Aluminum to steel

[Lash]

Has any teams got any recommendations for composites that will safely bond aluminum to steel? What other processes have other teams used to attach their shear plate to the bottom of the chassis? WE used rivets last year, seems like a lot of drilling!! Any suggestions would be great!

[Lash]

Has any teams got any recommendations for composites that will safely bond aluminum to steel? What other processes have other teams used to attach their shear plate to the bottom of the chassis? WE used rivets last year, seems like a lot of drilling!! Any suggestions would be great!

[Cement Legs]

Shear plate?

[Lash]

Shear Plate...the piece of metal that seperates the open chassis from the ground. Its in the rules. Maybe I'm calling it something different....

[Agent4573]

most people refer to it as a seatbottom. We just use rivets.

[DJHache]

We're probably going to go with marine glue. I think it's called Marinetex.

[BStoney]

Dzus clips will work well depending on what shape and construction your undertray is. Then it's also easily removable to get all the pebbles and other dirt that builds up on the undertray after racing.

My .02

[Cement Legs]

Hose clamps will also work if you fab your undertray with notches for them...

[Foote]

as everyone else has already said, fasteners are probably a pretty good idea. Unless you curve your around your tubes, you'd be loading a glue or composite in peel (which is a really bad idea). We've got a really old car around the shop with body panels rivetted to the steel tubes, it seems like a pretty efficient way of eliminating all stiffness of a steel tube.
If you are bonding the joint correctly, you can expect pretty good performance.
James has a picture of testing our a-arm inserts, made from tap threaded aluminum, bonded into a steel tube.
The steel tube necked down and failed befor the bond or the cut threads. I'd post it, but i can't find it on our server, and i can't upload it from home. Maybe James knows where it is.

[James Waltman]

Justin,
I keep that picture hidden here (http://dot.etec.wwu.edu/fsae/viking35adhesives.htm).
http://dot.etec.wwu.edu/fsae/images/A-arm%20test%203_jpg.jpg

For adhesive joints - shear is good and peel is bad.
A similar topic came up last year. (http://fsae.com/eve/forums/a/tpc/f/125607348/m/94310935211/r/94310935211#94310935211)

[Jeff The Pyro]

looks like your test piece fractured right at the boundary of the heat effected zone from he weld. you might see very different results if you normalized/heat treated the test piece after welding and before putting in the insert. or maybe you already did that? or maybe you are using mild alloy steel... just my 2 cents.

[Jeff The Pyro]

err... mild steel (mild alloy steel doesnt really make any sense)

[Travis Garrison]

Jeff,

Heat treat or not you can break the steel with a bonded joint pretty easily (6000 psi * area with the only real limit for this case being the thread strength)...but that wasn't the point of the test...

I guess you could say the experiment was a bust for actually testing bond strength...but we found out what we were looking for, that our technique for bonding the inserts wasn't smearing off too much epoxy, and that we were in fact getting good bonds

Edit: Jeff, just to clarify I'm 90% sure that the tube pictured was 4130...I think it was cut off the same stock as our a-arms...so no not mild steel.

DJHache, like Justin said, avoid the bonding unless you can setup something that eliminates most of the peel forces...and definetly use some high quality epoxy (loctite E120HP maybe?) I'm not familiar with the marine stuff you mentioned but it sounds like cheap hardware store epoxy, make sure you check the strength of it if you do go that route...

-Travis Garrison

[GTmule]

we're gonna use some rivits to help in peel, and E120HP (got it out of mcmaster, if you wanna find some easily).

[Jeff The Pyro]

gonna have to call you on the 6000psi after welds claim. Last year we calculated the max pullrod force to be right around 3000lbs in the front. The pullrods were made from .75 x .063 wall 4130 tubing, but being a first year team we ran out of time and never even got them heat treated. Anyways, i just ran the numbers through my calculator and found a cross sectional area of .071" squared for that tube... corresponding to a factor of safety of something like .15.

so either i'm a REALLY good welder... or maybe you missed a zero in that number. at any rate 4130 can be conservatively heat treated to over 120,000psi so i'm guessing welded joints can see close to 100ksi.

regardless... if the glue is stronger than the 4130 tube as welded... its probably plenty strong.

[Denny Trimble]

psi <> pounds

Travis is talking about the shear strength of the bonded joint, 6000 pounds per square inch of bond area.

Not 6000 pounds force on that sample.