Cup-and-cone fracture in single-phase ductile metals appears to originate at holes formed by drawing away of material from non-metallic inclusions, as suggested by Tipper. In copper, the holes expand under the triaxial stresses in the neck and coalesce in a macroscopic fissure;​ in α iron fine cracks are formed by the stress concentrated at the holes. In coarsegrained material shear cracks are formed on the surface of the neck.

Pure polycrystalline aluminium separates at the neck of a tensile specimen by slipping-off along a plane of shear. This is thought to be the usual mode of failure in materials in which work-hardening has been exhausted.