Regular Article Magnetorheological damper behaviour in accordance with flow mode ★ Joanes Berasategui * , Ainara Gomez, Manex Martinez-Agirre, Maria Jesus Elejabarrieta, and M. Mounir Bou-Ali Mechanical and Industrial Manufacturing Department, MGEP Mondragon Goi Eskola Politeknikoa, Loramendi 4, Apdo. 23, 20500 Mondragon, Spain Received: 20 June 2018 / Received in final form: 19 September 2018 / Accepted: 8 October 2018 Abstract. The objective of this article is to determine the optimal flow mode in an MR damper to maximize its performance. Flow mode is one of the main design issues in an MR damper, as it determines the velocity profile and the pressure drop across the gap. In this research, two MR dampers were designed and manufactured with two flow modes: valve and mixed. The response of these two dampers was compared experimentally. Additionally, the experimental tests were correlated by theoretical results that were obtained considering the rheological behaviour of the MR fluid, the shear stress distribution in the gap, and the damper movement. Interestingly, the obtained results suggest that flow mode is not a significant parameter for determining the behaviour of a MR damper. 1 Introduction Dampers are used to attenuate oscillatory movements. In many mechanical systems, establishing the correct damp- ing factor is essential for the comfort and safety of the user. For a given mechanical system, the damping ratio is determined considering the working conditions [1]. In industrial applications where working conditions are not stable, the optimal attenuation of vibrations is obtained by an adjustable damping ratio. Different approaches to obtain such ratio were analysed by Sun et al. [2]. Among them, magnetorheological (MR) dampers present advantages of a large force range, quick response, and low energy consumption [3]. MR dampers have been applied in many mechanical systems, such as washing machines [4], automotive suspensions [5], prosthesis-knees [6], and bridge dampers [7]. Nevertheless, applications of MR dampers are habitually limited to high-end products. Consequently, in order to extend this range of applications, a deeper understanding of MR damper behaviour is required. In MR dampers, oil of conventional hydraulic dampers is replaced by a MR fluid [5]. Such specific fluids are magnetic particle suspensions in a carrier fluid [8]. The rheological properties of these fluids can be modified repeatedly by applying an external magnetic field. To apply the above-mentioned magnetic field, MR dampers include a magnetic circuit [5]. Due to the magnetic field- dependent rheological behaviour of MR fluids [9], with an increasing yield stress according the magnetic field intensity [10], MR dampers present an adjustable damping ratio that allows an optimal attenuation of vibrations when the working conditions are not stable. One of the determinant parameters in the damper design is the geometry of the orifice. Depending on this geometry, two flow modes can be obtained. On the one hand, the valve or Poiseuille mode (Fig. 1a) is solely determined by a pressure difference (P 1 > P 2 ) between inlet and outlet. On the other hand, the mixed mode (Fig. 1b) is not only determined by a pressure difference but also by a shear stress (t C ) due to the wall movement. Each flow mode involves a different velocity profile (u) in the orifice. In order to define the flow mode in a MR damper, design and behaviour considerations must be taken into account. On the one hand, a valve flow mode allows a simpler design. On the other hand, an MR damper with a mixed mode is considered to be more efficient as the obtained damping force is the addition of both the contribution of the shear and the valve flow mode [11]. Subsequently, the objective of this research was to investigate MR damper behaviour in accordance with the flow mode of the MR fluid. For this purpose, two MR dampers were designed and manufactured with two flow modes, such the valve and the mixed one. To do so, a description of the design of the used MR dampers is developed first, alongside with the used fluid within both the dampers and describing the magnetic circuit of each. Next, a theoretical analysis performed in accordance with flow mode, rheological behaviour of the MR fluid, and damper movement is presented. Finally, experimental results are discussed and correlated with the theoretical analysis. ★ Contribution to the topical issue “Materials for Energy harvest- ing, conversion and storage (Icome 2017)”, edited by Jean-Michel Nunzi, Rachid Bennacer, and Mohammed El Ganaoui. * e-mail: jberasategui@mondragon.edu Eur. Phys. J. Appl. Phys. 84, 21101 (2018) © EDP Sciences, 2018 https://doi.org/10.1051/epjap/2018180182 THE EUROPEAN PHYSICAL JOURNAL APPLIED PHYSICS 21101-p1