Potential Catastrophic Frame Failer Averted ….sort of.

e-beach

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So I was replacing the hall senor in my throttle again,…(the second time since October!!!) and I noticed that my aluminum frame was beginning to crack on the down tube just behind the head tube. The crack is on both sides of the down tube.

My guess is the welding will cost as much as a new frame so looks like I am in the market for a new frame and / or whole bike. …….DANG!!!!!!! :cry:

Just what I didn’t want to do during the cold month, build a new e-bike.

On the up side, at least I caught it before it cracked and I did a flying face plant at speed.

FrameCrack.JPG

:(
 
e-beach said:
So I was replacing the hall senor in my throttle again,…(the second time since October!!!) and I noticed that my aluminum frame was beginning to crack on the down tube just behind the head tube. The crack is on both sides of the down tube.

My guess is the welding will cost as much as a new frame so looks like I am in the market for a new frame and / or whole bike. …….DANG!!!!!!! :cry:

Just what I didn’t want to do during the cold month, build a new e-bike.

On the up side, at least I caught it before it cracked and I did a flying face plant at speed.

FrameCrack.JPG

:(

The first (e-)bike example of stuff I've seen with Al in other applications, that made me say: Choose wisely!
 
Well, that is not catastrophic failure. It is progressive, and with frequent inspection it could probably ride safe until the springtime.

Then, buy a good used DH frame while they are cheap in the winter, and transfer your components when nice days come.
 
craneplaneguy said:
That's spooky stuff, frankly I have never inspected my bikes for frame cracks like that, makes me think I ought to! Thanks for posting.

When riding the mountain trails fast and hard, we inspect everything everyday. That is basic safety. We check for very small cracks, on 2500$ frames that are lifetime guaranteed. After a few years, frames are well documented and we know those models that have damage history.

That is why I always recommend building poweful ebikes on good used DH frames a few years old, models that have a history of reliability.

It is not a matter of frame material. It is about design, pre-production testing, and manufacturing quality control procedures.
 
MadRhino said:
Well, that is not catastrophic failure. It is progressive, and with frequent inspection it could probably ride safe until the springtime.

Are you going to put his kids through college when he is gone? :roll: Seriously? Did you take out life insurance on him? :lol: Fix it or park it. No one should ever ride something that broken unless they were limping it home IMO. MR, you are one wild dude my friend.
 
I have been riding 50 MPH down nountain trails on frames that had that kind of cracks. So I must be wilder than you think.

This crack didn’t happen yesterday. It’s been growing slowly, and it will continue to grow slowly with every hit. On the side like that, it won’t break dramaticly, not until it does extend through the welded joint.

OK, it is a sh*t frame that is not worth fixing. Yet if it is inspected daily, it could be commuting on the street safely until the damage does reach the top of the down tube, or break through the welded joint. I would drill a hole to stop the crack, and check it often.

Let me bet that on his bike, there is a much more dangerous flaw right now, and it is not on the frame.
 
MadRhino said:
This crack didn’t happen yesterday. It’s been growing slowly, and it will continue to grow slowly with every hit. On the side like that, it won’t break dramaticly, not until it does extend through the welded joint.

Probably a discontinuous first weld, puddle welded over to disguise it; and/or no or poor heat treatment after.

And I wouldn't ride it. I saw the aftermath of a welded duralamin tube snapping suddenly when I was an apprentice. The local swimming pool had commissioned a set of shallow wide steps to allow disabled people to get in and out of the pool. The whole thing was made from duralamin so that it could be lifted in and out of the pool when not it use.

The handrails were formed from 2 1/4" tube. I don't remember the gauge, but fairly substantial. At the bottom ends where they attached to the side plates, the tube had been flattened and welded both sides and across the bottom.

A 6'+ 200+# male nurse was helping a 300# wheelchair user down the steps and they slipped and lent heavily on the rail. and it snapped clean both ends. It was less than two years old.

No heat treatment post welding; and the corrosive affects of chlorinated water; plus the work hardening of being manhandled in and out of the water meant that it snapped through the tube about 3/4" above the weld on either side where the heat from welding had changed the nature of the metal.

Aluminium work hardens, and does snap.

Wouldn't happen with steel.
 
Steel suffers hydrogen embrittlement, deep corrosion, and other critical failures issues that aluminum doesn't. Steel is a little easier to build into a reliable bike frame-- but that doesn't make every steel frame reliable, nor every aluminum frame unreliable.

