The thermomechanical behavior of polycrystalline Ni-rich pseudoelastic NiTi shape memory alloys is analyzed. Special focus is on regions within the stress strain diagram which are regarded as linear elastic in common phenomenological material models, i.e. the region between zero stress and the beginning of the pseudoelastic plateau as well as the region within the hysteresis. In both cases, severe temperature changes can be observed. A possible explanation for this effect is twofold: On the one hand, it might be explained by the presence of an R-phase transformation. On the other hand, unstructured martensite of the B19' phase may form. However, the assumption of a purely thermo-elastic material behavior in those regions does not seem to hold true in general.
Experimental analysisThe setup for the following experiments is described in [2]. Two inductive transducers measure the axial displacement between two aluminum discs, which are clamped on the gauge length of the tubular sample. The sample has an hourglass shape with a radius-to-wall-thickness ratio of 1.5. Concerning the heat treatment of the 50.2at% NiTi material, the sample was solution annealed for one hour at 850 • C and aged for 30 minutes at 350 • C. Between these two steps the sample was quenched by water at 21 • C. During the experiments the temperature is measured by eight thermocouples distributed on the gauge length.
A coupling device for damping within a drive train is presented. For conventional damping couplings, damping is often realized by the dissipation of energy due to material damping or friction. In opposite to this, the damping effect of the presented coupling is based on the dissipated energy during the stress induced phase transformation of pseudoelastic NiTi shape memory alloys. In this contribution the design principles, experimental results, and a numerical simulation using the material law for shape memory alloys developed by Raniecki B. Lexcellent C. and Tanaka K. (Arch Mech 44(3:261-284)) are presented.
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