UNIVERSITY OF TENNESSE-MARTIN

2015 SAE BAJA FRAME

JACOB GANSERT

4/21/2015

TABLE OF CONTENTS

Scope of Project……………………………………………………………………………………………………………………….

Team Members………………………………………………………………………………………………………………………..

Project Goal and Objectives……………………………………………………………………………………………………..

Design Requirements……………………………………………………………………………………………………………….

Use of Previous Course Work…………………………………………………………………………………………………..

Engineering Standards……………………………………………………………………………………………………………..

Realistic Constraints…………………………………………………………………………………………………………………

Iterative Design Process……………………………………………………………………………………………………………

Suggested Improvements…………………………………………………………………………………………………………

1

1

1-3

3

3-4

4

4-5

5

23

2

Scope

The scope of the project was the design and fabrication of a frame that allows the team to win the SAE Baja competition.

Team Members

Team Member Role & System

Steve Breazeale Team Captain, Drivetrain

Brandon Anderson Vice President, Front Suspension & Steering

Jacob Gansert Frame

Colin Bennett Rear Suspension

Mustafa Alhalal Brakes

James Lee Fuel & Safety

Jason Benne Body & Molds

Adel Alnahdi Seat

Goal

The goal of the project was for the team to win the Baja competition. Winning the competition would have brought prestige to the University of Tennessee at Martin and possibly would have increased funding for future UTM SAE Baja teams.

Objectives

The team objectives for the Baja were based on the weighted point totals in the competition. Certain events, such as the endurance race, contributed more to the scoring than other events, such as the

prototype cost. Therefore, objectives were prioritized on the contribution to a first place finish in the competition. The frame objectives were based on the team objectives in order to maximize the

contribution of the frame to the overall team goal.

Speed

The most important objective was making the Baja fast. Speed was an important factor in all of the dynamic events. Changes in speed were due to multiple factors such as weight, air drag, CVT calibration, and wheel alignment. Speed had a large part in 700 of the 1000 points in scoring. The frame impacted the speed through weight and drag caused by the surface area of the Baja. The frame was made out of the lightest material possible with the least amount of welds and nuts.

Durability

3

The next most important objective was making the Baja durable. The Baja had to finish each event in order to score. Also, any breakdown in the structure of the Baja could possibly have caused the Baja to lose speed or mobility. The frame impacted durability by being the skeleton of the car. The frame was made stronger by minimizing stress concentrations and distributing stress loads encountered by the Baja.

Mobility

The third most important objective was making the Baja mobile. Mobility impacted four dynamic events. The most notable of the four was the endurance event. The frame impacted mobility through the length and width of the Baja. A shorter and thinner Baja had a much easier time turning through obstacles, notably the trees at Auburn.

Ergonomic

The fourth most important objective was making the Baja ergonomic. The third most possible points came from the design event. Factors which influenced this event were the appeal of the car to the eye, comfort, and innovation. The frame impacted ergonomics through its design of the chassis. A frame with curves caused a more appealing look to a buyer. A frame designed for ample room for the driver provided a comfort appeal to the design judges.

Inexpensive

The fifth most important objective was making the Baja inexpensive. Prototype cost was the third most influential event in the scoring. Cost was affected mainly by the materials chosen to build the Baja followed by efficiency of use of the materials. The frame impacted expenses through the amount of metal and time used on the frame. A frame with more bends and less welds saved metal costs, energy costs, and manpower costs. A frame that contained longer, continuous pieces typically required less time to put together.

Serviceable

The sixth most important objective was serviceability. One of the scoring criteria in the design and sales event was serviceability. The Baja also had to be relatively easily repaired in the middle of competition, especially in the endurance race to assure better scores. The frame impacted serviceability through its design for the stress concentrations. Stress concentrations in a certain area of the frame could have caused the easily replaced parts to break instead of the hard to replace parts in fatigue failure and crashes. Fewer parts also allowed simpler fixes with less moving parts.

Manufacturable

The seventh most important objective was manufacturability. It was another scoring criterion in the design and sales events. A Baja produced quickly and simply was more appealing to the companies that would mass produce the Baja for profit. The frame impacted manufacturability through its fabrication process. The frame could be compared to a jigsaw puzzle. A puzzle with fewer pieces can be

4

put together faster, costing less in labor. The frame also had to be designed for assembly line production.

The above objectives had to be fulfilled to the point that allowed the Baja team to win the competition. The desired result was that the drivers were the difference between winning and losing.

