scholarly journals Comparison of Bending Fatigue of NiTi and CuAlMn Shape Memory Alloy Bars

2020 ◽  
Vol 2020 ◽  
pp. 1-9 ◽  
Author(s):  
Haoyu Huang ◽  
Yuan-Zhi Zhu ◽  
Wen-Shao Chang
Keyword(s):  
Fatigue Life ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Damping Ratio ◽  
Strain Curve ◽  
Fatigue Properties ◽  
Functional Fatigue ◽  
Cyclic Bending ◽  
Structural Fatigue ◽  
Secant Stiffness

The behaviour under cyclic bending and in particular the fatigue properties of shape memory alloy (SMA) bars are important for civil engineering applications. In this paper, structural and functional fatigue is studied for both NiTi- and copper-based shape memory alloys. The results are presented from cyclic bending tests on 7 mm diameter NiTi and 12 mm diameter CuAlMn SMA bars targeted at 100,000 cycles. During the tests, dynamic loading at 1 Hz, 5 Hz, and 8 Hz was applied for different strain levels (0.5%, 1%, 2%, and 6%). The stress-strain curve, damping ratio, and secant stiffness were analysed for material characterisation, and the evolution of these parameters was studied to assess functional fatigue. The fatigue life is extended dramatically when the strain is below 1%, and the structural fatigue life of CuAlMn is shown to be better than that of NiTi and to depend on the loading rate. However, decay in stiffness can be found in the CuAlMn SMA, which is considered to be caused particularly by its long grain boundary.

Advances in enhancing structural and functional fatigue resistance of superelastic NiTi shape memory alloy: A Review

2021 ◽  
pp. 1045389X2110235
Author(s):  
Kiran Nargatti ◽  
Sandeep Ahankari
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Fatigue Resistance ◽  
Fatigue Behaviour ◽  
Research Literature ◽  
Fatigue Performance ◽  
Fatigue Properties ◽  
Niti Shape Memory Alloy ◽  
Functional Fatigue ◽  
Structural Fatigue

Nitinol (NiTi), a shape memory alloy (SMA) of nickel and titanium, exhibits two unique properties: the shape memory effect and superelasticity. It is a material of choice for applications demanding extraordinary flexibility and motion. It is subjected to greater fatigue strains compared to ordinary metals. The structural and functional fatigue properties are important for assessing the fatigue life and reliability of the superelastic NiTi. The advances made in the experimental analysis to improve the structural and functional fatigue resistance of superelastic NiTi are reviewed in this paper. Various aspects of fatigue behaviour of NiTi in biomedical and cooling applications, along with fatigue failure mechanism, are elaborated under structural fatigue. Importance of functional fatigue and its connect with structural fatigue performance of NiTi is discussed citing recent research literature. Furthermore, the effect of processing parameters involved in additive manufacturing on the fatigue performance of NiTi is also discussed.

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.

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.

Understanding the Fatigue Behaviour of NiTiCu Shape Memory Alloy Wire Thermal Actuators

2008 ◽  
Vol 378-379 ◽  
pp. 301-316 ◽  
Author(s):  
S.K. Bhaumik ◽  
C.N. Saikrishna ◽  
K.V. Ramaiah ◽  
M.A. Venkataswamy
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Fatigue Behaviour ◽  
Cyclic Stress ◽  
Continuous Change ◽  
Functional Fatigue ◽  
Structural Fatigue ◽  
Thermal Actuators ◽  
Working Stress ◽  
Mechanical Cycling

This paper deals with the fatigue behaviour of NiTiCu shape memory alloy (SMA) wire actuators on thermo-mechanical cycling (TMC). Cyclic loading in SMA actuators is invariably associated with both functional and structural fatigue. The characteristic of the actuators such as austenite (hot shape) remnant deformation and recovery strain undergo changes upon TMC. These in turn result in continuous change in strain response (functional fatigue) during application. It has been shown that the functional fatigue can be minimized by adopting TMC at higher stress than that of the working stress prior to the application. On the other hand, failure of the actuators by fracture (structural fatigue) due to cyclic stress/strain is inevitable. Study shows that the fatigue life of the actuators is strongly dependent on the type of loading and the temperature range of operation. This has been explained in terms of damage accumulation, crack initiation and fracture behaviour.

scholarly journals Relationship Between Functional Fatigue and Structural Fatigue of Iron-Based Shape Memory Alloy FeMnNiAl

