gotdurt

So, I've read various threads here and on other forums regarding repairing metal frames with carbon fiber, and it seems there are a few knowledgeable people on this forum regarding the topic... my question isn't about repair, however; my question is about preventative reinforcement...

I have an aluminum full suspension frame that broke where the chain stays meet the main pivot yoke; the stays were replaced under warranty, but it took a while, and in the meantime I bought a different frame with the intention of selling the old one.

Unfortunately, I'm just not getting along with the new frame after a few months, and haven't sold the old one yet, so now I'm considering selling the new one and going back to the old frame... the only problem I have though, is that I've lost confidence in the old frame, even though the stays are new... since the warranty's up now, I was thinking about stripping the black paint to raw so I could more easily watch for cracks at the welds (I prefer the raw look anyway). But this got me thinking, what if I did a carbon fiber reinforcement at the "problem area"? Would this add any strength, enough to prevent future problems?

HerrKaLeun

your reinforced frame would only be as strong as the bond you can make between the Al and CF. And it would have to be properly engineered and the CF designed for the location (different weaving of the fibers etc.). There is probably a way, but to do it properly you would have to spend a lot of R&D money and have the tooling.

And you add weight, may then as well buy a steelframe.

You are better off just watching out if there are new cracks. if you don't trust the frame (manufacturer), better buy a different frame of similar geometry from a different brand.... but unless you have framign knowledge you won't be able to tell if that is any better. with name brand frames, I doubt this was more than a fluke. There aren't ton of people dying from broken frames.

RobotGuy

I’d just sell them both and get the frame you really want.

alcjphil

It would be better had you given specific information about the make and model of the bike in question. I had the same issue with my Commencal Super 4, I broke the chainstay section of the rear triangle. I bought a replacement and the new part was reinforced in the area where the original failed. A part that was replaced under warranty should not negate faith you had in the bike before. It is probable that you were not alone in this and that the replacement part was redesigned so as to eliminate future problems.

Andrew R Stewart 

Klein did somewhat the same back in the 1980s. Some of his frames had stays wrapped with a boron fiber tow. I've heard more then a few people in the know who suggested that the gains were mostly on the sales floor. Andy

gotdurt

That's actually what I did, but there's more to frames than just matching numbers in a chart. On paper they are almost the same (besides suspension design), but on the trail, they are different beasts.
I actually went with the new one due to the brand's stellar reputation for being, well, "Nukeproof", lol. The break may have been a fluke, but the drop that it failed on was one of the tamer, lower speed ones that I ride, and I was still injured (sprained wrist); I was lucky in that respect.

See above... unfortunately, I can't keep buying frames and selling them at a loss of hundreds, in search of the one that I "gel" best with... I've been mountain biking for 30 years, and the frame that broke was one of the best I've owned as far as ride and performance goes. This is also the first aluminum frame I've owned in so many years that has failed catastrophically, and without warning. It may have been due to Friday-afternoon welds, and it may have been a design flaw...

Regardless, it seems that if some can successfully repair cracked frames with CF, then it would be even better to do it pre-failure...

I'm keeping it mum until I decide whether or not to sell; lots of buyers google frames that they are looking at buying used. It's a small company, so it'll come up in a search. I have discussed it on brand and model-specific forums, and haven't found anyone yet with a similar experience. No redesign on this one; the replacement was 100% identical. The company has done redesigns on other models though, in problem areas.

70sSanO

I would think that it would be next to impossible to strengthen a welded area. I agree that it is probably a known issue and the manufacturer has either designed a fix or has moved on from that frame. Not unlike the early 90's Cannondale cantilever dropouts.

Build it, ride it, and look for a replacement of the same or something else you want.

Edit Added: Was typing when you posted your response. If new frame design is the same and it is not a well know issue, just ride it. Not every product made is perfect without a flaw. You may have just gotten a bad weld. It happens.

Then again, if it effects your riding get rid of it. If you are concerned on every drop, it will effect how you ride and that will be a worse outcome.

John

AnkleWork

Those frames are consumables. Ride (abuse) until failure, then replace. You just got lucky with the warranty.

Andrew R Stewart 

"That's actually what I did, but there's more to frames than just matching numbers in a chart. On paper they are almost the same (besides suspension design), but on the trail, they are different beasts."

