CLEAVAGE ANISOTROPY IN TUNGSTEN SINGLE-CRYSTALS

We have performed an extensive study of the cleavage fracture of tungs ten single crystals between 77 K and room temperature. The dependence of the fracture toughness on temperature and on crack propagation dire ction as well as the river line patterns on the fracture surfaces clea rly indicate that the intrinsic brittle fracture process is anisotropi c with respect not only to the plane but also to the direction of crac k propagation. This anisotropy cannot be explained within Griffith's t hermodynamic theory of brittle fracture. However, it compares well wit h atomistic simulations, which suggest that it may be a consequence of anisotropic lattice trapping.