For what it's worth, I'd take a five pound aluminum frame over a five pound steel frame every time for reliability. Three times as much bulk of metal offers a lot better odds of getting it right.
 
Chalo said:
Steel suffers hydrogen embrittlement,

So does Al; but only at higher temps. But HE is only a problem with hardened steel; and takes way longer than work hardening of Al, at normal temps.

deep corrosion,

Al and NaCl!


and other critical failures issues that aluminum doesn't.

?!

but that doesn't make every steel frame reliable, nor every aluminum frame unreliable.

Agreed.

For what it's worth, I'd take a five pound aluminum frame over a five pound steel frame every time for reliability.

Agreed. But I wouldn't use a 5 pound frame for ... well anything.

For TdF and other racing events they makes some sense, but then the seasons loads are distributed over a dozen or more frames for each racer; and they get an new suite of this years frames each year.

Using anything with so small a factor of safety for anything else is asking for trouble. The airline industry use 1.5; everyone else uses 2.5 to 5 to 10.


Three times as much bulk of metal offers a lot better odds of getting it right.

Hm. Trouble is you don't get 3 times the bulk with equal weight steel and Al. 3 times the material, but (as you recently stated yourself) you have to go big on diameter for stiffness, so wall thickness comes back down towards the steel. Throw in the hardening affect welding heat has on Al, and poor/non-existent heat treatment and you have fracture zones primed for action.

And once the fractures start, the movement they permit increases the rate of hardening geometrically. Look at the catastrophic failures in the comets.

I'm quite sure that Al frames can be made safe, but not to also satisfy the weight weenies desires.
 
A good frame is good in any material, and a crap frame can be made of any material too.

One need to be a fervent believer of steel, to think that a Chinese steel wallbike is safer than a 2000$ alu DH racing frame that had been designed to jump 50 ft.

Then, it doesnt mean that a cheap, or even a broken frame can’t be safe to ride consciously. Many mountain riders I know, are giving a broken frame a very hard last ride before sending it for guarantee replacement. After you broke a few, you can tell what it is still capable of.

You can be scared of the crack in your frame, but most likely you’ve been riding it like that for quite a while. I would be more scared of crappy fork and brakes.

Do yourself a favour, buy a good bike. Even if it is old and full of scuff and scratches, it will make a much better ride.
 
She's dead Jim.
This is giving me flashbacks........I've sheared the headtube off of two bikes. One from BADLY casing a jump, and the other snapped out of nowhere more than likely from a similar crack that I failed to inspect for (never again after that).
Ditch the frame and start anew.
 
MadRhino said:
One need to be a fervent believer of steel, to think that a Chinese steel wallbike is safer than a 2000$ alu DH racing frame that had been designed to jump 50 ft.

I don't want or need to jump 50 feet. Nor do I need 200mm of travel. Nor spend $2000 on a bike. And by the time the price of that DH racing frame -- that is totally unsuited to stable low speed commuting with panniers and all -- has dropped in price to the point I could afford it, it will likely have been thrown down so many rock strewn gullies, that the entire frame is work hardened to the point that its one good bang away from failure.

All the other components of my bike can be upgraded as the need arises.
 
All structural metals work harden; all of them fatigue. I've never put more miles or years on a bike than my 1991 Cannondale aluminum MTB (with all-aluminum fork to boot), which is still in fine shape. I think a steel frame would have to have been twice as heavy to have lasted as long. (But at twice as heavy, it still wouldn't result in a noticeably heavy bike.) I've cracked plenty of aluminum bikes, but I've bent at least as many steel bikes.

When I build a bike from tubes, I use steel. It's forgiving to design and easy to weld, and I don't have to heat treat after welding. But if I were doing commercial level production, I'd probably use aluminum. It can make a bike way stronger for the same weight, or way lighter for the same strength. Remember when the tubes get bigger, stresses get lower.
 
Chalo said:
All structural metals work harden; all of them fatigue.

One difference that steel has compared to aluminum, is that after repeated loads, aluminum will fatigue. Steel has an indefinite fatigue life, which means it has enough strength to withstand repeated load cycles, and hence, it lasts longer, or is preserved.

Chalo said:
I've never put more miles or years on a bike than my 1991 Cannondale aluminum MTB (with all-aluminum fork to boot), which is still in fine shape.

But how many times have you ridden it down a mountain, or up a river bed or jumped 50 ft?

When I buy second hand, the stronger, more well built the frame is known to be, the more likely it has be well used if not abused. I have simply no way to know.

