fracture mechanics and birthday parties

[Fulvio Romano]

I propose a question, which may seem stupid, and if it is, I declare myself stupid, because I couldn't solve it.
Tonight I was at a party of a friend's daughter, and like every birthday party there were balloons. balloons, you know, they burst, but...

If I have a balloon, I swollen it and the hole with a needle, the balloon bursts.

If I have a balloon, the hole with a needle and then I inflate it, it doesn't burst.

Why?

the material should be perfectly fragile, so it should be in perfect agreement (better than steels) with the fracture mechanics saying that a lesion immersed in a field of tensions, becomes unstable in certain conditions. the law therefore depends only on the local conditions and not on the previous history, moreover to throw a swollen balloon means to make a hole even bigger.

p.s.http://www.youtube.com/watch?v=jephfmsymge

 

[Er Presidente]

I propose a question, which may seem stupid, and if it is, I declare myself stupid, because I couldn't solve it.
Tonight I was at a party of a friend's daughter, and like every birthday party there were balloons. balloons, you know, they burst, but...

If I have a balloon, I swollen it and the hole with a needle, the balloon bursts.

If I have a balloon, the hole with a needle and then I inflate it, it doesn't burst.

Why?

the material should be perfectly fragile, so it should be in perfect agreement (better than steels) with the fracture mechanics saying that a lesion immersed in a field of tensions, becomes unstable in certain conditions. the law therefore depends only on the local conditions and not on the previous history, moreover to throw a swollen balloon means to make a hole even bigger.

p.s.http://www.youtube.com/watch?v=jephfmsymge

I think the balloon when it swells stretches the fibers and deforms them permanently.
when the "skin" breaks down and tensions decrease.

 

[marcof]

If I have a balloon, I swollen it and the hole with a needle, the balloon bursts.
If I have a balloon, the hole with a needle and then I inflate it, it doesn't burst.
Why?http://www.youtube.com/watch?v=jEphfmSymgE

the inflatable balloon has the walls in tension
the needle when entering produces first a bending towards the inside of the part. at the moment when the elastic wall yields it makes it sufficiently fast to continue for inertia around the material no longer tense and thus exceeds the breaking limit of the rubber, further widening the hole and causing a failure that propagates in an expulsive manner.
when drilling before and deopo inflating the hole for the tension of the wall is gradual and does not exceed the breaking limit of the material.
If you took a few balloons at the party (you confess that you did it:tongue you should try to inflate it, then "pizzicarne a portion between your fingers so as to make it floss, pierce it with the needle and release your fingers slowly and check if it swells or bursts. I say he's swelling.
I don't know if I explained, but I saw the "film" in my head:smile: in ultra-fast shooting, more "ultra" than the video you linked.
Maybe I have to eat lighter in the evening....

 

[PierArg]

Hi.
I would not like to say a cretin but I think it is all explained by the law of spherical pressure vessels bussinesq.

 

[PierArg]

Hi.
I would not like to say a cretin but I think it is all explained by the law of spherical pressure vessels bussinesq.

I add that I am very tired, so tomorrow you have some patience for what I wrote.

I didn't see, but I'm convinced that boussinesq had something to do with it.

 

[gerod]

I never really thought about it but I think marcof gave the right thesis.
interesting video.... I bet you are now home with balloons inflated with water and you are testing them!!!

 

[Alberto.E]

I'm sorry if I say something, but besides what's been said, I think it's also about pressure. when I drill a balloon already inflated I create a high-pressure air spill and in a very short time and this creates me burst. If I punctuate the balloon and begin to inflate it, it would only inflate because the amount of air I admit is greater than that coming out of the hairpin, but there is still a vent that does not allow me to reach high pressures. You should try to inflate a balloon in a sudden way, I don't know, using compressed air... and see if it bursts or swells. a little twisted but I think I explained.

 

[linch]

I propose a question, they burst, but...

If I have a balloon, I swollen it and the hole with a needle, the balloon bursts.

If I have a balloon, the hole with a needle and then I inflate it, it doesn't burst.

Why?

Because maybe you had to use it as evidence for the etylometer,ah,ah.
hello fulvio, and well found.

 

[zeigs]

I propose an alternative thesis
In my opinion the inflatable balloon has the material of the ribbed walls, according to me with also of the thinned areas compared to other adjoining (while the swell can be noticed of the streaks, with darker areas corresponding to thicker walls). if you break it on one side explodes because the material gives off fragibly and does not have the possibility to reassert the tensions: is already at the limit, and the peak of tensions due to the hole causes the fracture. I say side by side because if you hit it in the head, where the material didn't get ripped, it doesn't explode, but it just swells. I say it because I remember reading it years ago in one of those books of illusionist tricks on Sunday. and this would explain why if I hole it before inflating it does not explode: I imagine that around the pre-existing photo there is a redistribution of tensions that enlarge it. I also imagine that with the hole you can not reach the size of the balloon without hole (even imagining to provide enough air to compensate for the loss from the hole) because being a peak of tensions the hole will tend to widen by exploiting the ductility of the material around.
a counterprova is to pierce a balloon inflated but without getting to the rinse of the material. or at the center of a darker area (so not completely swollen)
I hope I've explained

Hi.

