Elastic Anisotropy vs Crystal packing

[handsomecat]

I have calculated the dependence of (1/s11) ie. single-crystal young's modulus on crystallographic direction for an inorganic crystal.

I've noticed that certain peaks correspond to closely-packed planes eg. a psedo-hexagonal arrangement is seen in directions where the peaks (ie. local maxima) for (1/s11) occur.

I wonder if one can immediately conclude that the strength of the bonding and/or peak in the young's modulus is due to the way the atoms are packed. Any comments?

 

[Mapes]

According to Hertzberg's Deformation and Fracture Mechanics of Engineering Materials, it is not typically the case that close-packed directions are stiffest. In fcc Al and Au and in bcc Fe, the <111> direction is stiffest. In bcc Mo, the <100> direction is stiffest. There doesn't seem to be a pattern.

 

[handsomecat]

ok, great, thank you so much, that settles a lot of things.

I should then say that (1) some directions are stiffer than others (2) these directions happen to have close-packing.