scholarly journals Anisotropic Material Characterization of Human Cervix Tissue Based on Indentation and Inverse Finite Element Analysis

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Lei Shi ◽  
Wang Yao ◽  
Yu Gan ◽  
Lily Y. Zhao ◽  
W. Eugene McKee ◽  
...  
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Fiber Composite ◽  
Material Behavior ◽  
Ground Substance ◽  
Cervical Tissue ◽  
Constitutive Material Model ◽  
Significant Difference ◽  
Anisotropic Mechanical Properties ◽  
Human Cervix

The cervix is essential to a healthy pregnancy as it must bear the increasing load caused by the growing fetus. Preterm birth is suspected to be caused by the premature softening and mechanical failure of the cervix. The objective of this paper is to measure the anisotropic mechanical properties of human cervical tissue using indentation and video extensometry. The human cervix is a layered structure, where its thick stromal core contains preferentially aligned collagen fibers embedded in a soft ground substance. The fiber composite nature of the tissue provides resistance to the complex three-dimensional loading environment of pregnancy. In this work, we detail an indentation mechanical test to obtain the force and deformation response during loading which closely matches in vivo conditions. We postulate a constitutive material model to describe the equilibrium material behavior to ramp-hold indentation, and we use an inverse finite element method based on genetic algorithm (GA) optimization to determine best-fit material parameters. We report the material properties of human cervical slices taken at different anatomical locations from women of different obstetric backgrounds. In this cohort of patients, the anterior internal os (the area where the cervix meets the uterus) of the cervix is stiffer than the anterior external os (the area closest to the vagina). The anatomic anterior and posterior quadrants of cervical tissue are more anisotropic than the left and right quadrants. There is no significant difference in material properties between samples of different parities (number of pregnancies reaching viable gestation age).

scholarly journals Retrospective Evaluation and Framework Development of Bone Anisotropic Material Behavior Compared with Elastic, Elastic-Plastic, and Hyper-Elastic Properties

2021 ◽  
Vol 9 (1) ◽  
pp. 9
Author(s):  
Farah Hamandi ◽  
James T. Tsatalis ◽  
Tarun Goswami
Keyword(s):  
Bone Tissue ◽  
Material Properties ◽  
Anisotropic Material ◽  
Material Behavior ◽  
Imaging Data ◽  
Premature Failure ◽  
Elastic Plastic ◽  
Significant Difference ◽  
Hyper Elastic

The main motivation for studying damage in bone tissue is to better understand how damage develops in the bone tissue and how it progresses. Such knowledge may help in the surgical aspects of joint replacement, fracture fixation or establishing the fracture tolerance of bones to prevent injury. Currently, there are no standards that create a realistic bone model with anisotropic material properties, although several protocols have been suggested. This study seeks to retrospectively evaluate the damage of bone tissue with respect to patient demography including age, gender, race, body mass index (BMI), height, and weight, and their role in causing fracture. Investigators believe that properties derived from CT imaging data to estimate the material properties of bone tissue provides more realistic models. Quantifying and associating damage with in vivo conditions will provide the required information to develop mathematical equations and procedures to predict the premature failure and potentially mitigate problems before they begin. Creating a realistic model for bone tissue can predict the premature failure(s), provide preliminary results before getting the surgery, and optimize the design of orthopaedic implants. A comparison was performed between the proposed model and previous efforts, where they used elastic, hyper- elastic, or elastic-plastic properties. Results showed that there was a significant difference between the anisotropic material properties of bone when compared with unrealistic previous methods. The results showed that the density is 50% higher in male subjects than female subjects. Additionally, the results showed that the density is 47.91% higher in Black subjects than Mixed subjects, 53.27% higher than Caucasian subjects and 57.41% higher than Asian. In general, race should be considered during modeling implants or suggesting therapeutic techniques.

