What will be the appropriate load and boundary conditions for motorcycle front frame?

[masterymw]

I am determined to find out the stress level at front frame of motorcycle in worst case scenario. I have prepare two model. One is MBD FLEX body model and another is FEA 1_D element model.


Geometry of Front Frame of motorcycle

MBD FLEX Model

MBD FLEX MODEL gif
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/video/upload/v1649136545/tips/mbd_gif_i640vs.mp4[/url]

FEA MODEL

From Flex MBD model, I came to know that maximum von misses stress are in the front frame's neck area. I have checked hot spot stress value. It is around 534 Mpa at neck area. I cannot trust this stress level blindly. So I decided to make FEA model using line element( I think line element is the best for this kind of geometry).But the problem is How do I apply constraints and loads in my model?. I have applied constraints in the head tube and loads in the suspension mount and swing-arm pivot points. I don't have much confidence in applying such B.C. What would be the accurate boundary condition in my case? Should I include inertial relief method for this ?

 

[ThomasH]

Hi
Is this some kind of school assignment or something you do out of personal interest? The reason I ask is because I expect a professional motorcycle designer would have that type of data. I suspect that the data should be based, at least to some extent, on test data.

Thomas

 

[masterymw]

It's just a personal interest. Not a professional motorcycle designer.

 

[FEA way]

Which software did you use for MBD analysis ? MSC Adams ? In such cases it's usually best to perform MBD simulation on rigid bodies and then import the loads from it to stress analysis, but it depends on the capabilities of particular software.

 

[masterymw]

Yes. I have used MSC adam for the Flex body MBD model and MSC Patran/Nastran for my FEA model. For my Fea model, I have imported the maximum load case but I have to apply constraints at some points in the FEA model and the problem is where and how so that it will be equivalent to my Adams model flex body stress analysis ( I don't know my mbd flex body model is accurate or not.) If you guys have any experience in this field ( motorcycle chassis analysis ), I need serious help.

Thank you!

 

[GregLocock]

So you identify all the forces at all the attachment points to the frame in ADAMS, and apply those to your FE model. There may of course be some steady state accelerations which you will have to prevent or simulate by any of the usual methods in FEA.

Cheers

Greg Locock


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[masterymw]

@GregLocock, Can you elaborate further what you mean?

 

[GregLocock]

No, because I've never done it.

Cheers

Greg Locock


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[NRP99]

I am not into motorcycle frame analysis so these are general comments.

IMO applying directional fixity/use of symmetry BC's instead of completely fixing things would be way to go since motorcycle is dynamic body moving in the space coordinates. For conservative calculation purpose, I am not sure though, you can apply fixity at some points like you applied at front. But then you would have to deal with peak stresses which I would guess you need to compare with actual test data and come to conclusion.

Have a look at "Fundamental of vehicle dynamics by Gillespie" for forces acting on vehicle and then may be you can translate that into required boundary conditions.

 

[GregLocock]

But that negates the advantage of using ADAMS to generate the required forces, which will of course be in equilibrium with the d'Alembert pseudo forces. I suppose you could restrain the rear with bcs and hope that the stresses at the front end aren't overmuch affected, but you'd need to be careful not to overconstrain it and provide artificial stiffening. Inertial relief is probably an appropriate technique.

Cheers

Greg Locock


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[ThomasH]

Hi
A possible solution might be to use the ADAMS forces. Then the frame should be in equilibrium. And Inertia relief should help in managing the the constraints.

I have never analyzed a motorcycle frame but I suspect that this model woult be made with shell elements. I think that would give a better description of the joints. But that is just me guessing .

Thomas

 

[masterymw]

You guys have any recommendation of article, tutorial, research paper or books related to motorcycle frame FEA analysis implementing inertia relief method, I would be very grateful. Its a hard time for me to do this kind of analysis without any test results and parameters.

Thank you!

 

[NRP99]

Search in FEA software help manual for example problems on inertia relief. There may not be direct examples of motorcycle frame analysis and if its there may not accessible without cost. I think motorcycle frame analysis or testing is proprietary information to be published in books or given as tutorial since this is of commercial interest. Search research papers available online to take a look and find relevant information.

Your best bet is to rely on the available information in research papers and engineering judgment. I think its sufficient for the personal interest analysis.