 

[myface]

Does anyone know how to explain why when I read this discussion I was thinking about my reproductive apparatus? :biggrin:

 

[PaoloColombani]

Does anyone know how to explain why when I read this discussion I was thinking about my reproductive apparatus? :biggrin:

I hope you didn't blow something up!

 

[PaoloColombani]

According to me the elastom when it is swollen has all the polymer chains that besides being close to the yielding voltage are also all beautiful stretches, a small stress as the drilling of a needle could cause the interruption of continuity and the failure of some fiber with the immediate propagation of the fracture in the direction of the fiber that has been interrupted. this should not happen with the restless elastom all the fibers would be "reached" and the penetration of a needle should allow the scaffolding of the polymers and their bending widely within the elastic field without causing any interruption. the hole marked by the needle should therefore expand along with all the polymer (when the balloon is inflated) with a edge edge edged by the fibers that have let the needle pass without interrupting. but it's just my guess.

 

[Fulvio Romano]

According to me the elastom when it is swollen has all the polymer chains that besides being close to the yielding voltage are also all beautiful stretches, a small stress as the drilling of a needle could cause the interruption of continuity and the failure of some fiber with the immediate propagation of the fracture in the direction of the fiber that has been interrupted. this should not happen with the restless elastom all the fibers would be "reached" and the penetration of a needle should allow the scaffolding of the polymers and their bending widely within the elastic field without causing any interruption. the hole marked by the needle should therefore expand along with all the polymer (when the balloon is inflated) with a edge edge edged by the fibers that have let the needle pass without interrupting. but it's just my guess.

interesting thesis...but if so, handling a little rubber the hole should be able to close, and so it is not.

Moreover, from several films to the moviola of balloons that burst, the lesion always opens on a longitudinal plane, according to the theory of pressure vessels.

So far it seems to me that marcof, with his inertial theory, went in the most credible direction. . .

I have to do some experimental evidence. I'm not so sure that inflating a hole balloon this doesn't break...confid on next birthday. . .

 

[PaoloColombani]

interesting thesis...but if so, handling a little rubber the hole should be able to close, and so it is not.

Perhaps it could close if the imprint was about two or three times the order of magnitude of a fiber, but the diameter of a pin will be about 103 orders of magnitude of a fiber, so the sliding of the fibers one on the other to leave space to the fingerprint of the brooch would be remarkable and hardly reversible. However, these considerations of mine are simple hypotheses, which would have no value without analytical-experimental verification.

For the rest I had already read the other interventions before I intervened, with some of which I certainly agree, mine did not want to be an alternative but if anything a possible compendium. :wink:

 

[peloritano]

bibliographical reference "engineering materials"
The fragile fracture (i.e. the balloon explosion) is caused by the growth of a [bleep] at the speed of sound. to explain why this phenomenon takes place we need to know a minimum of theory of fracture propagation and the energy criterion of griffith. a material is usually characterized by some mechanical paramentaries such as the tension of yielding the breaking load etc. Another defining paramenter is the kc that is the factor of intensity of critical efforts, this paramenter is defined experimentally by taking an audition and creating a carving. Then he puts it hard so as to have a porpation of the fracture... at this point the traction porvin is subjected and the kc is determined which is equal to tension reached at the break* the square root of (lazy* area of the lesion which is measurable by analyzing the pig)
generico k=sigma*sqrt(pigreco*area)
the piece is safe if k<kc k="" mentre="" se="">=kc then the piece collapses.
in the case of the balloon we imagine having obtained the kc of the material
inflatable balloon case
the walls of the balloon are woven and therefore have an extremely high sigma tension but being the lesion (provoked by the pin) for the moment of area nothing is has that k=sigma for sqrt(pi*area(nothing))=0 therefore surely k<kc accadere="" ad="" area="" causata="" che="" come="" creiamo="" da="" di="" esempio="" infinitesima="" k="" lesione="" potrebbe="" punta="" quella="" se="" spillo="" una="">kc and in this case the balloon explodes
if the balloon is unflattered and has a cut you have that k=sigms(a balloon is nothing)*sqrt(pigreco*area of the squarcio)=0 therefore k<kc anche="" appena="" avrebbe="" crescita="" della="" dello="" di="" e="" gonfiare="" il="" in="" k="" ma="" palloncino="" parete="" poter="" presenza="" quindi="" se="" si="" squarcio="" stesso="" sulla="" supponessimo="" tensione="" una="">=kc you have that the ***** propagates increasing the section of the squarp but drastically decreasing the tension on the walls and this would bring again k<kc...
It concludes that a swollen balloon showing a squirrel will never explode</kc></kc></kc>