Issue 32

N. Golinelli et alii, Frattura ed Integrità Strutturale, 32 (2015) 13-23; DOI: 10.3221/IGF-ESIS.32.02 13 Design of a novel magnetorheological damper with internal pressure control Nicola Golinelli, Andrea Spaggiari Department of Sciences and Methods for Engineering University of Modena and Reggio Emilia, Italy nicola.golinelli@unimore.it , andrea.spaggiari@unimore.it A BSTRACT . In this work we designed and manufactured a novel magnetorheological (MR) fluid damper with internal pressure control. Previous authors’ works showed that the yield stress τB of MR fluids depends both on the magnetic field intensity and on the working pressure. Since the increase of the magnetic field intensity is limited by considerations like power consumption and magnetic saturation, an active pressure control leads to a simple and efficient enhancement of the performances of these systems. There are three main design topics covered in this paper about the MR damper design. First, the design of the magnetic circuit; second the design of the hydraulic system and third the development of an innovative pressure control apparatus. The design approach adopted is mainly analytical and provides the equations needed for system design, taking into account the desired force and stroke as well as the maximum external dimensions. K EYWORDS . Magnetorheological damper; Design and manufacturing; Squeeze-strengthen effect. I NTRODUCTION owadays, there are several industrial applications in which magnetorheological fluids (MRFs) are used [1-3]. In particular, this paper focuses on the optimal design methodology for magnetorheological dampers (MRDs). The purpose of traditional dampers, or so-called shock absorbers, is to dissipate energy. MRDs compared to traditional dampers, exploit the change in the rheological behavior of MR fluids in order to achieve variable damping properties. The changing of the properties of MR fluids occurs when a magnetic field is applied. The magnetic field is typically generated by an axial coil, for which connecting leads are usually brought out through the hollow piston rod [4]. The main classification for MRDs concerns the methods by which the insertion volume of the rod is accommodated. This is a major design problem because the oil itself is nowhere near compressible enough to accept the internal volume reduction of 10% or more associated with the full stroke insertion. The aim of this work consists in exploiting the effect of pressure on MRFs to generate further controllable damping force, so accommodating the change in volume is very important. Clearly, a static pressure can be applied only when nearly incompressible material are used in the system, so no air or gases are allowed in the design. Several studies have been carried out in order to comprehend the influence of pressure on the properties of MRFs. In [5], a novel compressible MR fluid has been synthesized with additives that provide compressibility to the fluid. MR fluids are influenced by the presence of internal pressure [6-11]. In combined squeeze-shear mode, with a magnetic field of 300 mT, passing from 0 to 30 bar the yield shear stress to doubles its value. In flow mode instead, with a magnetic field intensity of 800 mT, the yield stress τ B increments its value by nearly ten times. There are three basic MRDs architectures [4], as is shown in Fig. 1: single-tube, double-tube and through-rod. The single-tube architecture (Fig. 1a) is based on a single-rod cylinder structure, in which the piston head divides the damper into extension and compression chamber. During piston movement, MR fluid passes through the control valve which is obtained into the piston head. A floating piston separates the MRF from the accumulator filled with compressed N