5298 - SELF-ORGANIZATION OF SCALE LEVELS OF PLASTIC FLOW IN FRACTURE MESOMECANICS

In the basic concept of physical mesomecanics, a deforming solid is viewed as a multilevel system in which the evolution of plastic flow and fracture occurs consistently on the micro-, mesoand macro-scale levels. The self-organization of plastic flow, which takes place on the mesoand macro-scale levels in the deforming material at the prefracture stage, has been investigated using dual-phase pseudo-alloy Cu-25%Cr and highstrength construction martensitic steel (VKS-12). In the former case, material fracture involves shearing and in the latter, it is “cone-cap” type fracture. It has been found that the fracture of the binary pseudo-alloy Cu-25%Cr occurs by three stages. At the first stage in the deforming material there forms a wide symmetric neck. At the second stage within of the neck along the “chromium particle-matrix” interface there occurs crack nucleation. As the self-organization of plastic flow, which involves the above two processes, a second system of Ux and Uy isolines characteristic of geometric stress concentrator (crack) appears on the background of Ux and Uy isoline pattern typical for a symmetric neck. At the third stage the self-organization of stress-strain state on the meso-scale level results in the formation of a extended local shear macro-band, with the line and shear components and strain-rate intensity along the latter macro-band having maximal values. Fracture in such specimens occurs by shearing along the same macro-band. The deforming austenitic steel specimens at the pre-fracture stage form a symmetric neck. The maximal values of the principal line components, e1 and e2, and strain-rate intensity, ei, occur in the center of the neck region; the shear component, exy, reaches a maximal value and reverses sign at every other quarter of the neck length. The above distribution of e1, e2 and ei values remains unchanged until the onset of fracture in the center of the neck where the strain-rate intensity, ei, reaches a maximal value. An analysis of the results obtained suggests that the type of fracture is determined by the distinctive characteristics of plastic flow self-organization, which takes place within of the neck at different scale levels.