Numerical Analysis of Mechanical Phenomena in Coronary Stent Made of Titanium Alloy Ti-13Nb-13Zr

2016 ◽  
Vol 687 ◽  
pp. 191-198
Author(s):  
Aneta Idziak-Jabłońska
Keyword(s):  
Internal Diameter ◽  
The Finite Element Method ◽  
Titanium Matrix ◽  
Expansion Pressure ◽  
Stent Expansion ◽  
Stent Geometry ◽  
Pressure Limitation ◽  
In The Beginning ◽  
Number Of Segments ◽  
Mechanical Phenomena

Using the finite element method, this study determined mechanical characteristics of slotted-tube stents. The numerical calculations were carried out using ADINA v.8.8 software. Three models with different number of segments were used. The analysis was carried out for the titanium-matrix alloys Ti-13Nb-13Zr. Assuming the actual conditions of stent implantation, the stent is expected to expand to the diameter of 3.0 mm i.e. until it reaches the internal diameter of a healthy coronary vessel. The effect of the stent geometry was analysed, with emphasis on examination of the effect of key mechanical phenomena such as expansion pressure and suitable level of stress and plastic strain in stents. Analysis of the degree of foreshortening and dogboning after stent expansion was also carried out. The following assumptions were adopted in order to determine mechanical properties of stents: implantation at low expansion pressure, limitation of foreshortening ≤ 2%, low increase in the implant diameter in the beginning and at the end of the stent (dogboning effect).

DESIGN AND ANALYSIS OF NEW STENT PATTERNS FOR ENHANCED PERFORMANCE

2020 ◽  
Vol 20 (06) ◽  
pp. 2050039
Author(s):  
NISANTHKUMAR PANNEERSELVAM ◽  
SREEKUMAR MUTHUSWAMY
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Blood Flow ◽  
Coronary Artery ◽  
Mechanical Behavior ◽  
Internal Diameter ◽  
Cell Design ◽  
The Finite Element Method ◽  
Stent Expansion ◽  
Stenting Procedure

Deploying a stent to restore blood flow in the coronary artery is very complicated, as its internal diameter is smaller than 3[Formula: see text]mm. It has already been proven that mechanical stresses induced on stent and artery during deployment make the placement of stent very difficult, besides the development of complications due to artery damage. Various stent designs have already been developed, especially in the metallic category. Still, there are possibilities for developing new stent designs and patterns to overcome the complexities of the existing models. Also, the technology of metallic stents can be carried forward towards the development of bioresorbable polymeric stents. In this work, three new stent cell designs (curvature, diamond, and oval) have been proposed to obtain better performance and life. The finite element method is utilized to explore the mechanical behavior of stent expansion and determine the biomechanical stresses imposed on the stent and artery during the stenting procedure. The results obtained have been compared with the available literature and found that the curvature cell design develops lower stresses and, hence, be suitable for better performance and life.

Numerical Study of the Flow Forming Process of AISI 630 Stainless Steel

2011 ◽  
Vol 264-265 ◽  
pp. 24-29 ◽  
Author(s):  
Seyed Mohammad Ebrahimi ◽  
Seyed Ali Asghar Akbari Mousavi ◽  
Mostafa Soltan Bayazidi ◽  
Mohammad Mastoori
Keyword(s):  
Feeding Rate ◽  
Surface Defects ◽  
Numerical Study ◽  
Internal Diameter ◽  
The Finite Element Method ◽  
Forming Process ◽  
Flow Forming ◽  
Cold Forming ◽  
External Variables ◽  
Experimental Process

Flow forming is one of the cold forming process which is used for hollow symmetrical shapes. In this paper, the forward flow forming process is simulated using the finite element method and its results are compared with the experimental process. The variation of thickness of the sample is examined by the ultrasonic tests for the five locations of the tubes. To simulate the process, the ABAQUS explicit is used. The effects of flow forming variables such as the angle of rollers and rate of feeding of rollers, on the external variables such as internal diameter, thickness of tube and roller forces are considered. The study showed that the roller force and surface defects were reduced with low feeding rate and low rollers attack angles. Moreover, the sample internal diameter increased at low feeding rate and low rollers attack angles. The optimum variables for flow forming process were also obtained.

