Design of a Pinch Mode Magnetorheological Flow Bench: Magnetic Field Analysis

Magnetorheological (MR) fluids are known representatives of smart materials. The technology has been used commercially in, e.g. controlled semi-active dampers. In the (existing) conventional flow-mode valves the MR fluid is energized by magnetic flux perpendicular to the fluid flow path. The effect is an increase in the material's effective resistance-to-flow. The so-called gradient pinch mode (GPM) follows a different principle – the flux in the flow channel is directed to activate the fluid in the areas adjacent to the channel walls. Then, high yield stresses are induced in the material layer near the walls and low yield stress are achieved in the middle of the channel; the yield stress distribution is non-uniform. A Venturi-like contraction is formed solely by material means, i.e. without changing the flow path geometry. This may lead to a new category of controlled semi-active valves. However, a fundamental research is still required to characterize the rheology of MR fluids in this mode. In the study the authors explore opportunities for building a pinch mode valve assembly for the experimental work with MR fluids. The authors consider a solenoid assembly that can be integrated into a flow bench, and then proceed with a finite-element (FE) magnetostatic study of the valve's model. The results are then presented in the form of flux density maps and averaged flux density vs current (ampere turns) characteristics, respectively, for a range of gap diameters and the pinch gap lengths.