
7.845
86
1200
752
7.87
95
900
772
7.852
96
2000
1015
7.85
99
4500
670
7.85
92
1500
1020
7.85
99
1600
1282
7.85
100
1800
Table 4: The above table shows different properties of some considered steel alloys. [4, 5]
Based on the table of steel alloys, AISI 1095, 4130, 4140, 4340 are critical candidate materials
for the production of an off-road vehicle. All of them have high strength to weight ratios. The
4130 is used because it is the most cost efficient of these alloys. AISI 4130 is a low alloy steel
which contains molybdenum and chromium as strengthening agents. With low carbon content of
0.3%, 4130 alloy is an excellent option, and it can be easily welded which is also crucial [6].
This welding property and other properties of 4130 make this alloy one of the most attractive
options to use for the frame. However, the chosen material will still have certain limitations that
the design team will have to consider.
Relationship to other subsystems
The dependency of this stage is critical for the finite element analysis. Once the computer model
is finalized, material properties must be applied so the program knows how to accurately account
for the physical reactions of the material.
18
F13-60-Baja
Conclusion/Remarks/Fault Analysis
The steel alloy material chosen is a very tough material. It offers un-paralleled ductility, yield
strength, and hardness. 4130 Chromoly beats out all but one of the 1000 series AISI steel
candidates listed. This material is used heavily throughout the off road community and is held as
the standard frame material for serious off road enthusiasts. From experience, in a low speed
application such as SAE Baja vehicles that are essentially large go carts, and with the use of
computer verification, this frame material should be structurally sound enough for any loads or
impacts seen. If the material were to fail, the consequences could be very serious to users,
implying serious injury or death. And if one member of the frame were to crack, it would
severely compromise the structural integrity of the entire frame.
Frame Design
Functional Description
The frame design process focused on safety, durability, manufacturability, and weight. It
consisted of designs for the primary sections including: the cockpit, front end, and rear end. A
3-D model of the frame with exact dimensions for frame members was created using Autodesk
Inventor Professional software.
Option Comparison
With the use of SolidWorks FEA package, and Inventor 3D modeling, a frame was modeled that
included all support bracing needed, met all geometric requirements of SAE, accommodated a
functional suspension design, and ended up being structurally sound to heavy loading scenarios
with little modification needed. The design eliminates wasted space everywhere, and promotes a
comfortable and safe cockpit for the recreational user.
Relationship to other subsystems
Designing a structural frame is a very iterative process and using Finite Element Analysis helps
the designer speed up these iterations. The program assures the strongest structure by numerical
analysis.
Design Process
The design of the three frame sections begins with the SAE Rulebook. It notes all important
needed dimensions, and provides a structurally sound platform that engineering students modify
to optimize space and individual requirements. Basic information about the required frame
members is provided in figure 3.
The following are the primary members of the roll cage [1]:
 Rear Roll Hoop (RRH)
 Roll Hoop Overhead Members (RHO)
 Front Bracing Members (FBM)
 Lateral Cross Member (LC)
 Front Lateral Cross Member (FLC)
19
F13-60-Baja
Figure 3: The figure to the left
shows the different members
associated with the frame.
The following are the secondary members of the roll cage:





Lateral Diagonal Bracing (LDB)
Lower Frame Side (LFS)
Side Impact Member (SIM)
Fore/Aft Bracing (FAB)
Under Seat Member (USM)
Cockpit
The roll cage is the main part of the vehicle that all other components are built off of. The
purpose of the cockpit is to protect the driver during collision and rollover. The cockpit is
designed to allow a 5 second egress (exit) in case of an emergency. There are many guidelines
that must be followed according to the 2014 SAE Baja Rule Book. One main requirement is that
a 6” buffer must exist between any member of the cockpit and the helmet of the driver. The
primary members must be of at least 1” in diameter and of 0.120” wall thickness. Also all
members should be triangulated at intersection points to avoid any direct shear moments put on
any beam. As long as the rules are met, there are countless options that could be chosen. The
cockpit is by far the most complex section of the frame. Design features incorporate a 12.5
degree layback of the firewall for driver comfort. The trailing arm pivot point [1] is located 8” in
front of the firewall, and eliminates the need for wasted space behind the RRH. The roll cage is
comprised of three different tube wall thicknesses to save weight.
