Risk assessment of motor sheath material with shaftless rim-driven thruster

Shaftless rim-driven thruster is a new type of marine propulsion system which realizes the integrated design of permanent magnet motor, propeller and rudder. Underwater motor puts forward higher requirements for the reliability of motor sheath. This paper investigated the tribological properties and wear mechanism of two sheath materials, epoxy resin and carbon fiber. The friction and wear tests were carried out under different loads and rotational speeds in clear water and sediment water respectively. Wear characteristics of the two materials were analyzed and compared by weighing calculation. The damage risk of two materials were evaluated using a risk assessment method based on risk priority number. The wear risk level of motor sheath is also discussed. The test results show, under the same load the friction coefficient of carbon fiber material decreases obviously with increasing rotational speed, as for epoxy resin it increases first then decreases. Under certain rotational speed, the friction coefficient of carbon fiber material decreases with increasing load, and the friction coefficient of epoxy resin material increases obviously. Under the same working conditions, the friction coefficient of carbon fiber material is only 20%-30% of the friction coefficient of epoxy resin material. The wear volume results of carbon fiber materials is 5%-10% of the wear volume of resin materials under the same working conditions. In general, carbon fiber material has better tribological properties, and the risk of damage caused by wear is reduced by about 66.7%, which can effectively reduce the risk level of motor failure caused by motor sheath wear, which provides a reference for the failure risk assessment of shaftless rim-driven thruster.