Structure and Interaction Force in a Model Magnetorheological System

The force-displacement behavior of specific arrangements of 1.6 mm dia. steel spheres in a magnetic field of 4.2 kGs was determined in tension and shear. The maximum attractive stress between the particles in a single-row chain in tension was 411 kPa, independent of the number of spheres in the chain beyond four. The shear stress r-strain oy curve of a single-row chain exhibited a single peak with raX = 248 kPa at a shear strain -y = 0.32, providing the spheres in contact with the magnet walls were glued in position. Without gluing slippage of a chain or cluster occurred during shearing, giving a maximum stress only about 1/6 that without slippage. The r vs -Y curves for clusters of particles exhibited multiple peaks which corresponded to the movement of the spheres in breaking and reforming bonds. The maximum tensile and shear stresses tended to be smaller for clusters compared to equivalent single-row chains when the number of particles in a row is small.