Mean strain effects on the fatigue properties of superelastic NiTi

Abstract

lowered from 110 J in the peak-aged condition (5 hours) to but not in high-cycle fatigue. This difference is also reflected 70 J in the overaged condition (10 hours). Since the fracture in the S-N curves, where lines with different slopes are occurred in a mostly transgranular manner, [8,9] the embrittleneeded to fit the high-cycle and low-cycle data. ment was not severe, as compared to the intergranular The martensitic transformation is the basis of the superembrittlement, which produced very low impact toughness elastic and shape-memory properties. Yet, most existing values below 10 and 5 J, even at 300 ЊC, in the Mo and studies do not explore the influence of the martensitic trans-MoW steels, respectively. In the overaged condition, since formation on fatigue properties. The study by Miyazaki [4] the presence of cementite [9] indicates that there are sufficient shows that the martensitic transformation can influence the amounts of W available to tie up the P, no severe intergranufatigue properties, but does not explicitly examine it. We lar embrittlement could occur.propose to examine the influence of the martensitic transformation on the fatigue properties of NiTi by exploring meanstrain effects on the fatigue properties. Mean stress and mean-strain determine the phase of the material in superelas-This work was partly supported by the POSCO. tic specimens. Depending on the mean strain, a specimen may contain austenite (A), martensite (M), or both phases (AM), and different deformation modes are associated with REFERENCES each of these cases. In numerous applications, loads cycle 1.

Nitinol Fatigue: A Review of Microstructures and Mechanisms

“…Testing under simulated in vivo conditions of processoptimized Nitinol is then required to gain insight into the fatigue behavior of biomedical devices. Tabanli et al (Ref 14,15) were the first to explore the effects of mean strain on the fatigue behavior of superelastic Nitinol hypotubing (A f = 5°C). Room temperature cycling was conducted at a constant strain amplitude of $0.22%.…”

Design of a Medical Non‐Linear Drilling Device: The Influence of Twist and Wear on the Fatigue Behaviour of NiTi Wires Subjected to Bending Rotation

“…Thus, the increase of the external twist leads to an increase of the effective mean strain during BRF cycling; and it has been observed that a non-zero mean strain may well increase the fatigue life of NiTi under certain circumstances [25].…”

Fatigue Strength of a Novel Heart Valve Bioprosthesis

“…Fatigue strength was assessed using Goodman diagram recommended by FDA for the analysis of this kind [13][14][15]. This method realizes the concept of infinite fatigue life (IFL).…”