scholarly journals Numerical simulation of the functionality of a stent structure for venous valve prostheses

2019 ◽  
Vol 5 (1) ◽  
pp. 477-479
Author(s):  
Julia Schubert ◽  
Kerstin Schümann ◽  
Sabine Kischkel ◽  
Wolfram Schmidt ◽  
Niels Grabow ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Minimally Invasive ◽  
Constitutive Law ◽  
Long Term Results ◽  
Uniaxial Tensile ◽  
Common Disease ◽  
Uniaxial Tensile Test ◽  
Venous Valve ◽  
Valve Prostheses ◽  
Venous Vessel

AbstractChronic venous insufficiency (CVI) is a common disease characterized by impaired venous drainage leading to congestion in the lower limbs. Currently, there are no artificial or biological venous valve prostheses commercially available. Previous minimally invasive design concepts failed to achieve sufficient long term results in animal or in vitro studies. The aim was to implement structural numerical simulation of clinically relevant loading cases for minimally invasive implantable venous valve prostheses. A bicuspid valve design was chosen as it showed superior results compared to tricuspid valves in previous studies. The selfexpanding support structure was developed by using diamond-shaped elements. Using finite-element analysis (FEA), various loading cases, including expansion and crimping of the stent structure and the release into a venous vessel, were simulated. A hyperelastic constitutive law for the vascular model was generated from uniaxial tensile test data of unfixated human vein walls. This study also compared numerical and experimental results regarding compliance and tensile tests to validate the vein material model. The calculated performance concerning expansion and crimping, as well as the release of the stent into a venous vessel, demonstrated the suitability of the stent design for minimally invasive application.

scholarly journals Assessment of heart valve performance by finite-element design studies of polymeric leaflet-structures

2017 ◽  
Vol 3 (2) ◽  
pp. 631-634
Author(s):  
Sylvia Pfensig ◽  
Sebastian Kaule ◽  
Michael Sämann ◽  
Michael Stiehm ◽  
Niels Grabow ◽  
...  
Keyword(s):  
Finite Element ◽  
Minimally Invasive ◽  
Heart Valve ◽  
Constitutive Law ◽  
Uniaxial Tensile ◽  
Valve Prosthesis ◽  
Design Studies ◽  
Heart Valve Prostheses ◽  
Valve Prostheses

AbstractFor the treatment of severe symptomatic aortic valve stenosis, minimally invasive heart valve prostheses are increasingly used, especially for elderly patients. The current generation of devices is based on xenogenic leaflet material, involving limitations with regard to calcification and durability. Artificial polymeric leaflet-structures re-present a promising approach for improvement of valve performance. Within the current work, finite-element ana-lysis (FEA) design studies of polymeric leaflet structures were conducted. Design of an unpressurized and axially-symmetric trileaflet heart valve was developed based on nine parameters. Physiological pressurization in FEA was specified, based on in vitro hydrodynamic testing of a commercially available heart valve prosthesis. Hyper-elastic constitutive law for polymeric leaflet material was implemented based on experimental stress strain curves resulting from uniaxial tensile and planar shear testing. As a result of FEA, time dependent leaflet deformation of the leaflet structure was calculated. Obtained leaflet dynamics were comparable to in vitro performance of the analyzed prosthesis. As a major design parameter, the lunula angle has demonstrated crucial influence on the performance of the polymeric leaflet structures. FEA represented a useful tool for design of improved polymeric leaflet structures for minimally invasive implantable heart valve prostheses.

scholarly journals Numerical simulation of a transcatheter aortic heart valve under application-related loading

2018 ◽  
Vol 4 (1) ◽  
pp. 185-189
Author(s):  
Sylvia Pfensig ◽  
Sebastian Kaule ◽  
Robert Ott ◽  
Carolin Wüstenhagen ◽  
Michael Stiehm ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Aortic Valve ◽  
Minimally Invasive ◽  
Heart Valve ◽  
Aortic Root ◽  
Constitutive Law ◽  
Ar Model ◽  
Valve Prosthesis ◽  
Target Region ◽  
Opening And Closing

