Abstract
An experiment is described in which a thin slab of granular material was shortened 70% in progressive pure shear between thick glass windows, at room temperature, 290 bars confining pressure, and 10 −4 sec −1 strain-rate. The aim was to study the relation between microkinematic history and microstructural changes in the material. This was done by making transmitted light photomicrographs of the specimen in seven successive configurations, and reconstructing the six incremental displacement fields relating the seven configurations. The prominent structures formed are several conjugate faults, that correspond to discontinuities in the incremental displacement fields. Faulting is responsible, however, for only about half of the observed total shortening. The other half results from displacements without production of new planar features, termed flow. The photographs show that faulting and flow are synchronous. The faults thus rotate toward the principal direction of maximum elongation, and suitably oriented fault segments change in length while slip upon them continues. Slip continues on faults inclined at angles as low as 30° to the long axis of the total strain ellipsoid. Flow mechanisms include pore collapse and distortion, grain boundary sliding, slicing, and crystal plasticity. Pore collapse is seen in one case to play a role in accommodating displacements around the end of a fault. Experiments of this general type seem attractive for studying the relations between kinematic history and progressive structural changes in many kinds of materials, including materials that recrystallize, or melt, or undergo pressure solution during deformation. The implications of synchronous flow and faulting are discussed briefly.
Published Version
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