SHEAR CELL MEASUREMENTS OF POWDERS - PROPOSED PROCEDURES FOR ELUCIDATING MECHANISTIC BEHAVIOR OF POWDER BEDS IN SHEAR

A variety of procedures for the use of a shear cell are devised in hopes of elucidating mechanistically the behavior of powders in shear. The processes considered are plastic deformation at regions of true contact and structural changes in the powder bed. Possible structure changes are: (a) consolidation or dilation; (b) blockage to resist the continuation of motion in the same direction; and (c) particle orientation. A series of pulls to just initiate shear is used. These are made either monodirectionally, i.e., all pulls in the same direction, or bidirectionally, i.e., consecutive pull directions reversed. A series of pulls proceeds until a steady state or plateau condition exists. A relative shear force, M, is defined as M = (μ1 — μp)/μp, where μ1 and μp are the respective friction coefficients using first pull and plateau data. The retention of plateau‐condition‐shear‐strength upon removal of the applied load is obtained by measuring the shear force for the first pull after reducing the load. An index of retention value is defined. Also, an indication of the relative extent of conditioning at plateau condition for various loads is based on a comparison of the shear force observed for one additional pull after increasing the load to an arbitrary constant value. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company