We tend to think of glass as fragile–but in fact, glass is pretty strong stuff.

 

　　A flawless fiber of glass pulled lengthwise is five times stronger than steel! Although glass is quite strong, it’s also very brittle–and the brittleness explains why glass breaks so easily.

 

　　But windshields in cars and airplanes are much more resistant to breaking than regular glass.

 

　　What Makes Windshield Glass So Tough?

 

　　Glass is commonly made more resistant to breaking in one of two ways: by tempering or by laminating it. Tempered glass is first heated just below melting, then exposed to bursts of cold air. The cold cools and shrinks the surface of the glass faster than the inside, compressing the surface inward.

 

　　This more dense, inwardly compressed surface makes the glass stronger, so it takes a lot more force to break it. Tempered glass shatters into tiny bits, rather than large, jagged shards like regular glass. If you’ve seen little squares of a car windshield scattered on the street, you’ve seen how tempered glass shatters.

 

　　Car windshields are also commonly made from laminated glass, which has a tough, thin layer of plastic sandwiched between two layers of glass. If laminated glass shatters, it remains sticking to the plastic rather than scattering in splinters or shards.

 

　　Airplane windshields and bullet-resistant glass take this concept to a whole new level, with several layers of plastic layered with, and bonded to, layers of glass. That makes a composite material strong enough to withstand high pressures, varying temperatures, and even the impact of a bullet or an unlucky bird.

 

 

 

 

　　挡风玻璃为何如此牢实？

 

　　我们往往认为玻璃是易碎的—但事实上，玻璃很坚固。

 

　　无裂缝的玻璃纤维纵向拉长后其坚固程度是钢的五倍！玻璃虽然足够坚固，但同时它也非常脆—这也解释了为何玻璃如此易碎。

 

　　但汽车和飞机上的挡风玻璃却比普通玻璃牢固多了。

 

　　挡风玻璃何以如此牢实？

 

　　有两种办法可以造出更牢固的玻璃：钢化或是层压。制造钢化玻璃首先要将玻璃加热升温接近其熔点，然后直接暴露于冷空气中。低温促使玻璃表面比内部冷却和收缩得更快。

 

　　由于密度增加，表面收缩内陷，玻璃的强度也增加了，因此打碎玻璃需要的力量也就更大了。钢化玻璃破裂时不会像普通玻璃那样形成大块，锋利的碎片，而是会碎成细块。如果你见过街上散落的汽车挡风玻璃的小碎块，你就会知道钢化玻璃破碎后是怎样的了。

 

　　汽车挡风玻璃也经常采用层压玻璃，这种玻璃表面坚硬，两层玻璃之间有一层薄塑料，层压玻璃损坏时，玻璃碎片会沾在塑料上，而不会散落得到处都是。

 

　　通过将多层塑料夹层和多层玻璃叠压在一起，飞机挡风玻璃和防弹玻璃将层压玻璃的概念提升到了一个全新高度。这种复合材料牢固到能经受高压、温度变化，甚至是子弹的影响，更不用说撞到飞机上的倒霉的鸟儿了。