lect6-propertiesandglasses

lect6-propertiesandglasses - Lecture 6: Biomaterials...

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Lecture 6: Biomaterials Properties and Glasses Last time, we learned the basics of processing  metals and ceramics. So, How can we use processing to our advantage to control  properties? We’ll start by looking at the mechanical properties and  consider the tensile test (the workhorse of mechanical testing  for many materials) 1
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Elastic region: linear and reversible Plastic region: nonlinear and nonreversible. (after yielding) ε= l l     σ= F A    E = s e Ok. How do we take a brittle material like sapphire, and make  it more ductile?  Increase the interfaces. At interfaces, there is disorder. Grains can slip past each other.  Therefore, if there are enough grains per area  (nanocrystalline  ceramics) One can increase the ductility. 2
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Ductile fracture vs. Brittle fracture Defects such as   GRAIN BOUNDARIES  work for us. Now, if we want to increase the strength of steel to match that  of sapphire? WORK HARDENING So, a line defect lowers the modulus. However, if you have  3
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enough line defects, they get ENTANGLED and cannot move.  Therefore, the modulus INCREASES. (imagine two half  planes next to each other – it takes more energy to shift the  planes. We introduce line defects via WORK HARDENING
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lect6-propertiesandglasses - Lecture 6: Biomaterials...

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