Torque-Based Assessment of Abrasive Wear in Rotating Shaft–Seal Systems Under Lunar Regolith Simulant

Despite extensive research on the abrasive properties of lunar regolith, the use of in-process tribological signals for wear assessment remains insufficiently studied. The aim of this work is to evaluate the relationship between torque response and abrasive wear severity in rotating shaft–seal systems exposed to lunar regolith simulants. Rotating EN 1.4404 stainless-steel shafts and spring-loaded natural polytetrafluoroethylene (PTFE) lip seals were tested under three-body abrasive wear conditions. Five particle-size fractions of LX-M100 Lunar Mare and LX-TH100 simulants were investigated at test durations of 15 min, 30 min and 1440 min. Frictional torque was continuously recorded, while post-test shaft surface roughness was used to characterize wear severity and Scanning Electron Microscope (SEM) analysis of the PTFE counterface was used to identify wear mechanisms. The results showed that torque response systematically depended on particle-size fraction and simulant type. Furthermore, the torque-response descriptors provide in-process information related to abrasive interaction severity, with peak torque events (Tmax) showing the strongest relationship with abrasive surface modification. The statistical analysis was based on 27 complete observations, and considering the prematurely terminated test runs and the resulting limitations of the dataset, the obtained relationships are interpreted as exploratory. These findings provide a physical basis for torque-based wear monitoring in sealed rotating mechanisms for future lunar applications.