AbstractFor the treatment of severe symptomatic aortic valve stenosis, minimally invasive heart valve prostheses have more recently become the lifesaving solution for elderly patients with high operational risk and thus, are often implanted in patients with challenging aortic root configuration. A correct prosthesis deployment and stent adaption to the target region is essential to ensure optimal leaflet performance and long-term prosthesis function. The objective of this study was the development of a suitable in silico setup for structural numerical simulation of a transcatheter aortic valve (TAV) in different cases of clinical relevance. A transcatheter valve prosthesis comprising an unpressurized trileaflet heart valve and an adapted stent configuration was designed. An aortic root (AR) model was developed, based on microcomputed tomography of a native healthy specimen. Using the finite-element analysis (FEA), various loading cases including prosthesis biomechanics with valve opening and closing under physiological pressure ratios throughout a cardiac cycle, prosthesis crimping as well as crimping and release into the developed AR model were simulated. Hyperelastic constitutive law for polymeric leaflet material and superelasticity of shape memory alloys for the self-expanding Nitinol stent structure were implemented into the FEA setup. Calculated performance of the valve including the stent structure demonstrated enhanced leaflet opening and closing as a result of stent deformation and redirected loading. Crimping and subsequent release into the AR model as well as the stent adaption to the target region after expansion proved the suitability of the TAV design for percutaneous application. FEA represented a useful tool for numerical simulation of an entire minimally invasive heart valve prosthesis in relevant clinical scenarios.

Numerical Simulation Analysis of Aluminium Alloy Wheels Casting Defects and Casting Process Optimization

2013 ◽  
Vol 749 ◽  
pp. 125-132 ◽  
Author(s):  
Lv Ming Yang ◽  
Li Li Zhao ◽  
Qing Qing Zhang ◽  
Tie Tao Zhou
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Aluminum Alloy ◽  
Casting Process ◽  
Shrinkage Cavity ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Casting Defects ◽  
Pressure Casting ◽  
Aluminum Alloy Casting

In the low pressure casting process of A356 aluminum alloy wheel hub, casting defects including shrinkage cavity, shrinkage porosity, impurity and pore usually occur inside the casting. These defects affect the mechanical properties of the casting. To solve this problem, we conducted a study based on a cooperation project with a well-known domestic automobile wheel manufacturer. In the present study, uniaxial tensile test of aluminum alloy casting containing defects was simulated and analysed, and the effect of types and number of defects on mechanical properties was studied by finite element analysis software. Statistical analysis of the data was provided by the manufacturer. It has been found that the degassing technology is effective by the quantitative analysis method. Based on the analyses of experimental data and the numerical simulation it is deduced that the tensile strength of casting increases with the increase of the defects due to the presence of impurity. This was confirmed in this research project, it has been observed that the defect rate of the casting sample is reduced from 5%-6% to less than 1%.

Strain Analysis of Bimetal Material Based on Uniaxial Tensile and ANSYS

2014 ◽  
Vol 988 ◽  
pp. 27-30 ◽  
Author(s):  
De Hai Zhang ◽  
Duan Qin Zhang ◽  
Yan Qin Li ◽  
Jian Xiu Liu ◽  
Dai Ping Bai ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Strain Analysis ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Theoretic Analysis ◽  
Combined Method ◽  
Experiment Research ◽  
Test Experiment ◽  
Existing Problems ◽  
Semi Solid

With a combined method of theoretic analysis, numerical simulation and uniaxial tensile test experiment research, the properties of bimetal materials are system studied. The researches are concentrated on the followings contexts:The fabricating method of bimetal materials by semi-solid compressive joining is studied by ANSYS, and then the tensile property relationships of the clad material are established. The stress and their strains alongx,yandzdirections of the clad material are analyzed, respectively. The different performance of composite materials, find materials conform to the existing problems so as to optimize treatment.

