New development of shear fracture research

Limitations of the models that are used to describe the development of strains in shear zones are examined. The assumptions about the identical value of strain along the shear zone and the way in which the width of the latter increases have been found to be the main limitations of such models. These assumptions make the correct interpretation of the development of strains and of the propagation of a fracture in the shear zone impossible. It is shown that it is necessary to separate the real strain localization zone from the general background which the whole shear zone forms. A model of the shear zone with a distinguished strain localization zone and a related model of shear fracture are put forward. These models take into account the fact that the value of strain changes along the strain localization zone and they point to the phenomena which cause an increase in the width of this zone. The proposed model of shear fracture explains the concurrent effects of the state of stress and the way in which the dislocation structure evolves in the course of fracture in the shear zone. Examples of the interpretational possibilities of the presented model of fracture are given. The importance and the directions of further research into the development of strains and the propagation of a fracture in the shear zones which occur in rocks, soils and metals are indicated. (C) 2000 Elsevier Science B.V. All rights reserved.