Macroscopic scaling and microstructural evolution in shear band phenomena

摘要

Concerning the mechanisms governign shear band phenomena and induced failure, there are two interrelated but different aspects: macroscopic scaling and microstructural evolution. Scaling laws relate important mechanical and physical parameters involved in shear banding. For this sake, scalign laws are required to be insensitive to microstructural evolution. It was found that the competition of different diffusions, i.e. heat and momentum diffusions, plays a crucial role in the temporal and spatial pattern dynamics of shear banding. A scaling map was proposed to sketch out the mechanisms. But, at the stage of shear band induced failure, we noticed that the micro-damage evolution, rather than thermal softening, may be responsible for the collapse of material strength. Hence, scaling laws may have to give their places to evolving microscopic structures. In this aspect, we developed a modified SHTB to examine the evolution of microscopic structures. The observations show that a series of events (dislocation patterns, grain rotation, microdamage accumulation etc.) successively appear and eventually lead to fracture along shear band.