Mysterious Glass Shatter: What Caused It?

[Ergo606]

I was recenlty on the phone with my friend who moved into a new house. The house has been around for a little while...nothing too long. He was on the phone when his mom told him to hang up and look at this. As it turned out, a pane of glass in the bathroom shattered. He looked at it and watched the cracks get longer right in front of him. It began from the middle and worked its way towards the edges. There was no one in that room. The facts that I know are that it was like about room temperature in there. Most of the windows in the house were open. The glass was about ten years old. The water wasn't on and no apparent forces were acting on it. We're really curious to find out what happened considering that we're both really into physics. His guess was that a sudden pressure change from opening a door might have bent the glass slighlty enough to cause it to crack and send small pieces on the floor. More facts...his mom used CLR on the glass to clean it three weeks before the incident. Any help or suggestions would be appreciated, thanks!

 

[James R]

The glass may have been pre-stressed, though this is more common in car windscreens than in bathroom windows.

 

[PerennialII]

"Cool!" Initial defects, residual stresses, sudden loading (? really windy out there ...) combined with the first two ... considering a simply supported / uniformly streched etc. plate the cracks starting from the middle would be a logical place stress - wise -- crack path curvature / crack branching (if there is any) might imply residual stress effects and crack path orientation about whether the residual stress or an initial defect & applied loading were the dominant causes (curved against straight crack paths relative to panel width). Wonder how glass does with respect to environmentally assisted cracking (always considered it inert if there is one?), stress corrosion cracking arising from the cleaning ?

... probably really difficult to find any initial cracks (especially afterwards ), but sounds like something having a fracture mechanical explanation.

 

[FredGarvin]

I highly doubt the pressure difference theory. The only way that would hold water is if the rest of the room were sealed, including the door.

If it's a new-ish house, my first thought would be an improperly framed window opening. If the header for that window was not large enough or not installed properly, the roof loading could have been transferred through the window. I'd bet if that window was removed, the window frame itself is twisted slightly.

 

[StirlingA]

Which way was it cracking?? Vertically? Horizontally?

My guess would be a settling house.

 

[Danger]

That's kinda strange. At least I've never seen a stress fracture start anywhere but the edge of a pane. Are you sure that nothing impacted it, like maybe some kid with a pellet gun or something? I'm not saying that it doesn't happen, but I've never heard of it. I have friends who own a glass shop; I'll see if they can shed any light. It might take a while; I don't get around so well any more.

 

[Ergo606]

Thanks guys for all the responses. Yeah, only two ppl live in that house. My friend who was on the phone playing his guitar in his room...and his mom who was in her bedroom on the bed. No one else was in the house. The crack was vertically straight down the center.

 

[PerennialII]

That's kinda strange. At least I've never seen a stress fracture start anywhere but the edge of a pane. Are you sure that nothing impacted it, like maybe some kid with a pellet gun or something? I'm not saying that it doesn't happen, but I've never heard of it. I have friends who own a glass shop; I'll see if they can shed any light. It might take a while; I don't get around so well any more.

In common stress fracture theories one rule of thumb is that the crack propagates from the edge with about 89% of the load that it does from the center.

 

[Danger]

In common stress fracture theories one rule of thumb is that the crack propagates from the edge with about 89% of the load that it does from the center.

Could you clarify, please? Do you mean that it takes 89% as much stress to start one from the edge as it does from the middle?

 

[PerennialII]

Yeah, if the initial defect is identical in size and the applied stress can be considered far - field tension. It comes from one 'principal' solution of linear-elastic fracture mechanics.

 

[mapper]

houses are always shifting, specialy new ones. All that happened was the house shifted ever so slightly to put more stress on the frame of the window and poof.

 

[Ergo606]

Well if it helps, I thought of the settling house theory. Then I found out that the glass nor the frame touch the cieling. Would it be possible that one wall moved inwards causing more stress on the glass? Btw, you guys are fast at responding, lol.

 

[FredGarvin]

Then I found out that the glass nor the frame touch the cieling. Would it be possible that one wall moved inwards causing more stress on the glass?

Nor should it. However, the framing that holds the window definitely does. The whole purpose of the header above a window or door is to transfer the roof/ceiling loads to the two supporting side members that hold the window. If that header is not right the load or part of it will go through the window as well. See the diagram below.

http://www.hammerzone.com/archives/window/new/window_framing_2xq.gif

 

[Danger]

Yeah, if the initial defect is identical in size and the applied stress can be considered far - field tension. It comes from one 'principal' solution of linear-elastic fracture mechanics.

Ya learn somethin' every day... Thanks.

 

[Ergo606]

Oh, oops. I failed to mention that this wasn't a 'window' window...Its the glass in a shower...I can't explain better. It was like the picture below only not as fancy. It was also sliding instead of on hinges.
http://www.glassnet.co.za/images/pic17s.jpg

 

[mapper]

lol its a shower door window. That stuff should be tempered and shouldn't break like that. Its most likely defective. How old is it, about the same as the house i would imagine. Over time the steam and heat from the showers may have weakened it. That or ghosts.

