Abstract: Go Kart Frame of square tubing design had questionable tube placement and section issues. The Finite Element Analysis (FEA) was chosen to maximize the strength of the frame in question and minimize weight.

Frame Under Consideration: Gamblighini Phi-Alpha 10 with no roll cage.

Loading Considerations:

- Twisting Load
- Bump Load

Weight of Frame: 300 lbs

Weight of person 200 lbs

Initial sectional properties: 1 x 1 inch .109 (12 GA) stepping down to .070 wall to see effects.

Material Properties: ASTM A-36: 36,000 psi yield

Introduction to Finite Element Analysis (FEA)

Finite Element Analysis (FEA) is a program that places many small “elements” on the model in question and then calculates the load effects on the element. The load effects are stress and strain. Stress being the amount of load the particular element can handle and strain, the amount of deflection the element will produce.

FEA can be conducted by hand using Matrix Math, however even then, high powered computers are needed to crank through the mathematical nightmare efficiently. FEA is a fantastic tool for crunching down the complex into the simple, instead of doing it all by hand, the computer can crunch through millions of calculations in a matter of minutes.

What we are looking to do on this frame is to maximize the strength and minimize the weight.

As an introduction, there are several ways to run the analysis on this frame:

-Solid Model
-Shell Model
-Truss Element Model

Solid Modeling

The solid model require high powered CAD software to begin with that draws the model in 3-D and as “real life” tube structures. The model will have many element, up towards the millions and would actually be very difficult to run even in a very high powered computer. So typically “mental gymnastics” has to be performed to reduce the model size and allow it to be computed without using so much computer brain power.

For those who are going the route of solid modeling, the ideal is to reduce the high stress areas into chunks that can be managed. If you are guessing as to what the frame is going to handle initially and have no idea where the stresses are going to show up, then the best route is to either cut the frame in half, reduce the number of elements, and reduce the amount of passes the computer must make to calculate.

For all those new to FEA, it uses high level math (ie Calculus on steroids) and actually is like shooting an arrow at a target. The first calculation is trying to get you into the general area of the bull’s-eye, the second calculation recalibrates and gets a lot closer. Subsequent passes get closer gradually. Typically two passes is enough to get a close answer.

So imagine the computer cranking through 100,000 equations all at one time. That is what FEA demands of a computer, if using solids.

Shell Modeling

The second method is shells. Shells take a tube and assume it to be as thin as paper (in its representation) then it slaps on to the cross section the thickness and the moment of inertia values (I). The nice thing about shells is that it uses less brain power and can actually give you an answer that is just as good as a solid model. The problems though are joining shells together. The assumption of the shell modeling software can be deceiving.

Example: A square tube welded to a square tube sideways. The intersection point is assumed to be completely welded across the whole boundary of the tube. You and I know that the tube only gets partial penetration, and the weld itself may or may not be large enough at the intersection. With that in mind, solids can yield a better result. If a higher result is needed, resort to solids at the higher stress sections.

Truss Modeling

The third method is the truss calculation method. This is the lowest HP solution of them all and yield good results as well. A truss model can be slapped together in about 10 minutes and results attained using a low powered computer. And to make things even better, a typical program can cost less than $1000.

The overall frame design has been introduced into the FEA software as a wireframe, and will be calculated using the truss method. So next time we will show how to put the go kart frame on a FEA program using truss modeling.

The Go Kart Guru is a Go Karting Design, Fabrication and Performance specialist. Topics ranging from Turbo Charged Go Karts to Wood Go Karts, the Go Kart Guru has something to say (that will help you!) about it. Visit http://GoKartGuru.com for more details.

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