Same can be said of steel, but I can buy (cheap) steel new. And the cheaper a steel frame is, the more likely it has been over-specified rather than tuned to lightest possible limits. Recalls and fixes cost money and there is no margin for that on cheap frames.

The rest of the components may be the lowest cost options with limited shelf life, but will Shimano risk their brand by marketing a derailleur --even their lowest cost model -- that is dangerous, rather than just adequate?
 
Buk___ said:
MadRhino said:
One need to be a fervent believer of steel, to think that a Chinese steel wallbike is safer than a 2000$ alu DH racing frame that had been designed to jump 50 ft.

I don't want or need to jump 50 feet. Nor do I need 200mm of travel. Nor spend $2000 on a bike. And by the time the price of that DH racing frame -- that is totally unsuited to stable low speed commuting with panniers and all -- has dropped in price to the point I could afford it, it will likely have been thrown down so many rock strewn gullies, that the entire frame is work hardened to the point that its one good bang away from failure.

All the other components of my bike can be upgraded as the need arises.

DH is a world where 7000$ bikes are sold 1000$ after a few years. It is also a world where most who try, soon realize that they don’t have the balls to play their skin and bones speeding down mountain trails. It is also a world of kids with rich parents, who value very little a bike that is sleeping in the garage in february.

I have bought 5 years old bikes that don’t have the wear of one single DH race, for the price of the fork that is on it.

Some DH racing frames a few years old, were overbuilt to survive huge drops and none of them ever been replaced on guarantee. They are making a better ride than cheap motorcycle frames 5 times their weight. Geometry can be set when you built it, and wheel size too for their BB clearance is huge.

Anyway. Your bike, your ride, your call. Nobody can force experience in your brain.
 
MadRhino said:
I have bought 5 years old bikes that don’t have the wear of one single DH race

How do you know? You ultrasound the frames and stanchions before you buy them?

Or just assume that because they are clean.

MadRhino said:
I have bought 5 years old bikes that don’t have the wear of one single DH race, for the price of the fork that is on it.

Those forks may have that value for you, to fit to a bike you intend to once again prove the size of your balls, but for the mostly metalled or hogged roads and tracks I ride, at that speed I ride them, they are simply expensive overkill, with the wrong geometry.

MadRhino said:
Some DH racing frames a few years old, were overbuilt to survive huge drops and none of them ever been replaced on guarantee. They are making a better ride than cheap motorcycle frames 5 times their weight.

Are we comparing with Harley Hardtails or the likes of KTM, Aprillia or Maico motocross machines here?

MadRhino said:
Geometry can be set when you built it, and wheel size too for their BB clearance is huge.

Both my wheels are 26" and both clear their frame members just fine.

To my knowledge the only way of changing the geometry of DH to something resembling that of a stable road frame, would be to put a smaller wheel on the front or a bigger one on the back to correct the head angle, but doing so would screw with every other critical design element -- rear suspension, BB height, seat tube angle etc.

Unless your suggesting doing a cut&shunt on your Al DH frames for road use?!

MadRhino said:
Anyway. Your bike, your ride, your call.

And yet ...

MadRhino said:
Nobody can force experience in your brain.

So true. And nor can they remove the 40 years of engineering experience already in there.

Not directly bike related; but general and specific engineering principles that apply in large part to the very simple and very pure engineering of bicycles.

Engineering principles that remain true whatever the field, and that aren't influenced by "it costs more so it must be better", or how many XXXs are in the product name.
 
Buk___ said:

That's not quite it. Steel has a fatigue threshold, which is to say that below a certain amount of stress, no fatigue cracking will occur. But every steel frame experiences forces above this threshold, if it is ridden. A frame would be annoyingly bulky and heavy if it were built to stay under its fatigue threshold all the time.

Correspondingly, because aluminum has a low density, it's easier to build in a way that lowers stresses enough to avoid low-cycle fatigue entirely, and moves high-cycle fatigue into the millions or billions of cycles range before failure. That's why we can have all-aluminum B-52s and airliners that are are several decades old and have been working all that time. Heck, there are still DC-3s running regular scheduled service, and that plane was built when metal fatigue was poorly understood. Few if any steel tube framed aircraft can claim that kind of longevity-- I'm guessing none, in terms of flying hours.
 
I will just assume that your 40 years of engineering had nothing to do with bikes.

A DH race does wear components very fast, and shuttles are scratching them all at the same plsces. When a 5 year old DH racing bike has all its original components, original wheels and no shuttle marks, it shure was never ridden in a DH race.