20
F13-60-Baja
Figure 4: Shows a
side-view of the
wireframe drawing
with motor
assembly mounted.
Front End
The front end is attached
to the front of the roll
cage. The purpose of the
front end is to connect
the steering, suspension,
and braking systems to
the rest of the car. The
geometry is specified to
accommodate an existing
suspension design. The
upper and lower planes
are 6” apart to permit
appropriate spacing for
the dual A-Arm setup. The
Figure 5: Shown is a drawing of front-end with dimensions.
entire section is inclined
with 11 degrees of positive
caster to keep the steering stable at high speeds, and absorb impacts easier. This area will be the
most likely to take the largest impacts, so it was tested using FEA accordingly. It features 1.25”
and 1” by 0.065” wall tubing to assure minimal deformation in the harshest of impacts.
21
F13-60-Baja
Rear End
The rear end of the vehicle is attached to the cockpit. It
also serves as support to the cockpit by dissipating top
impacts throughout the entire frame. The entire rear end is
modeled around a Dana Spicer H12 Gearbox, and Briggs
and Stratton 10 horsepower engine. The design optimizes
space while still allowing functional working room for the
clutching system, and engine itself. The rear end will hold
brackets for the rear sway bar links that permit 12 inches of
travel using an independent trailing arm design.
Figure 6: Shows a rear
view of the wireframe
from the upper left side.
22
F13-60-Baja
Finished 3D Model with 95th percentile person:
Figure 7: Above shows an upper
right-side view of the finished
frame.
Figure 8: Above shows a rightside view of the finished frame.
Figure 9: Above shows a
left-side angled view of the
finished frame.
23
F13-60-Baja
VII.
Fabrication:
The fabrication of the frame used a very standardized procedure for each member that comprised
the entire frame. The frame was divided into subsections and built in the following order: Base
Frame, Rear Roll Hoop, Front End Frame, Rear End Frame, Roll Hoop Overhead, Side Impact
members. To begin fabrication of a section, a 1:1 model of the section was drawn using Inventor,
this drawing was then plotted on a 1:1 printer. These sheets were affixed to solid sheets of
particleboard. With the drawings taped down, wooden blocks were cut square and placed on the
outline of each tube, producing a jig that would ensure part accuracy and trueness. Once the jigs
were set up, metal cutting and bending could begin. A visualization of this process can be found
on the following pages.
Figure 10: The figure to the left
shows a sample engineering
drawing of a tube that was to be
coped at an angle for our frame.
24
F13-60-Baja
Figure 11: Shows a tube member
of the frame that was coped at a
right angle.
Figure 12: Shows a member of
the frame drawn to certain
specifications as desired.
25
F13-60-Baja
Figure 14: The top right image shows an
example 1 to 1 drawing print-out with
wooden blocks screwed to the underlying
board to hold the chromoly tube in place
while being tacked.
Figure 13: The top left image shows an
example 1 to 1 drawing print-out used in
the building of the frame.
Figure 15: The image to the right
shows the roll-hoop lying on a 1
to 1 printout.
26
F13-60-Baja
Cutting and Coping:
Tubing was rough cut to length from 18 foot stock sections using a horizontal band saw per the
tube diagrams created for each individual member. Once rough cut, the part was faced off square
using the digital readout on the vertical mill to get an overall length. This is where the process
varied for each member. For the simplest members intersecting at 90 degrees, one side of the
tube was touched to the coping mill bit. Then depending on the size of tube that the current part
would be welded to (OD = 1”/1.25”), half the diameter (0.5/0.625 inches) was subtracted, and
the part was coped.
E.G. For a 1.25” tubing to be coped to 1”, the part was faced, zero set on the mill X-axis, and
0.625” was removed using a 1” carbide cutter.
.
Figure 16: Shows
coping of the frame
members with the
vertical mill in
progress.
