MODE SWITCHING AND RECURSIVE BIFURCATION IN GRANULAR-MATERIALS

The existence of the ''mode switching'' and ''recursive bifurcation'' behavior in granular materials (sand triaxial-compression-test specime ns) under shearing is revealed. Group-theoretic bifurcation theory is employed to categorize bifurcation modes through the observation of de formation patterns of these materials, and hence to detect the occurre nce of recursive bifurcation. A bifurcation point search technique is developed and applied to a strain versus stress curve of a specimen to identify the presence of a series of bifurcation points associated wi th the recursive bifurcation. In addition, an imperfection sensitivity law is employed to testify the occurrence of mode switching between t wo dominant bifurcation modes. Curves of strain versus stress undergoi ng mode switching and recursive bifurcation are simulated well by the bifurcation equation. The predominant role of mode switching and recur sive bifurcation in shearing behavior of the granular materials is cle arly demonstrated and fully described with the use of the bifurcation theory. (C) 1997 Elsevier Science Ltd.