Cheap motorcycle frames are not anything having a name like Harley or Aprilla, KTM and such. One doesn’t need an engineering background to know that.

A fork you don’t need, can be sold on ES if it is a good one. It could also be mod and tuned for street riding, and will ride a decade of good service.

Ever heard of variable geometry and suspension tuning ? Basics are enough: variable angle headset, variable dropout height. Yet many DH racing frames offer even more options.

I should not have to explain those things to you, especially with your engineering background.

Why don’t you just say ‘alu is not for me thanks‘, instead of trying to prove with false or biased arguments that it can’t be used to make a good bike ?

I have a 2006 Demo 8 frame here, that was built as a 60 mph ebike 6 yrs ago and did ride over 30,000 miles of street and dirt. Guess what: it is ugly but doesn’t have a crack.

I have spent enough time trying to inform you. Take it or leave it.
 
Chalo said:
One difference that steel has compared to aluminum, is that after repeated loads, aluminum will fatigue. Steel has an indefinite fatigue life, which means it has enough strength to withstand repeated load cycles, and hence, it lasts longer, or is preserved.

That's not quite it. Steel has a fatigue threshold, which is to say that below a certain amount of stress, no fatigue cracking will occur. But every steel frame experiences forces above this threshold, if it is ridden. A frame would be annoyingly bulky and heavy if it were built to stay under its fatigue threshold all the time.

Sorry, but that interpretation does not gel with the engineering principles for steel and Al that I practiced for 40 years.


Chalo said:
Correspondingly, because aluminum has a low density, it's easier to build in a way that lowers stresses enough to avoid low-cycle fatigue entirely, and moves high-cycle fatigue into the millions or billions of cycles range before failure. That's why we can have all-aluminum B-52s and airliners that are are several decades old and have been working all that time. Heck, there are still DC-3s running regular scheduled service, and that plane was built when metal fatigue was poorly understood. Few if any steel tube framed aircraft can claim that kind of longevity-- I'm guessing none, in terms of flying hours.

Guess away.

Do you realise that every commercial passenger and transport aircraft has a schedule of maintenance that in addition to per flight, daily, weekly, monthly/400 flying hours has extended inspections:

A-check: every 600 flying hours: 6 engineers and 12 hours. Includes all the checks performed above plus more.

2A-check: every 99 days. 3 shifts of 30 engineers per shift; All of the above plus more including " partial strip down of structure and engines for detailed inspections, replacement of worn components"

4A-check: every 190 days. 4 shifts of 30 engineers per shift. All of the above plus more including " Detailed inspections of flying controls, structure and engines."

C-check: Every 18 months. 6-7 days of 3 shifts and 30 engineers per shift. All of the above plus more including "Detailed inspection and repair of aircraft structure, engines, components, systems ".

C2-check: Every 3 years. 10-12 days; 3 shifts of 30. All of the above plus more.

D-check: After 8 years and the every 6 years. 25 days/3 shifts 30+. "Involves major structural inspections including attention to corrosion. Aircraft is virtually dismantled, repaired and rebuilt as required, with systems and parts tested and repaired or replaced as necessary. Opportunity taken to carry out major modifications as required Corrosion prevention and control tasks carried out."

Around 20 years ago I was contracted to KLM at Schipol Airport. After working straight through a long weekend fighting and finally putting out fires on the systems; I and 4 others were rewarded with a guided tour around under and through a 747 heavy "in the green"*; undergoing its D schedule.

*So called because of the green color of the anti-corrosion coating on the entire internal Al structure of the plane; As we walked through the body -- you cannot believe how huge they are internally when all the seats, internal paneling and insulation, windows, headliners et al has been removed -- there were entire chunks 3 or more meters wide and high of missing paneling in the sides and roof prior to total replacement.

Every single pop rivet and its holes in both the external skin and the internals spars are ultrasound tested. If any of the hundreds of rivet holes around each panel shows signs of fatigue hardening, the entire panel is replaced. If the corresponding spar hole also shows any of the same signs, it (and all the other panels that attach to it) are replaced. The attention to detail, along with the logistics, work rates and time pressures are mind boggling.

The particular jumbo I walk through was having it second D check (14 years), and over 30% of the skin, 12% of the spar structure and all 4 engines were being replaced. When you read that a plane flew commercial service for 40 years, less than 20% of what left the factory is still original. That's mostly the landing gear (steel or titanium), wiring, flap actuator mechanisms (steel) etc.

