Periodic and propagating instabilities in superelastic NiTi wire twists

Abstract eng:
Shape memory alloy cables made from stranded NiTi wires are a relatively new adaptive structure that has only recently been explored. While straight SMA wires typically have a single nucleating front that propagates along the length of the wire, SMA cables have a varied propagation behavior from wire-like to a more spatially diffuse transformation. Experiments on 1x3 twists with varying twist helix angles were performed to establish the role of helix angle on the superelastic response of the material. The strain and temperature fields were also captured using stereo digital image correlation and thermography to record the propagation behavior. Finite element analysis simulations of the twists with a material model calibrated from straight wire data were shown to accurately predict the experimental data. The larger helix angle twists were shown to have increased stiction and relative motion between the wires leading to more wear.

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