Influence of stress concentrations on failure of shape memory alloy actuators

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Shape Memory Alloys (SMAs) are drawing much attention from the active materials community due to the solid-solid phase transformation which exhibits large actuation strains at large actuation stress levels. As SMAs become better understood, SMAs may become more commonly utilized as components of a system. Such systems would require SMAs to be attached to other components, often leading to a stress concentration at the attachment point. Therefore it is necessary to develop a more thorough understanding of how stress concentrations affect the failure in SMA actuators. One such stress concentration which is often encountered when attaching structural components together is a hole or notch, which lead to triaxial states of stress around these stress concentrations. In this work, notched cylindrical SMA specimens are investigated to elucidate how the triaxiality of the notches affect the stress profiles and phase transformation behavior. Numerical results indicate that by changing the radius of the notch in cylindrical specimens, the evolution of the phase transformation is directly affected, which also impacts the distribution of stress along the area of minimum cross-sectional area. Experimental results are also presented, providing evidence that phase transformation in the presence of a stress concentration while at sufficient loads may lead to failure of the SMA.