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how much pressure?

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Endert

PostPosted: Sat Jun 17, 2006 8:48 am


ok this is just a place to pose the question how much pressure an object can take. I would like to ask the first one.

How much pressure can a glass bottle take before exploding?
PostPosted: Sat Jun 17, 2006 9:30 am


I don't know the answer to it, but I know it will depend on the chemical makeup of the bottle and design. Weather the bottle has elements that strengthen the glass or the producer wanted to stay cheap and use conventional glass ingredients. I would say overall there is not one answer to this question; there may be a range of pressures but not one single atm pressure. Also are you talking about internal pressure inside the bottle or external pressure on the bottle. I assumed internal since you said "... take before exploding..."

torasenshie


nonameladyofsins

PostPosted: Sat Jun 17, 2006 9:31 am


Endert
ok this is just a place to pose the question how much pressure an object can take. I would like to ask the first one.

How much pressure can a glass bottle take before exploding?


Depends how you wanna crush it. It will take less pressure to break the bottle if you apply it as the bottle is laying on its side, than if you applied it as the bottle was standing up. To calculate exactly the breaking pressure point of a plastic bottle of water, you need it's thickness, and it's dimensions. You also need to know if it's a perfect cylinder, cause then the calculations are easier. Also if the bottle isn't a perfect cylinder, and has grooves, then it shall break more easily, along the grooves. IF we assume that the bottle shall be broken from the side, then we can use the simple equation

sigma = PD/4t
where D = diameter, P = pressure, sigma = stress, t = thickness

if we kow the ultimate stress of the water bottle material, plastic (which can be looked up in tables, or found experimentally) and the dimensions of the bottle, we can easily figure out the pressure needed to break the bottle. But you need sigma, and I don't have it for plastic in my table, so you can probably find it on the internet. Then just plug it in the equations and there you go.
PostPosted: Sat Jun 17, 2006 1:09 pm


The problem with this question is that it is too imprecise. Glass bottle of what dimensions? The thickness of the walls is a critical parameter. How is the pressure applied? If more or less uniform external pressure, the bottle will be in compressive stress, while internal pressure would put it in tension instead. The compressive strength of brittle materials like glass can be several times higher than tensile strength, so this is important. Additionally, what kind of glass is it and of what quality? For example, the tensile strength of glass varies by more than a factor of two. Since glass is not ductile, it is very responsive to internal flaws, which accumulate over time. If design strength is considered rather than the nominal strength, as would be proper for safety reasons, a further drop of about an order of magnitude becomes realistic.

The formula poweroutage gave, σ = PD/(4t), is the longitudinal stress in cylindrical pressure vessels for which the wall thickness w≪D. The hoop stress is double this amount. This might not be very accurate if your bottle has very thick walls, but considering the unknown parameters of the glass, the loss of accuracy here should be the least of your concerns.

Finally, while glass already has an unimpressive tensile strength, it is even less tolerant of shear. The easiest way to break glass is to put it under a transverse load, even tempered glass.

VorpalNeko
Captain


xXDevils_AdvocateXx

PostPosted: Sun Jun 18, 2006 3:01 am


[ Message temporarily off-line ]
PostPosted: Tue Jun 20, 2006 9:05 am


Endert
ok this is just a place to pose the question how much pressure an object can take. I would like to ask the first one.

How much pressure can a glass bottle take before exploding?


Not to mention, are you talking about total plastic failure, or rather just the beginings of dislocations in the materials? You would have to look at a stress strain curve for the object to really find the point of what level of force would be needed to cause failure. If you look past "Hoop Stress" and such and go even further, you can find failure points far before Sigma would show, but it takes alot more calculations I really dont feel like typing out.

KaitlynintheGoal


Uber_Pwns119

PostPosted: Wed Jul 05, 2006 4:07 pm


I know that I've had a few incidents with exploding glass bottles in my car. The volume was 1 liter, I'd estimate the glass was around 5 mm thick. Let's do some math-the-matics. Unfortunately I don't have my brain abouts me. Here's the info.
To Solve this you can use boyle's law of gasses. (where n and V are constant.
The temperature before the warmup of the gas within the bottle was roughly 60 degrees at 1 atm. After the warmup the temperature was roughly 110 degrees. WHo wants to do the math? (remember to convert to kelvin!)
PostPosted: Wed Jul 05, 2006 4:08 pm


and on a side not, the bottle was cracked just before it exploded, but there was shrapnel.

Uber_Pwns119


sugar-baby-2004

PostPosted: Sat Oct 14, 2006 3:57 pm


maybe a few kilograms
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The Physics and Mathematics Guild

 
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