Experiments on deformation behaviour of functionally graded NiTi structures

Abstract

Functionally graded NiTi structures benefit from the combination of the smart properties of NiTi and those of functionally graded structures. This article provides experimental data for thermomechanical deformation behaviour of microstructurally graded, compositionally graded and geometrically graded NiTi alloy components, related to the research article entitled “Functionally graded shape memory alloys: design, fabrication and experimental evaluation” (Shariat et al., 2017) [1]. Stress–strain variation of microstructurally graded NiTi wires is presented at different heat treatment conditions and testing temperatures. The complex 4-way shape memory behaviour of a compositionally graded NiTi strip during one complete thermal cycle is demonstrated. The effects of geometrical design on pseudoelastic behaviour of geometrically graded NiTi plates over tensile loading cycles are presented on the stress–strain diagrams.

Experimental and numerical data for transformation propagation in NiTi shape memory structures

“…One of the methods to alter and engineer the properties of NiTi shape memory alloys to suit different applications is to design functionally graded NiTi materials [2,3]. The main idea of this method is to combine the unique behaviour of shape memory alloys (SMAs), i.e., shape memory effect and superelasticity, and the functionality of the graded material structures to achieve desired performance or new properties for various applications.…”

Nonuniform transformation behaviour of NiTi in a discrete geometrical gradient design

“…One approach to solving this problem is to design functionally graded NiTi. These materials provide widened transformation stress (and temperature) windows, thus better controllability of the SMA element [24,34]. In addition, FG NiTi can also exhibit new and unique properties, such as the "fishtail-like" behaviour of a compositionally graded NiTi thin strip [34,35].…”

“…These materials provide widened transformation stress (and temperature) windows, thus better controllability of the SMA element [24,34]. In addition, FG NiTi can also exhibit new and unique properties, such as the "fishtail-like" behaviour of a compositionally graded NiTi thin strip [34,35]. The functional gradient can be created by variation in composition [36][37][38], microstructure [39,40], or geometry [41,42].…”

Computational and experimental analyses of martensitic transformation propagation in shape memory alloys

“…These variations originate from gradients in such factors as microstructure, composition, and geometry [6]. In NiTi, the material gradient can be acquired in microstructure by variation in heat treatment [7][8][9] or in composition by variation in Ni/Ti ratio [10][11][12]. In addition, by variation in the geometry of NiTi structure, the alloy experiences a nonuniform stress field upon loading, thus progressive martensitic transformation within the structure is achieved [13][14][15].…”