"Regardless, it seems that if some can successfully repair cracked frames with CF, then it would be even better to do it pre-failure..." gotdurt


I would suggest that the OP hasn't read deeply enough into the "numbers", doesn't yet understand the "numbers" or has limited his search to brands that don't publish complete info. As a roadie who builds frames I know that what seems like little difference can add up to a significant difference on the road. Then add the complexities of suspension travel, wheel paths, damper design/tuning and such and those small differences grew even greater. This is why the industry has embraced demo days and bike park rentals, most consumers don't have the skill set to understand the designs and how they affect the ride. But this is a problem that we've brought on ourselves by how we buy.


I haven't heard of legit businesses that fix broken metal frames using carbon. Please educate me. Andy

fietsbob

Dual suspension MTB frames even more so .. IF aluminum alloy contains Zinc , 7000 series alloys do ,
a wrapping of carbon and that Zn content, is making it like a battery ..

a wrap of glass fiber between the Zn-Al & C, insulates a bit.

IF thinking of preemptive reinforcement before it breaks..











...

Kontact

Wrapping a metal part in carbon tow will make it stronger - especially if the wrap was tightly executed. That's how many Calfee's are built.


But if you wrap aluminum with carbon fiber you are creating a circuit for galvanic corrosion. So if you do want to do this, start with a layer of fiberglass as an insulator.


Personally, I would keep the bike warranty-able and ride it - unless the failure is likely to cause you to get hurt. The replaced part might be stronger than the original.

79pmooney

I had a sport ~'90 Peugeot I picked up very cheap, damaged from being hit by an SUV height bumper. Noticed two weeks onto riding that both chainstays were about to break behind the chainstay bridge. So I wrapped the BB, chainstays and bridge with carbon fiber and boat building epoxy. (I used to build fiberglass boats and have worked with epoxy many times.)

The repair worked. Held up 8000 miles. (I retired the frame for other reasons.) Turned that flexy Peugeot's BB to the stiffest Peugeot BB ever.

Carbon fiber and epoxy are not easy to work with. It would be well worth your time to make up a dummy and practice on it first.

Kontact has a point re: corrosion. You could brush paint some epoxy resin over the are you have stripped of paint for the repair and let it harden before you begin to seal off the aluminum and defeat the electrical current need for galvanic corrosion.

Ben

gotdurt

It appears you missed my point; there is much more to it than numbers in a chart, and the info that is typically available to the consumer... alloys, suspension design and the construction of a AM/enduro frame all have a huge impact on the performance and ride characteristics, and everyone has their methods and gimmicks, resulting in countless nuances. As I stated earlier, I've been mtb'ing for 30 years, and I also wrenched in shops during my college years, and have spent time on more bikes than I can count...

"I haven't heard of legit businesses that fix broken metal frames using carbon. Please educate me."

Me either, and I haven't seen anyone suggest that there was such a business...?

The bottom line is that I have finally stumbled upon a frame that works for me really well with minimal compromise, and I'm tired of playing musical bikes... so I'm exploring the possibility of preserving it.

Now, let's get back on topic...


These are useful, thought provoking posts that give me some direction for research; exactly what I'm looking for, thanks. I'm looking for carbon fiber knowledge, and it's compatibility with aluminum alloys in this application... specific experiences are equally valuable. I'm not saying I'm absolutely going to do it, but I'm an adventurous sort that is always open to exploring interesting options.

Kontact, the warranty expires this month, which is the reason I'm open to playing with it.

fietsbob

It was Direct from Craig Calfee i got the info , 7075 aluminum and 7005 are containing Zn 5.6% and 4.5%..
these alloys are the 7000 series ones I see used used in the bike biz...

Of the 6000 and other aluminum alloy ANSI standard groups, only 6253 , has 2% Zn..


Ref Machinery's handbook, 23rd edition..

...

fietsbob

By the way a method of getting out air bubbles in the resin , to make a solid composite, uses a vacuum pump & plastic bags..

CliffordK

Thanks,

I was wondering why some aluminum/CF junctions are a problem, and others aren't.

So, 6061 Al has about 0.25% Zinc Max, and 7075 has about 6% Zinc.

So, if the OP's bike uses 6061, he may be ok.

As far as wrapping, I'm having troubles visualizing the area of fault. For a traditional road bike, one could wrap the entire bottom bracket and chainstays... somewhat like a bamboo bike, and it should make a pretty strong joint, especially if one uses several layers of wrap.