Design Requirements

The full list of requirements for the 2015 Baja is listed at http://bajasae.net/content/2015%20BAJA%20Rules%20.pdf. The requirements specified for the frame are found on pages 21-30.

The requirements for the frame were mainly specified for driver safety. Requirements included dimensions, angles, spacing, and strength minimums of tubing to ensure that, in the event of a major collision or crash, the driver would not suffer serious complications.

Use of Previous Course Work

Course Number Course Topic Information Used

ENGR 101 Engineering Graphics Exported AutoCAD files to DXF file to cut sheet metal on the plasma cutter

ENGR 121 Statics Calculate static forces on frame members using free body diagrams

ENGR 241 Dynamics Calculating bearing forces and moments to use the Finite Element Analysis

ENGR 301 Computer Aided Engineer/Design Tools

Modeled parts for the frame in Autodesk Inventor

ENGR 310 Engineering Materials Use of stress-strain curves for prediction of yield and absolute stress. Use of S-N curves to predict endurance limit for tubing

ENGR 317 Comp Methods and Numerical Analysis

Use of Matlab to calculate dynamic forces

ENGR 409 Engineering Design and Project Management

Use of project planning to determine design criteria

ENGR 220 Strength of Materials Use of formulas to calculate

5

tubing bending stiffness and bending strength

ENGR 476 Applied Finite Element Analysis Lab

FEA on frame to test for worst stress and worst axial loads. FEA to ensure proper spring rates for front and rear suspension

PHYS 220/221 Physics I/II Calculate drag force on firewall to estimate top speed reduction

ENGR 390 Special Topics: CAM Use of CNC and manual input on plasma cutter, mill, and lathe to fabricate parts

Engineering Standards

2015 Collegiate Design Series Baja SAE Rules

Realistic Constraints

The six most important risk factors were inexperience, manpower, lack of equipment, teamwork, cost, and time.

Inexperience

Inexperience was a constraint due to the fact that only the team leader had prior experience in the project. Frame design had certain caveats that are learned through previous failures. Also, optimal design of certain aspects of the frame relied on visually seeing ideas from other teams. Fabrication design was the most difficult part of the frame to achieve without prior experience. The jigging, bending, and welding all required previous experience to execute correctly the first time.

Manpower

Manpower was a constraint due to the schedules of all the designers. Every team member had conflicts with scheduling due to school, work, and hobbies. Most of the design aspects of the frame were heavily influenced by the design of the front suspension, rear suspension, drivetrain, brakes, and seat. Therefore, delayed design of any of those aspects led to delays in the finalization of the frame design.

Lack of Equipment

Lack of equipment was a constraint due to design choices based on construction capabilities. The tube bender used was able to perform only two axis bends. That limitation led to designing the frame for primarily two axis bends in spots where a three axis bend would have been more sufficient. Another lacking construction capability was a three axis tubing notcher. The notcher used was capable

6

of only two axis notching. That limitation led to designing certain joints with less than four members intersecting.

Lack of Teamwork

Lack of teamwork was a constraint due to communication issues. The group of designers on the Baja team had never worked together as a unit before the project. The lack of chemistry as a group led to some difficulties in communication and cooperation. Those difficulties led to a delay in certain design requirements being finished.

Cost

Cost was a constraint due to general underfunding of the Baja team. Design choices were made based on limiting the overall cost of the Baja in the fabrication phase. These choices led to some less than optimal design aspects of the Baja.

Time

The final constraint was time due to a lack for suitable iterations. Certain design flaws could have been caught before the fabrication of the Baja had the design team been assigned earlier than August. If the flaws had been caught, iterations could have provided suitable designs for the flaws.

7

Iterative Design Process

The iterative design process for the frame started with choices independent of the variables of other designs for the Baja. Most of these choices were related directly to the rules requirements listed in the SAE Baja Manual.

Tubing

The first design choice was that of tubing. The minimum requirement for the primary tubing was tubing with an equivalent bending stiffness and bending strength to 1 in OD x .12 thickness 1018 steel. The material chosen for the tubing was 4130 Chrome Moly. Chrome Moly is a standard material choice for race cars. It is an air quenched steel, meaning that it can be heated and left alone to cool without significantly altering its properties in the heat affected zone. That characteristic is optimal for cars due to the amount of welds contained in the frames. Also, it is stronger than average steel due to the alloy elements added to its composition. Therefore, it is stronger per unit weight than 1018 steel.

