Effect of Pre-Strain on Nitinol Fatigue Life

Multiple levels of pre-strain ≤15% were studied in tensile-tensile loading to explore the limits of pre-strain cycles and their influence on fatigue life.  A significant positive correlation was observed between the level of pre-strain and extending specimen fatigue life ≤30% which advocates for pre-straining to improve material resistance to fatigue.  Various analyses; crack propagation critical distance, critical plane analysis, Kandil-Brown-Miller damage model, are fit to the data for comparison.  The likely mechanisms of pre-straining’s contribution to fatigue resistance are presented.