Thermal effects in a mechanical model for pseudoelastic behavior of NiTi wires

Abstract

A mechanical model for pseudoelastic behavior of NiTi wires is proposed with the aim to predict the behavior of Shape Memory Alloys(SMA) damping wire elements in model structures. We have considered at first a simple linearwise stress-strain relationship to describe the basic isothermal behavior of the SMA members. Then, this basic model is modified in order to include the effect of the strain rate. The model is based on detailed experimental characterization performed on a Ni rich NiTi superelastic wire which included the study of the localized character of the deformation and the local heat generation associated with the stress induced martensitic transformation occurring in these alloys. Heat conduction along the wire and heat interaction with the surroundings was also considered. In that way, the resulting local temperature field around the transformation front is assessed and its effect on the progression of the transformation is evaluated. It is shown how the simple mechanical model reproduces the global mechanical behavior, including the existence of a maximum in the damping capacity with the transformation rate.

Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading

“…The phase transformation is clearly a localized process occurring over this region within the wire, whereas no transformation or deformation occurs in the rest of the gage length. The finite width of the transformation zone determined here is in good agreement with previous theoretical considerations that predict the zone to scale with the diameter of the specimen [70][71][72]. Moreover, our straightforward experimental analysis complements recent surface observations by digital image correlation [73] and modeling results on the strain fields in thin NiTi ribbon specimens which exhibit transformation zones with similar finite widths [30,[74][75][76].…”

Pseudoelastic fatigue of NiTi wires: frequency and size effects on damping capacity

“…The complete analysis of the problem is however much more complex, requiring, firstly, the consideration of the full heat transfer problem. Furthermore, the appearance of additional fronts of transformations is another important issue that has to be addressed if a more realistic modeling of the damping behavior is desired [18]. The presence of multiple fronts modify the local temperature at the transforming interface with consequences for the maximum overstressing necessary for further propagation.…”

Analysis of Wire Position and Operating Conditions on Functioning of NiTi Wires for Shape Memory Actuators

“…1-D models ( Ref 14,16,17) have been used to investigate the deformation mechanism based on detailed descriptions of the transformation rate and generally, results indicate that the overall temperature response and thus the displacement response is mainly driven by the heat convection phenomenon. For this reason, this approach considers a simple empirical model that does not incorporate physical aspects describing the nature of phase transformation but it can be useful for obtaining practical information concerning the influence of the operating conditions on the SMAs wire response time.…”

“…Moreover, Bhattacharyya (Ref 13) did not provide any information on the influence of the wire diameter and position on the convective coefficient. Following this approach, other papers are reported in literature (Ref [14][15][16][17][18] but, in all these cases, the convective coefficient value used in the numerical computations was independent of temperature.…”