A couple of months ago there was a topic on how to stiffen the frame in C3's, and I just wanted to update you on where I stand with the computer model I"m building. I've got the base frame made, I will be trying out some stiffening ideas pretty soon (i.e. backbone, x-braces, etc.). I'll keep you posted on my progress and any good ideas I come up with.



http://temp.corvetteforum.net/c3/greatwhite/

 

Will you be doing FEA on the model or is it just a way of visualizing. Also - did you use actual dimensions for the assembly?

Just curious as I do 3d modelling at work and enjoy all kinds of stuff like that - was even thinking about using 3d models to design my new exhaust - just a lot of work is all. :lol:

 

Put a six or eight point roll cage on it, it'll be plenty stiff then!

 

Yes, I intend to do a finite element analysis (FEA) on it. I am going to load it in both bending and torsion. Then I intend to add stiffeners and see how much reduction I get. Just FYI. I'm using shell elements - probably QUAD 8's.

As for the accuracy, well its a bit of a rough model; I took measurements of the frame while laying underneath the car so they're not perfect. Hopefully, they are close enough to get a decent comparison between stiffener designs.

 

Thanks Jason, I was hoping you hadn't forgotten about it. I look forward to seeing what you come up with. JIM

:party: :hurray: :party:

 

I have often wondered about mounting a C3 body on a C5 drivetrain, can you design that?
:D :cool:

 

Good project, Jason,
I'd like to see the effect of the frame stiffeners offered by Tom's differentials and by the recommendations from GM for prepping the C3 to race.

 

I have frame dimensions scanned out of a book if you wish them - between them and what you have done it might be of benefit

 

... and they are up on http://www.corvettefaq.com , also.

 

Jason,

What software package are you using to model the frame with. Also how do you plan on loading the frame in our FEA mode. Just curious. I spent a lot of time in college running analysis on tube chassis's for a Formula SAE race car and its various components. If you need any help let me know. I have access to pro/e, unigraphics, ideas, and autocad.

 

Neat stuff. Goes to show what a big forum of technical professionals can come up with

 

Looks good! To me that looks like Nastran / Patran model and one stress guy confirmed that quad8 is Nastran element... He also proposed that it might be better to use beam elements instead of quad8's. Also, do yuo have a mesh included to the model? Without the mesh the the accuracy is not very good...

I'm just a designer, so I don't know personally much about stress. This is just what our stress guy told me...

Your frame stiffening model looks anyway good! And I can't wait to see some results! Keep up the good work! :cheers:

 

There is an article, I think it was published by GM, that helps people stiffen the frame for racing. This may save you some time. I think I have a copy of it on my home computer HD. If I do I'll e-mail it to you.
John


[Modified by theandies, 11:07 AM 2/6/2003]

 

excellent work. keep us updated. i have no idea how much work and headache this stuff is or how to do it so this is why the forum is so benificial.

 

Really cool! Are you getting college credit for this or do you just have a lot of free time? :lol:

I haven't done finite analysis for almost 14 years. We had to create the elements indiviually and link them to each other . . . very time consuming and you always had a bust on one of your links. T o give you an idea how far this has come with the improvements in desktop computing power, one of the grad students I went to school with was studying rebar pull out strength in concrete based upon bar diameter, depth of embedment and most importantly, depth of the concrete pour and relation of the rebar in the pour vs the depth. After he got a model defined and told the appollo workstation (a bit faster than a 386) to run, it would run all night. Several times when he sifted through the data in the morning, he realized one or more of the links between elements was defined wrong.

Took me back to the memories school! Miss those days, but I'm glad I finally have some money! :yesnod:

 

Yes, It is a Patran / Nastran model I am working with. I dont have a element mesh on the model yet, but there will be at least 5 nodes across each surface to account for bending in the walls of the frame. That is actually one of the reasons why I am not doing the model with beams; the other is it just didn't seam to be very easy to build it correctly with beam elements. I like using them for tubing and simple structures (i.e. I-beams), but for sheet metal and plates I usually use 8-node shell elements (4 node elements give too stiff of a result unless you use a lot of them).

I agree GM's arctile is very good about how to stiffen these frames. In my model, I'm assuming the frame has been completely welded up as recommended in the article (i.e. no tack welds). Also, this model is too rough to even analyze these type of small details. It could if I had more "free time" :) , but I'm doing this model by staying over a few minutes at work each day so its proceeding but kind of slowly. :banghead:

I also, agree that a role cage is the best way to stiffen a chassis. I have one in my Cutlass that I drag race. You just can't beet the benefit of an all out role cage. However, this is a little design study I am doing to see if anything can be done beyond what GM recommends and not as drastic as a role cage. It's my weekend driver for cruising, just having fun with, and I'm also 6'2" & 240 lbs so there just isn't much room left in the poor car's interior for extra tubing.

I intend to add a back bone down the trany hump and some triangulated bracing maybe after this weekend. I need to get back under the car and figure out what I can actually make fit in the poor car first.

 

Hey Why don't you email that article to the corvettefaq.com guy and let him store
it up there for others to view...

 

Can somebody be so kind to send me a copy of the GM article?
my mail is pacha72@hotmail.com
Thanks

 

Great stuff. Are you strictly looking at the frame structure itself, or adding any of the bolt on stuff to your model as well? Specifically, the upper A-arm cross brace comes to mind as a known useful tool to reduce flex in the front cross-member/front suspension area. I would guess the rear 6-link would also help...

Hans

 

Hey Jason, I was just thinking about asking how the model was going. It's good to see you've made some progress. I will be very interested to see what the stress looks like. The other day I was jacking the car and noticed how the frame would flex as the weight was set down on its wheels. I could see the frame move about .125" (or more) relative to the inner fender well.