79pmooney

Re: that repaired Peugeot (and having zero to do with this thread) - that was my second bike to ever get a name. (My moniker, the 1979 Peter Mooney is named Pete. Not for the builder, my brother or uncle, all known as Peter. Was JRA year two and realized this bike I was riding had that name. Why? I'll never know. It's stuck. Next paint job he will finally wear his name.)

The Peugeot has the name Jessica. (The custom it inspired has been Jessica J since inception.) When I picked up the Peugeot frame at the coop's "as is" sale for $20, I knew if it was rideable that it would wear "Team Dumpster" in block letters on the downtube as it was a given that if I didn't take that frame home, it was going in the coop recycled steel dumpster that night. Threw parts I had on it plus ~$80 for a fork, French seatpost, 1/8" chainring, brakes ... First ride, wow! Fun I hadn't seen since my race bike 30 years before. Week two, saw the cracks. A couple of months later I listened to a recovered drug addict tell her story, talking about expecting many mornings to be found in a dumpster for the people she had crossed. That's it! Team Dumpster is named her name, Jessica! When Jessica got a paint job, her name went on the top tube (near the seat tube over the dent!). Six years later, it was a given the the bike she inspired would wear her name. So, Jessica J. She now wears that on her right (painted steel) fork blade. (The small lettering of the decal just wouldn't stay undamaged on the bare ti top tube.) White script on a fire engine red fork.

jadocs

I'm no engineer (so take that for what it's worth), but great job on that repair...aluminum bike, fiberglass and carbon overlapped.....I bet it holds up just fine.

Yellowlab

I took the bike on a 30 mile ride today with a buddy and absolutely hammered on it. I kept a watchful eye on the repaired top tube but I wasn't gentle. I'm not entirely positive what exactly would translate to the most stress on the top tube but I put all I had into uphill bursts, hilly, winding, undulating roads with some pretty quick downhill slopes. Some rougher patches with larger cracks, potholes, etc. We even did some gravel. (We're in New England, so.....) The repaired top tube took everything I could throw at it. The bike felt great, even confidence inspiring. During and after the ride, while inspecting the repair, there were no visible signs of separation or peeling or cracking or anything. I know this was just a small, first initial test and the real test will be what shape it is in after 1000 miles but for now I feel pretty good that it's going to safely hold for some time to come.

Also, as an added safety precaution I decided that rather than paint the top tube black, I'm just going to spray it clear for now. That will enable me to still be able to visually inspect it as time goes by so I can see any early signs of failure. The clear will also still protect it from the elements so win-win. Thanks again to everyone for sharing your opinions and thanks also to those of you with experience working with these materials taking a minute to give me some confidence in the integrity of the repair. I really appreciate the feedback I got!

Thank you!
Cliff

CargoDane

"Hammering it", even.

Remember that there will be galvanic corrosion (of the aluminium) under there where it is in contact with the carbon. I'd not be "hammering it" for years.

My emphasis:

https://www.corrosionpedia.com/galva...olymers/2/1556

Wrapped up in carbon, you can definitely say that the alu is experiencing an "oxygen reduction".
Just remember that this is not a permanent fix by any means, regardless of how much you're "hammering it".

Yellowlab

Sounds like somebody didn't read the entire OP. There is a layer of fiberglass between the aluminium and carbon fiber for that exact reason. To eliminate galvanic corrosion. I really hammered it on there.

CargoDane

Well, for some reason, I missed that part.

Darth Lefty 

Very good work, I think. You probably could have just gone with fiberglass. The only improvements I can think of would be to use uni, and maybe try to be more clever with the tapering (like lugs), but there’s enough material there.

Yellowlab

Thank you Darth Lefty! Ive never heard of UNI and a Google search brings up a million things I am sure you aren't referring to. Can you help me out a little more with that one please?

Thanks again for kind compliments!

Darth Lefty 

Unidirectional, instead of weave. But it’s not like you’re doing it over...

Koyote

If it's just a trainer bike, I think it's fine.

