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2017 Chevy Volt...
Car is parked all day in an underground parking garage. After work I get in and close the door and hear a noise similar to ice crumbling on the rear window. I look back and see that my rear window has shattered. It looks like the glass is pushed outwards like the pressure of closing the door caused it to bubble out and pop.
Surely, a car's windows should be able to withstand that air pressure.
Any ideas on what would cause this?
Rear and side windows are generally made from tempered glass which has been heat treated to set up residual stresses in the plate which put the interior under compression. This is what causes it to break into small granules rather than long shards.
However, although it has decent tensile strength it is still a brittle material and very notch sensitive. The most likely thing is that there was a pre-existing scratch or crack in the glass and the impact of closing the door was enough to make the whole thing fail.
It is also possible that it had received some significant impact while it was parked and you just didn't notice the damage and closing the door was enough to make the damaged glass collapse completely.
I suspect that the bowing outwards is just a combination of the fact that the normal slight curve is made more obvious by the fact that there is now a big hole in it and the fact that it can't support its own weight anymore exaggerating the curve further.
Most likely the back window was already broken but still in place, this happened to me recently on my 2016 Volt. Fortunately I noticed it before opening/closing doors, but even closing the door gently made the glass puff up and resettle (really glad it didn't collapse into the car).
I covered the entire window with packaging tape, gingerly applying the tape horizontally on the outside and then vertically on the inside (yes it took forever). Then I taped the window to the frame to hold it on and prevent air flow inside to outside. This allowed me to drive around for the 1-2 weeks (very stressful) while the OEM glass was being manufactured/shipped. I made sure to keep the windows up the whole time so it wouldn't rip the back window out.
As far as the pressure goes, usually cars have a vent that looks like one of those external dryer vents, hidden inside the rear bumper. This vent allows the majority of the pressure spike to dissipate safely among other things. https://jalopnik.com/heres-what-those-rubber-flaps-are-hidden-behind-your-re-1828016409
The window was hit by kids with either a ball, soccer, baseball or hockey puck. Or water balloon. It didn't shatter until you moved the vehicle. When living in a condo I saw kids throw a ball at a vehicle from the apartment building next door. As soon as the vehicle moved the next day the window shattered. I also had a relative throw a water balloon from a moving vehicle onto our windshield . We were both moving slowly opposite directions. My windshield shattered.
