Quote:
Originally Posted by lucid
If there is a thick relatively flat metal panel that is running through, that doesn't make sense to me from a structures and optimization perspective. It would be much more efficient to run thinner individual members across with the optimal cross section for the torsinal stiffness one is trying to increase. Regardless, it is clear that there is something structural running across behind the seats, and I did not expect it to make such a difference. It would still be useful to find out through which axis the data were taken though.
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Pure speculation on my behalf:
There are not too many possibilities for torsional testing of a chassis. I would bet that they either mount the chassis on the suspension mounting points with some rigid arms assembled so that they can not pivot relative to one another or simply use the shock tower mounts for the front of the car. Then opposing forces are probably used so it is a pure torque and no net force is applied. The angular measurement can then be across the front or rear shock or suspension mounting points.
You may also be able to use the 1st torsional mode shape frequency to get the stiffness. If you used a free-free mode shape the mounting issues may be totally removed from the picture.