Eli5 Why do broken/cracked car windsheild seem to still hold together?
In: Engineering
In cars, two types of glass are used: laminated glass, and tempered glass.
The windshield (and in some rare cases, also the rear window) are made of **laminated** glass. This is two sheets of glass, with a sticky plastic layer in between. Kind of like a double sided tape, only perfectly see-through. Once the glass cracks, the pieces are still glued to the double-sided tape and so the windshield will not fall apart. Even more impressive, usually only one of the two glass pieces break, so the other takes on the task of giving full structural rigidity once the other is compromised. It is because of the sticky layer in between that the glass doesn’t shatter and fall apart.
The reason is quite simple: the windshield is your protection from whatever debris may be flying towards your car. A rock that kicked up by the car in front of you needs to not be able to break through the windshield and cause harm to the driver. The windshield has to be see-through, but also be able to take quite a serious blow and not collapse.
It needs to be said that the windshield is different from your side windows, which are **tempered**. Tempered glass has been treated in a specific way that makes them extremely hard but also extremely brittle. Tempered glass is able to withstand quite some force, even a blow of a hammer, and not break. However, like a Pyrex measuring cup, once it does break, it shatters completely and in a million small pieces.
Tempered glass is used for the side windows for a good reason: with an escape hammer, that’s a hammer with a very pointy end to put a lot of force on a very small area of the hard glass, you’re able to break it and escape your car if you were to hit water with your car. A laminated window would break but you will not be able to break through it with one such hammer. Only escape through the side windows of the car! Side windows are not laminated for that reason (as well as costs); you’d be done for in case your car hits water. You’d have no escape.
Lastly: why not regular glass? Well, durability (regular glass would probably break if you would shut the door a little hard), and the severity of wounding in case of a crash. If your car were to be T-boned, that window will break. With regular glass, you’d have a risk of being cut by a large piece of glass that comes flying off at a high speed due to the impact. This can cause seriously deep wounds and will kill the passengers. That’s why we use tempered glass, that shatters into a million small pieces. All the individual pieces are only moderately sharp and are too light to cause any serious cuts or other injuries.
The glass is tempered which makes it crumble not shatter, and then it is sandwiched between two layers of clear material that hold it in place.
It’s 2 pieces of glass sandwiching a piece of sticky plastic. So instead of shattering the sticky plastic holds everything together
It’s how they’re made. They’re made to not shatter. They are tempered. They’re are Theo layers of glass with the temper between them so they don’t break like a glass cup now do you under stand
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