For members that intersected at angles, such as the ones in figure 18, the geometry was read
from the drawing and placed in the vice at the specified angle using a digital level (accurate to
1/10th degree). The part was then coped on either side. This part proved to be very tricky, and
before each cope was made, all measurements and angles were double and triple checked using
individual engineering drawings created for each member.
Once each member was cut, bent and coped, it could be placed in its respective jig and double
checked for accuracy. Once all dimensions were verified, the piece was welded. After the
individual sections of the frame were completed, we started to build in three dimensions. Each
1:1 had the location and size of tubes needed to locate important 3D features like the angles of
the RRH, FEF. This method was also used to set the location of the trailing arm pivot point, in
figure 18, at point a and side impact member triangulation node at point b. All other 3D members
like the vertical members in figure 18 could be coped to the intersecting piece.
27
F13-60-Baja
Figure 17: Shows image of rear-end
setup and tacked to the roll-hoop.
Figure 18: The above figure shows the side of
the cockpit where intersecting members had
to be coped to fit the trailing arm pivot point.
Bending:
To bend tubing, one must understand how a tubing bender works. The apparatus consists of a die
(size matches the outer diameter of tube being bent), clamp, and lever arm. Die radii used in our
project were 4.5/3 inch dies for 1.25/1 inch tubing respectively. With the tube size and die
selected we are ready to bend with a few dimensions. These dimensions are shown in figure 12.
Inventor’s drawing program was used to turn the individual tubes into 2D drawings that could be
dimensioned. Dimensions included overall length, length from a face to the beginning of the
bend, and the angle (degrees) of the bend. The next step is to cut the tubing to the overall length,
then measure the length from the end of the tube to the start of bend. After subtracting 1 inch
from that length, mark the tube (second mark). This is where the tube will line up with the face
of the tubing bender die. These marks should be scribed around the entire tube. The tube is now
put in the tubing bender with the second mark lined up with the edge of the die face. The tubing
bender clamp is tightened. Pressure is applied to the tube with the tubing bender lever arm to seat
the tube in the die. The angle finder is zeroed for accuracy. Then, using the lever arm, the tube is
bent to 2 degrees past the appropriate angle to account for spring back of the tube. The angle
finder/level is used several times in this process in order to ensure the tube is bent to the correct
angle and in one plane. The bend is complete when all angles match the drawings, and any
excess tube used as a buffer in the beginning stage is removed.
Welding:
28
F13-60-Baja
Figure 19: The image to the
left shows tig welding in
progress.
(a)
(b)
Figure 20 a & b: The image below shows a finished cross joint weld.
Welding is the process in which high current is ran through metal objects, creating a resistance
and in turn heat. When the metal reaches its melting point, the two objects can be fused together
with a filler metal. Tungsten Inert Gas (TIG) welding is a more controllable welding process
because heat and the input of a filler metal can be controlled individually, unlike Metal Inert Gas
(MIG) welding. Due to the small wall thickness of the tubing, it is important to have control over
the heat so the welder does not burn through the material.
29
F13-60-Baja
VIII.
Finite Element Analysis
Functional description
Finite Element Analysis is a numerical analysis technique for finding approximate solutions to a
physical problem defined in a finite region or domain by using a computer software. In this
project, Dassault Systemes SolidWorks was used to analyze critical failure points, increase
quality of design, ensure the safety, and achieve weight reduction goals.
Relationship to other subsystems
To perform an accurate finite element analysis, an engineer needs 5 things: material, geometry,
mesh, loads, and boundary conditions. The first two in this list are dependent on the other
sections of the defined design process. The dependency of FEA on material selection is explicit.
To perform FEA, geometry and material properties are a necessity to calculate how the structure
will react. Meeting the rulebook specifications while incorporating existing subsystem
constraints establishes a conceptual design. The first iteration of design is done with “sound
engineering judgment”, but needs numerical verification. In today’s technologically advanced
world, FEA is how the numbers are calculated. After testing, the design either holds to
specifications or it fails. If it fails the analysis, the engineer changes the design and repeats this
process until a suitable design is found.
