Abstract: Micron-scale molybdenum (Mo) wires are vital in numerous technological applications, including micro-electromechanical systems and nanodevices. Understanding their mechanical behavior under cyclic tor-sion loading is critical in designing reliable and durable components. This work investigates the mechan-ical behavior and fracture characteristics of micron Mo wires under various torsional loading conditions, including monotonic, symmetric, and asymmetric cyclic torsion. The results reveal that the fractures ob-served in Mo wires exhibit a relatively planar characteristic with noticeable clockwise river-patterned cleavage steps under monotonic torsion, mirroring the direction of the torsional stress applied during the experiment. In terms of symmetric cyclic torsion, it is notable that cyclic softening becomes increasingly pronounced as the increase of strain amplitude. The fractures exhibit distinctive stratification, character-ized by the longitudinal cracks propagating radially. When the unloading strain is less than the loaded strain, the extent of the strain hysteresis effect amplifies with an increase in unloading strain. And the observed fracture characteristics are consistent with those under monotonic torsion. Differently, when the loading strain equals the unloading strain, a distinctive fracture pattern emerges in the Mo wire, characterized by a "peak" shape. This research provides valuable insights for optimizing the mechanical reliability of micron wires in microscale and nanoscale applications.

Key words: Micro-torsion, Molybdenum wire, Cyclic deformation, Fracture characteristics, Cyclic softening