Why glass breaks? February 25 2014, 0 Comments

How glass break is basically related to two things: Surface micro crack/flaw and stress. 

The micro crack/flaw geometric KIC AKA stress concentrator factor. When you examine the glass surface under microscope, you will find the surface are full of micro cracks, flaws. these flaws act as stress connector which can amplify the applied stress. There are two main parameters both related to the micro crack geometry. The crack length and Crack radius, so the sharper and longer the crack the more stress it amplified.
This can be visualised by just imagine one have a piece of paper with a little cut in the middle, all you need is very little pulling force (compare to flawless paper) to tear up the paper. this is the reason why airplane window has round edges, so the crack will not built up and propagate from the edges. (Airplane engineer learn this the hard way after a few plane disintegrate in Air due to sharped edge windows, Flight 781 BOAC). 
What makes Gorilla glass tough?
what gorilla glass does is a process known as Chemical strengthening, what this does essentially is soak the glass into a molten (heat favour the kinetic process) salt (potassium) bath. the glass will undergo a diffusion process, where the sodium diffuse out of the bath and potassium diffuse into the glass surface. therefore the surface of glass is basically replaced by bigger atom K+>Na+, thus surface is in compression force and therefore close up all the crack. hence the enhanced toughness!
I hope it didnt bored you too much. :P

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