Multiaxial fatigue modeling for Nitinol shape memory alloys under in-phase loading.

Area of Science:

• Materials Science
• Mechanical Engineering
• Fatigue Analysis

Background:

• Multiaxial stress conditions are common in real-world component loading.
• Nitinol (Nickel Titanium) alloys are widely used due to their unique properties.
• Understanding fatigue behavior under multiaxial loading is crucial for component reliability.

Purpose of the Study:

• To review and evaluate classical and critical plane fatigue models for martensitic Nitinol.
• To assess model performance under torsion and in-phase axial-torsion loading.
• To identify the most suitable models for predicting multiaxial fatigue life in Nitinol.

Main Methods:

• Review of stress-based fatigue models including von Mises, Tresca, Findley, McDiarmid, and a novel Fatemi-Socie-type model.
• Evaluation of model application to martensitic Nitinol under torsion and axial-torsion fatigue.
• Focus on shear stress as the primary damage parameter due to observed crack plane behavior.

Main Results:

• The proposed Fatemi-Socie-type model demonstrated superior prediction accuracy compared to other models.
• Critical plane approaches showed greater suitability for multiaxial fatigue prediction in martensitic Nitinol.
• Experimental data from literature were used for validation.

Conclusions:

• Critical plane models are more appropriate for predicting multiaxial fatigue in martensitic Nitinol.
• The developed Fatemi-Socie-type model offers improved fatigue life predictions.
• Recommendations are provided for calibrating more robust multiaxial fatigue models for Nitinol.