Mechanical Behaviours of Coronary Stents

2006 ◽  
Vol 49 ◽  
pp. 91-96 ◽  
Author(s):  
György Ring ◽  
Eszter Bognár ◽  
János Dobránszky ◽  
János Ginsztler ◽  
László Major
Keyword(s):  
High Cycle Fatigue ◽  
Mechanical Strain ◽  
Fatigue Tests ◽  
Coronary Stents ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Energy Dispersive Analysis ◽  
Before And After ◽  
Mechanical Behaviours

The role of the stents is to prevent restenosis. The rapid growth of stents’ application in the treatment of cardiovascular diseases resulted in the unique development of these implants. This is mainly due to the effective clinical trials, the success of which determined the use of these endoprostheses. In this study the surface properties of the coronary stents were described by using different methods (stereomicroscopy, scanning electron microscopy and energy dispersive analysis) before and after balloon expansion. Furthermore, the most frequent failures caused by the expansion were introduced. For investigating fatigue properties two high cycle fatigue test equipments were used: the first one simulates the bending stress, and the second one simulates the effect of the pulsating mechanical strain. Surface features of the stents were examined after the fatigue tests as well: macroscopic damages were not originated on the stents, and the implants were not broken down. Only small traces of fatigue occurred on the surface, which became rough; and slip lines and grain boundaries were outlined.

On the Effect of Deformation Mode on Fatigue: Simple Shear vs. Pure Shear

2008 ◽  
Vol 584-586 ◽  
pp. 797-802 ◽  
Author(s):  
Alexei Vinogradov ◽  
Shintaro Yasuoka ◽  
Satoshi Hashimoto
Keyword(s):  
Simple Shear ◽  
High Cycle Fatigue ◽  
Pure Shear ◽  
Deformation Mode ◽  
Equivalent Strain ◽  
Fatigue Properties ◽  
Shear Mode ◽  
Cycle Fatigue ◽  
Mechanical Behaviours

The role of the deformation pre-history in high-cycle fatigue properties of copper produced by severe plastic deformation is discussed. The focus is placed on comparison of the structures and mechanical behaviours of two types specimens produced either by rolling or by ECAP, i.e. by the pure shear or simple shear mode, respectively. It is shown that the deformation either by simple or pure shear mode to the same equivalent strain results in alike mechanical properties, both monotonic and cyclic. The significant influence of the initial stages of strain hardening on fatigue is highlighted.

Effect of Plasma Nitriding on Ultra-High Cycle Fatigue Behaviors of Ti-6Al-4V

2011 ◽  
Vol 295-297 ◽  
pp. 2386-2389 ◽  
Author(s):  
Ren Hui Tian ◽  
Qiao Lin Ouyang ◽  
Qing Yuan Wang
Keyword(s):  
High Cycle Fatigue ◽  
Plasma Nitriding ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Ultrasonic Fatigue ◽  
Ultra High Cycle Fatigue ◽  
Stress Ratios

In order to investigate the effect of plasma nitriding treatment on fatigue behavior of titanium alloys, very high cycle fatigue tests were carried out for Ti-6Al-4V alloy using an ultrasonic fatigue machine under load control conditions for stress ratios of R=-1 at frequency of ƒ=20KHz. Experiment results showed that plasma nitriding treatment played the principal role in the internal fatigue crack initiation. More importantly, plasma nitriding treatment had a detrimental effect on fatigue properties of the investigated Ti-6Al-4V alloy, and the fatigue strength of material after plasma nitriding treatment appeared to be significantly reduced about 17% over the untreated material.

High Cycle Fatigue Properties of Multi-Directionally Forged Commercial Purity Grade 2 Ti Plate

2018 ◽  
Vol 916 ◽  
pp. 166-169
Author(s):  
Ilhamdi ◽  
Toshifumi Kakiuchi ◽  
Hiromi Miura ◽  
Yoshihiko Uematsu
Keyword(s):  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Pure Titanium ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Commercially Pure Titanium ◽  
Cycle Fatigue ◽  
Subsurface Crack ◽  
Initiation Mechanism ◽  
Fish Eye

Tension-tension fatigue tests were conducted using ultrafine-grained commercially pure Titanium (Ti) plates fabricated by multi-directional forging (MDFing). The MDFed pure Ti plates with the thickness of 1 mm were developed aiming at dental implant application. The fatigue properties of MDFed pure Ti plates were superior to those of the conventional rolled pure Ti plates. The higher fatigue strengths in MDFed plates could be attributed to the much finer grains evolved by MDFing. Fatigue crack initiated from specimen surface, when number of cycles to failure was shorter than 106 cycles. In the high cycle fatigue (HCF) region, however, subsurface crack initiation with typical fish-eye feature was recognized in the MDFed pure Ti plate in spite of the thin thickness. Fractographic analyses revealed that no inclusion existed at the center of fish-eye. The subsurface crack initiation mechanism could be related to the inhomogeneity of microstructure with some coarse grains in the inner part of the plate.

