scholarly journals Influence of Strain Ratio on Bending Fatigue Life in TiNi Shape Memory Thin Wire

2007 ◽  
Vol 340-341 ◽  
pp. 1193-1198 ◽  
Author(s):  
Ryosuke Matsui ◽  
Hisaaki Tobushi ◽  
Yoshiyasu Makino
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Shape Memory ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Strain Ratio ◽  
Thin Wire ◽  
Bending Fatigue ◽  
Rotating Bending ◽  
Plane Bending

In this study, we performed the bending fatigue test and investigated the influence of strain ratio on fatigue life in TiNi shape memory thin wire. The pulsating plane bending, alternating plane bending and rotating bending fatigue tests were carried. Additionally, we carried out the observation of the fatigue fracture surface by a scanning electron microscope. The behavior of fatigue crack was investigated. The results obtained are summarized as follows. (1) The martensitic transformation (MT) stress of the superelastic thin wire (SE-NT) is higher than that of the SMA thin wire (SME-NT) and the fatigue life of SE-NT is shorter than that of SME-NT. Maximum bending strain at the fatigue limit is the MT starting strain. (2) The low-cycle fatigue life curve in plane bending for SE-NT is expressed by a power function of maximum strain εmax and the number of cycles to failure Nf. The smaller the strain ratio for the same εmax, the shorter the fatigue life. (3) In both the rotating bending and the plane bending, fatigue cracks nucleate on the surface of the wire and one fatigue crack grows preferentially. The region in which fatigue crack propagated is fan-shaped.

scholarly journals Influence of Strain Ratio on Bending Fatigue Life and Fatigue Crack Growth in TiNi Shape-Memory Alloy Thin Wires

2006 ◽  
Vol 47 (3) ◽  
pp. 759-765 ◽  
Author(s):  
Ryosuke Matsui ◽  
Yoshiyasu Makino ◽  
Hisaaki Tobushi ◽  
Yuji Furuichi ◽  
Fusahito Yoshida
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Crack Growth ◽  
Strain Ratio ◽  
Bending Fatigue ◽  
Thin Wires

Mechanical Properties of Cast Shape Memory Alloy for Brain Spatula

2011 ◽  
Vol 674 ◽  
pp. 213-218 ◽  
Author(s):  
Hisaaki Tobushi ◽  
K. Kitamura ◽  
Yukiharu Yoshimi ◽  
K. Miyamoto ◽  
K. Mitsui
Keyword(s):  
Fatigue Life ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Power Function ◽  
Tensile Deformation ◽  
Low Cycle Fatigue ◽  
Fatigue Properties ◽  
Bending Fatigue ◽  
Deformation Properties ◽  
Plane Bending

In order to develop a brain spatula or a brain retractor made of a shape memory alloy (SMA), the bending characteristics of the brain spatula of TiNi SMA made by the precision casting were discussed based on the tensile deformation properties of the existing copper and the TiNi rolled-SMA. The fatigue properties of both materials were also investigated by the plane-bending fatigue test. The results obtained can be summarized as follows. (1) The modulus of elasticity and the yield stress for the cast and rolled SMAs are lower than those for the copper. Therefore, the conventional rolled-SMA spatula and the new cast-SMA spatula can be bent easily compared to the existing copper-brain spatula. (2) With respect to the alternating- and pulsating-plane bending fatigue, the fatigue life of both the copper and the SMAs in the region of low-cycle fatigue is expressed by a power function of the maximum bending strain. The fatigue life of the conventional rolled SMA and the new cast SMA is longer than that of the existing copper. The fatigue life of the new cast and rolled SMAs in the pulsating-plane bending is longer than that in the alternating-plane bending. (3) The fatigue life of the rolled-SMA and the cast SMA for alternating- and pulsating-plane bendings can be expressed by the unified relationship with a power function of the dissipated work.

scholarly journals Rotary bending fatigue analysis of shape memory alloys

2017 ◽  
Vol 29 (6) ◽  
pp. 1183-1195 ◽  
Author(s):  
Maede Hesami ◽  
Laurent Pino ◽  
Luc Saint-Sulpice ◽  
Vincent Legrand ◽  
Mahmoud Kadkhodaei ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Low Cycle Fatigue ◽  
Dissipated Energy ◽  
Uniaxial Tensile ◽  
Temperature Phase ◽  
Stress Plateau ◽  
Bending Fatigue ◽  
Numerical Predictions

In this work, a one-dimensional constitutive model is used to study rotary bending fatigue in shape memory alloy beams. The stress and strain distributions in a beam section are driven numerically for both pure bending and rotary bending to show the basic differences between these two loading types. In order to verify the numerical results, experiments are performed on NiTi specimens with an imposed bending angle using a bending apparatus. Since the specimens show significant stress plateau for forward and backward transformation in their stress–strain response, an enhanced stress–temperature phase diagram is proposed in which different slopes are considered for the start and finish of each transformation strip. In order to study low cycle fatigue of shape memory alloys during rotary bending, the stabilized dissipated energy is calculated from numerical solution. A power law for variations of the fatigue life with the stabilized dissipated energy is obtained for the studied specimens to predict their fatigue life. The numerical predictions of the present approach are shown to be in a good agreement with the experimental findings for rotary bending fatigue. Uniaxial tensile fatigue tests are further performed on the studied specimens to investigate effect of loading type on the fatigue lifetime.

