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Purpose Fretting wear exists widely in the field of matching mechanical parts whereas previous research studies mostly focus on the point contact through a ball-plate tribometer. This paper aims to study the influence of wear debris on the fretting wear characteristics of the nitrided medium carbon steel under line contact condition at elevated temperature. Design/methodology/approach Fretting wear behavior of the nitrided medium carbon steel was experimentally investigated under line contact condition at elevated temperature and different normal loads without lubrication. Wear loss, worn surface and wear debris were studied to analyze the wear mechanism of nitrided steel. Findings The results showed that surface hardness of the medium carbon steel was notably improved because of the generation of a 230 µm nitrided case. Wear loss increased with the normal load, which was associated with the damage of a thin solid film formed by the wear debris, consisting of iron oxides and chromium oxide rather than only iron or iron oxides. The wear debris became partially amorphous and spherical because it was trapped within the contact interface and was ground, rolled, oxidized under line contact conditions. The spherical wear debris acted as a third body and formed a lubricating film between the contact faces. This lubricating film helped to stabilize the friction coefficient and reduced the wear rate, which further caused the acceleration of wear volume to gradually decrease. The wear mechanisms of the nitrided steel were oxidation wear, abrasive wear and fatigue spalling of the oxide layer. Originality/value The findings are helpful to understand the fretting wear behavior of the friction pair under line contact and enrich the fretting tribology theory.

In order to examine the effect of polysaccharides from morinda officinalis (MOP) on bone quality of osteoporosis rats. The osteoporosis in rats was induced by ovariectomy, and MOP (100 or 300 mg/kg) was orally administrated once daily. The animals were assessed 30 days after the operation for bone mineral density, serum cytokines level and mineral element concentration. MOP administration in rats resulted in an increase in bone mineral density and mineral element concentration, a decrease in serum cytokines level, which indicated that MOP administration may play an important role in the development of osteoporosis.