Prediction of Springback in Straight Flanging Operation

1999 ◽  
Author(s):  
Jian Cao ◽  
Zhihong Liu ◽  
Wing Kam Liu
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Deformation Mechanism ◽  
The Finite Element Method ◽  
Moment Distribution ◽  
Analytical Formulae ◽  
Typical Distribution ◽  
Number Of Segments ◽  
Springback Angle ◽  
Energy Element

Abstract A straight flange problem is investigated with the expectation that this will lead to a better understanding of the deformation mechanism and to more complicated flanging problems. The “in-die” shape of the part is subdivided into a number of segments and individual springback of each segment is investigated, by releasing the elastic energy element by element, using the Finite Element Method (FEM). Typical distribution of the springback angle along the blank is obtained and found to be quite different from the widely used constant springback assumption for the curved part of the flange. A new model incorporating a non-uniform moment distribution at the curved part is proposed which reflects the above observation. Explicit analytical formulae are derived and the analytical predictions match with the experimental results very well.

scholarly journals NUMERICAL SIMULATION OF RIVETING PROCESS USING BLIND RIVET

Aviation ◽  
2006 ◽  
Vol 10 (2) ◽  
pp. 7-12
Author(s):  
Lucjan Witek
Keyword(s):  
Stress Distribution ◽  
Strain Distribution ◽  
Initial Stresses ◽  
Aviation Industry ◽  
The Finite Element Method ◽  
The Core ◽  
Riveting Process ◽  
Nonlinear Computation ◽  
Core Displacement ◽  
Mechanical Phenomena

This paper is concerned with an analysis of the mechanical phenomena occurring in the process of blind riveting. Blind rivets are commonly used in the aviation industry and allow riveting with one‐sided access. To solve this problem, the finite element method was used. In results of the nonlinear computation performed for a joint containing one rivet, the stress distribution in the separate phases of riveting were analyzed. The plots of riveting force in function of rivet core displacement for different friction coefficients between the rivet and the core and the plastic strain distribution also were obtained. The main purpose of this work was to obtain the initial stress distribution occurring in the rivet and sheets after the mandrel was broken. This analysis showed that after finishing the riveting process the initial stresses occurring in the rivet have high values.

PALMAZ–SCHATZ STENT-OPENING MECHANICS USING A SIMPLE APPROACH INVOLVING THE BALLOON–STENT AND STENT–ARTERY CONTACT PROBLEM: APPLICATION TO BIOPOLYMER STENTS

2019 ◽  
Vol 19 (03) ◽  
pp. 1950009 ◽  
Author(s):  
PLAMEN BOKOV ◽  
PHILIPPE DANTAN ◽  
PATRICE FLAUD
Keyword(s):  
Simple Approach ◽  
Comsol Multiphysics ◽  
The Finite Element Method ◽  
Elastic Recoil ◽  
Metal Stent ◽  
Artery Wall ◽  
Stent Geometry ◽  
Plla Stent ◽  
Arterial Damage

We used the finite element method-based toolbox COMSOL Multiphysics to address the important question of biopolymer coronary stent mechanics. We evaluated the diameter of the stent, the immediate elastic recoil, the dogboning and the foreshortening during deployment while using an idealized model that took into account the presence of the balloon and the coronary artery wall (equivalent pressure hypothesis). We validated our model using the well-known mechanics of the Palmaz–Schatz metal stent and acquired new data concerning a poly-L-lactic acid (PLLA) stent and some other biodegradable co-polymer-based stents. The elastic recoil was relatively high (26.1% to 31.1% depending on the biopolymer used) when taking into account the presence of both the balloon and artery. The dogboning varied from 31% to 46% for the polymer stents and was 62% for the metal stent, suggesting that less arterial damage could be expected with biopolymer stents. Various strut thicknesses were tested for the PLLA stent (114, 180 and 250[Formula: see text][Formula: see text]m) and no significant improvement in elastic recoil was observed. We concluded that the stent geometry has a greater impact on the scaffolding role of the structure than the strut thickness, or even the mechanical properties of the stent.

Estimation of Residual Stresses in Hydraulically Expanded Tube-to-Tubesheet Joints

1998 ◽  
Vol 120 (2) ◽  
pp. 129-137 ◽  
Author(s):  
M. Allam ◽  
A. Chaaban ◽  
A. Bazergui
Keyword(s):  
Residual Stresses ◽  
Heat Exchangers ◽  
Structural Integrity ◽  
Theoretical Method ◽  
Pressure Level ◽  
The Finite Element Method ◽  
Material Parameters ◽  
Deviation Analysis ◽  
Upper Limit ◽  
Expansion Pressure

The knowledge of residual stresses introduced in the tubes of heat exchangers during their expansion in the tubesheet holes is important because of their effect on the structural integrity of components. This paper presents a simplified theoretical method to calculate the maximum residual stresses introduced in the transition zone of expanded tube-to-tubesheet joint. The higher positive values of tensile residual stresses and their corresponding axial locations are determined by using a standard deviation analysis. The validation of the proposed equations was accomplished by comparing their results to those obtained by the finite element method for some arbitrary cases. An upper limit has been imposed on the expansion pressure level, depending on the combination of the geometrical and material parameters that are involved in the design of the tube-to-tubesheet joints.

scholarly journals The effect of restraints type on the generated stresses in gantry crane beam

