SELF-ORGANIZATION OF SCALE LEVELS OF PLASTIC FLOW IN FRACTURE MESOMECANICS R. V. Goldstein 1 , V. E. Panin 2 , L. S. Derevyagina 2 , N. M. Osipenko 1 Institute for Problems in Mechanics of the RAS, Moscow 117526, Russia Institute of Strength Physics and Materials Science, SB RAS, Tomsk 634020, Russia ABSTRACT 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-, meso- and macro-scale levels. The self-organization of plastic flow, which takes place on the meso- and macro-scale levels in the deforming material at the prefracture stage, has been investigated using dual-phase pseudo-alloy Cu-25%Cr and high- strength 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 U x and U y isolines characteristic of geometric stress concentrator (crack) appears on the background of U x and U y 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, ε 1 and ε 2 , and strain-rate intensity, ε i , occur in the center of the neck region; the shear component, ε xy , reaches a maximal value and reverses sign at every other quarter of the neck length. The above distribution of ε 1 , ε 2 and ε i values remains unchanged until the onset of fracture in the center of the neck where the strain-rate intensity, ε i , 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. 1 INTRODUCTION According to the basic concept of physical mesomechanics [1], a deforming solid is thought to be a hierarchic system; therefore the underlying processes responsible for its plastic flow and fracture will occur in a self-consistent fashion on the micro-, meso- and macro-scale levels. In the present investigation we consider the self-organization of plastic flow that occurs at the pre- fracture stage on the meso- and macro-scale levels. The investigation was performed using binary pseudo-alloy Cu-25%Cr whose fracture involves shearing and high-strength construction martensitic steel (VKS-12) which undergoes “cone-cup” type fracture. Using television-optical method and a specially designed measuring complex (TOMSC) [2, 3], the evolution of local stress-strain state of a deforming material within a neck was examined in detail for flat specimens. Moreover, the processes involved in the self-organization of plastic flow on the above scale levels and their effect on material fracture were investigated. For quantitative specification of local stress-strain state, displacement vector fields and those of their longitudinal and transverse components were constructed. The distribution patterns derived for individual line and shear components and strain-rate intensity were matched against the strain-induced relief and the distinctive features of macro-fracture in the specimens tested.