https://doi.org/10.1177/0309524X18756963 Wind Engineering 1–5 © The Author(s) 2018 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0309524X18756963 journals.sagepub.com/home/wie An accelerated test stand to assess wear in offshore wind turbines rolling bearings Nicola Pio Belfiore 1 , Carlo Costa 2 , Rosanna Pileggi 2 , Fabio Botta 1 and Claudio Guarnaschelli 2 Abstract Rolling bearings are universally adopted to serve as revolute joints in almost all mechanisms or machines, because they offer a convenient solution to the problem of minimizing friction and, simultaneously, providing a large load-carrying capacity at any kinematic regime, including slow or alternate rotations. However, in offshore wind turbines not only they reach large dimensions but also they move within strong electromagnetic fields created by the turbine generators. For example, considering the last amplification stadium epicyclic gearbox, they may serve to sustain elements rotating around floating shafts (planetary) which also move around a fixed principal shaft (solar). This article illustrates an original experimental test bench that simulates sliding and rolling contacts through which a test current is flowing. Unexpected and interesting results disclose how this particular field is challenging and how more investigations are still required to achieve an adequate and complete interpretation. The understanding of this phenomenon could give rise to modification to the composition and the microstructure of rollers and rings employed in offshore wind turbines. Keywords Rolling bearings, currents, wear, offshore wind turbine Introduction The behavior of a pair of tribo-elements with sliding and rolling contact has been extensively studied in literature as an important branch of Tribology. Both experimental and theoretical works have been dedicated to a huge amount of applica- tions. In order to name a few of them, and only those which the authors have been involved into, it is worth noticing how the variety of the applications has been extended to very different fields, such as special transmissions (Belfiore and De Stefani, 2003; Belfiore et al., 2006a), gears (Belfiore, 2004; Belfiore et al., 2006b), metal forming (Belfiore et al., 2007), cold rolling (Bolt et al., 2010), and microsystems (Belfiore et al., 2014). However, more recently, the applications where an electric current is induced to flow through a pair of tribo-elements have received a certain attention in literature. The influence of current flowing through a contact is particularly evident in electric railway vehicles pantograph, where an arc discharge takes place on the contact strip, and in electric motor brushes. For these reasons, a certain attention has been paid to the behavior of such tribo-systems. Since 1978, current flow through tribological contacts has been investigated on copper-graphite brushes at high speeds (160 m/s) and high current densities (870 A/cm 2 ; Casstevens et al., 1978). Although the presence (or absence) of electric current flow appeared to have a limited impact on the measured wear rate, some interesting results have been found. For example, for the same speed, the positive brush appeared to be less exposed to wear than the negative one. Moreover, the contact electrical resistance appeared to be decreasing with increasing loads. The effects of current on friction and wear in powder metallurgy brushes have also been studied in another investigation (Feng et al., 2005), where, through scanning electron microscope (SEM) observations, current appeared to stimulate roughness and abrasion. 1 Department of Engineering, Roma Tre University, Roma, Italy 2 RINA Consulting—Centro Sviluppo Materiali S.p.A., Roma, Italy Corresponding author: Nicola Pio Belfiore, Department of Engineering, Roma Tre University, Via della Vasca Navale 79, 00146 Roma, Italy. Email: nicolapio.belfiore@uniroma3.it 756963WIE 0 0 10.1177/0309524X18756963Wind EngineeringBelfore et al. research-article 2018 Special Issue Article