Effect of Ductile Damage Evolution in Sheet Metal Forming: Experimental and Numerical Investigations

2010 ◽  
Vol 446 ◽  
pp. 157-169 ◽  
Author(s):  
Fethi Abbassi ◽  
Olivier Pantalé ◽  
Sébastien Mistou ◽  
Ali Zghal ◽  
Roger Rakotomalala
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Rolling Direction ◽  
Constitutive Law ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Plastic Behavior ◽  
Marquardt Algorithm

The numerical simulation based on the Finite Element Method (FEM) is widely used in academic institutes and in the industry. It is a useful tool to predict many phenomena present in the classical manufacturing forming processes such as necking, fracture, springback, buckling and wrinkling. But, the results of such numerical model depend strongly on the parameters of the constitutive behavior model. In the first part of this work, we focus on the traditional identification of the constitutive law using oriented tensile tests (0°, 45°, and 90° with respect to the rolling direction). A Digital Image Correlation (DIC) method is used in order to measure the displacements on the surface of the specimen and to analyze the necking evolution and the instability along the shear band. Therefore, bulge tests involving a number of die shapes (circular and elliptic) were developed. In a second step, a mixed numerical–experimental method is used for the identification of the plastic behavior of the stainless steel metal sheet. The initial parameters of the inverse identification were extracted from a uniaxial tensile test. The optimization procedure uses a combination of a Monte-Carlo and a Levenberg-Marquardt algorithm. In the second part of this work, according to some results obtained by SEM (Scaning Electron Microscopy) of the crack zones on the tensile specimens, a Gurson Tvergaard Needleman (GTN) ductile model of damage has been selected for the numerical simulations. This model was introduced in order to give informations concerning crack initiations during hydroforming. At the end of the paper, experimental and numerical comparisons of sheet metal forming applications are presented and validate the proposed approach.

scholarly journals Numerical analysis and experimental verification of elastomer bending process with different material models

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Stanislaw Kut ◽  
Grazyna Ryzinska ◽  
Bernadetta Niedzialek
Keyword(s):  
Numerical Simulation ◽  
Numerical Analysis ◽  
Bending Test ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Material Models ◽  
Material Constants ◽  
Elastomeric Material ◽  
Bending Process ◽  
Tension Testing

Abstract The article presents the results of tests in order to verifying the effectiveness of the nine selected elastomeric material models (Neo-Hookean, Mooney with two and three constants, Signorini, Yeoh, Ogden, Arruda-Boyce, Gent and Marlow), which the material constants were determined in one material test - the uniaxial tension testing. The convergence assessment of nine analyzed models were made on the basis of their performance from an experimental bending test of the elastomer samples from the results of numerical calculations FEM for each material models. To calculate the material constants for the analyzed materials, a model has been generated by the stressstrain characteristics created as a result of experimental uniaxial tensile test with elastomeric dumbbell samples, taking into account the parameters received in its 18th cycle. Using such a calculated material constants numerical simulation of the bending process of a elastomeric, parallelepipedic sampleswere carried out using MARC / Mentat program.

scholarly journals Calculated Shoulder to Gauge Ratio of Fatigue Specimens in PWR Environment

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 376
Author(s):  
Igor Simonovski ◽  
Alec Mclennan ◽  
Kevin Mottershead ◽  
Peter Gill ◽  
Norman Platts ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Water Environment ◽  
Hysteresis Loops ◽  
Constitutive Law ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Material Behaviour ◽  
Pressurized Water ◽  
Elastic Plastic ◽  
Gauge Section

A ratio of shoulder to gauge displacements (S2G) is calculated for three different fatigue specimens in a pressurized water environment. This ratio needs to be known beforehand to determine the applied shoulder displacements during the experiment that would result in the desired strain amplitude in the gauge section. Significant impact of both the applied constitutive law and specimen geometry on the S2G is observed. The calculation using the fully elastic constitutive law results in the highest S2G values and compares very well with the analytical values. However, this approach disregards the plastic deformation within the specimens that mostly develops in the gauge section. Using the constitutive laws derived from actual fatigue curves captures the material behaviour under cyclic loading better and results in lower S2G values compared to the ones obtained with the fully elastic constitutive law. Calculating S2G values using elastic–plastic constitutive law based on the monotonic uniaxial tensile test should be avoided as they are significantly lower compared to the ones computed with elastic–plastic laws derived from hysteresis loops at half-life.

