Best chassis frame rails bends or humps design to crumple in a crash?

[DasKleineWunder]

What the best design for it to absorb energy in a crash, pretty mucu like a crumple zone, while still having good torsional stiffness?

Something like this:

http://books.google.com.gt/books?id...BDge#v=onepage&q=car frame rails crash&f=true

On psge 128 where it says Example of a more crushable design.

What about a four tube chassis design.
Something like this

http://cs.scaleautomag.com/sca/modeling_subjects/f/31/t/115242.aspx

Would the triangulation in the front rails (the ones on the left side of the picture) hinder crumple-zone like deformation?

Has any spaceframe with straight frame rails been tested in a crash? Or at least a computer simulation?

tnx

 

[MikeHalloran]

In the photo you posted, the tube most likely to bend in a crash is the one that's already bent, at the base of the A-pillar.

You can use column theory to estimate how much load a straight tube will support before it buckles. ... but the reason why crumple zones don't comprise straight tubes is that once the tube column buckles, it takes relatively little additional energy to fold it to effectively zero length.

When the real car guys design crumple zones, they use rectangular tube with weak corners and corrugated walls, so a lot of energy is expended splitting the tube corners and compressing each of the corrugations so the result looks a little like ribbon candy.

Note also that street cars are engineered specifically to allow survival in particular crashes as modeled by standardized crash tests. They may not be the best thing to copy in an environment where the crashes are not standardized, as in racing.




Mike Halloran
Pembroke Pines, FL, USA

 

[DasKleineWunder]

Would drilling some holes in the corners of a square or rectangular tube frame rails help it crush in an impact?

Something like this

The frame rails/crumple zones have some holes, I guess they are to improve deformation, aren't they?

Do you have some links to some technical papers or studies on drilling such holes?

 

[GregLocock]

Mass production cars don't use holes (holes are expensive) instead they use darts in the corners of the box section. They work the same way.

The job of the engineer is to calculate the force/deflection profile after the beam has buckled. Nowadays it is done using LS Dyna, back in the day you worked out the fully plastic moment of each side of the box and used a work equeation.



Cheers

Greg Locock


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