Option comparison
When comparing the options of SolidWorks FEA simulation package to performing full scale
tests on a prototype; the cost and time constraints make the decision. In terms of FEA analysis
options, one must first choose the desired result. In our case deformation, internal stresses, and
strains were areas of interest. Static analysis was chosen because it takes the least computing
time, can represent worst case loading scenarios, and give reliable data. Fatigue analysis was also
used because specific areas of the frame will see repeated loading. As engineers there is always a
need to calculate how long the design will perform safely. Other perks of these simpler
simulations is the more accurate results by refining the mesh to pinpoint stress concentration
areas.
Methodology for choosing forces/design process
Being an engineer requires some intuition. The ability to visualize where a structure will take
loads on a macro scale, how the frame should be supported for testing, and how to
mathematically break down the structure for analysis comes with the territory. Once the general
idea is present, the application of engineering procedure and laws of physics can take place. With
the geometry and material established, the simulation programs still needs the boundary
conditions, loads, and a mesh to execute.
Loads
Understanding that the vehicle frame will face forces from the front, rear, side, and top due to
rollover is the intuitive part. Naturally we can estimate relatively where these forces should be
placed as well. To calculate forces we used two methods. Newton’s second law (F=ma), and the
conservation of energy method are shown in table 8. To use Newton’s method, assumptions were
made for the weight of the car, the speed at impact, and time of impact were made. These are
summed up in table 10. For the energy method, the same assumptions were made, but in addition
the stopping distance, or the distance the frame could crush, was taken into account
30
F13-60-Baja
Meshing
Meshing is the breakdown of a structure into finite elements for which displacements, stresses,
and strains can be calculated using matrices. Generally it is thought that “the finer the mesh, the
better the result.” Unfortunately meshing is what takes the majority of computational time, so the
goal is to not mesh elements smaller than needed. Optimum mesh sizes are found using
convergence studies, like the one shown in figure 19. This study verifies for the model that over
a mesh element size ranging from 5 inches to 0.1 inch there is only 0.5% change in the maximum
displacement, this determines that the program controlled mesher converges to a max value very
quickly. Taking into account the calculation time, a mesh size of 0.5 inches was used in all
simulations.
Mesh Convergence
SolidWorks Auto Mesher
Element Size (in) Nodes
Max Displ Mesh Time (s)
5
276
0.883
0.74
4
350
0.8825
0.83
1.77
592
0.882
1.00
1
976
0.8821
1.20
0.5
1845
0.8821
2.00
0.1
8715
0.8801
15.70
Table 5: The above table shows
mesh convergence information
used in SolidWorks.
Figure 21: Shows a display of
meshing convergence for SolidWorks
using an 8G frontal impact.
Boundary conditions
Boundary conditions for each simulation varied and is yet another intuitive part of the process.
For example, in the front impact study, the car was constrained by four points on the firewall
(shown as green arrows, figure 20). The same constraints were used for the rear impact case. To
isolate the trailing arm pivot point, the side impact case was restrained as shown in figure 21.
Finally, the top impact case was isolated as in figure 22 to allow the maximum stress to be
determined for the roll hoop overhead support bracing. Beware that this is where FEA becomes
unrealistic. It must be understood that fixing those specific nodes allows for no movement at all,
which in turn pushes the stresses, and displacements to unrealistically high values. In reality
using the principles of momentum, the car will simply bounce away from the object instead of
permanently deforming.
31
F13-60-Baja
Figure 23: The above right image
shows the side of frame in FEA
boundary condition
Figure 22: The above left image
shows the front of frame in FEA
boundary condition
Figure 24: The figure to the right
shows the top side of frame in FEA
boundary condition
Conclusions/Remarks
With the car restrained as shown above, and the loads applied from the energy method, a mesh
size of 0.5 inches for all studies, the following results can be observed. The appendix
summarizes the results of displacement and stress for the impact scenarios. Realize that the
displacements and stresses shown for the simulations have the possibility of being up to 100%
incorrect. The reactions seen are very high due to the way the model was constrained. Values
less than half of these shown could actually be expected when the frame faces a momentary
impact under a far less loading. The analysis software has allowed the determination that our
frame, as built, far exceeds any requirements for the chosen impact scenarios.
