  The propagation path of quasistatic cracks under monotonic loading is known
to be strongly influenced by the anisotropy of the fracture energy in
crystalline solids or engineered materials with a regular microstructure. Such
cracks generally follow directions close to minima of the fracture energy. Here
we demonstrate both experimentally and computationally that fatigue cracks
under cyclic loading follow dramatically different paths that are predominantly
dictated by the symmetry of the loading with the microstructure playing a
negligible or subdominant role.
