Material Science -- using materials without specifying crystal directions

Why in most practical applications, most materials properties are given without specifying crystal directions. Are they trying to say all materials are isotropic?
 

berkeman

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Why in most practical applications, most materials properties are given without specifying crystal directions. Are they trying to say all materials are isotropic?
Can you give some examples of the applications you have in mind? Certainly there are applications where crystal axes do matter...
 
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Why in most practical applications, most materials properties are given without specifying crystal directions. Are they trying to say all materials are isotropic?
What are you talking about? Many material properties are measure in both the transverse and machine direction. Of course amorphous materials have no crystal structure.
 

Mapes

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Why in most practical applications, most materials properties are given without specifying crystal directions. Are they trying to say all materials are isotropic?
Polycrystalline materials are approximately isotropic when the length scale of interest is much larger than the grain size and the grains are randomly oriented. (Subtlety: materials can have a so-called "texture," which in a materials science context refers not to roughness but to a predominant crystalline orientation, due to processing history.) For example, a handful of iron is going to have a bulk stiffness of 210 GPa, even though the (111) stiffness of each microscopic grain is 270 GPa and the (100) stiffness is 125 GPa. For that matter, the stiffness of low-alloy steels is generally also around 200 GPa because steel is predominantly polycrystalline iron. For certain bulk properties such as stiffness, what you're measuring at the macroscopic scale is essentially the average value of a huge number of randomly oriented microscopic grains.
 

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