914 Chassis Stiffness, want input on chassis stiffness measurements Options

[Curbandgutter]

I want to check the stiffness of the 914 chassis two ways: the flexural stiffness (as in measure the shock tower movement as you lift it from the middle), and the torsional stiffness ( measuring the shock tower movement as you lift three wheels).

Then I want to input a 914 chassis into a 3d structural software that I use. I will design a tube chassis and check the flexural and torsional stifness with different tubing and thickness layouts.

Then construct the tube chassis and compare the real world results.

I want input from others as to how they would go about doing this. Or maybe give me some pointers. Or maybe someone already knows the factory stiffness?

What do you think?

[Katmanken]

The 914 chassis is also pretty easy to model in sheet metal mode, particularly in the areas of worst torsional and flexural stiffness - which is under the doors.

Having modeled many things by hand and with FEA, I bet you get 90% there, Or, you can always measure the real thing with a jack and indicators which eliminates all the FEA guesses and gives real results.

Think about it. If you jack up one front wheel and measure for deflection at the rollbar, the torsional stiffness will be related to the point at where the front wheel moves up a little at a time until the chassis finally twists enough to move the rollbar torsionally. For flexural stiffness, jack it up in the front a little at a time and measure the point at which the front of the rollbar finally moves up.

[Curbandgutter]

Thanks for the suggestion. I have access to a 3D laser scanner that is used for surveying. I am planning on scanning the car to get the 3D surface. Drape a finite element grid on it with sheet metal elements like you said. Then I'll have a model to work with. I can then try different scenarios to see what works and what doesn't. Additionally modeling it this way will allow me to model the tubing/strut tower interface which will have some flex and will model the the way it would behave in real life. I've seen some tube frames done that I know will not work. I can always run one or two real world test as you mentioned and see if the results are in agreement with the model.

Then we can torsional stiffness bench race the modified 914 chassis with the supercars (IMG:style_emoticons/default/w00t.gif) (IMG:style_emoticons/default/w00t.gif) (IMG:style_emoticons/default/w00t.gif)