Experimental and theoretical investigation of the frequency effect on low cycle fatigue of shape memory alloys

Strain-controlled tests are performed at different total strain amplitudes, and stress-controlled ones are performed at different maximum stress values. As the frequency increases, the fatigue lifetime under strain controlled loading shows a decreasing trend for all the strain amplitudes tested. The situation in stress controlled tests is however more complicated because the fatigue lifetime shows a maximum stress-dependent trend: for different maximum stresses, the trend in variation of fatigue lifetime with frequency is different. Based on some considerations related to the thermomechanical coupling in SMAs, a theoretical explanation for the evolution of the mechanical response and fatigue lifetime with loading frequency is presented. A new strain-energy based fatigue model is proposed, and is validated by experiments performed under different load ratios.