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Old 06-05-2013, 11:22 AM   #1
snorky18
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Default Why did the rear window shatter on this car?

So my wife is in Madison AL (basically Huntsville) with my son in a parking lot. She had the back seat door open, all the other doors closed. She heard a loud boom (in the distance), then heard the rear hatch glass shatter. The sound of the glass breaking continued for several minutes. No other cars in the parking lot seemed to be affected.

I have no idea what the boom was. She is close to Redstone Arsenal and to a rock quarry, but I called the local PD, and they were not aware of any weapons testing or other “loud booms” that occurred around 10:23AM local time.

From the pattern, it doesn’t look like the cracking it radiated from a single point (as would be expected if a projectile hit the glass in one spot), the pattern looks very even.

Anybody have any idea what could have caused this?





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Old 06-05-2013, 11:26 AM   #2
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Default Re: Why did the rear window shatter on this car?

You might want to look at those pictures again if you think it doesn't radiate from a certain point.
Not only does it, but I can see the impact point in the outside picture and that was at a glance!

At 8:30 to your washer nozzle.
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Old 06-05-2013, 11:32 AM   #3
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Default Re: Why did the rear window shatter on this car?

Damn that's odd. Would've freaked me out for sure.
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Old 06-05-2013, 11:37 AM   #4
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Default Re: Why did the rear window shatter on this car?

I've seen laminated safety glass do that when firemen hit it with an automatic centerpunch to break it during a jaws of life demo. it's not clear but it does look to radiate from just to the right of the washer nozzle/stop lamp area at the top of the glass in pic 1 and especially 2.

That really sucks.
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Old 06-05-2013, 11:42 AM   #5
snorky18
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Default Re: Why did the rear window shatter on this car?

The (inside) picture that blown up larger looks pretty even, but when I look at the one taken from the inside from further back, I can see that faint pattern now coming from the driver side of the wiper nozzle area.

I guess I'm used to thinking it would spiderweb from one place from an impact, not shatter every square inch of glass with a similiar pattern.
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Old 06-05-2013, 11:47 AM   #6
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Default Re: Why did the rear window shatter on this car?

Quote:
Originally Posted by snorky18 View Post
I guess I'm used to thinking it would spiderweb from one place from an impact, not shatter every square inch of glass with a similiar pattern.
Safety glass is weird like that
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Old 06-05-2013, 11:50 AM   #7
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Default Re: Why did the rear window shatter on this car?

seen a shorted rear defrost shatter windows but that doesn't look like the case here this looks more like a projectile IMO
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Old 06-05-2013, 11:53 AM   #8
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Default Re: Why did the rear window shatter on this car?

Quote:
Originally Posted by snorky18 View Post
The (inside) picture that blown up larger looks pretty even, but when I look at the one taken from the inside from further back, I can see that faint pattern now coming from the driver side of the wiper nozzle area.

I guess I'm used to thinking it would spiderweb from one place from an impact, not shatter every square inch of glass with a similiar pattern.
That is what that kind of glass is meant to do when hit with something or some other kind of trauma. I believe the idea is when it breaks, the pieces are small enough that they "won't" cut you. At least not like a shard of say plate glass will. Doesn't take much to do that either. One time in my high school days I was removing the rear window of my soon to be derby car.....I was on the trunk leaning on the glass and was using a screw driver to pry the seal out from around the glass so I could cut the window out (like I said, high school days....) well I just barely caught the edge of the glass one time when I was prying and it made a tiny "click" sound and I though "ohh shi...." and then glass shattered like that and I found myself laying in what was the rear seat area on the metal floor in a pile of glass.....but i didn't get cut since the glass did what it was suppose to do.....was a huge bitch to try and vacuum up ALL those tiny pieces....


some kid might have gone by with a handful of broken spark plug porcelain and thrown them at the car......you know kids these days.....the tiniest piece of broken porcelain from a spark plug will instantly shatter any kind of safety glass like that (but not the windshield since its laminated)
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Last edited by neel2008; 06-05-2013 at 11:57 AM.
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Old 06-05-2013, 11:59 AM   #9
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Default Re: Why did the rear window shatter on this car?

I cracks that way every single time, by design. So will sliding glass doors, shower doors, most refridgerator shelves. THAT'S what makes it safety glass.

They sell, for considerable money, a glass panel. It is three layers of safety glass laminated together. Then a punch is used [like during the jaws of life demo] and the center one is shattered; held in place, but with the pattern of your rear window, by the two outside panels. They make the coolest panels of decorative glass. One is in my future for the Behemoth.
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Old 06-05-2013, 12:03 PM   #10
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Default Re: Why did the rear window shatter on this car?

It's amazing, just a tiny chip of something hard and sharp thrown at low speed can cause it to shatter.

http://www.youtube.com/watch?v=QhlmKHbPFhU

I understand that bomb disposal robots use something similar (a ceramic chip in a air gun) to break car windows because due to the lack of force the it does not trigger movement sensors.
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Old 06-05-2013, 12:04 PM   #11
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Default Re: Why did the rear window shatter on this car?

