Shape Memory Alloys (SMAs) are a class of smart materials that, through recognizing different aspects of their behavior, different applications have been simultaneously found for them in last decades. Shape Memory Effect and Pseudoelasticity are main responses of SMAs, and they are employed in different configurations such as wire, spring and tube. SMA springs tolerate higher recoverable strains in comparison to traditional springs. Their damping ability and thermomechanical response have imported them into wide range of applications such as sensors and actuators. They are used in different fields including aerospace, automotive and robotic industries. Due to the growth of SMA spring applications, their fatigue analysis also needs to be investigated. Fatigue life estimation of SMA springs under different loading conditions can be achieved by determining related fatigue curves. Various methods such as stress-life and strain-life are used to estimate fatigue life of SMAs. According to important advantages of energy approach, it has been used in this research for analyzing fatigue life of SMA springs. Due to the effect of geometric characteristics on dissipated energy, effective geometric factors have been also investigated, and conditions in which geometrical characteristics need to be optimized is also presented. Required specimens were fabricated and tensile and fatigue tests were conducted. Force-displacement response of specimens have been obtained by rate-dependent modeling for SMA springs. By using the values of dissipated energy in stabilized cycle and number of cycles to failure (which was acquired by fatigue tests), fatigue curves have been finally presented. Through given correlation (which has been acquired by statistic approach), a user can be able to estimate the fatigue life. Also the effect of large deformation, convective heat transfer coefficient and mean applied displacement on SMA springs have been studied. Seeing good agreements of the numerical results with empirical findings, it can be concluded that energy approach is an applicable and appropriate method for fatigue analyzing of SMA springs. Keywords: Shape Memory Alloy, fatigue, helical spring, rate-dependent model, large deformations,pseudoelasticity.
