Cyclic Deformation and Fatigue of a TiNi Shape-Memory Alloy Wire Subjected to Rotating Bending

Abstract

The cyclic deformation and fatigue of a TiNi shape-memory alloy wire were studied by carrying out rotating-bending fatigue tests at various strain amplitudes, temperatures, and rotational speeds in air and in water. The results were summarized as follows: (1) for strain amplitudes in the rhombohedral-phase transformation region, the fatigue life was longer than 107 cycles and the deformation properties did not change under cyclic deformation; (2) for the strain amplitudes in the martensitic transformation region, the fatigue life was shorter than 105 cycles and the higher the temperature, the shorter was the fatigue life; (3) the rotational speed did not affect the fatigue life in water but a higher rotational speed led to a shorter fatigue life in air.

Predicting in vivo failure of pseudoelastic NiTi devices under low cycle, high amplitude fatigue

“…At smaller strain amplitudes, the device lifetime measured in the current study significantly exceeds that measured by others, either in air or in water environments. For example, at a strain amplitude a ϳ 2.3% in air, average lifetime was measured as 530 cycles and 372 cycles in the studies of Pruett et al 17 and Tobushi et al, 11 respectively, whereas N f ϭ 4663 cycles in the current study.…”

“…As evidenced by Figure 3, Tobushi et al [11][12][13][14] have contributed significantly to the study of NiTi rotating-bending fatigue for a limited to 0.5-2.5%. These materials engineering studies utilized NiTi wire of slightly larger diameter (0.75 mm), and systematically varied temperature, strain amplitude, environmental fluid, and rotational speed (100 -1000 rpm).…”

“…In the endodontic research community, Pruett et al 17 reported a negligible effect of rpm on N f for a Ͼ 2.5% and rpm Ͼ 1000. Conversely, the materials engineering analysis of Tobushi et al 11 indicated a strong effect of rpm on N f for a Ͻ 2.5% and rpm Ͻ 1000. The logarithmic relationship quantified by the expanded range of experimental conditions in the current study explains this apparent contradiction well.…”

“…This shortcoming is due chiefly to the distinct approaches to research adopted by these two fields. Materials engineering studies such as those reported by Tobushi et al [11][12][13][14] relate the cycles to failure N f of pseudoelastic NiTi as a function of systematically varied and normalized quantities such as strain amplitude and relative temperature. In such studies, experiments are conducted on model NiTi specimens-smooth wires for which the cross-sectional diameter and the strain amplitude are constant over the length of the wire-but do not consider the range of strain amplitudes consistent with endodontic applications.…”

Surface Crack Development in Transformation Induced Fatigue of SMA Actuators

“…However, most of the results pertain to a limited number of cycles and mainly focus on the development and stability of two-way transformation strain and the evolution of plastic strain. Mechanical fatigue properties of SMAs have been primarily studied based on the pseudoelastic response of SMAs with some key results presented by Tobushi et al [5] and Miyazaki et al [6]. However, thermally induced transformation fatigue is a more recent subject, where the applied level of stress has a major influence on the development of plastic strains and therefore on a low cycle fatigue performance of SMA actuators (Bigeon and Morin [7], De Araujo et al [8], Lagoudas et al [9], Cuellar et al [10]).…”