32
F13-60-Baja
Table 6: Shows certain desired and achieved criteria for FEA analysis of the frame.
F13-60-Baja FEA Design Criteria
Displacement (in)
Expected Achieved Allowable/Achieved
Side impact (G
force)
Rear impact (G
Force
Front impact (G
force)
Top impact (G
force)
IX.
Axial Stress (psi)
Allowed/Achieved
3
11
6/0.1
106,022/61,701
4
11
12/0.88
106,022/46,995
8
46
12/0.6
106,022/99,421
5
32
6/7.88
106,022/300,000
Cost and schedule
Finite Element Analysis is a very time consuming process. Its time schedule can vary widely
depending on the complexity of the model, errors found during the process, and computing time.
An entire thesis could be based on the small study done here and expanded on to find much more
accurate results. The approximate time schedule for this project is shown in table 3.
Faults analysis
The simulations in this report gave rough numbers that verified the integrity of the frame,
however when doing static representation of dynamic analysis there is error. When fixing certain
points, deflections and stresses become magnified beyond reasonable values. To fix this, much
more time should be spent simplifying the model so it could be meshed as a whole, and do
dynamic collision testing. This feature is offered by many FEA softwares, but requires more time
than was allotted for this project to learn, and apply effectively.
Global considerations
The impact of FEA in a project may seem somewhat intangible. But, when the main criteria of a
product is protecting a recreational user from injury, engineers take on the responsibility of
someone’s life. Though FEA is only a software that tests theoretical cases, when applied
correctly it becomes a reliable system that provides numbers. This method of testing is far less
expensive and time consuming than the other option of full scale prototype testing. The impacts
on safety and health of the user are direct. Testing the frame to the most extreme cases provides
tangible data to the engineer that the design will hold up under these extreme loads.
33
F13-60-Baja
X.
Appendices
Vendor list
Wick Aircraft Supply
Rix Enterprise
McMaster Carr
Airgas
Derivations
Simulation results
Side impact at 13mph, set crush distance of 6 in, fixed nodes shown with green arrows.
Figure 25: Shows that a 13mph side impact yields only a 0.1592” deflection.
34
F13-60-Baja
Figure 26: Shows an impact to the trailing arm pivot point.
It can be seen here that even a direct collision to the trailing arm pivot point, that the axial stress
is only half of the material maximum.
Rear impact at 18mph, set crush distance of 12 in, fixed nodes shown with green arrows.
Figure 27: Shows the rear end can easily sustain an impact from a vehicle up to 25 mph.
35
F13-60-Baja
Figure 28: It can be seen that the maximum displacement in the rear collision is 0.8851”
Top impact at 22mph, set crush distance of 6in, fixed nodes shown with green arrows.
Figure 29: The above shows a simulation of a rollover, and related stresses.
36
F13-60-Baja
It can be seen that when the thickness of the roll hoop support members size is increased to
0.065” from 0.035” that the axial and bending stress reduces by 100,000 psi. The frame was built
using 0.035” tubing for these members with confidence in the event of any impact.
Figure 30: The above screenshot shows the likely displacement in an actual rollover.
It can be seen that the maximum displacement is 7.334 in, but in reality we could expect
deformations of less than 3 inches keeping the driver completely safe.
37
F13-60-Baja
Figure 31: The above image shows more rollover FEA simulation.
In the rollover scenario the main concern was the structural integrity of the roll hoop overhead
support members. It can be seen that the stresses exceed the ultimate strength of the material, but
in a real world roll over, the vehicle would not be seeing these kinds of accelerations.
38
F13-60-Baja
Frontal impact at 37mph, set crush distance of 12 in, fixed nodes shown with green arrows.
Figure 32: Shows frontal impact data generated in FEA.
It can be seen in this 1:1 representation that the worst case frontal impact case yields only a
0.6046 in displacement.
Figure 33: Shows more impact data from FEA with a fixed frame.
The frontal impact loading case is by far the most destructive, and approaches the compressive
strength of the material, but in reality the vehicle will not be fixed in this impact, and the stresses
seen will be much lower.
