Der Mischbruch im Zugversuch

Mixed fracture in the tension test If a tensile test specimen does not break before by cleavage, voids are nucleated at second-phase particles and inclusions during plastic deformation. At the center of the necked region these voids coalesce by internal necking or shearing of the material between them forming a fibrous crack which expands radially. In a temperature range which is dependent on the material cleavage fracture is initiated by the fibrous crack, resulting in a mixed fracture. If no cleavage fracture is initiated a completely fibrous fracture is formed. Mixed fracture surfaces consist of a cleavage fracture zone surrounding the central fibrous fracture zone and the tensile specimen behaves like a fracture mechanics specimen. Fracture toughness can be calculated by equations for tensile specimens with a central penny shaped crack. A comparison of fracture toughness values obtained by the use of unnotched tensile specimens and of fracture mechanics specimens show good agreement inbetween the temperature range of valid K_lc values according to standards of linear-elastic fracture mechanics.