The bending stiffness and bending strength of many tubing configurations was calculated using the table format found in Figure 1. The primary tubing chosen was 1.25 OD x .065 thickness based on the strength to weight ratio and the minimum requirements.

Figure 1: Leading tubing choices for the primary members in the SAE Baja frame were made based on strength to weight ratio. Calculated weight gain for the different tubing types based on the estimated frame weight divided by the weight/in were used to determine differences in total weight based on

tubing choice. The weight gain calculation was used to optimize the balance of strength and weight of the frame.

To confirm the tubing choice, a graph of the strength to weight ratio was made with all the tubing as seen in Figure 2. The 1.25 OD x .065 thickness Chrome Moly was also visually confirmed as the optimal tubing choice due its balance of weight and bending strength.

MaterialOD ThicknessID Length

Modulus of Elasticity (psi)

Second Moment of Area

Distance from neutral Tensile StrengthYield Strength(psi)Bending StiffnessBending Strength

Density(g/cm^3)

Density(lb/in^3

Cross Sectional Area Volume(in^3) Weight/in

Strength/Weight Ratio

4130 1.25 0.065 1.12 1 29732728.5 0.042602 0.625 95000 75,000.00 1,266,682.56 5,112.28 7.85 0.283599 0.241981 0.241981174 0.0686257 1,092,885.384130 1.125 0.065 1 1 29732728.5 0.030516 0.5625 95000 75,000.00 907,309.78 4,068.74 7.85 0.283599 0.216456 0.216455734 0.0613867 66,280.444130 1 0.065 0.87 1 29732728.5 0.020965 0.5 95000 75,000.00 623,356.75 3,144.80 7.85 0.283599 0.19093 0.190930294 0.0541477 58,078.211018 1 0.12 0.76 1 29732728.5 0.032711 0.5 52,938.76 972,580.31 3,463.33 7.87 0.284322 0.331752 0.331752184 0.0943244 561,241.58

50 60 7050 60 70

28.7 34.443 40.1840785232.5 39.048 45.5562815336.4 43.653 50.928484544130 Moly 1.25 OD .065 t

Calculatable Differences in Weight and StrengthEstimated Baja Weight

1018 Weight4130 Moly 1 OD .065 t4130 1.125 OD .065t

8

Figure 2: The bending strength vs weight ratio was used to visually confirm the tubing choice of the primary material. The point chosen was the red dot which represented 1.25 OD x .065 thickness Chrome

Moly.

A similar process as that shown above was used to determine the tubing choice for the secondary members. Secondary members were required by SAE Baja rules to be a minimum of 1” OD x .035 thickness of any steel tubing. Chrome Moly was again chosen as the material due to its welding properties and strength. 1 in OD x .049 thickness tubing was chosen for the dimensions due to its strength and light weight as shown in Figure 3.

9

Figure 3: The table for secondary members used weight as the primary factor for those tubes that fit the minimum specifications of SAE Baja.

Tubing with .035 thickness was considered but ultimately denied at this point in the design process due to a few factors. First, .035 was difficult to weld properly due to the lack of thickness in its walls. Its welding difficulty could have compromised the strength of the rear of the roll cage which contained the drivetrain. A failure in the endurance event in the rear of the frame would have been catastrophic. That scenario conflicted directly with the team’s objective of durability. Second, .035 tubing could not be bent without compromising its bending strength and stiffness. With welds in place of bends, the .035 tubing would have directly conflicted with the team’s objective of ergonomic since a curved frame looks more appealing than a straight line frame. Also, welds cost more than bends according to the SAE Baja Cost Report. Welds cost $.35/in. For a 1 in OD tube, one complete weld would cost $1.10. Also, one of the tubes would have to be notched at the end, costing $.75 per notch. In contrast, one bend would cost $.75. The savings of $1.10 for every weld replaced with a bend led to a savings of about $23 on the cost report. The lack of savings through welds with .035 tubing would have directly conflicted with the team’s objective of inexpensive.

CAD Model

After the tubing was selected, a model of the team’s largest driver was developed to ensure compliance with the driver spacing requirements in the chassis. According to the SAE Baja Manual, “the driver’s shoulders, torso, hips, thighs, knees, arms, elbows, and hands shall have 76 mm (3 in.) clearance to the side surfaces.” Also, “the driver’s helmet shall have 152 mm (6 in.) clearance from any two points among those members that make up to top of the roll cage. These members are: the RHO members (exclusive of any covering or padding); the RRH upper, LC; and the LC between points C. In an elevation (side) view, no part of the driver's body, shoes, and clothing may extend beyond the envelope of the roll cage.” Therefore, a picture of the driver’s body was taken using a camera as shown in Figure 4 and imported into Autodesk Inventor.