Study on Tensile and High Cycle Fatigue Properties of TiC Particle Reinforced Titanium Matrix Composite

2007 ◽  
Vol 546-549 ◽  
pp. 1535-1540 ◽  
Author(s):  
Li Ying Zeng ◽  
Yong Qing Zhao ◽  
Xiao Nan Mao ◽  
Yun Lian Qi
Keyword(s):  
Matrix Composite ◽  
High Cycle Fatigue ◽  
Load Ratio ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Titanium Matrix ◽  
Titanium Matrix Composite ◽  
Tic Particle ◽  
Hcf Strength

Tensile and high cycle fatigue (HCF) property for TiC particle reinforced titanium matrix composite has been studied in this paper. The results indicated that the composite possessed favorite comprehensive properties. The tensile properties for the composite are superior to that of the common high temperature titanium alloys, e.g. IMI834, Ti-1100. Smooth axial fatigue tests were taken at a frequency of 76Hz with a load ratio R of 0.06 and –1, respectively. And HCF strength for the composite at ambient temperature is 595MPa and 494MPa, respectively.

scholarly journals Experimental Study on Forged TC4 Titanium Alloy Fatigue Properties under Three-Point Bending and Life Prediction

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5329
Author(s):  
Bohan Wang ◽  
Li Cheng ◽  
Dongchun Li
Keyword(s):  
Titanium Alloy ◽  
Life Prediction ◽  
High Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fracture Morphology ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Three Point Bending ◽  
Tc4 Titanium Alloy

Ultrasonic fatigue tests of TC4 titanium alloy equiaxed I, II and bimodal I, II obtained by different forging processes were carried out in the range from 105 to 109 cycles using 20 kHz three-point bending. The results showed that the S-N curves had different shapes, there was no traditional fatigue limit, and the bimodal I had the best comprehensive fatigue performance. The fracture morphology was analyzed by SEM, and it was found that the fatigue cracks originated from the surface or subsurface facets, showing a transgranular quasi-cleavage fracture mechanism. EDS analysis showed that the facets were formed by the cleavage of primary α grains, and the fatigue cracks originated from the primary α grain preferred textures, rather than the primary α grain clusters. From the microstructure perspective, the reasons for better equiaxed high-cycle-fatigue properties and better bimodal ultra-high-cycle-fatigue properties were analyzed. The bimodal I fatigue life prediction based on energy was also completed, and the prediction curve was basically consistent with the experimental data.

Specimen Size Effect on Fatigue Properties of Surface-Micromachined Al-3%Ti Thin Films

2007 ◽  
Author(s):  
Jun-Hyub Park ◽  
Man Sik Myung ◽  
Yun-Jae Kim
Keyword(s):  
Thin Film ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Evaluation Method ◽  
High Cycle Fatigue ◽  
Test Procedure ◽  
Fatigue Tests ◽  
Test Method ◽  
Fatigue Properties ◽  
Cycle Fatigue

This paper presents high cycle fatigue properties of an Al-3%Ti thin film, used in a RF (radio-frequency) MEMS switch for a mobile phone and also describes new test method for obtaining static and dynamic characteristics of thin film and reliability evaluation method on MEMS device with thin film developed by authors. Durability should be ensured for such devices under cycling load. Therefore, with the proposed specimen and test procedure, tensile and fatigue tests were performed to obtain mechanical and fatigue properties. The specimen was made with dimensions of 1000μm long, 1.0μm thickness, and 3 kinds of width, 50, 100 and 150μm. High cycle fatigue tests for each width were also performed, from which the fatigue strength coefficient and the fatigue strength exponent were found to be 193MPa and −0.02319 for 50μm, 181MPa and −0.02001 for 100μm, and 164MPa and −0.01322 for 150μm, respectively. We found that the narrower specimen is, the longer fatigue life of Al-3%Ti is and the wider specimen is, the more susceptible to stress level fatigue life of Al-3%Ti was.

High-Cycle Fatigue P-S-N Curve Estimating Method Based on Maximum Likelihood Method for Turbine Coupling Bolt Materials

2014 ◽  
Vol 541-542 ◽  
pp. 592-598 ◽  
Author(s):  
Yu Jiong Gu ◽  
Tie Zheng Jin ◽  
Hai Dong Zu ◽  
Jing Xu ◽  
Dong Chao Chen
Keyword(s):  
Maximum Likelihood ◽  
Fatigue Limit ◽  
High Cycle Fatigue ◽  
Maximum Likelihood Method ◽  
Fatigue Tests ◽  
Likelihood Method ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Modified Method ◽  
Tensile Fatigue

The tensile fatigue tests and S-N curve fitting results of the coupling bolt material 25CrMo were given in this paper. It has been proved that the high-cycle fatigue properties of the bolt material can be accurately described by the three-parameter exponential S-N curve model by comparing the fitting results based on different S-N curve models. The fatigue limit of the high-cycle P-S-N curve calculated by the traditional maximum likelihood method was proved to have a high probability of being higher than the accurate fatigue limit. Therefore, a modified method based on maximum likelihood method was proposed so as to calculate the high-cycle P-S-N curve more accurately. The P-S-N of 25CrMo calculated using the modified method was given in this paper.

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