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