Fatigue Properties of Stainless Steel Wire Ropes for Electrodes in Functional Electrical Stimulation Systems

抄録

The fatigue properties of stainless steel wire ropes with 19 strands developed for a functional electrical stimulation (FES) electrode in simulated body fluids were investigated. The wire ropes were made of a new austenite stainless steel (Fe–22Cr–10Ni–6Mn–2Mo–0.4N alloy) and Type 316L stainless steel. Fatigue properties of the wire ropes were evaluated in Hanks’ solution and 1 mass% lactic acid solution at 310 K using a dual axel-driven rotating-bending fatigue machine. After fatigue testing, the wire ropes were examined by scanning electron microscopy and the metal ion concentrations in the solutions were quantitatively determined. Corrosion products in the solutions were analyzed by transmission electron microscopy. Under low maximum cyclic bending stress level, the Fe–22Cr–10Ni–6Mn–2Mo–0.4N alloy wire rope exhibited a higher cyclic life than the Type 316L stainless steel wire rope. Metal ion concentrations in the lactic acid solution increased with increasing of number of fatigue cycles, and no corrosion products were detected. In Hanks’ solution, ferric oxyhydroxides (FeOOH) were formed as corrosion products during fatigue testing and the concentrations of metal ions were lower than those in the lactic acid solution for cyclic tests over 10⁴ cycles.