Rotary bending fatigue analysis of shape memory alloys
Abstract
In this work, a one-dimensional constitutive model is used to study rotary bending fatigue in shape memory alloy beams. The stress and strain distributions in a beam section are driven numerically for both pure bending and rotary bending to show the basic differences between these two loading types. In order to verify the numerical results, experiments are performed on NiTi specimens with an imposed bending angle using a bending apparatus. Since the specimens show significant stress plateau for forward and backward transformation in their stress–strain response, an enhanced stress–temperature phase diagram is proposed in which different slopes are considered for the start and finish of each transformation strip. In order to study low cycle fatigue of shape memory alloys during rotary bending, the stabilized dissipated energy is calculated from numerical solution. A power law for variations of the fatigue life with the stabilized dissipated energy is obtained for the studied specimens to predict their fatigue life. The numerical predictions of the present approach are shown to be in a good agreement with the experimental findings for rotary bending fatigue. Uniaxial tensile fatigue tests are further performed on the studied specimens to investigate effect of loading type on the fatigue lifetime.
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