Anisotropy & Zener
Whether a lattice is equally stiff in every direction — and a single number that measures it.
One number for directional stiffness.
An isotropic material has the same stiffness in every direction; an anisotropic one does not. For cubic-symmetric lattices the Zener ratio captures the degree of anisotropy in one number: A = 2C₄₄ / (C₁₁ − C₁₂), from entries of the stiffness tensor. A = 1 is exactly isotropic; A > 1 is stiffer along the cell diagonals than the axes, and A < 1 the reverse.
Anisotropy is a design lever, not a defect. A lattice tuned to be stiff along the load path and compliant across it puts material only where it is needed.
Read it on the stiffness plot.
The design tools show anisotropy as a directional-stiffness plot — a surface that is a sphere when A = 1 and bulges along stiff directions otherwise — and report the Zener ratio beside it. In grain and bundle the directional-bias and fiber controls set anisotropy directly; in beam the cell topology does.
No single stiffness when A is far from 1.
Read A before trusting a lone stiffness number: a lattice with A far from 1 has only a stiffest and a softest direction. Align the stiff direction with the load.