Lecture06 - ME 382 Lecture 06 Crystal Structure Modulus of...

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ME 382 Lecture 06 20/ix/10 1 Crystal Structure Modulus of a material depends on Bond strength Packing of atoms (bond density) Density of a material depends on Atomic weight of atoms Packing of atoms Two forms of packing solids: amorphous and crystalline Amorphous : Position of atoms completely random Structure like a liquid, but resists shear like a solid E.g. , window glass, metallic glasses, amorphous polymers (PMMA, PC) Crystalline: Atoms are in well-ordered positions relative to each other E.g. , most metals and ceramics, and crystalline regions in some polymers Ordered region where atoms have the same crystal structure and the same orientation Silicon wafers are huge single crystals Most engineering materials are a collection of crystals - polycrystalline Individual crystals are known as grains (typically nm to cm in size) Atomic packing in crystals Can be useful to think of atoms as hard spheres of radius r o Random arrangement of spheres gives a packing density of 64 %
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This note was uploaded on 01/26/2011 for the course ME 382 taught by Professor Garikipati during the Winter '08 term at University of Michigan.

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Lecture06 - ME 382 Lecture 06 Crystal Structure Modulus of...

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