What Can Be Done With Structural Epoxy?

[Wrecked944]

I keep reading how Lotus is doing amazing things with structural epoxies. Supposedly, the whole Elise unibody is constructed with epoxy.

So here is a crazy question. Can these epoxies be used to bond dissimilar materials? For instance, can a fiberglass fender flare be attached to a galvanized steel chassis with this stuff? And if I had a floor pan made from carbon fiber, could I cut away the old and rusty floor pan and bond the c/f to the OEM steel?

[Shaun @ Tru6]

Originally posted by JanusCole

For instance, can a fiberglass fender flare be attached to a galvanized steel chassis with this stuff?

yes, this is what Gunnar Racing uses.

Originally posted by JanusCole

And if I had a floor pan made from carbon fiber, could I cut away the old and rusty floor pan and bond the c/f to the OEM steel?

Sorta. Steel is omnidirectionally strong while carbon fiber/glass fiber is unidirectional in nature, which is one reason for carbon mat triaxial weaves.

When bonding dissimilar materials together, you have all kinds of things to consider in determining if they will work together: coefficient of thermal expansion, various stress constants for each material, and conductivity... graphite and Al don't get along for example.

More to consider is that you would almost certainly need a structural foam/honeycomb center between two layers of carbon to achieve any kind of real torsional rigidity.

But there's certainly no reason not to try it!

[JeremyD]

yes and yes - but as Shaun said - one is unidirectional (see the strings in a racing sailboat sail)

And really the elise is a composite construction - aluminium and carbon fiber and fiberglass all glued together in a messy construction (the glue is orange urethane, you would think they would run a finger down the joint to try and clean up the glue line)

I have thought about replacing the floors in a long nose car with honeycomb and epoxy - it would stiffen it up nicely.

[Wrecked944]

Oooh, I like that idea...carbon fiber sheets (maybe with varying weaves) sandwiched around a honeycomb interior epoxied to the frame. Sexy.

The expansion rate thing sounds like a serious problem. I would think that folks like Gunnar would experience cracking over time with fiberglass flares epoxied to steel fenders as they expand and contract at different rates. Have they figured out a solution?

Shaun: Do you still have the link to that guy who wanted to bond c/f or something like that to his car? My memory on that one is toast.

[JeremyD]

Pretty sure GrantG has something similiar with his RS clone (and weighs around 1800lbs)

[Shaun @ Tru6]

Originally posted by JanusCole
Have they figured out a solution?

Shaun: Do you still have the link to that guy who wanted to bond c/f or something like that to his car? My memory on that one is toast.

flares aren't structural, so there's a lot of give and take. the epoxy they use is their solution at the end of the day. It's a good bridge beween two surfaces that are stress free. Oh to dream.

if you were to only drive your car over a certain temperature range, the thermal expansion wouldn't be an issue on structural mating. It's when you are putting stress and strain on bonded components outside of their temperately happy range that you will have issues.

consider that you have the yin and yang of surface area bondage. Lot's of surface area, good bonding, but lots of dimensional change between two mating surfaces. Little surface area, weak bond, but shrinkage/expansion would be less of an issue.

Obviously, Lotus and the likes have put in years and millions determining the best products, surface area, angles, etc.

I don't think I do Janus, but I'll look for the link.

[Wrecked944]

Originally posted by JeremyD
Pretty sure GrantG has something similiar with his RS clone (and weighs around 1800lbs)

...from GrantG's signature...

73 Carrera RS 2.7 Carbon Fiber Replica (1,890 lbs)

Whoah, I think I missed the build thread on THAT puppy...sweet...

[billyboy]

I bonded my fiberglass flares to the steel body with West Systems epoxy mixed with high density filler to make a thick glue consistancy . I have used epoxies many times on boat repairs. The steel was sandblasted first to near white metal and then cleaned with acetone to remove any trace of moisture. The flares were held on with screws until the epoxy went off. The steel is going to rip before that glue does.http://www.westsystem.com/ Here is what the website says about the filler #404 404 High-Density Filler
404 High-Density filler is a thickening additive developed for maximum physical properties in hardware bonding where high-cyclic loads are anticipated. It can also be used for filleting and gap filling where maximum strength is necessary. Color: off-white

[Jack Olsen]

I made my track wing out of $25 worth of aluminum and $50 worth of structural adhesive. It ain't pretty, but it holds together and it gets the job done.

[JeremyD]

yeah, if you haven't discovered the magical world of two part epoxies = you ain't living...

[Jeff Alton]

I have been using the West System stuff for years. It is great.

I think KevinP73 had a thread where he detailed bonding a flair onto a car....

Cheers

[Wavey]

We use several of this company's products:

http://www.lord.com/tabid/3383/Default.aspx

for aluminum fabrication in my sign shop. Incredible stuff. The 2-part glue tubes and the mixing tubes look exactly like Shaun's picture above. Neat little 2-plunger gun with different plungers for different mixes. We use it to fabricate sign cabinets from aluminum extrusions, and for bonding sheet aluminum faces to frames; stainless too. One benefit is there is no heat damage to the sheet metal surfaces.