TWSME of a NiTi strip in free bending conditions: experimental and theoretical approach

Abstract

This paper deals with the two-way shape memory effect (TWSME) induced on a strip of a nearequiatomic NiTi alloy by means of the shape memory cycling training method. This procedure is based on the deformation in martensite state to reach the desired cold shape followed by cycling the temperature from above A f to below M f . To this end, the sample was thermally treated to memorise a bent shape, thermomechanical trained as described and thermally cycled in unloaded conditions in order to study the stability of the induced TWSME. Heating to A f was reached by a hot air stream flow whereas cooling to M f was achieved through natural convection. The evolution of the curvature with the increasing number of cycles was evaluated. The thermomechanical behaviour of the strip undergoing uniform bending was simulated using a one-dimensional phenomenological model based on stress and the temperature as external control variables. Both martensite and austenite volume fractions were chosen as internal parameters and kinetic laws were used in order to describe their evolution during phase transformations. The experimental findings are compared with the model simulation and a numerical prediction based on the approach proposed in [25].

Simulation of Shape Memory Alloy (SMA)-Bias Spring Actuation for Self-Shaping Architecture: Investigation of Parametric Sensitivity

“…The MVF reaches 100% in pure stress-induced martensite, whereas it becomes zero in full austenite. In other cases (M f < T < A f ), SMAs always exist as a mixture of austenite and martensite, and ξ is approximated by the following formulas [2,19] with experimental curve-fitting parameters in an elementwise format…”

“…Equation (9) depends on the direction of the transition, i.e., martensite to austenite ( M → A ; heating) or vice versa, and N A and N M represent the influence of the loading and its direction to MVF. N A and N M can be experimentally computed from the slope of a σ − T curve [1] or derived from the Clausius-Claperyron relation [19], such as:…”

“…In Equation 24, it should be also emphasized that the shear modulus is not directly associated with the spring length limit. Now, introducing Equation 20to Equation (19), and rearranging it for δ S , we obtain a comprehensive deformation function of SMA-bias coil spring actuation:…”

Vision based supervised restricted Boltzmann machine helps to actuate novel shape memory alloy accurately

“…The shape change intrinsically occurs only during heating from martensite to austenite phases, not cooling from austenite to martensite, referring to one-way-SME, non-reversible. By applying a series of heat treatments or “training” processes, SMA can have two-way-SME with a limited degree of reverse actuation that are of little usefulness 11 , 12 , e.g., less than 20–30-degree angles for a reversible bending strip 13 . Therefore, most of the commercial SMAs are supplied only for performing a single-point, mostly one-way, actuation—i.e.…”

Vision Based Supervised Restricted Boltzmann Machine Helps to Actuate Novel Shape Memory Alloy Accurately

“…By applying a series of heat treatments or "training" processes, SMA can have two-way-SME with a limited degree of reverse actuation that are of little usefulness [11][12], e.g. less than 20-30-degree angles for a reversable bending strip [13]. Therefore, most of the commercial SMAs are supplied only for performing a single-point, mostly one-way, actuation -i.e.…”