Trek Domane frame failure

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Brucey
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Re: Trek Domane frame failure

Postby Brucey » 12 Aug 2019, 11:09pm

Image

Boeing 787 wing flex.

The wings on the plane above can be made more flexible than many others because they are made from carbon fibre. In normal flight the wing tips are elevated by 12ft. The most deflection is 26ft at the maximum design load. If you ever see aluminium wings moving this much, they are just about to (or have just) come off.

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tatanab
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Re: Trek Domane frame failure

Postby tatanab » 13 Aug 2019, 6:58am

Boeing chose not to test to destruction on the 787. They tested to 150% of maximum anticipated service load, giving the deflection shown. In 1995 the 777 WAS tested to destruction and it failed at 154%.

Samuel D
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Re: Trek Domane frame failure

Postby Samuel D » 13 Aug 2019, 8:20am

It surprises me that rim brake callipers fail so rarely that I haven’t heard of an incident. My BR-R650 callipers bent visibly when pulling the brake lever hard, and my current Campagnolo Super Record arms bend forward on hard application as the rim drags the pads forward. I guess this is only made viable by the low cycle count, but still.

I recall reading that the 747 wing fails at about 10 metres of tip deflection. And that’s made chiefly of aluminium. Clearly the maximum deflection depends on the geometry of the spars as well as their material, since that geometry defines the stress at a given tip deflection.

The 747 wing is a visibly floppy thing. I recall boarding a 747-400 with the wing-tip at a particular height in the cabin window and seeing it having risen greatly by the time we came to a stop at the other end, having burned something like a hundred tons of fuel from the wing tanks. However, aluminium aeroplanes are subjected to rigorous, enormously expensive checks from nose to tail at planned, conservative intervals. I understand that parts on them do fail often, but they’re caught before they kill anyone.

It’s still amazing the wing can flop around like that and yet maintain predictable aerodynamic performance so that things like stall speeds are meaningful. The engineering that goes into these things is remarkable.

A Trek Domane, on the other hand, is engineered and made with less care and rarely checked by the owner for cracks, because failure is seen as acceptable.

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Cugel
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Re: Trek Domane frame failure

Postby Cugel » 13 Aug 2019, 8:55am

pwa wrote:I would never trust anything that has aluminium alloy in an application that is meant to flex. It seems like a recipe for disaster. Aluminium for rigid things, fine, and all the flexy things in a material that can take flexing to the degree to be expected.


I also have two Specialized Tricross Comp bikes. These have an aluminium main frame triangle but flexy "zertz" bits in the seat stays, forks and seat pin. All of the flexy bits are made of carbon fibre. These bikes are now 10 and 11 years old, with no sign of fatigue (and I do look most carefully).

Specialized seems to have anticipated the possibility of the flexy bits fatiguing quickly if their design was rendered wholly in aluminium. On the other hand...

I had a Giant Cadex frame that did thousands of racing miles and is still now going out in the hands of another owner albeit not that often; and no longer being raced. It has carbon fibre frame tubes glued into aluminium lugs and an aluminium fork. The fork (being a fork) twanged a lot as part of it's function yet hasn't shown any signs of fatigue yet. It's now about 30 years old.

Cugel

pwa
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Re: Trek Domane frame failure

Postby pwa » 13 Aug 2019, 9:27am

Cugel wrote:
pwa wrote:I would never trust anything that has aluminium alloy in an application that is meant to flex. It seems like a recipe for disaster. Aluminium for rigid things, fine, and all the flexy things in a material that can take flexing to the degree to be expected.


I also have two Specialized Tricross Comp bikes. These have an aluminium main frame triangle but flexy "zertz" bits in the seat stays, forks and seat pin. All of the flexy bits are made of carbon fibre. These bikes are now 10 and 11 years old, with no sign of fatigue (and I do look most carefully).

Specialized seems to have anticipated the possibility of the flexy bits fatiguing quickly if their design was rendered wholly in aluminium. On the other hand...

I had a Giant Cadex frame that did thousands of racing miles and is still now going out in the hands of another owner albeit not that often; and no longer being raced. It has carbon fibre frame tubes glued into aluminium lugs and an aluminium fork. The fork (being a fork) twanged a lot as part of it's function yet hasn't shown any signs of fatigue yet. It's now about 30 years old.

Cugel

I wouldn't trust that fork. Everything we know about aluminium says that it has an expiry point but we don't know when it is. It may be further down the line than we would have anticipated but it is coming, as sure as night follows day.

But for the Tricross, ally for the stiff bits and something else for the flexy bits seems a sensible solution to the issue. Another solution, which exists on a couple of bikes in our garage, is to have a stiff ally fame that simply doesn't flex much. They last okay.

Brucey
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Re: Trek Domane frame failure

Postby Brucey » 13 Aug 2019, 9:31am

my understanding is that aircraft wings are designed such that, at any point along the length, the section's centre of pressure coincides with the position of the main spar, so that the wing ought to experience minimum twisting along its length, in normal use.

Obviously when the control surfaces are used, the wing is much more likely to see an unbalanced load e.g. that twists it; there are always secondary effects when using control surfaces but in some aircraft, under some conditions, the intended effect of the controls is greatly diminished or even reversed by such secondary effects. In some older types, the secondary effects impinge on the normal flight envelope and have to be taken into account during nearly every manoeuvre.

Modern aircraft design dials out most of the secondary effects but it is impossible to eliminate them completely. Main wing spars tend to be somewhat overengineered; not only are the consequences of failure very unforgiving, but if cracks develop, repair costs are likely to be very high indeed.

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NATURAL ANKLING
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Re: Trek Domane frame failure

Postby NATURAL ANKLING » 13 Aug 2019, 10:33am

Hi,
Not that I know a lot about the subject of aircraft wings, It's much a science.
I I RC material used for aircrafts and maybe much like processed parts of the jet engines, use pre-stressed aluminium and magnesium alloy's?
Rolls Royce develop their own special secret alloys, well that's what the marketing says anyway.
There is much in material technology, where materials are not only heat treated, the way they are cooled in manufacture Affect the structure.
Brucey will no doubt fill us in on details Where he can.
If You Don't Try You Don't Do.....Don't Do You Don't Get...I'm Still Trying....Well Very..
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Brucey
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Re: Trek Domane frame failure

Postby Brucey » 13 Aug 2019, 10:40am

NATURAL ANKLING wrote:Brucey will no doubt fill us in on details Where he can.


I can't empty a lifetime's worth of knowledge into a post you know; not one that anyone else would read, anyway.... :wink:

cheers
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paddler
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Re: Trek Domane frame failure

Postby paddler » 13 Aug 2019, 11:10am

Brucey wrote:
NATURAL ANKLING wrote:Brucey will no doubt fill us in on details Where he can.


I can't empty a lifetime's worth of knowledge into a post you know; not one that anyone else would read, anyway.... :wink:

cheers


I'd read it....I might not understand it, but I'd read it! :D

Dave