Fracture Energy = Energy required to separate surfaces / Area J / m2
Strength and Toughness
Work must be done to break the bond between two atoms. To separate a sample completely in two the work required is just this work multiplied by the number of bonds broken. The energy per unit area is known as the fracture energy.
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Fracture Energy = Energy required to separate surfaces / Area J / m2 |
Materials with a large fracture energy are usually tough, like copper or steel.
Materials with a small fracture energy are usually brittle, like ceramics or glass.
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Glass can fail explosively when it cracks. It can shatter into many pieces which go flying in all directions. This is because glass has quite a high breaking stress so before it breaks it stores a lot of strain energy. When it does fracture only a small amount of this energy is needed to actually fracture it so the rest transfers into kinetic energy. |
Tough materials do not shatter like this because any stored energy is used up in breaking bonds.