Fatigue properties of a TiNi shape-memory alloy wire subjected to bending with various strain ratios

2003 ◽  
Vol 217 (2) ◽  
pp. 93-99 ◽  
Author(s):  
Y Furuichi ◽  
H Tobushi ◽  
T Ikawa ◽  
R Matsui
Keyword(s):  
Fatigue Life ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Strain Ratio ◽  
Fatigue Properties ◽  
Test Machine ◽  
Shape Memory Alloy Wire ◽  
Alloy Wire ◽  
Rotating Bending ◽  
Alternating Bending

A fatigue-test machine for alternating bending of a wire under strain-controlled conditions was developed. Bending-fatigue tests on a TiNi shape-memory alloy wire were then performed for various strain ratios. The results obtained can be summarized as: (1) the fatigue life curves under alternating bending and pulsating bending, as expressed by the relationship between maximum strain and the number of cycles to failure, systematically follow the order of strain ratio; (2) the larger the strain ratio, the longer the fatigue life; (3) the fatigue life under rotating bending is shorter than that under alternating bending; (4) the increase in temperature during cyclic bending becomes larger in the order: rotating bending, alternating bending, pulsating bending. The fatigue life decreases in proportion to the increase in temperature; and (5) the fatigue limit of strain for alternating bending, pulsating bending and rotating bending is in the region of R-phase transformation.

Effect of machine scatter on the rotating bending fatigue life of materials

2018 ◽  
Vol 27 (3-4) ◽  
Author(s):  
Shashidhar M. Banavasi ◽  
K.S. Ravishankar ◽  
Padmayya S. Naik
Keyword(s):  
Fatigue Life ◽  
Fatigue Cracks ◽  
Test Results ◽  
Angular Misalignment ◽  
Bending Fatigue ◽  
Transverse Vibrations ◽  
Bending Fatigue Test ◽  
Rotating Bending Fatigue ◽  
Rotating Bending ◽  
Set Up

AbstractRotating bending fatigue test results vary from specimen to specimen even if materials are tested in a standard laboratory set up because rotating bending fatigue life or fatigue strength depends upon various factors due to its dynamic action. One method of testing may be machine scatter (offset and angular misalignment). Angular misalignments are unavoidable in dynamic machines due to continuous operation leading to transverse vibrations in specimens. The magnitude of transverse vibrations was measured manually by dial gauge arrangement. Experiments were carried out until fracture either with smooth running conditions or with the effects of offset and angular misalignment. The enhanced effect of misalignments on fatigue life was done through the histogram normal distribution technique. There was a clear distinction between the appearances of the fracture surfaces between the specimens subjected to smooth running conditions and specimen vibration, which reveals general fatigue fracture phenomena and intergranular fatigue cracks, larger decohesion of graphite nodules and isolated cleavage facets. The manual technique used without any resistance strain gauges, as they were not efficiently sustainable under repetitive loads, helped in understanding the dynamic machine scatter on fatigue life in an economical way where there were lesser concentrations in these areas.

scholarly journals Effect of Periodic Overloads on Short Fatigue Crack Behavior in CuNi2Si Alloy under Rotating Bending Load

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1267
Author(s):  
Yahang Qin ◽  
Bing Yang ◽  
Bo Feng ◽  
Yifan Li ◽  
Shoune Xiao ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Constant Load ◽  
Multiple Cracks ◽  
Short Fatigue Crack ◽  
Crack Behavior ◽  
Bending Load ◽  
Rotating Bending

In this study, the short fatigue crack behavior in a precipitation-strengthened CuNi2Si alloy was investigated using a replica technique under rotating bending loads with periodic overloads, an overload ratio of 1.5, and the stress ratio of both was R = −1. The results show that all the fatigue cracks originated from the surface of the specimen and displayed a trend of slow initiation and then rapid propagation. The introduction of overloads significantly reduced the fatigue crack initiation time and the fatigue life of the sample. The average life of the overloaded samples was only 31% that of the constant load samples. For overload specimens, multiple cracks grew at the same time and merged at different stages, causing the crack length to increase instantaneously after they merged, thereby considerably reducing the fatigue life. Fractographical analysis and observation of the surface-etched sample replica film showed that cracks in samples with and without overload both propagated along the grain boundaries.

Tensile Deformation and Rotating-Bending Fatigue Properties of a Highelastic Thin Wire, a Superelastic Thin Wire, and a Superelastic Thin Tube of NiTi Alloys

2004 ◽  
Vol 126 (4) ◽  
pp. 384-391 ◽  
Author(s):  
R. Matsui ◽  
H. Tobushi ◽  
Y. Furuichi ◽  
H. Horikawa
Keyword(s):  
Tensile Deformation ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Fatigue Properties ◽  
Thin Wire ◽  
Bending Fatigue ◽  
Niti Alloys ◽  
Thin Tube ◽  
Rotating Bending Fatigue ◽  
Rotating Bending

The tensile deformation and rotating-bending fatigue properties of a highelastic thin wire, a superelastic thin wire and a superelastic thin tube, all made of NiTi alloys, were investigated experimentally. The results obtained are summarized as follows: (1) The stress-strain curve of the highelastic thin wire is approximately linear up to a strain of 4 percent with a stress of 1400 MPa and shows little dependency on temperature and strain rate; (2) The modulus of elasticity for the initial loading stage of both the highelastic wire and the superelastic tube is low, showing superior bending flexibility as is necessary for medical applications; (3) The slopes of the strain-life curves of the alloys are steep in the low-cycle fatigue region (the strain amplitude of the fatigue limit is in the region of 0.6–0.8 percent); and (4) In the tube, fatigue cracking initiates on the rougher inner surface, resulting in a shorter fatigue life than in the case of the wire.

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