[Drivingforfun]

During a Covid lockdown I had a windscreen replaced due to a crack then needed another one within 3 months. I put it down to coincidence and/or the roads being grittier due to less use

I just had the same thing happen again though... had a new windscreen in early December and heard another stone chip and lo-and-behold it's cracked again

Is it common or known that new windscreens are for whatever reason more delicate, due to a bedding-in period or something...or just another coincidence?

[olduser]

A bonded in windscreen has to flex with a cars body, it is part of the cars structure.
Glass will flex like most solids, as long as the surface is intact, (the highest stress is at the surfaces when flexing) but if the surface is damaged that will become the start of failure as it is weaker than the rest, that weak point becomes the start of a crack or cracks.
Its equates to cutting glass, the surface is damaged along the line of the cut by the cutters wheel then the glass is stressed (bend or sharp tap) and breaks along the damaged line - it follows that old already damaged glass is very difficult to cut as it already is damaged so the crack may run in any direction as it moves to the next nearest weak point.

If the cars body is stiff without the windscreen then the bonded windscreen can tolerate more surface damage due to less flexing.

In the past, when windscreens were toughened glass, they were mounted in rubber.
The glass was toughened by rapidly cooling its surfaces putting the surfaces under tension, the slightest chip caused them to shatter into many small pieces.

[Santa]

Windscreens are complicated. They are two layers of glass with a vinyl layer between them, which is the reason they don't shatter. Well, the glass shatters, but the vinyl holds it together.

This five-minute video is interesting:
How It's Made Windshields

[Drivingforfun]

Thanks for the replies, interesting but some went over my head!

I should clarify I wasn’t talking about “new” windscreens as in “modern” vs “old”. I mean as in newly fitted. I go years between getting cracks but the last 2 instances (2020 and today) I’ve had a replacement windscreen fitted, a new crack has developed within weeks so I’ve had to have them re-done

I’m wondering if that’s normal; is the windscreen delicate for the first few weeks or something