39
F13-60-Baja
Figure 34: The above represents the stresses the trailing arm pivot point displays after
absorbing a force when the rear wheel hits a bump.
This loading on the trailing arm pivot point is equivalent to the rear wheel hitting a bump and
causing at most a 0.005913 in displacement. This effect could be neglected.
40
F13-60-Baja
Figure 35: Shows an extreme case scenario of a frontal impact simulation.
Even in this worst case scenario axial force graph, the stresses for the front end frame members
range from 57,000- 99,000 psi, well below the 106,022 psi compressive limit.
41
F13-60-Baja
Figure 36: Shows the displacement relating to frontal impact
In this figure the maximum displacement of 1.352 in can be seen at the bend in the base frame. A
tube could be added in the highlighted area to reduce this displacement.
Figure 37: Shows the displacement in direction of the applied load.
It can be seen in this frontal loading situation the maximum displacement, in the Z (direction of
load) direction, when the firewall is fixed is 0.9785 in
42
F13-60-Baja
Spreadsheet calculations:
Type
Strength to
Weight Ratio
Ultimate Tensile
(Kn-m/kg)
Material Comparison for Baja Frame Components + (A Arms)
Shear Modulus
Modulus of
Weight of 12in
Tensile Strength
3
Density (Ibs/in )
Ultimate (psi)
length, 1.25in OD,
Price/ft
Elasticity (psi)
(psi)
0.65 Wall thickness
1020 Carbon Steel
48-53
58015.08
29007547.55
11600000
0.281793
0.8226 Ibs
4130 "Chromoly"
71-130
97175.26
29732736.23
11600000
0.281793
0.8226 Ibs
It can be recognized that with ASME 4130 Steel, the strength to weight ratio is greatly higher. In order for ASME 1020 Steel to be as effected, a greater
$3.00
$3.89
wall thickness is needed, increasing the overall weight of the frame. 4130, although more expensive, gives a suitable advantage is weight reduction to
allow for a durable and light weight frame.
Material Comparison for Baja Sub Systems (Spindles)
Type
Strength to
Weight Ratio
Ultimate Tensile
(Kn-m/kg)
Tensile Strength
Weight of 12in X
Modulus of
3
Price/ft
Density (Ibs/in )
Ultimate (psi)
Elasticity (psi)
1in Rod
4140 Tool Steel
83-130
116030.16
29007547.55
0.281793
2.6733Ibs
$15.70
Ti 6-4 "Titanium Alloy"
73-260
137785.82
16505294.55
0.159683
1.5052Ibs
$111.75
Grade 5 Titanium Allow was chosen for the fabrication of spindles. Previous years spindles constructed from 4140 steel could not with stand the forces
applied to them during competition and bent. Since titanium has a high amount of resilience, it can with stand bending forces without permanent
deformation occuring. Another factor is the weight reduction, titanium is almost half the weight of 4140
Material Comparison for Baja Sub Systems (Knuckles)
Strength to
Weight Ratio
Ultimate Tensile
Tensile Strength
Weight of 2 X 4 X
Modulus of
3
Price/Block
12in block
2024 Aluminum
66-170
68022.68
10602258.63
0.100073
9.61Ibs
$149.44
7075 Aluminum
200
82961.56
10399205.80
0.101156
9.71Ibs
$152.28
The material selected for fabrication of the knuckles is 2024 Aluminum. As it is cheaper and slightly weighs less than 7075. The same material was used
Type
Density (Ibs/in )
Ultimate (psi)
Elasticity (psi)
the previous year without any flaws during competition
Material Comparison for Baja Sub System (Body Paneling)
Weight of 12 X 12 X Price 12in X 12 X *Thickness and mass will vary
Type
with fiberglass and carbon
Density (Ibs/in3)
0.025in Sheet
0.025 Sheet
fiber
2024 Sheet Aluminum
0.100073
0.36 Ibs
$7.51
Fiber Glass
0.0918
0.33Ibs
$5.00 (ft2)
Carbon Fiber
0.0578
0.21Ibs
$5.00 (ft2)
Table 7: The preceding table shows a comparison of used and considered materials.