Material OD ThicknessID Length

Modulus of Elasticity (psi)

Second Moment of Area

Distance from neutral axis to Tensile StrengthYield Strength(psi)Bending StiffnessBending Strength

Density(g/cm^3)

Density(lb/in^3

Cross Sectional Area Volume(in^3)Weight/in

Strength/Weight Ratio

4130 1.25 0.049 1.152 1 29732728.5 0.033389 0.625 95000 75,000.00 992,754.98 4,006.72 7.85 0.283599 0.18488 0.1848796 0.052432 76,417.804130 1.125 0.049 1.027 1 29732728.5 0.024021 0.5625 95000 75,000.00 714,212.18 3,202.81 7.85 0.283599 0.165637 0.1656373 0.046975 68,181.724130 1 0.049 0.902 1 29732728.5 0.016594 0.5 95000 75,000.00 493,382.47 2,489.09 7.85 0.283599 0.146395 0.1463951 0.041518 59,952.691018 1 0.035 0.93 1 29732728.5 0.012367 0.5 52,938.76 367,718.57 1,309.44 7.87 0.284322 0.106107 0.1061073 0.030169 43,403.94

50 60 7050 60 70

68.809 82.571 96.332804477.853 93.424 108.99484586.898 104.28 121.6568864130 1.25 OD .0.49 t

Calculatable Differences in Weight and StrengthEstimated Tubing Weight

1018 Weight4130 1 OD .049 t

4130 1.125 OD .049 t

10

Figure 4: Front, side, and rear pictures of the driver were used as the template for the 3D model of the driver.

From there, the pictures were traced in Inventor using the spline function. The traced loops were then extruded and scaled into a properly sized 3D model representing the driver as show in Figure 5. The driver was 6’4” tall and weighed 230 lbs.

Figure 5: The Colin Model was used as the primary instrument for sizing the chassis to the spacing requirements of SAE Baja.

In addition to the Colin Model, a previously purchased human model as shown in Figure 6 was used to simulate the team’s smallest driver, who was 5’6” tall and weighed 140 lbs.

11

Figure 6: The human model of the smallest driver was used to ensure that the smallest driver could reach the pedals and wheel of the Baja.

Once the drivers were properly modeled, the design of the chassis began with an overview of all the rules. Drawings were started in Autodesk Inventor in 2D drawings. A rear roll hoop (RRH) angle of 15 degrees was chosen based on the team’s objective of ergonomic. A seat with an angle of 15 degrees was much more comfortable than that with a 5 degree angle from the previous year. The RRH was modeled in Inventor originally as a box. To comply with the objective of speed, the edges of the firewall were removed with iterations to reduce the drag area of the RRH as shown in Figure 7.

Figure 7: The original concepts of the RRH were found to be insufficient for the objectives and were modified through time.

12

As time passed, the firewall corners were continually reduced to reduce drag area. The lower frame side members (LFSM) were joined with the side impact members (SIM) to create the nose of the car. The original nose was created with a width of 14 in at the bottom as shown by Figure 8 to allow for a more comfortable driver fit, aligning with the team objective of ergonomic. Around this time, it was determined that the model would eventually have to be exported into a 3D point model to properly model the dimensions of the tubing in the model with the sweep function in Inventor.

Figure 8: The original leg area of the frame design was large to embrace driver comfort.

To finalize the design of the RRH, the drag area was calculated with a firewall with the projected area shown in Figure 9. The finalized RRH had an area of 1000 in2

which would affect drag. Using the equations in Figure 9, the top theoretical velocity was 28.76 mph. That speed was right around the team goal of 30 mph. The lower speed was mainly due to the gear reduction chosen by the drivetrain designer for a better acceleration at the tradeoff of lower top speed.

13

F=

v=sqrt(2*F/(p*A))

p 1.2041 kg/m3 0.002336 slug/ft3 1.35205E-06 slug/in3F 14.42959 lbfA 1000 in2 6.944444 ft2

vmaxtheo 42.17502 ft/s28.7557 mph

Tires

rpm 3800 11.49417 inHP 10 0.9578475 ftT 13.82135 ftlb

F 14.42959T 13.82105

Figure 9: The speed term in the equation on the top right was isolated on its own side. The max engine rpm at 10 HP was used to calculate the torque transferred to the tires. The torque was converted

to the force the tires put out. The projected area (left) was plugged into the velocity equal to obtain 28.76 mph.

