18

While browsing a local news site, I stumbled upon this picture of a broken bus door. The glass was fractured due to a rock impact. As far as i know there are no heating elements on the window section in the picture. Now, what interests me is the apparent periodicity and structure of the fracture pattern.

Are periodic fractures something commonly encountered in tempered glass? Is the mechanism that generates such fractures understood? Is it a consequence of the manufacturing process? Perhaps the way the glass is affixed to the door?

Thanks in advance

Glass fracture

shay s
  • 183
  • 5

1 Answers1

21

It's an artifact of production - in particular, the construction of the conveyor belt of the machine performing the quenching process.

The pattern can be observed through a polarizing filter in the undamaged glass:

enter image description here source

and it's a result of the structure of the conveyor belt through which the surface of the glass is cooled to generate the stress that gives it the special properties:

enter image description here source

The contact area of the glass with the conveyor is small enough that it doesn't negatively impact the process - all throughout the surface the stress is introduced in sufficient amount, but the amount of stress applied differs by the "openness" of given area, creating this pattern.

SF.
  • 6,125
  • 25
  • 45