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What Causes a Stress Crack in your Windscreen?

Posted on Wednesday, March 20th, 2019

We’ve all had it happen: you notice a small crack in your windscreen, then it just grows and grows. But you can’t remember any significant impact on your windscreen. You also take good care of your car. So where on earth did the crack come from? Stress cracks have a whole range of causes – many of which are largely unknown. That’s why we’ve put together this list of some common stress crack causes. After all, if you know the cause, you’re better placed to prevent stress cracks in the future!

Stress cracks often develop in windscreens as a result of stone chips – but there’s a difference

First, let’s look at the most common cause of windscreen stress cracks: stone chips. Stone chips are relatively common, and their cause is hardly a secret. Stone chips usually occur on the highway, when passing traffic flicks small rocks into your windscreen at high speed. They can give you a fright, and leave an immediate mark, but how is that related to stress cracks? After all, stress cracks are noticeably different; they extend long distances in relatively straight lines. Well, stone chips are the most common cause for a simple reason: they weaken the glass. Automotive glass relies on its outermost layer of laminate for strength and ductility. When that outer layer is compromised, the inner, more brittle layer of glass can be affected. When it is, stress cracks tend to develop.

Sudden temperature changes are a little known cause of stress cracks in windscreens

Stone chips aren’t the only cause of stress cracks, though. Another little known stressor of windscreens is temperature. When materials change temperature, they expand or contract. If heated, they expand; if cooled, they contract. Windscreens are no different. If you leave your car out in the summer sun, chances are that windscreen is going to expand. You won’t be able to see it with your eyes, but it will be doing so on a molecular level. If a storm then passes, or you wash your car, and cold water falls on your windscreen, it will cool pretty rapidly. Of course, rapid cooling will be rapid contraction. And if your windscreen is in any way compromised, that temperature change can cause a stress crack.

Impact: it can both cause and worsen stress cracks in windscreens – here some common causes

If you’re driving on a bumpy road, you might see an existing stress crack extend before your eyes. Such is the effect of bumps and impact on stress fractures. But it doesn’t always have to been extreme impact. In truth, windscreens lose some of their strength when they’re cracked. That means a cracked windscreen is easier to crack further. As a result, even minor impacts, such as a slammed car door, can lengthen windscreen cracks.

Age is another factor in stress cracks; old windscreens tend to be more brittle than newer ones

Finally, let’s talk age. Automotive glass technology has come a long way in recent years. Newer windscreens are stronger, more flexible, and more durable than ever. So it won’t come as a surprise to learnt that older windscreens crack much more easily than new ones. Old four wheel drives are particularly notable in that regard; they sustain a few knocks over their lifetimes, and it can often result in windscreen stress cracks.

What should you do if there’s a stress crack in your windscreen? Take it to an expert ASAP

So what do you do if there’s a stress crack in your windscreen? Our advice: get it fixed by an expert as soon as you can. The crack won’t get better on its own; rather, it will continue to deteriorate with increasing speed. So don’t take the risk; get your cracked windscreen sorted as soon as possible!

Contact us for expert windscreen replacement.

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