On the other hand, for the suspension MTB, is there even room to get a good wrap, with adequate overlap on the ends? Perhaps a photo of a broken frame member or photo of the new member plus a mark where it failed would help.

I don't think preemptive wrapping would be a solution I'd choose, especially as it may obscure developing faults.

gotdurt

Thanks, this one is 7005.

More good stuff. I've watched countless videos on CF repair (haven't had the best luck with CF frames and components) and it seems tape is the most popular method for simple repairs, but I think I might play with a vacuum instead, first...

fietsbob

cracking the book, again,

6061, Si 0.6, Cu .28, Mg 1.0, Cr 0.2/ balance elemental Al, zero zinc.

7075 is the 5.6% Zn, 7005 the 4.5%.. (+ other elements)



so 7005 , the glass fiber cloth under the carbon my give you less galvanic activity..


....

CliffordK

So, based on what fietsbob has found, wrapping with carbon fiber could be worse than doing nothing. You might be able to isolate the two, but it may not be worth the risk.

If you choose to do the project, perhaps search for non-reactive fiber reinforcement.

The primary difference between carbon fiber and fiberglass is weight. How much of that stuff are you going to put on it?

You might also look at kevlar fiber. Perhaps it is less reactive than the carbon fiber. Plus it often comes in better colors.

Kontact

I don't know where this zinc stuff is coming from, but aluminum - all aluminum - is relatively anodic compared to cathodic materials like steel, ti and graphite. Add water and they form a circuit which moves electrons in a way that produces oxide in the anodic metal. So all aluminum alloys should be treated the same way.



The obvious solution is to use an insulator, and the less obvious solution is to just use all fiberglass instead of CF. It has more stiffness than Kevlar and is cheaper. (But you could do this with even cotton cloth [micarta] and it would strengthen the wrapped area.)

Regarding Andrew's comments, of course there is no business that fixes broken metal bikes by wrapping gunk around it - it's ugly, changes the way the bike is likely to ride and isn't really a repair as much as a stop gap. You could create such a business, but who are your customers?


Since this really isn't a very elegant solution we're talking about (due to the joys of less-than-lifetime warranties), you don't need vacuum pumps to do this. The easist way is using tow where the compression comes from how tightly you wrap it. Just secure the bitter end and wipe off the excess resin.

The other simple solution is wrap the composite section with a stretchy tape like electrical, pierce it with pin holes to let the resin flow out and leave it to cure. Slow cure epoxies are better.


The final product is not going to look very nice, unless you choose to sand it flat - which is a good way of getting really carcinogenic CF fibers and resin in your lungs. But the reinforcement will add structural strength to the wrapped area, and if that's all you need, go for it.


I'd be inclined to take the frame with it's newly warrantied parts and sell it. I would never really enjoy a bike with a CF booger on it.

AnkleWork

Considering the usage, in the end it won't matter. The frame will die in the same way as the previous one, long before corrosion might take effect. Neither can a band-aid be applied in such a manner as to take enough stress to extend the frame's life.

Required engineering: long bond lines and pre-tensioning are both needed to transfer stress to the fibers.

79pmooney

Another way is to make strips ahead of time from innertube. Wrap your repair in the innertube. It will squeeze both the air and a lot of resin out of the repair. (I put the first wrap on not so tight so I wouldn't pull the carbon fiber out of place, taping the clean and dry ends of the innertube to the frame beyond the repair. Then I did the same with a second wrap but tighter for the squeeze.)

Ben

79pmooney

I pushed the life of my Peugeot from maybe 2 weeks to several years and 8000 miles with my repair and have no reason to believe the repair isn't just as good now as when I put it on or that my repair is not stronger than the original bike. (Bike is retired now for other reasons.)

I had cracks around both chainstays. The left ran 1/3 of the way around. The right, 2/3. That frame was not long for this world.

Ben

AnkleWork

So your frame had already yielded, thus transferring stress to the patch was a foregone conclusion. Congratulations on producing an effective repair. How much jumping did you expose your bike to? How much bending stress was applied to your chainstays compared to the OP's?

Scabbing a patch over intact metal rarely does anything useful for the reasons stated.

Kontact

Many composite bike parts are made by wrapping metal with CF, notably forks. Why would it not work in this case?