why poles break...

[dheldr01]

can we make a list of reasons poles break?

1. factory defect(unlikely but possible)
2. overbending
3. A crack from not taking care of/or storing properly

what am I missing?

[KirkB]

4. Getting run over by a car. That's what happened to mine, when I didn't tape the tube up tight enough and my coach slammed on the brakes!

Kirk

[achtungpv]

4. Getting run over by a car. That's what happened to mine, when I didn't tape the tube up tight enough and my coach slammed on the brakes!

Kirk

Years ago I was coaching a kid that taped his poles to his roof rack with athletic tape. One flew off going 70 and bounced end over end down the highway and miraculously didn't get hit by a car. It did have a 2"x1" hole completely through the compression side wall. I told him to toss the pole but he kept it and tried to jump on it before I got there and it actually lasted for a couple of jumps before exploding.

[Decamouse]

got a real good list - but need to talk to Becca first --

Will try not to get to anal eng on everyone

[master]

Will try not to get to anal eng on everyone

Ahhh.... go ahead!

[KirkB]

Will try not to get to anal eng on everyone

You lost me in your lingo. What the heck is "eng"?

Kirk

[rainbowgirl28]

Engineer

[73-vaulter]

I just must state the obvious; poles break becouse they are subjected to stress greater then that for which they were designed.

[Decamouse]

Stress greater than designed - I would look at it as - in its current condition - loading results in levles greater than the stress it can withstand -

why - because every standard strike, spike, overbend - minutely change that limit (not for the good)

when a tube or hollow column bends - basically three things happen

1. the pole has part of the material in tension (outer fibers and glass) ,
2. the inner side of the bend is in compression,
3. the tube trys to oval (which also results in less compressive and tensile loads - but also reduces the Moment of Inertia - so again a trade of)

Why do they fail -- if anyone of those three conditions exceed what that design or material is capable of withstanding - a failure results -- here also is the part that gets overloooked at lot -- what happened on the vaults leading up to the ultimate failure!!!!

I will e-mail anyone who wants a 10 page Engineers ramblings -- jpwatry@hotmail.com

Quick basics -- failures

Tensile failure -- either major overbend or a real localized overbend (take off flat, under and drive the bend real low) --- hard to over elongate regular glass fibers, carbon does not allow the same degree of elongation -
Put a ding or scratch - in the wrong place (high stess area) and you reduce your margin of safety

Compressive failure -- since to bend a pole you have all three happening (tension, compression and ovalling) if compressive forces are to high you crack the glass -- this type failure is usually seen as a failure when the pole is starting to recoil - compressive load is deccreasing crack opens and propogates - this is why a spike make or scratch on the compression side of the pole is so dangerous -- you have lowered the limit so now it only a matter of time until high stress cycling will initiate a failure

Hoop Failure -- probably the most common failure -- when the forces are such that the tube collapses in after it ovalled and then flattens - inner wall folds --

Want a pole that will almost never break - the old training poles -- thick wall - small diameter - some even filled with faom core to help hoop strength - heavy - slow recoil --

So do you want a diesel or a race car -- one is more reliable - one has higher performance - there is a trade off --

Since I rarely bend a pole to mid/high 70's (77%) of its original length - (called older, slower, a not skinny) -- I do not tend to overstress poles -- leave that to the fast kids

[KirkB]

Stress greater than designed - I would look at it as - in its current condition - loading results in levels greater than the stress it can withstand ...

OK ... great explanation ... but why is it that poles often break into 3 pieces?

I understand that the 2 weak points of a pole might be just above the sail piece and just below it ... the 3 pieces ... but what causes it to break in BOTH places at once? Actually, it's more than just a break ... it's an EXPLOSION.

If I hadn't seen it happen dozens of times with my own eyes, I would guess that it would break just in the weakest place ... not TWO places! You would think that as soon as the WEAKEST point starts to break, that would relieve (not increase) tension on the 2ND WEAKEST point. So is there some sort of chain reaction once the weakest place starts to break?

Kirk

[Decamouse]

Lets assume perfect world first - pole is designed and vaulter vaults such that the stress is perfectly distributed throughout - - it would fail in multiple places at the same instant -- real world -- on a vault where the energy input into the pole is at or even exceeds it capabilty to store - a fraqcture/failure occurs - could even occur it a few spots nearly at the same time --- if you had a super high speed camera you would probably see that one spot fails first - and the shock wave of this added to the already highly stressed areas initiates the other breaks

I have seen in testing where you could get a many as fiften other fracture points (not complete failure of the composite - but failure of layers) --

More later - need to get working on finishing railing on daughters back deck

[dnike13]

I had a kid one time try to get on a pole that was too big for him (which I told him not to even try). So one day as I was fishing for a crossbar in our closet he decided to try to use it. I came out of the closet and there he was, on the runway. He took off and did get enough penetration into the pit, however he was not used to being on a pole that much bigger. So he crunched into what I can best describe, "a ball," his hands were holding onto the pole and his knees were to his chest, but his feet were also on the pole. When he landed he pushed out with his legs, kinda like dead lifting the pole but his feet were in between. It broke and it was the next pole in the series for the better jumper we had. Needless to say, he got very strong from doing push-ups, inch-worms, and my personal favorite, Roman chair. Long story short, sometimes poles break from high school kids not listening and/or stupidity.