Design and investigation of a new mixed-mode magnetorheological damper

Abstract

Magnetorheological (MR) fluids are field-responsive material with the ability to change its rheological behavior by having an external magnetic field. Therefore, they are commonly used in vibration damping, clutches, actuators and haptic devices. Generally, MR devices are fabricated utilizing the operational mechanism of a single working mode which is either flow, shear or squeeze. However, for this study a special MR damper was designed and fabricated to carry out a dynamic loading test and analyze the effect on a hydrocarbon-based MR fluid in a combination of shear and squeeze working modes. The damping force generated by shear mode is measured based on the force-displacements relationship of applied current and piston stroke length. The cushion effect generated by the squeeze mode is evaluated by the magnitude of the damping force at various piston stroke lengths. The MR damper could produce a damping force ranging from 50 to 270 N with zero input of current, up to 0.8 A without any saturation occurring from 15 to 25 mm of the piston stroke length. However, when the piston was closing to the bottom of the cylinder from 25 to 26 mm, a high peak force was observed confirming the existence of the squeeze mode. The cushion effect started as soon as the current was applied showing a high magnitude of 722 N at only 0.2 A. As the applied current increased further to 0.8 A, a very high squeeze force up to 1030N was produced when the piston nearly reached the cylindrical end. This proves that the cushion effect induced by the squeeze mode helps strengthen the damping force and consequently brings a positive impact towards a mixed mode damper when the piston is nearly closing the gap at the bottom of the cylinder. In conclusion, a high yield stress MR damper at a small gap clearance was successfully produced and this uniqueness can be utilized as a replacement of the conventional rubber stopper in dampers.