Pretty much every scrap of aluminium in the plane will have been replaced at least once, and much of it more than once. Aluminium is used in planes because of its low density; no other reason.

Which is why Boeing and Airbus are moving to replacing it with CF composites as fast as they can. Its not that much lighter or stronger; and its far more expensive to construct, but its fatigue life is so much greater that is doesn't need to be replaced. It is projected that the carbon fibre wings on the A350 XWB with last the entire 30+ years service life of the aircraft.
 
Buk___ said:
Aluminium work hardens, and does snap.

Wouldn't happen with steel.

In case your are unconvinced by the other posts, you might want to read this article and the tests that were done. Steel frames were the worst of the bunch. But that's not to say that steel is bad. It isn't. In fact, it can be quite good. The point is that it all comes down to the design and how the design is implemented.

https://www.sheldonbrown.com/rinard/frame_fatigue_test.htm
 
MadRhino said:
I will just assume that your 40 years of engineering had nothing to do with bikes.

That's like assuming a Michelin starred chef couldn't operate a barbeque.

MadRhino said:
I have spent enough time trying to inform you. Take it or leave it.

Inform me of what? And who asked you to do so? Cos it wasn't me!

Weren't you the one advocating the OP should continue to ride his bike when the most highly stressed area on the frame is 2/3rd of the way cracked through from side to side?

I'm sorry, you may build spectacularly powerful e-bikes that can climb mountains; and have the big hairy balls enough to ride them back down at stupid speeds; but if that advice is an example of your engineering nounce ... please refrain from offering it. To me at least, I'll let others make up their own minds.
 
wturber said:
In case your are unconvinced by the other posts, you might want to read this article and the tests that were done.

TOUR entered eight light frames weighing between 1,200 and 1,500 grams in the running.

Stupidly light frames. Steel trying to compete on weight. Predictable.

My frame is probably 5 times that weight; probably 3 times less finely stressed under normal cycling loads; and would probably pass that test just fine.

In this way, conditions of pedaling out of the saddle which impose the greatest loading on the frame are simulated. Two pneumatic cylinders alternately apply the pedaling forces to the cranks at an angle of 7.5 degrees (corresponding to the leaning of the bicycle when pedaling out of the saddle), and a lever mechanism conveys chain tension to the rear of the frame. The cranks are at a 45 degree angle below the horizontal, the angle where the cyclist applies the greatest force. Alternating between sides, first 100,000 cycles at 1200 N, then another 100,000 at 1,300 N are applied.

Do you regularly exert 1300N forces to your pedals, whilst cranking the bike over at 7.5 deg to the direction of the force? I don't.
 
Buk___ said:

That's not exactly correct. Steel only has an indefinite fatigue life if stresses are limited to less than its fatigue strength. And yes, aluminum has no such fatigue limit. But aluminum components can be designed to have such a long fatigue life that it is doesn't matter practically.

Take a gander at the stress tests done on the bicycle frame in my previous post. The steel bikes performed the worst. The bottom line is that the best we laypersons can go by is the track record of particular frames from particular companies - or possibly by choosing designs made for particular purposes. Picking by material for durability is putting on blinders.
 
Buk___ said:
wturber said:
In case your are unconvinced by the other posts, you might want to read this article and the tests that were done.

TOUR entered eight light frames weighing between 1,200 and 1,500 grams in the running.

Stupidly light frames. Steel trying to compete on weight. Predictable.

Not stupid at all. First, the steel frames were heavier than 1,500 grams. They don't compete in the tested category. They were included because they felt the need to include some steel examples. Secondly, those steel frames typically work quite well for their intended use. But you might want to think twice about putting a 3000 watt electric motor on one.

And designing for light weight is exactly why aluminum aircraft frames have the inspection requirements you needlessly described in some detail. You could probably build an aircraft out of aluminum that wouldn't need that kind of inspection. But it would be a very heavy and impractical aircraft. But clearly, aluminum bicycle frames don't have to be built with those extremes of lightness in mind and can clearly be made to be quite durable and robust.

Buk___ said:
My frame is probably 5 times that weight; probably 3 times less finely stressed under normal cycling loads; and would probably pass that test just fine.

A light, high quality road frame comes in at around 4 lbs from what I recall. If your bike frame weighs 20 lbs, then sure, if well built that should last indefinitely. But it is also well outside the normal or even heavy duty range of bike frames that I thought we were discussing here.
 
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