Why in a specific bus the windshield is being cracked over and over ?!

The front windshield of a bus cracked for no apparent reason several times repeateclly. This sunshade is the fifth in number that was replaced in a period of about 6 months !! According to the description given by the driver, all the events occurred during routine journey, without the bus having undergone any accidents or damage.

The macroscopic examination of the glass found that the crack had a branched pattern. Except for the first failed window that was the manufacturer's original, all four windows that replaced the original, were made in Israel.

After a thorough examination of the glass several factors may explain the recurrence of the failure and the appearance of the cracking specifically on this bus:

• Improper installation in Israel.
• A flaw in the windshield material, a hidden flaw.
• A flaw in the structure of the windshield seat within the bus.

The batch records of the cracked windshield was reviewed and it was found that at the same time, windshields of the same batch were installed in other buses, with no cracking reported. Therefore, the possibility that there is a defect in the windshield material proved to be unreasonable.

The chemical composition of similar glass units were examined in the labatory and found to be very simple and similar to others. Moreover, the garage in which the windshield was installed dozens of units of the same type, were already assembled without any complains. Measurement of the diagonals of the bus indicated that there was a deviation to the right of the structure, and it seems that this deviation introduced stresses within the windshield, which effected the window during the use of the bus, up to actual cracking.