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Is that factory tint or aftermarket? What was the outside temperature? Direct sun? Possible contributing factors?
Aftermarket tint, 1 year old. ~70-75°F. Exposed to the sun, but partly cloudy conditons.
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Old 06-05-2013, 12:10 PM   #12
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Default Re: Why did the rear window shatter on this car?

I broke the rear window on the wifes car with a tiny bit of gravel flicked up by a line trimmer, couldn't have been any bigger than 5mm square. Glass is funny old stff, sometimes you can whack it really hard and it just bounces, catch it in the wrong place though and boom it's gone. Was there anyone using a line trimmer or even a mower or leaf blower nearby?
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Old 06-05-2013, 12:11 PM   #13
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Default Re: Why did the rear window shatter on this car?

hmm, hadn't thought of the defogger. The manager at the shop I used to work at told me about some car of his from 3 centuries ago, one of the first with a rear defogger. after a while it had a nick in one of the lines (no current=no heat) and the temp differential on a particularly cold winter night caused the whole window to shatter and be lost to the wind (didn't stay together like yours back then) on the interstate. However I've seen and had cars even 20 yaers old with bad defogger lines that didn't explode.
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Old 06-05-2013, 12:44 PM   #14
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Default Re: Why did the rear window shatter on this car?

Now, if you have to drive that for a little before getting it fixed, by a little I mean a day or a week....not for weeks....
Go get some clear shelf paper laminating stuff and apply it to both sides

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Old 06-05-2013, 12:53 PM   #15
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Default Re: Why did the rear window shatter on this car?

You can also flick a piece of Ceramic Insulator from a Spark Plug at a window and it will do that. There is usually an obvious point of impact though.

The boom then the impact makes me wonder though. Maybe talk to people in your area and see if they remember anything. Maybe your wife heard an accident in the parking lot or nearby Construction. Especially something like an Excavator or Dump Truck banging on something. Weird though.

I like the idea of clear Contact Paper to put over the window for now though. You just have to be SUPER careful when applying as not to push too hard or you will push right through. Also be careful closing your doors. Roll the window down slightly before closing your door or the pressure inside of the cabin may push the glass outwards making it come apart.
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Old 06-05-2013, 01:20 PM   #16
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Default Re: Why did the rear window shatter on this car?

Most side and rear windows in autos are toughened or tempered glass which is much stronger than normal glass. It is heat treated for strength, but when broken, due to internal stresses, it breaks into relatively small unjagged chunks.

Windshields, which are also a type of safety glass, are laminated with a plastic film sandwiched between two pieces of glass. When an object hits a windshield, it often spiders and stays intact so as not to completely inhibit the driver's visibility.

Also, tempered glass is quite often used in movies, as it is more dramatic when it breaks. Generally in a film, to break a piece of tempered glass, an electric detonator is secured to the edge of the glass.

I've see tough guys fail to break a side window with a sledge hammer. Basically, the easiest way to break one is to impact the edge with something sharp.
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Old 06-05-2013, 01:22 PM   #17
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Default Re: Why did the rear window shatter on this car?

Laminated = WINDSHIELD. The windshield is made up of two sheets of TEMPERED glass, sandwiching an adhesive inner sheet of tough flexible plastic. In the event of a broken windshield, the plastic sheet holds the crumbled glass together and prevents it from falling in on the driver / passenger.

Tempered = ALL OTHER glass on a car (though some high end cars can have laminated glass elsewhere in addition to the windshield).

Tempered glass is created by first heating a pane of regular glass and then cooling it with streams of cool air (called "quenching"). When looking at a piece of tempered glass with sunglasses, you can often see the alternating pattern left by the air streams on the glass (alternating dot type pattern).

Tempered glass is very resitant to impact load along it's surface, but can be very fragile along it's edges, because of the stress induced into the glass by the tempering process. This is why windshields, & back glasses are set into beds of urethane sealant and/or rubber gaskets. Vibrations transmitted through metal contact with the glass could cause breakage.

If there are any imperfections or contaminants in the glass, they can over time cause a spontaneous shattering of the glass, although that is quite rare. Normally any glass with imperfections in it will shatter during the tempering process. Dark tinting can increase this possibility because it traps more heat into the glass.

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Old 06-05-2013, 01:32 PM   #18
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Default Re: Why did the rear window shatter on this car?

i always wondered what those patterns were on car windows. they only appear when i wear polarized sun glasses.
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Old 06-05-2013, 01:50 PM   #19
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Default Re: Why did the rear window shatter on this car?

In looking at your pictures, it does indeed appear that something happened to the glass along it's edge, near the washer nozzle. The boom heard by your wife was probably something hitting the glass, or more likely; the glass releasing tempering tension as it fractured.

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Old 06-05-2013, 01:53 PM   #20
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Default Re: Why did the rear window shatter on this car?

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Tempered = ALL OTHER glass on a car (though some high end cars can have laminated glass elsewhere in addition to the windshield).
And some others as well. Buick's QuietTuning uses laminated side glass on their vehicles for noise reduction. GM's full-size vans use laminated side glass on some panels to assist seat belts with occupant containment during some collisions.



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