rublow

While trying to locate a noise from a fork/headset I push a top tube with my hand. I felt how it bent and returned to a previous shape. There are no obvious visual damage, a paint seems to be uncracked, however I am wondering how my unwise behavior could influence a frame performance?

jimc101

Would be very suspect that the carbon 'bent', as the material doesn't do that (in the frame application), thinking you wrist bent naturally, and you took this to be the frame.

rublow

Of course it is possible, however I pushed it very strong with a body weight and felt this 'point bent'.

le mans

where do you clamp the bike on a workstand, top tube? mightta crushed it

fietsbob

An engineering decision was made on how many layers of carbon fiber cloth was enough
for the stresses a part of the frame would see, then using minimal material where it is sufficient to save weight.

you wish your carbon bike weighed more?

RobotGuy

fietsbob

Double butted steel tubes at thicker tube wall on the ends than the middle for basically the same design goal..

But remember the Pros have a truck full of spares.. an so they are disposable..
And every season the truck gets restocked with new stuff..

Now with Carbon fiber racing yachts they are going for light too
and they are patching them together between many races..



...

RobotGuy

Andrew R Stewart 

Jeeze... Frame materials are not infinitely stiff. Any tube can be compressed and rebound if done within it's "strength" limit. We use to do this with lightweight steel tubes decades ago and can still do this with carbon. The question, or trick, is to use enough pressure for some deflection but not deformation. One way to see the deflection is to watch the light reflection around one's finger/thumb. As the tube's surface deflects the light's reflection distorts. When the pressure is released the light reflection shows no distortion so no surface deformation remains.

One could use a controlled clamping device to really test this, oh that's right a repair stand jaw is such. measure the tube diameter at 90* to the clamp's compression before, during and after and report back.

there seems to be a miss guided, "on a pedestal", impression (yes, a pun that's fitting) of what constitutes tube damage and what happened before said damage is real. Andy

RobotGuy

Darth_Firebolt

Yes, you can flex the top tube on most carbon frames by hand. I showed this to a guy I saw sitting on his top tube. It was his first carbon bike and he doesn't sit on the top tube anymore.
​​​​​​
You can easily see the frame deflection if you angle the lighting just right.

Andrew R Stewart 

The frame tubes of any material have not been optimized for forces running radially into the tube's surface to any extent. As a bike sees far greater stress along the tube torsionally and bending/beam like the tubes are shaped (or with carbon the plies are oriented and numbered) to best handle the riding forces. Denting tubes (beer canning as example of a failure mode most here are familiar with) is quite easy, mere handle bar swings can do this. But as long as the forces don't result is the tube's skin failing (carbon cracking, delaminations-- metal denting/crimping) there's no problem but what's between the rider's ears. Andy

Jiggle

Make, model, location of pliable carbon?

RobotGuy