Sonofamechanic 

So many opinions!! . I offer this only as a thought—since the top tube is mostly about compression, do you think it would have helped to “pull out” the dent where possible before the patch was put in? Despite the gash, it looks like your tube maintained almost 2/3rds of its circumference intact and (purely guessing from your pics) pulling out the dent might have improved that to 3/4ths? The carbon fiber patch will certainly stiffen the tube from bending/buckling at that (laterally) weakened point.....but it really wont help with compression specifically, right? Just trying to think this thru. If that is the case, your bi-directional fiber was the best choice and your excessive wrapping over a good portion of the tube was spot on.

Yellowlab

You got that right, sooo many opinions . Fortunately the bad responses are expected so it's easy to ignore them. However, whether or not I did the repair correctly, I most like reading feedback like this where intelligible thought has gone into the response rather than just being a clown and telling me I'm riding a death trap with no meaningful hypothesis as to why. My biggest consolation in this thread is that the people that seem to actually have experience with this type of thing have been the biggest advocates for the quality of the repair.

That being said, you just got me to google "bike frame compression" and I take it to mean that if I were strong enough, I could grab the top tube in my hand and squeeze it so that it would mis-shape a bit to take the load and then bounce back to it's original form? If that is the case then you could very well be right, there may be some benefit to pulling as much of the dent out as possible before placing a rigid material in the hole that basically has no compression.

And while I'm only just trying to wrap my head around what you are saying, it seems to initially make sense to me that if I am compromsing the ability of the tube to compress, then it would be prudent to have overkill with the carbon fiber in both depth over the damaged area but also in overall length in the top tube to compensate since the carbon fiber is bad at compression but very laterally strong. And it would then also make even more sense to taper the carbon fiber at the ends so as to create a better "handshake" between the compression of the aluminum in the top tube and the rigidity of the carbon fiber?

I think I may understand what you are saying or I may have butchered that lol. Either way, thank you for your response, I am learning because of it.

CargoDane

No, it's in "compression" because if without it, the other points it contacts (head tube and seat tube) would go together. They would be (com-) pressed together. It is stopping that force.
This is the reason you can make a bike with a wired downtube, but need a stiff toptube to resist those compressive forces:

Sonofamechanic 

Like that....but in terms of inline compression on the tube ...you stomp down (“hammer” in your words ) on the pedals and really the top tube (in the bigger picture) is just keeping the steerer tube and seat tube from from collapsing in on each other—so the top tube is being “compressed” between the steerer tube and seat tube. (Like when you stand on top of a soda-pop can to crush it.) As long as that top tube stays straight and doesn’t buckle (which is really what your patch is essentially solving for) then the tube can handle the compression—like a pillar holding up a roof beam. ...Anyway...I agree its great to think thru these things...thanks for bringing this to the forum!

Sonofamechanic 

LOL...what CargoDane said...exactly. (We must have posted simultaneously)

Yellowlab

Ahhhhh ok! I get it now. Well if that's the case then I would think that the repair should be plenty capable of handling the compression between the steerer tube and seat tube? Even when I am hammering on it? Especially given the length of the repair and the strength of the carbon fiber, in particular the thickness of it right over the damaged area? If that is the only / main force the repair has to deal with, in light of what I feel is a very structurally sound repair, why would anyone have any real objections or complaints?

I'm now mentally using your analogy of a pillar holding up a roof beam. If you took a typical cylindrical steel beam that you would find in many basements or industrial buildings, and that beam was dented or had damage in the middle, I would think one could weld a properly sized collar over the damaged area and it would be structurally as sound as before if not more so? Provided the welding was done properly? In this case the welding would be analogous to the epoxy and resins used for this particular repair?

Thanks for sticking with me through this, it is a great help!

CargoDane

Although I think the repair is strong enough because you have a lot of of CF, CF as a material isn't really that good in compression (fibres crack).

Yellowlab

Ok, so it's more the properties of carbon fiber having a propensity to crack under pressure. That I can understand. So basically just the sheer volume of carbon fiber is what will hopefully prevent it from cracking under pressure. Kind of like a sheet of paper won't stop a bullet but a phone book will.

