Composite anti-inrusion bar questions

[Rink]

Hi all,

I've designed a composite anti-intrusion bar that will go into a race car. The part is in the shape of an 'I" beam with the web horizontal and the caps facing the door skin and interior. The dimensions are: Bar length = 41cm, Cap widths 25mm, Web height = 70mm. The proposed web thickness is 12.7mm. The proposed construction (w/vacuum bagging) is two layers of carbon with core material for the web (12.7mm thick) and the inner cap (3.2mm thick) Outer cap bonds to the door skin.

My question are:

1) What core material is suggested? I have looked at end-grain balsa and H80 Divinycell Plain (density=80 kg/cu m). I'm leaning towards the Divinycell.

2) I have carbon fiber tape (5.7 oz./yd.?, Graphite Tape, 3K, 12.5 X 12.5) that I would like to use. Better choices?

3) What materials are suggested to beef up the compression load rating on the outer cap? Unidirectional fiber? Core material?

4) Estimates for beam stiffness and failure load?

Thanks for comments and suggestions.

Reinking

 

[Rink]

Correction-

The designed cap widths in my original post are 51mm (2") wide.

Reinking

 

[kognition]

Anti Intrusion bar? You mean like a side impact beam that comes into the door cavity and close to the door skin? Is this a part of your roll cage?

 

[berkshire]

Rink (Automotive)
How were you proposing to carry your loads through the shear web? Were you going to lay your plies at 45 Degrees to the axis of the beam? Unidirectional material in the caps will carry the load on the inner cap. Are you proposing to use the door skin to carry some of the compression load's, if you do not the most likely failure will be buckling of the fibers in the spar cap against the door skin. Followed by fiber breakage in tension on the inner cap. Unless of course you add additional plies of carbon fiber to the outer cap. One other item you may look at as a core material is Rohacell it is a little harder than the Conticell/Divinycell material. I have to add that a lot of what I say here is speculative because I do not know your actual loads, neither do I want to be responsible for calculating them.
B.E.

 

[Rink]

kognition,
Yes, like a side impact beam. Not part of roll cage.

berkshire,
Loads carried through hinge and latch mounting points. Yes, 45 deg to axis of beam. Beam will be bonded to CF x 2 and Kevlar skin w/3mm core. Re: actual loads- car weighs 1400 lbs. Top speed is only 80 MPH, average ~65 MPH. One car at a time autocross vehicle but some nearby obstacles.

All,
I certainly would not hold posters accountable for errors in failure analysis. I realize that large contribution to the strenth is in the construction and that's my responsibility. I can put the beam in a home-made 3-point test and find the stiffness. But I don't want to test to failure. I'd just like to know an approximate value or possible range of values, particularly at failure.

Thanks for the ideas so far, further comments welcome...

Rink

 

[Oceania]

Just for information, I used to work for a company building all composite bodied cars, and sponsored an Indy race version. We never had composite door bars, safety was paramount and we wouldn't put the driver at risk for the associated weight saving. I would suggest use a steel door bar and look else where for weight saving in non-critical areas or apply carbon to stiffen the chassis to help in road holding, you may gain in performance here.

 

[MechanicalChef]

Agreed. Use steel....add horsepower.