Behavior of Low Roughness NiTi Wire in Rotary Bending Fatigue

Surface roughness and fatigue are terms often referred to when discussing the stability and functionality of superelastic NiTi wires.   A low-roughness NiTi wire (0,20, 0,40 and 0,60mm) surface was developed to study the fatigue behavior and fracture characteristics during rotary bending fatigue.  In the study, wire specimens of low-roughness, oxide-free NiTi wires were subjected to rotary bending loads and compared with oxide-free chemically etched wires.  The strain-controlled fatigue was investigated at room temperature.  It will be shown that low surface roughness can alter the fatigue performance.  This can be used for the development of controlled roughness with modified fatigue performance.   In addition, a concept on fatigue-fracture will be proposed to assist in the understanding of the wire performance in applications that require rotary bending performance.

Keywords—nitinol; wire; surface roughness; rotating bending fatigue