 

[Ergo606]

Haha, yeah. A 'shower door window', there we go. I don't know what else to say. What I told him is what all of the suggestions I read combined together were. Basically, defect+deterioration+some other things...Yeah.

Steam would deteriorate tempered glass over a while? Whoa.

 

[dtmaurer]

Years ago. I simply touched a drinking glass as I was about to pick it up and it disintegrated into very tiny pieces.

2 days ago, I was holding a pane of shower door glass which I had just replaced. I was holding it with both hands and had hold of the long edge. As I slowly rotated with it, it suddenly disintegrated and I watched the tiny (1/4 inch maximum) pieces drop into a long pile on the floor. It was so fast, I don't know if I let go or I simply had nothing to hold any longer. But what was even stranger, pieces of glass continued to "pop" for another 45 minutes, even after I had put the remains into a carton. It was like watching popcorn pop.

 

[Ki Man]

How old was the house? Sometimes in older houses the wood will very slightly contract and expand with rising and dropping temperature, maybe over the years its taken its toll on the window.

Dont rule out calling the ghost busters yet either

 

[KingNothing]

Years ago. I simply touched a drinking glass as I was about to pick it up and it disintegrated into very tiny pieces.

2 days ago, I was holding a pane of shower door glass which I had just replaced. I was holding it with both hands and had hold of the long edge. As I slowly rotated with it, it suddenly disintegrated and I watched the tiny (1/4 inch maximum) pieces drop into a long pile on the floor. It was so fast, I don't know if I let go or I simply had nothing to hold any longer. But what was even stranger, pieces of glass continued to "pop" for another 45 minutes, even after I had put the remains into a carton. It was like watching popcorn pop.

That is...incredibly strange.

 

[MonicaL]

The samething happened to our shower door yesterday, it just shattered out of nowhere. We are very confused with the reasons why that happened.

I noticed that the little wheels in which the door slided were a bit rusty, the house was renovated two years ago but since we live in Macau where the humidity level is very high I was wondering if that might have something to do with.

I was hoping someone could shed a light on this because we have no ghost busters here and our landlady will never believe we didn't brake it

thanks

 

[AlephZero]

For a brittle material, the initial flaw that starts a crack can often be too small to see. Once the crack starts to propagate, it goes fast.

I once dropped an empty ceramic coffee mug on the floor. The floor was carpeted, and there was no obvious damage to the mug.

One day, about 5 years later, I filled the same mug with water (at room temperature, not hot or cold), there was a "ping", and the mug instantly cracked into two pieces. Imagine slicing through the sides and bottom of the mug vertically through the centre, 90 degrees away from the handle.

I guess a micro-crack started when I dropped it, and took 5 years to grow big enough to matter.

Your shower door may have had some similar "invisible" damage, a long time ago.

 

[SS1994]

Something similar happened to me today: me and my brother were washing up, he picked up a glass and it suddenly shattered in his hand. Not like a slow crack, it pretty much exploded. He wasn't putting any pressure on it, the water I was washing up with wasn't that hot, and we've had these glasses for maybe 3/4 years now, and have had no problems like this whatsoever so far. Any ideas?

 

[elterrible]

Old thread, but I am calling dibs on the guitar doing it. Amps can get pretty loud, that creates a pressure wave. The glass could have had micro cracks that weren't visible and the sound pressure could be the straw that broke the camels back. If you could hear the guitar in the bathroom which you likely could, that means the air pressure waves were hitting the glass window.

Thanks guys for all the responses. Yeah, only two ppl live in that house. My friend who was on the phone playing his guitar in his room...and his mom who was in her bedroom on the bed. No one else was in the house. The crack was vertically straight down the center.

 

[elterrible]

For a brittle material, the initial flaw that starts a crack can often be too small to see. Once the crack starts to propagate, it goes fast.

I once dropped an empty ceramic coffee mug on the floor. The floor was carpeted, and there was no obvious damage to the mug.

One day, about 5 years later, I filled the same mug with water (at room temperature, not hot or cold), there was a "ping", and the mug instantly cracked into two pieces. Imagine slicing through the sides and bottom of the mug vertically through the centre, 90 degrees away from the handle.

I guess a micro-crack started when I dropped it, and took 5 years to grow big enough to matter.

Your shower door may have had some similar "invisible" damage, a long time ago.

I never seen glass spontaneously shatter, but thinking about it I have seen a ceramic bowl and a ceramic plate shatter.

With glass, the fact that it flows downward at a very very slow rate, certainly has some effect and would influence accumulated stresses, it isn't required or the sole reason glass spontaneously shatters because ceramic does it too.

Then of course getting real anal about it, you would have to question even calling it spontaneous when it is having heat transfer and thus energy transfer flowing through the glass via the air and creating thermal cycles or movement in the glass. If you had a time lapse camera with a microscope view, you would see the glass wobbling.