An article in The Anchorage Daily News with research from Michael Marder, a physics professor, at the University of Texas in Austin, sheds light on why a windshield chips and cracks. His research answers the questions others have asked me, why did my windshield get chipped, and why can a a big rock do little damage, yet a small pebble make a big star?
According to Marder, it's caused by the windshield having invisible flaws. When a stone strikes on or near a flaw you get a chip.
He cites moisture as a major cause for cracking a windshield. But also states that heat stress along with vibration will crack your windshield. I have long known that glass doesn't like to change temperature. Marder says that when it's extremely cold outside and you have the heater cranked up, a war is being waged within the glass. The cold outside is trying to contract, while the warm inside is trying to expand. Here in Oklahoma during the summer the opposite is true, the windshield is hot while the air conditioned inside is trying to cool you off.
The final blow that cracks your windshield is the slamming of the door or the trip down almost any Oklahoma road.
If repaired, the cracking process is stopped. He also recommends repairing quickly to prevent contamination which can hinder the repair process. A clean chip provides the best conditions for a strong repair.