CargoDane

Yes, and remember you also have fibre glass underneath, which is fine in compression.

Yellowlab

That's true and like Sonofamechanic pointed out there are still 2/3 of the top tube intact.

A question though. Now that I think about it, if Carbon fiber is so bad at handling compression, how are manufacturers able to so successfully and safely use it for entire top tubes in full carbon bikes? I have a Trek Emonda with the 700 OCLV (Optimum Carbon Low something or other) and that bike is light as all get out. It feels like the carbon fiber is super thin. Thoughts?

CargoDane

Prepreg CF and big ovens for curing, as well as only the bare minimum of epoxy in the layup. Also "vacuum bagging".

Hang on, I will show you a picture of something in my next post. 10-15 minutes max.

CargoDane

Wet layup (I don't know if it was vacuum bagged, but suspect so):




Autoclaved (cured in hot oven) prepreg (preimpregnated) carbon fibre:




By using prepreg (and to a lesser extent vacuum bagging), you can get the fibres to lay closer to each other, resulting in a more dense piece of material, yelding a stronger end-result.

The foot is a little dusty, because it is the part you put into a actual foot-shapped rubber/plastic thing so you can wear normal shoes: dust tends to settle there (I removed the plastic to take the photo.

Yellowlab

Huh, that is pretty crazy looking. Looks more like a prosthetic limb. What is that for anyway?

'm assuming preimpregnated means with epoxy? I didn't have a vacuum so I was only able to use the shrink tape and I obviously don't have a frame oven but I did put space heaters on it while the carbon was curing over night so that is something I guess.

That looks pretty awesome, way beyond my skillset. Thanks for sharing the pics and for the great explanation.

CargoDane

It is my left lower leg. So, yes, a prosthetic limb.


Yes. although in theory it could be, say, themoplastic.

The oven-cured epoxy is a special kind of epoxy that doesn't cure at room temperature, which means you can impregnate the cloth and transport it around, and only when laid up (and vacuum bagged to remove voids) do you autoclave it. If you used heat (autoclave level heat) for the normal cure-at-room-temperature epoxy, you will ruin the bond.

At home setups doesn't lend itself to autoclaves. Besides, you don't want to heat up your alu frame, it might produce some interesting results making it weaker and softer, depending on the alu alloy.

Now that you know it's my actual leg, I have to make it clear that I did not do that myself. I had professionals do that for me. The foot (delivered through those professionals) is from a supplier that does nothing but that - i.e. he doesn't make the holster for the stump, only the foot itself. Another supplier does the titanium sockets etc. I also have a foot with a vastly different design, but that one wouldn't show you how dense you can make carbon fibre.

The thick part of the foot itself (that connects to the "ankle" with a huge bolt) is unidirectional carbon fibre, btw. The "z-part" of the foot (I call it a "cow's foot") is made from woven CF. The round part is made from dense cut up CF pieces, then vacuum bagged, then autoclaved. I believe the term the bike CF guys use is "forged carbon" (there is nothing "forged" about it).

Yellowlab

Wow, that's pretty wild! I didn't realize even the z shaped part was carbon fiber also. Makes sense though, I guess anyone with a prosthetic leg would not want a solid metal foot to pull around. I'm assuming where you are on a bike forum that the prosthetic leg still allows you to cycle? If so that's awesome, good for you.

As far as heating the alloy frame, fortunately I wasn't sure about the level when I put it on the bike frame so I kept it pretty tame. Partly because the bike has internal cable routing through the top tube and I did not want to melt the plastic casing of the cable so I'm sure I did not get the frame heated to the point of damaging the aluminum but I'm glad you told me for future reference. The heat was largly because the repair was curing overnight in a pretty chilly garage (around 50 degrees or so) and I knew I did not want to leave it that cold. Basically it was at such a temperature that I could grab the top tube with my hand and it felt very warm but not hot.

Do you think a fully fiberglass repair would have been more appropriate here given the nature of compression on the top tube?