Effect of thermal effects on the wear behavior of copper-based powder metallurgy brake blocks under multiple braking conditions

During straight-rail and curved-rail braking of underground monorail cranes, copper-based powder metallurgy brake blocks exhibit distinct initial surface-, line-, and point-contact modes with the rail, resulting in different thermo-mechanical responses. However, the influence of thermal expansion on transient wear evolution under these contact modes remains insufficiently understood. To address this issue, thermo-mechanical wear models were established for straight-rail, outer curved-rail, and inner curved-rail braking, and braking processes with and without thermal expansion were compared. Braking-cycle experiments were also conducted to characterize surface damage and wear morphology. Without thermal expansion, the incremental maximum wear depth decreased progressively under all three contact conditions. With thermal expansion, during the three successive 0.1-s intervals following the initial 0–0.1 s interval, the corresponding increments were 31.22%, 8.66%, and 2.50% of the initial-interval increment for straight-rail braking and 16.80%, 10.71%, and 8.22% for inner curved-rail braking, both showing decreasing trends. In contrast, those for outer curved-rail braking were 80.72%, 88.41%, and 116.20%, showing an increasing trend. These results indicate that the time-dependent evolution of the incremental maximum wear depth under thermal expansion is closely related to the initial contact mode. The experiments further showed that surface roughness generally decreased and stabilized after the running-in stage, while the dominant damage evolved from pitting and spalling to abrasive wear characterized by pronounced plowing grooves. These findings provide a reference for optimizing brake-block contact geometry and controlling localized wear in underground monorail crane braking systems.