ABSTRACT
Due to the effect of structural characteristics and service environment of esophageal stent, fatigue damage of esophageal stent is developed easily, which may lead to serious complications. At present, the researches on fatigue performance of esophageal stent involve load spectrum, stress-strain relationship, fatigue crack and fatigue life prediction, and there are three main research method: theoretical analysis, numerical simulation and experimental research. In this paper, various analysis methods and limitations for measuring fatigue performance of esophageal stent are elaborated and summarized in detail, and the future research of esophageal stent is prospected.
ABSTRACT
In order to evaluate the safety performance of self-expandable NiTi alloy stents systematically, the dynamic safety factor drawn up by International Organization for Standardization, was used to quantitatively reflect the safety performance of stents. Based on the constitutive model of super-elastic memory alloy material in Abaqus and uniaxial tensile test data of NiTi alloy tube, finite element method and experiments on accelerated fatigue life were carried out to simulate the self-expansion process and the shape change process under the action of high and low blood pressure for three -type stents of 8×30 mm, 10×30 mm, 12×30 mm. By analyzing the changes of stress and strain of self-expanding NiTi alloy stent, the maximum stress and strain, stress concentration position, fatigue strength and possible failure modes were studied, thus the dynamic safety factor of stent was calculated. The results showed that the maximum stress and plastic strain of the stent increased with the increase of grip pressure, but the maximum stress and strain distribution area of the stent had no significant change, which were all concentrated in the inner arc between the support and the connector. The dynamic safety factors of the three stents were 1.31, 1.23 and 1.14, respectively, which indicates that the three stents have better safety and reliability, and can meet the fatigue life requirements of more than 10 years, and safety performance of the three stents decreases with the increase of stent's original diameter.
Subject(s)
Alloys , Finite Element Analysis , Nickel , Reproducibility of Results , Self Expandable Metallic Stents , Stress, Mechanical , TitaniumABSTRACT
Objective To analyze the relationship between fatigue strength and connector length of intracranial artery stents, so as to investigate the exact location of fatigue fracture for the stent. Methods The fatigue life for 3 kinds of artery stents were analyzed by finite element analysis method of fatigue fracture, and distribution map of dangerous points was drawn by means of Goodman curve. Based on F2477-07 standard from American Society for Testing and Materials (ASTM), the fatigue life for 3 kinds of stents was tested. Results If the length of the support connector was longer, the maximum equivalent stress and the average stress in dangerous points of the stent would be larger. If the distribution of dangerous points was more close to the curve of fatigue limit, and fatigue fracture was more likely to occur in the stent. Goodman curves indicated that 3 kinds of stents was safe to be used in the body for ten years. Finite element analysis and experimental result showed that fatigue life near the stent junction was relatively lower, and dangerous points of the stent was located at the arc junction. Conclusions It is reasonable to study stents by finite element analysis, whose results are basically coincided with the experimental data. Fatigue life can be extended by reducing connector’s length for the design of stent structure.
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OBJECTIVES: To determine the actual revolutions per minute (rpm) values and compare the cyclic fatigue life of Reciproc (RPC, VDW GmbH), WaveOne (WO, Dentsply Maillefer), and TF Adaptive (TFA, Axis/SybronEndo) nickel-titanium (NiTi) file systems using high-speed camera. MATERIALS AND METHODS: Twenty RPC R25 (25/0.08), 20 WO Primary (25/0.08), and 20 TFA ML 1 (25/0.08) files were employed in the present study. The cyclic fatigue tests were performed using a dynamic cyclic fatigue testing device, which has an artificial stainless steel canal with a 60° angle of curvature and a 5-mm radius of curvature. The files were divided into 3 groups (group 1, RPC R25 [RPC]; group 2, WO Primary [WO]; group 3, TF Adaptive ML 1 [TFA]). All the instruments were rotated until fracture during the cyclic fatigue test and slow-motion videos were captured using high-speed camera. The number of cycles to failure (NCF) was calculated. The data were analyzed statistically using one-way analysis of variance (ANOVA, p < 0.05). RESULTS: The slow-motion videos were indicated that rpm values of the RPC, WO, and TFA groups were 180, 210, and 425, respectively. RPC (3,464.45 ± 487.58) and WO (3,257.63 ± 556.39) groups had significantly longer cyclic fatigue life compared with TFA (1,634.46 ± 300.03) group (p < 0.05). There was no significant difference in the mean length of the fractured fragments. CONCLUSIONS: Within the limitation of the present study, RPC and WO NiTi files showed significantly longer cyclic fatigue life than TFA NiTi file.
