Non-Newtonian Effects on Ferrofluid Lubrication

The load carrying capacity of the ferrofluid lubricating films can be controlled directly by means of the applied magnetic field, since the viscosity of the ferrofluid increases in the case of magnetic field. The experimental investigations showed that the ferrofluid is an non-Newtonian fluid: it behaves simultaneously as a Binghamoplastic and as a pseudoplastic. The non-Newtonian behavior of the ferrofluid is dependent both on oreintation and on intensity of the applied magnetic field. The constitutive equation of the ferrofluid can be expressed as τ(H,D)= τ_s(H)+η₁(H)D+η₂(H)D². It is possible that the "solid" cores appear and adhere to the surfaces of bearing, since the ferrofluid has a yield shear stress τ_s(H). The pseudoplastic behaviors of the ferrofluid have an effect on the condition for core occurrence. The cross section C₀ of a pure Couette flow in the ferrofluid lubricated bearing is different from that in the ordinary Binghamoplastic lubricated bearing. The solutions of load carrying capacity and friction force of plane slider lubricated with ferrofluid are given as an actual example.