A brittle material under loading fails by the nucleation and propagation of a sharp crack. Combining annular dark-field scanning transmission electron microscopy and empirical molecular dynamics that are validated by first-principles calculations, researchers at MIT
have shown in ACS Nano
that local atomic distortions from different types of atoms causes a propagation anisotropy. Conventional conditions for brittle failure such as surface energy, elasticity, and crack geometry cannot account for this anisotropy because this kind of anisotropy has not been considered as a parameter in traditional theories.