Subject(s)
Fatigue , Radius , Stainless SteelABSTRACT
Objective To study the expansion behavior of stent in stenotic vascular, in stent blood flow and fatigue life of stent by finite element method. Methods ANSYS was used to simulate the expansion of stent in stenotic vascular. The blood flow model was created by constructing the entities based on deformation of the related nodes from the result of dilation process. A sample model was also built to simulate the in stent blood flow. Stent fatigue life was evaluated based on Goodman’s method and accumulated damage method, respectively. Results (1) Plastic deformation appeared on most parts of struts. The major stresses were localized in the corner of the slots. (2) Turbulent flow occured near the stent. Stresses of stent in cross section of bridge struts along the direction of blood flow were highest. (3) Goodman’s method showed that the stent was safe, and cumulative damage indicated that the largest cumulative damage occured in the second cross section of bridge struts. Conclusions Finite element method can be effectively used to simulate the stent expansion, in stent blood flow and stent fatigue life.
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Objective To evaluate the fatigue life of coronary stent under the effect of blood flow and thus optimize the stent design.MethodsA simplified model of the stent, blood, plaque and artery was established using Pro/Engineering, and the periodic blood flow impact on the vascular stent was simulated by finite element method via ANSYS. The result on hemodynamics from such stent was then used to evaluate its fatigue life. The geometric parameters of the stent were chosen as design variables for optimization. By using Latin Hypercubic sampling and ANSYS program, responses of the sample points could be obtained and the Kriging surrogate model was then constructed to optimize the fatigue life of the coronary stent.Results Goodman’s method showed that the optimized stent was safe. The cumulative damage method indicated that the largest damage occurred at the second cross-section of the bridge struts. The fatigue life of the optimized stent could be enhanced by 30.55%. Conclusions The finite element method can be used to evaluate the fatigue life of the coronary stent, and the optimization of stent by establishing Kriging model can effectively enhance the fatigue life of the stent.
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Objective After the implantation,coronary stent is expected at least to keep its integrity and maintain the predicated function for over 10 years or 4e8 cycles under the pulsatile loading conditions,so the fatigue property of the stent should be evaluated.Method The finite method was used to analyze the stress distribution of different phases and evaluate the fatigue life according to Goodman criteria,meanwhile,the accelerated fatigue experiment was also performed.Results It can be concluded that the dangerous points are all but located in the lateral inner surface of stent curvature.Conclusions The results prove that the fatigue property can be simulated through the finite element analysis,which can provide the theoretical guidance for the stent design.
ABSTRACT
Objective After the implantation,coronary stent is expected at least to keep its integrity and maintain the predicated function for over 10 years or 4e8 cycles under the pulsatile loading conditions,so the fatigue property of the stent should be evaluated.Method The finite method was used to analyze the stress distribution of different phases and evaluate the fatigue life according to Goodman criteria,meanwhile,the accelerated fatigue experiment was also performed.Results It can be concluded that the dangerous points are all but located in the lateral inner surface of stent curvature.Conclusions The results prove that the fatigue property can be simulated through the finite element analysis,which can provide the theoretical guidance for the stent design.
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Objective After the implantation, coronary stent was expected at least to keep integrity and maintain the predicated function for over 10 years or 4e8 cycles under the pulsatile loading conditions, and the fatigue property of the stent should be evaluated. Method The finite method was used to analyze the stress distribution of different phases and evaluate the fatigue life according to Goodman criteria, meanwhile, the accelerated fatigue experiment was also performed . Results It could be concluded that the dangerous points were located in the lateral inner surface of stent curvature. Conclusion The results proved that the fatigue property could be simulated through the finite element analysis, which can provide the theoretical guidance for the stent design.
ABSTRACT
Objective After the implantation,coronary stent is expected at least to keep its integrity and maintain the predicated function for over 10 years or 4e8 cycles under the pulsatile loading conditions,so the fatigue property of the stent should be evaluated.Method The finite method was used to analyze the stress distribution of different phases and evaluate the fatigue life according to Goodman criteria,meanwhile,the accelerated fatigue experiment was also performed.Results It can be concluded that the dangerous points are all but located in the lateral inner surface of stent curvature.Conclusions The results prove that the fatigue property can be simulated through the finite element analysis,which can provide the theoretical guidance for the stent design.