2020 ◽  
Vol 6 (2) ◽  
pp. 256-272 ◽  
Author(s):  
R. Sidharth ◽  
Y. Wu ◽  
F. Brenne ◽  
W. Abuzaid ◽  
H. Sehitoglu
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Functional Fatigue ◽  
Structural Fatigue ◽  
Iron Based

scholarly journals Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2738
Author(s):  
Roland Pawliczek ◽  
Tadeusz Lagoda
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Strain Curve ◽  
Mean Value ◽  
Fatigue Properties ◽  
Stress Strain ◽  
Reference Case ◽  
Block Loading ◽  
The Mean ◽  
Mean Strain

The literature in the area of material fatigue indicates that the fatigue properties may change with the number of cycles. Researchers recommend taking this into account in fatigue life calculation algorithms. The results of simulation research presented in this paper relate to an algorithm for estimating the fatigue life of specimens subjected to block loading with a nonzero mean value. The problem of block loads using a novel calculation model is presented in this paper. The model takes into account the change in stress–strain curve parameters caused by mean strain. Simulation tests were performed for generated triangular waveforms of strains, where load blocks with changed mean strain values were applied. During the analysis, the degree of fatigue damage was compared. The results of calculations obtained for standard values of stress–strain parameters (for symmetric loads) and those determined, taking into account changes in the curve parameters, are compared and presented in this paper. It is shown that by neglecting the effect of the mean strain value on the K′ and n′ parameters and by considering only the parameters of the cyclic deformation curve for εm = 0 (symmetric loads), the ratio of the total degree of fatigue damage varies from 10% for εa = 0.2% to 3.5% for εa = 0.6%. The largest differences in the calculation for ratios of the partial degrees of fatigue damage were observed in relation to the reference case for the sequence of block n3, where εm = 0.4%. The simulation results show that higher mean strains change the properties of the material, and in such cases, it is necessary to take into account the influence of the mean value on the material response under block loads.

Rate-Dependent Damping Capacity of NiTi Shape Memory Alloy

2011 ◽  
Vol 172-174 ◽  
pp. 37-42 ◽  
Author(s):  
Yong Jun He ◽  
Qing Ping Sun
Keyword(s):  
Shape Memory Alloy ◽  
Strain Rate ◽  
Shape Memory ◽  
Strain Curve ◽  
Tensile Loading ◽  
Niti Shape Memory Alloy ◽  
Damping Capacity ◽  
Environmental Condition ◽  
Mechanical Coupling ◽  
Rate Dependent

High damping capacity is one of the prominent properties of NiTi shape memory alloy (SMA), having applications in many engineering devices to reduce unwanted vibrations. Recent experiments demonstrated that, the hysteresis loop of the stress-strain curve of a NiTi strip/wire under a tensile loading-unloading cycle changed non-monotonically with the loading rate, i.e., a maximum damping capacity was obtained at an intermediate strain rate (ε.critical). This rate dependence is due to the coupling between the temperature dependence of material’s transformation stresses, latent-heat release/absorption in the forward/reverse phase transition and the associated heat exchange between the specimen and the environment. In this paper, a simple analytical model was developed to quantify these thermo-mechanical coupling effects on the damping capacity of the NiTi strips/wires under the tensile loading-unloading cycle. We found that, besides the material thermal/mechanical properties and specimen geometry, environmental condition also affects the damping capacity; and the critical strain rate ε.criticalfor achieving a maximum damping capacity can be changed by varying the environmental condition. The theoretical predictions agree quantitatively with the experiments.

Structural fatigue and fracture of shape memory alloy actuators: Current status and perspectives

2021 ◽  
pp. 1045389X2110572
Author(s):  
Md Mehedi Hasan ◽  
Theocharis Baxevanis
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Current Status ◽  
Structural Fatigue ◽  
Sma Actuators ◽  
Empirical Relations ◽  
Fatigue And Fracture ◽  
And Performance ◽  
Commercial Applications ◽  
Crack Growth Rates

Shape Memory Alloy (SMA)-actuators are efficient, simple, and robust alternatives to conventional actuators when a small volume and/or large force and stroke are required. The analysis of their failure response is critical for their design in order to achieve optimum functionality and performance. Here, (i) the existing knowledge base on the fatigue and overload fracture response of SMAs under actuation loading is reviewed regarding the failure micromechanisms, empirical relations for actuation fatigue life prediction, experimental measurements of fracture toughness and fatigue crack growth rates, and numerical investigations of toughness properties and (ii) future developments required to expand the acquired knowledge, enhance the current understanding, and ultimately enable commercial applications of SMA-actuators are discussed.

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