Suspension

[A]

Hey hi guys,
Currently I am working on the analysis of uprights and hubs .I have some doubts related to constraints to be applied on model.I am doing this analysis in ansys 13 workbench.
For knuckle I have totally fixed the points connected to wish bones and tie rod and applied forces and moments on the knuckle centre and for hubs, I have applied cylindrical constraint at centre of hub (part between brake disc and wheel) keeping its tangential movement free and have fixed its motion in lateral direction.I would also like to know method to perform fatigue analysis in ansys. I tried finding it on internet and tutorials but could not get any clue.Your suggestions on them would be valuable for me.
I have some more doubts related to suspension.We are trying to find out K value for our springs.But we don't know what would be the best estimate for stiffness of tyre.Right now we have assumed it to be 212384 N/m.And I would also like to know the best software for doing kinematic and dynamic analysis of car ,We are using adams car but I am not able to get FSAE database for that. I downloaded it from their official website but its not really helping. Whether using ARB would be good idea for first year team or not???. We are trying to keep our a arms trailing in rear( not trailing arm geometry).Will it cause any problems???

Thank you, hope you will reply

[acedeuce802]

Do you have TTC data? It says the spring rates in there. I don't see why you can't add load to the hub, and measure the tire deflection to get a rough estimate.

Kinematic software is really up to you. It's all going to give you the same results, but some may be easier or harder to work with, and it's also a personal preference.

Adams seems to have very good customer support, so you should contact them. I know there's a representative on the forums here that's really helpful. I'm sure you can find him, and PM him.

Using an ARB is up to you. Based on your ride frequency, do you need more roll stiffness for your target roll gradient?

[Sormaz]

How do your wishbones attach to your upright? If they are welded to your upright then it sounds like these boundary conditions are correct.

If you use spherical bearings (or rod ends) you may consider freeing the rotational movement (does a spherical bearing constrain rotation?...)

Also, for your a-arms, Z movement should be free (only constrain x and y) for one of them, depending on if you use a pushrod or pullrod spring actuation

Think about how the physical part is held...If you unbolt an a-arm, what type of movement is the upright free to do? If you remove that same constraint in your model, does it behave similarly?

The other thing I do not understand is your cylindrical constraint. What is your rational for this? Perhaps I misread, but this is not making sense to me


FEA is a huge game of garbage in, garbage out. If you give it incorrect inputs it is going to give you an incorrect output. Too often it seems like people expect the computer to be smarter than them and doing all the work. "Well the upright is bolted here here and here so I just constrain those and hit go!"

The same level of detail is required in your load application


Regarding fatigue analysis......do you know how fatigue works? Try a materials textbook before looking for a tutorial and again expecting the computer to do your work... I'll even be nice and give you a hint "S-N Curve"

I am not saying that computer programs are not useful...in fact they are extremely so. But the point is that it is a tool and you must treat it as such. You do not simply place a drill on a part and expect your holes to magically form, and you do not start drilling randomly and expect the holes to go in the correct location. You understand how the tool works, what it is doing and how to use it and you are able to use the tool to get the correct finished result.
If your response to this is "but I know how it works and I know where the button is to create a mesh and solve the model" you have missed the point and I have wasted some time. The beer...well that has not gone to waste

[SteveHarasym]

As I don't have much expericnce with the FEA, can't help you much there, sorry pal.

As for the spring coefficient of the tire, as acedeuce said you can get it from tire data, or testing, but tire data is better because many variables may affect it (temp, pressure, wear, etc.)

I use WinGeo to analyze the suspension. It's simple and gets all of the important information to you. I'd like to get AdamsCar working properly, but to this point I've just messed around in there a bit.

As for the ARB, I would say to definitely design one and use it. If for nothing else than simply having one for design judging. It will come off odd if you don't have one I think, and you may lose points there. It also allows adjustability in your roll gradient and roll distribution front/rear. Anything you can tune is good, with adequate testing time.

For trailing rear A-Arms, if you just mean that they are directed rearward from the pickups, it is not a big deal, we have run this since forever and I'm sure other teams have too.