Newton's 2nd Law Calculator
-3524.9
Gravity (m/s^2)
32.2
Estimated Weight Car
700
Top Speed (mph)
22.0
Speed (ft/s)
32.3
Estimated Time of
0.199
Acceleration (ft/s^2)
-162.1
Table 8: Shows calculations made using Newton’s 2nd Law of Motion.
43
F13-60-Baja
Researched Forces of Impact
Calculated forces
G-Force (G)
Force (lb) Mph at Impact Time of Impact (s) Force (lb)
Actual G-Force (G)
Frontal
8
5600
37
0.21
-5618
-8.0
Rear
4
2800
18
0.205
-2800
-4.0
Side
3
2100
13
0.197
-2104
-3.0
Rollover
5
3500
22
0.199
-3524
-5.0
Table 9: The above table shows possible impact forces pertaining to the operation of the
baja car.
Energy method Calculator F = 0.5*(mv^2)/d
Gravity (ft/s^2)
32.2 Frontal
Estimated Weight of
Vehicle (lb)
700 Rear
Top Speed (mph)
22.0 Side
Speed (ft/s)
32.3 Rollover
Acceptable
deformation (stop
distance (ft))
0.50
Force (lbf)
Modify crush distance to match acceleration
Varying
Speed of Distance to Force
impact stop (ft)
(lbf) G-Force (G)
37
5.70 5616
8
18
13
22
2.70 2755
1.88 2102
3.25 3482
Choosing crush distance
Set
Speed of Distance to Force
22633
impact stop (ft)
(lbf) G-Force (G)
Frontal
37
1.00 32009
Rear
18
1.00 7576
Side
13
0.50 7903
Rollover
22
0.50 22633
4
3
5
46
11
11
32
Table 10: Shows more calculations and parameters associated with crashes of the baja car
that were applied through FEA to the frame.
44
F13-60-Baja
XI. Completed Product
Passenger Side
Front View
Rear end
45
F13-60-Baja
XII.
References
[1]
“SAE Series Rules” SAE. 2014 Baja SAE Series Rules. SAE International 2014. 12 Sept. 2013.
<http://www.sae.org/students/2014_baja_rules_8-2103.pdf>
[2]
“Introduction to Material Selection Charts: Mechanical Properties in Physics, and
Design.” Internet: http://wwwmaterials.eng.cam.ac.uk/mpsite/physics/introduction/, Feb. 25, 2002 [Nov. 5, 2013]
[3]
SAE. 2014 Baja SAE Series Rules. SAE International 2014. 12 Sept. 2013.
<http://www.sae.org/students/2014_baja_rules_8-2103.pdf>
[4]
“MatWeb, Material Property Data.” Internet: http://www.matweb.com/index.aspx,
[Nov. 5, 2013]
[5]
“Alloy Steel Price Per Ton.” Internet: http://www.alibaba.com/showroom/alloysteel-price-per-ton.html, [Nov. 5, 2013]
[6]
“4130 Alloy Steels Material Property Data Sheet.” Internet:
http://www.supplieronline.com /propetypages/4130.asp, [Nov. 5, 2013]
[7]
FLA Webmaster, "Metal Ditributor," ASM Aerospace Specification Metals, Inc.,
[Online]. Available: http://www.aerospacemetals.com/contact-aerospacemetals.html.
MakeitFrom.com, "MakeitFrom.com," [Online]. Available:
http://www.makeitfrom.com/compare-materials/?A=Normalized-4130-Cr-MoSteel&B=SAE-AISI-1020-S20C-C22-1.0402-G10200-Carbon-Steel.
[8]
[9]
Performance Composites, "Carbon Fiber Mechanical Properties," Performance
Composites, July 2009. [Online]. Available: http://www.performancecomposites.com/carbonfibre/mechanicalproperties_2.asp. [Accessed 12 04 2014].
[10]
Azom.com, "AISI 1020 Low Carbon/Low Tensile Steel," Azom.com, 28 June
2012. [Online]. Available: http://www.azom.com/article.aspx?ArticleID=6114.
46