HELP! General queries regarding Inventor CAD and FEA

I'm a mech engineering student and I have no experience whatsoever using any CAD. For a project I'm doing, I want to produce (or even better, have someone do it for me!) a 3D CAD model for a bicycle frame, and then test it against industry standards for fatigue life.

I need to some guidance on what the best way to go about this is. I gather Inventor can be used to produce the model, although I have downloaded and started playing with Inventor Pro 2013 Student Edition, and it's intimidating to say the least. Getting to grips with it and trying to produce a model is going to take a very very long time. I don't want to invest this time if

A) there is a better route

B) I can find someone to do it for me

The project is not about my personal ability to produce models, and this part of it is only going to be a time-sink/distraction from my actual aims.

Furthermore I gather that Inventor cannot do fatigue-life analysis, but Autodesk Simulation does? I'm thinking that perhaps I can use the stress outputs from Inventor's FEA modelling to then hand calculate fatigue life - it would probably be quicker than spending days and days struggling with yet another package I don't know how to use. Is this feasible?

I'm pretty much all at sea with this (computer) stuff, I haven't been taught it practically, and any suggestions on how to proceed are gratefully received (even if those suggestions are 'Use this other package which is simpler and quicker to get up and running on').

What FEA software have you used and what has been the complexity of the FEA models you created? Have you considered modeling the bike frame in the FEA package? How crude a model can you accept? Would constructing the model from beam elements be sufficient for your needs?

I have no experience at all with any FEA, but a friend of mine has used ANSYS as part of her studies. I don't think a model using beam elements would yield any results close enough to be useful.

I suppose my basic question really is how long will it take me as a complete beginner to become proficient enough to end up with a 3D model of a bicycle frame which includes accurate tube thicknesses and weldments? 100 hours? 200? 500? And whether Inventor (or ANSYS) will give me figures for stress that I can use to (hand) calc fatigue life. Or whether this is a step to far for a project (of which this is just one part) that I have 8 months to complete

Have a look at this http://www.cadtutor.net/forum/showthread.php?87550-sports-car-(with-details) yes it can be done with practice.

Dear setspeed,

A Finite Element Model (FEM) is typically composed of four components that are used to do a Finite Element Analysis (FEA). The model includes a description of the geometry of the part to be analyzed, the object’s material properties (primarily the modulus of elasticity), the loads to be applied to the model, and finally, how the part is restrained in space (i.e., how it is kept from completely moving). For FEA the precise geometry of the part is approximated by an array of elements. Beam elements are often used for structures. They are defined as a straight line, a moment of inertia value for the cross section of the beam and a point that defines the orientation of the cross section. Since bikes primarily use round tubing the orientation of the beam is not relevant as the moment of inertia of its cross section is the same for any axis.

With FEA program like ANSYS and SAP, the user is responsible for directly creating the FEA elements that will be used for the analysis. With CAD program like Inventor, the FEA mesh is automatically created and invisible to the user. The geometry building tools of ANSYS and SAP are weak but acceptable for simple models. It is possible I know to import FEA information from AutoCAD to SAP by using layers to define nodes, elements, loads, etc. but I do not think it is worth your time to go that route. I think it best to perform a simple finite element analysis using whatever program is available to you and compare the result to “hand” calculations. Use a problem that you may have had in your strength of materials course.

Using beam elements might be a good first step in learning the process of FEA. A bike frame is roughly a structure composed of beams. Determining material properties is straightforward. I would start with static loads applied at the area where the seat attaches to the frame. You will need to decide whether to include the front fork as part of the frame. I would start by including it but consider that it is fixed with respect to the frame. With this configuration you can constrain the model of the frame at the locations where the wheel axles contact the frame. How the model is restrained is often misunderstood and will take some practice and experience to do it correctly. Start by fixing the x,y, and z position of the rear axle, but not the x axis of the front axle (assuming that the x axis goes in the direction of the bike).

After you have gained some experience with a beam model you can look into creating a detailed model of one of the joints of the frame with Inventor. I would precisely model a single joint and a few inches of the tubing coming out of the joint. You can then apply the load information you gained from the beam model to define the load and restraint parameters for the joint analysis.

I think you should be able to get some reasonable results within your 8 month time frame if you have a hundred or more hours to devote to the analysis.

~lrm

Thanks for the information, Irm - very helpful

I agree with the comments above, If you are taking this project on with next to no experience then this may be a long winded task. The FEA inside Inventor has an easy enough learning curve but you need to understand the results. Good luck

I'm a mech engineering student and I have no experience whatsoever using any CAD.

How does any mech engineering program in the 21st century not have any CAD component. These tools have an entire engineering curriculum deep inside - expert systems. CAD is no longer just computer version of the drafting board from last century.

A) there is a better route

Change schools to a 21st century curriculum.

B) I can find someone to do it for me

I am sure you can, what is your budget for the project?

... it is only going to be a time-sink/distraction from my actual aims.

I'm pretty much all at sea with this (computer) stuff, I haven't been taught it practically, .

Well, you don't want my opinion on this....

Good luck!

This is only enough info to get you into trouble

http://au.autodesk.com/au-online/classes-on-demand/class-catalog/2014/inventor/md6583