scholarly journals Development of a constitutive law for numerical simulation of artificial leaflet-structures for transcatheter heart valve prostheses

2019 ◽  
Vol 5 (1) ◽  
pp. 569-572
Author(s):  
Sylvia Pfensig ◽  
Daniela Arbeiter ◽  
Stefanie Kohse ◽  
Niels Grabow ◽  
Klaus-Peter Schmitz ◽  
...  
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Heart Valve ◽  
In Silico ◽  
Constitutive Law ◽  
Invasive Treatment ◽  
Heart Valve Prostheses ◽  
Transcatheter Heart Valve ◽  
Planar Shear ◽  
Valve Prostheses

AbstractWhile the current generation of devices for minimally invasive treatment of severe symptomatic aortic valve stenosis is based on xenogenic leaflet-material, artificial polymeric leaflet-structures represent a promising approach for future improvement of heart valve performance. For enhanced long-term success of polymeric leafletstructures, limitations regarding calcification and durability have to be addressed. The objective of the presented study was the development of a constitutive law representing the material properties of artificial polymeric leaflet-structures of transcatheter heart valve prostheses in numerical simulation to assess the in silico leaflet-performance. Mechanical characterization of cast films and nonwoven specimens of a polycarbonate based silicone elastomer were conducted by means of uniaxial tension and planar shear testing, respectively. For validation purposes, experimental data were compared with the results of finite-element analysis (FEA) using different hyperelastic models. Strain energy function for third-order ogden hyperelastic model achieved the best fit of the non-linear stress-strain behavior of the isotropic polymeric material with the experimental data. It was chosen for further FEA of valve leaflet-performance under physiological pressurization to analyze the suitability of various manufacturing processes for polymeric leafletstructures. Therefore a specific leaflet-design with a wall thickness of 400 μm was used. As a result of FEA, time dependent leaflet-deformation, leaflet coaptation surface area (CSA) and leaflet opening area (LOA) of cast and nonwoven leaflet-structures were calculated. While LOA was comparable for cast and nonwoven leaflet-structures, obtained leaflet-dynamics in a cardiac cycle under physiological pressurization demonstrated crucial influence of the manufacturing process. For nonwoven leafletstructures, an enhanced CSA could be demonstrated in comparison to cast structures. FEA using a validated hyperelastic constitutive law represents a useful tool for in silico performance evaluation of polymeric leaflet-structures under physiological loading and proves the suitability of the polymeric artificial leaflet-material for percutaneous heart valve prostheses.

A new pseudo-energy function to simulate the Mullins effect

2017 ◽  
Vol 50 (6) ◽  
pp. 554-575
Author(s):  
Eduardo Guilherme Mötke Wrubleski ◽  
Rogério Marczak
Keyword(s):  
Experimental Data ◽  
Pure Shear ◽  
Constitutive Models ◽  
Constitutive Law ◽  
Hyperelastic Material ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Mullins Effect ◽  
Softening Effect ◽  
Material Models

Several authors have proposed different parameters to include the softening effect in hyperelastic models; however, for a number of materials, softening parameters could be further improved. This article proposes a new softening parameter to include Mullins effect in hyperelastic material models. The methodology employed can be also used in cases with hysteresis or damage in a hyperelastic material, however this methodology modifies the behavior of the material differently from damage theories. Common hyperelastic constitutive models do not include dissipation effects and so the present work intends to fill this gap. Experimental data for silicone in uniaxial tensile test, equibiaxial, and pure shear tests were modeled in order to calibrate the models. The softening parameters essentially changes the constitutive law from the loading to the unloading path. Therefore, it is still necessary to use a hyperelastic model, and here Ogden and Hoss-Marczak material models were used. The obtained results show good agreement with experimental data even when simulating with a compressible finite element code and it can model isotropic Mullins effect.

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