2018 ◽  
Vol 157 ◽  
pp. 02046
Author(s):  
Leszek Sowa ◽  
Wiesława Piekarska ◽  
Tomasz Skrzypczak ◽  
Paweł Kwiatoń
Keyword(s):  
Cross Section ◽  
Equivalent Stress ◽  
Gantry Crane ◽  
Complex Task ◽  
The Finite Element Method ◽  
Force Load ◽  
Maximum Equivalent Stress ◽  
Load Movement ◽  
Modern Tool ◽  
Mechanical Phenomena

This paper includes an analysis of the mechanical phenomena in the gantry crane beam, because the cranes are currently one of the most common devices for the transporting loads. Designing modern mechanical structures is a complex task that requires the use of appropriate tools. Such a modern tool is the numerical simulation, which uses different numerical methods. One of the best known methods is the finite element method, also used here. Simulations are limited to analysis of the strength of the gantry crane beam that was the loaded of the force load movement along its length. The numerical analysis was made to the gantry crane beam which cross-section was an I-beam and ends were fixed in different ways. As the result of numerical calculations, the stresses and displacements of the structure of gantry were obtained. The influence of the restraints type and changing the loading force position on generate the Huber-Misses stress in the gantry crane beam was estimated. The aim was to ensure that the maximum equivalent stress generated in the gantry crane beam was less than the strength of material, because then the construction is safe.

Expansion Performance of Novel Balloon-Expandable Stent for Tapered Vessel

2015 ◽  
Vol 645-646 ◽  
pp. 1333-1338
Author(s):  
Xiang Shen ◽  
Yang Yang Sun ◽  
Bo Bo Wu
Keyword(s):  
Finite Element Method ◽  
Radial Displacement ◽  
Design Parameters ◽  
The Novel ◽  
Stent Design ◽  
Positioning Accuracy ◽  
Stent Restenosis ◽  
Expansion Pressure ◽  
Stent Expansion ◽  
In Stent Restenosis

In-stent restenosis still remains an obsession to cardiologist, especially in tapered vessels. In this paper, we designed a novel balloon-expandable stent for tapered vessel and proposed a finite element method (FEM) to study the expansion of the novel stent. The effect of stent design parameters on stent tapering and foreshortening were also researched. Results show that the radial displacement of stent proximal end was always larger than that of stent distal end during stent expansion, and the stent had a tapered shape as a whole after expansion. The degree of stent tapering observed increased with the expansion pressure increase. Besides, increasing the gradient of ring amplitude not only could increase the tapering degree of stent after expansion, but also could decrease stent foreshortening, improving the positioning accuracy after stent implantation. In conclusion, FEM can quantify expansion performance of novel balloon-expandable stents and help designers to devise and assess new stent designs for tapered vessel.

Plasticity as a Lifesaver in the Design of Cardiovascular Stents

2007 ◽  
Vol 340-341 ◽  
pp. 841-846 ◽  
Author(s):  
Matthieu De Beule ◽  
Peter Mortier ◽  
Jan Belis ◽  
Rudy Van Impe ◽  
Benedict Verhegghe ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stainless Steel ◽  
Yield Stress ◽  
Material Properties ◽  
Failure Strain ◽  
The Finite Element Method ◽  
Size Dependency ◽  
Stent Expansion ◽  
Nominal Strain

A common treatment to restore normal blood flow in an obstructed artery is the deployment of a stent (i.e. small tube-like structure). The vast majority of stents are crimped on a folded balloon and laser cut from 316L stainless steel tubes. Although, several numerical studies (exploiting the Finite Element Method) are dedicated to the mechanical behaviour of balloon expandable stents, there seems to be no consensus regarding the mechanical properties to describe the inelastic material behaviour of SS316L. Moreover, as the typical dimensions of stent struts (e.g. 100 μm for coronary stents) are of a similar order of magnitude as the average grain size in stainless steel (i.e. 25 μm), continuum approaches relying on macroscopic material properties may be questionable. In addition, an experimental study on stainless steel stent strut specimens showed a size-dependency of the failure strain. In this study the impact of the magnitude of the yield stress on the stent expansion behavior is examined. An increase in the yield stress (from 205 N/mm² to 375 N/mm²) results in an increase of the pressure (from about 0.3 N/mm² to approximately 0.4 N/mm²) which the clinician needs to exert for the balloon to unfold and to reach its cylindrical expanded shape. Furthermore, the effect of the size dependency behavior of the material is studied by monitoring the nominal strain during stent expansion. The maximum value of the nominal strain in the expanded stent (e.g. εn = 23 %) does not exceed the critical value of the failure strain, (i.e. εn = 33 %), moreover the critical values are nowhere exceeded in the whole stent during the expansion. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with pressure/diameter data supplied by the manufacturer. Consequently, this study shows that the free expansion of new generation balloon-expandable stents can be studied accurately with computational analysis based on the Finite Element Method (FEM) and relying on macroscopic material properties. In this context, there is no need to implement a size-based constitutive material model, but before accepting the results of the study, one should check in any case the maximum strain against the limit as shown above.

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