Investigation of the squeeze strengthening effect in shear mode

Abstract

This article deals with the squeeze strengthening effect which causes an enhancement in the shear stress of magnetorheological fluids. To obtain a boost of the shear stress, the magnetorheological fluid has to be normally compressed while it is exposed to a magnetic field in order to create stronger particle structures. First, experimental investigations are presented using a magnetorheological fluid test-actuator with a conical shear gap to compress the magnetorheological fluid. A modeling approach is then proposed which combines the rheological behavior with tribological effects to describe the squeeze strengthening effect. Although an enhancement in shear stress of more than factor two is achieved, the applied compression can only be sustained during a certain range of shearing because the magnetorheological fluid is displaced which breaks the created stronger particle structures. As shown by an extended test setup a control of the compression force by adjusting the shear gap height is only possible within a small range of operation due to mechanical limitations. Thus, a self-induced continuous compression is indispensable to utilize the squeeze strengthening effect in rotating devices. A concept for a new magnetorheological fluid test-actuator enabling a self-induced squeeze strengthening effect through an eccentric shear gap design by two independent rotations is presented and theoretically investigated.