Structural instability of an oscillating superparamagnetic micro-bead chain

Abstract

Issues concerning the structural instability of an oscillating micro-bead chain are addressed based on systematic experiments. The patterns of rupture are categorized into two distinct regimes, referred to as a weak ductile fracture and a strong ductile fracture. A weak ductile fracture describes a more rigid rupture, which often occurs in a pronounced oscillation driven by strong field strengths. The position of the rupture usually favors toward the two sides of the chain. An interesting phenomenon of a reversed rupture, wherein the ruptured segments oscillate in opposite directions, is observed when there is excessive field strength. An important consequence of the reversed rupture is to cause permanent failure of the chaining structure. On the other hand, a strong ductile fracture, featuring significant deformation before rupture, is favored in a more viscous solvent fluid. The positions of the breakages in this regime favor the central region of the chain. The prominence of rupture instability is enhanced by a weaker directional field or by a longer chain, which is in agreement with quantitative assessments by the normal forces acting between the interfaces of beads. In addition, results of the present experiments provide further validations of the global criterion for rupture instability given by where Mn and N, respectively, represent the dimensionless Mason number and the number of beads in the chain.