While the above design was retained, side bracing members (SBM) were added to the design to protect the driver from crashes into the side of the vehicle. These members were not required by the SAE Baja Manual. They were chosen based on the objective of ergonomics due to their contribution to driver safety in a crash scenario. Also, the rear of the Baja was designed at this point for and engine sitting on the tubing on the floor of the frame as shown in Figure 10. A low engine would give the car a lower center of gravity (COG) at the expense of a larger wheel base. A lower COG would deter the Baja from flipping compared to higher COG. However, it would also make the Baja turn radius larger. Both cases affected maneuverability but, in essence, equaled out.

Figure 10: The rear of the Baja, which held the drivetrain, was made wider at the bottom for the low engine. This led to a large triangle design along the top of the rear.

14

The full chassis was formed in design with the addition of the roll hoop overhead members (RHO). The RHO members were originally added as two welded tubes due to doubt about the capability of the tube bender. Also, the nose was reduced as shown in Figure 11 to reduce the Baja’s track width. A smaller track width allows for tighter turns through small openings. The design choice of a smaller front of the Baja aligned with the team objective of maneuverability.

Figure 11: Gradual iterations led to the first full model of a complete roll cage.

The next step in the design process was enhancing the front of the Baja and adjusting the rear of the frame to adjust for the drivetrain design as shown in Figure 11. The lower frame side members in the front were turned into bent tubes that curved inward at the heels of the feet and curved outward at the toes. This design was chosen for speed and ergonomics. The narrow, curved front simulated the front of a boat. The front would cut through air at an improved rate like a boat in the water. Also, the curved front was visually appealing compared to the straight line front. The nose was also reduced in length for a smaller track width. Another focus for the front was making the side impact members parallel to the lower frame side members to ensure ease of calculating suspension geometry for the front suspension designer. The rear of the frame was changed to a slimmer, taller version in Figure 12 to support the drivetrain layout in Figure 13. A different version of the rear as shown in Figure 14 contained a bend at the bottom of the back side. The version was not applied to the frame design due the complexity it would add to the rear suspension mounting points.

15

Figure 12: Changes in the front and rear allowed for many improvements in reaching team objectives. The stray lines on the bottom of each picture were projected lines off of the side impact members. These lines were used to make the lower frame side members parallel to the side impact

members.

Figure 13: The drivetrain layout was changed from the low COG layout (right) to the new higher COG layout (left) to allow for a shorter wheelbase. While the change equaled out in terms of

maneuverability, the change allowed from improved ergonomics with a shorter, more visually appealing rear.

16

Figure 14: While the bend in the back of the Baja was more visually appealing, it made the rear suspension mounting points very difficult to calculate.

The 2D model was exported into a 3D point format in Inventor by recording individual points into an Excel spreadsheet. The 3D point format allowed the modeling of each bend and the sweeping of the tubes to simulate tubing dimensions. The Colin Model was used to test the SAE Baja requirements of driver spacing in the chassis at this point as shown in Figure 15.

Figure 15: The 3D point frame finally had bends added. The Colin Model head and body spacing fit the requirements.

The next set of decisions came from the choice of frontal fore-aft bracing (FFAB) or rear fore-aft bracing (RFAB) as showing in Figure 16. RFAB was chosen due to its reduced weight for a similar

17

torsional stiffness in the frame. This decision aligned with the team speed objective. Also, at this time, the RHO members attaching to the RRH were angled out and bent in to the RRH attachment points. This decision allowed from more room to fit the SAE Baja driver spacing requirements in the chassis. Also, the bends assisted the ergonomics of the visual appeal.

Figure 16: The two RFAB pieces (right) along the floor of the frame saved a few lbs of weight compared to the long pieces coming down from the RHO in the front. The RHO members in the right photo are

angled out and then bent in to fit into the top of the RRH.

After the curved front had been designed, it was decided to implement a nose design in the frame for ergonomics. The nose would make the Baja look more like an actual car. A few versions were modeled before the box nose was chosen as shown in Figure 17. The side impact members were modified to join at same spot as the nose pieces to prevent bending moments and improve the look of the frame.

18

Figure 17: The left nose was the first design for a nose. It was determined that it would be weaker than a full length of bent tube. The right nose design was then chosen. However, due to spacing

problems with the steering and a conflict with the rules requirements, the bottom nose design was finally chosen and implemented.

