Biaxial tension-torsion coupling fatigue resonance of single-walled MoS2 nanotubes.

Fatigue characteristics of nanotubes are crucial for enhancing the reliability of flexible nanoelectronic devices. This work systematically investigates fatigue behaviors of single-walled MoS2 nanotubes subjected to biaxial tensile-torsion coupling loading. Results show that fatigue life decreases as torsion angle and axial excitation frequency increase. More interestingly, fatigue life exhibits a non-monotonic decrease with increasing excitation frequency for all torsion angles, presenting two distinct minima in the low-to-mid frequency range. We have developed a method for calculating natural frequencies under combined biaxial tension and torsion, and discovered that the first minimum corresponds to the tensile natural frequency, while the second corresponds to its first harmonic. In the high-frequency regime, however, fatigue life rapidly drops into a broad minimum plateau governed by strain-rate effects rather than sharp harmonic resonances. Namely, the minimum of these two fatigue lives is caused by fatigue resonance due to excitation frequency being equal to the system's natural frequency. We also find that fatigue energy is distributed and dissipated at the excitation frequency and natural frequency. When excitation frequency matches the natural frequency, fatigue life reaches a minimum due to the dissipation of most natural frequency phonons. These observations provide guidance for considering fatigue resonance under tension-torsion coupling to improve the service life of nanotube-based devices.