With the main roll cage designed, the rest of the CAD model was focused on fitting in the secondary pieces: the upper a-arm mounts, the three link mounts, the front hitch bar, the fuel tank mounts, the engine mounts, and the under seat members. All the pieces of the frame were finalized as shown in Figure 18. All the other designed sections were added in for the model of the complete Baja.

19

Figure 18: The completed model of the frame (top) was fitted with the other design models to complete the Baja model (bottom).

20

Finite Element Analysis

The main objective in FEA was to correctly model the suspensions and their attachments to the frame. If the suspensions were modeled correctly, then the stresses transferred to the frame can be assumed to be correctly modeled. To achieve proper suspension modeling, the suspension systems had to be modeled with a large degree of accuracy due to their complex geometries as shown in Figure 19.

Figure 19: The improper stress distribution (left) was caused to improper geometry and lack of modeled tabs. Bending moments out of the released rotational axes were causing residual stresses to appear.

Proper stress distribution (right) was due to tab and bushing modeling. The bushing end releases allowed for the correct 1 plane rotational motion of the front suspension.

Finite Element Analysis was separated into two different types of failure modules: impact and fatigue failure. Each needed to be tested in FEA to ensure integrity of the frame in the most common scenarios. The three main scenarios tested were front impact, maximum acceleration turn, and jumps. Testing of these scenarios ensured the durability of the frame in competition.

The front impact and maximum acceleration turn scenarios were impact, or immediate, failure modules. They were tested with a focus on the yield strength and ultimate strength of the tubing to see what parts would fail and how they would fail. The yield strength of 4130 Chrome Moly was 63 ksi; the ultimate strength was 97 ksi.

In the front impact scenario, the frame would yield in any moderate to high speed direct impact with the nose. The key to the simulation was to ensure that the chassis would not collapse on the driver. The model was transferred into Autodesk Simulation Mechanical and tested under the scenario as shown in Figure 20. The simulation showed that the frame would keep the driver safe under an extreme top speed collision with a .1 second deceleration.

21

Figure 20: At 20x displacement scale factor, the chassis was shown to deform outward, ensuring driver safety in the front impact scenario. The seatbelt lateral cross member and under seat member holding

the seat belts were shown to yield under the maximum and minimum stresses with a 230 lb driver.

In the maximum acceleration turn scenario, the frame was tested for stresses for a maximum speed turn at the minimum car turn radius. With an extreme scenario of 32 mph around an 8 ft turn radius, the simulation reported the results in Figure 21. Since the suspension systems had FEA performed individually, the stresses in the suspension members were ignored. The results showed that the frame sees only a stress of 40 ksi in its members except in the mounting points for the tabs as shown in Figure 22.

22

Figure 21: The simulated turn showed acceptable results with the stresses in the main parts of the frame below the yield stress.

Figure 22: The hot spots along the suspension mounting points were due to modeling. The tabs were not modeled for yielding. In this scenario, the tabs would yield before the frame members,

relieving the large stresses shown at the mounting points. Stresses are likely below 40 ksi at these points.

23

For fatigue failure, a bump or jump simulation was utilized. During the dynamic events at the SAE Baja competition, the Baja had to hit many large obstacles. Over time, these loadings accumulate like cyclical loadings in a fatigue failure test. Assuming an extreme scenario of a 5g drop with a 230 lb driver, the frame was tested for stresses over the endurance limit of 40 ksi as shown by Figure 23. The frame did not see stresses over 30 ksi as shown by Figure 24.

Figure 23: The worst case endurance limit for 4130 at room temperature was about 40 ksi. Reference: ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys

24

Figure 24: The most stress was seen along the mounting points of the springs and suspension pieces. The maximum stress did not hit the endurance limit of 40 ksi.

Suggested Improvements

After completion of the design project, a few areas of improvement were found for future Baja teams. First, the side nose members could be made parallel with the centerline of the frame. With a straight sided nose, the springs for the front suspension could be moved up on the nose, allowing simpler suspension geometry. Second, the side bracing members could be removed. Side impacts were unlikely in the SAE Baja Competition due to the wheels of the Baja cars. The reduced weight could help with speed and acceleration. Third, the top of the RHO connected with the RRH should be straightened. The judges at the competition did not support any bends in the RHO members. Fourth, the engine can be moved to the floor of the rear, and the transmission can be moved lower. The lower engine would lower the COG of the vehicle. The lower transmission would allow for better droop in the rear suspension. Finally, the top members of the rear should be reduced to .035 thickness tubing. They did not see much stress and would be at small risk of failing in any scenario.