Characterizing Guardrail Steel for LS-DYNA3D Simulations

1996 ◽  
Vol 1528 (1) ◽  
pp. 138-145 ◽  
Author(s):  
Amy E. Wright ◽  
Malcolm H. Ray
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Material Behavior ◽  
Finite Element Models ◽  
Type Ii ◽  
Material Models ◽  
Class A ◽  
Model Geometry ◽  
Simulation Results ◽  
Roadside Hardware

Finite-element models have three parts: geometry, connections, and material properties. As the visible parts of a model, geometry and connections are generally carefully considered. Material properties often are not chosen with the same degree of care although they are equally important to obtaining good results. Accurate simulations of vehicles striking roadside hardware require an understanding of both the material behavior and the mathematical material models in LS-DYNA3D. A method for comparing LS-DYNA3D simulations with typical ASTM materials tests is described. The behavior and modeling parameters of guardrail steel (AASHTO M-180 Class A Type II) are examined in this study. Experimental and simulation results of quasistatic coupon tests are compared for AASHTO M-180 Class A Type II guardrail steel, and parameters for guardrail steel are recommended.

scholarly journals Determination of the hyperelastic material behavior of hydrogel specimens for expandable lens implants

2019 ◽  
Vol 5 (1) ◽  
pp. 351
Author(s):  
Heiner Martin ◽  
Olga Sahmel ◽  
Thomas Eickner ◽  
Niels Grabow ◽  
Christine Kreiner ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Material Properties ◽  
Element Model ◽  
Material Behavior ◽  
Hyperelastic Material ◽  
Human Lens ◽  
Experimental Investigations

Abstract Theoretical and experimental investigations were carried out for development of human lens implants made from hydrogel material. The material properties were measured and implemented in a Finite element model. Though the material is still too stiff for accommodative lenses, the theoretical and experimental foundations for the implant development were established.

The Parametric Studies of Brain Materials in the Analysis of Head Impact

2006 ◽  
Author(s):  
Dalong Li ◽  
Mariusz Ziejewski ◽  
Ghodrat Karami
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Dynamic Behavior ◽  
Material Properties ◽  
Material Behavior ◽  
Material Models ◽  
Material Parameters ◽  
Multiple Materials ◽  
The Brain ◽  
Brain Tissues

Crash analysis and head injury biomechanics are very important fields in biomedical research due to the devastating consequences of traumatic brain injuries (TBI). Complex geometry and constitutive models of multiple materials can be combined with the loading conditions in finite element head model to study the dynamic behavior of brain and the TBI. In such a modeling, the proper regional material properties of brain tissues are important. Brain tissues material properties have not been finally determined by experiments, and large variations in the test data still exist and the data is very much situation-dependent. Therefore, parametric analysis should be performed to study the relationship between the material properties and the brain response. The main purpose of presenting this paper is to identify the influence of material constitutive properties on brain impact response, to search for an improved material model and to arrive at a better correlation between the finite element model and the cadaver tests data. In this paper a 3-D nonlinear finite element method will be used to study the dynamic response of the human head under dynamic loading. The finite element formulation includes detailed model of the skull, brain, cerebral-spinal fluid (CSF), dura mater, pia mater, falx and tentorium membranes. The brain is modeled as linear viscoelastic material, whereas linear elastic material behavior is assumed for all the other tissue components. The proper contact and compatibility conditions between different components have been implemented in the modeling procedure. The results for the direct frontal impacts will be shown for three groups of material parameters. The parametrical analysis of tissue material models allows to examines the accuracy of three different set of material parameters for brain in a comparison with the prediction of the head dynamic response of Nahum's human cadaver direct impact experiment. Three sets of suggested material parameters are examined. It is concluded that although all three groups of material models will follow the dynamic behavior of the head and brain behavior, but the parametric data considered in this paper have a closer resemblance to the experimental behavior.

The Effect of the Variation in ACL Constitutive Model on Joint Kinematics and Biomechanics Under Different Loads: A Finite Element Study

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Chao Wan ◽  
Zhixiu Hao ◽  
Shizhu Wen
Keyword(s):  
Finite Element ◽  
Constitutive Equation ◽  
Constitutive Model ◽  
Constitutive Models ◽  
Transversely Isotropic ◽  
Joint Kinematics ◽  
Material Behavior ◽  
Ground Substance ◽  
Anterior Tibial ◽  
Hyperelastic Model

The biomechanics and function of the anterior cruciate ligament (ACL) have been widely studied using both experimental and simulation methods. It is known that a constitutive model of joint tissue is a critical factor in the numerical simulation. Some different ligament constitutive models have been presented to describe the ACL material behavior. However, the effect of the variation in the ligament constitutive model on joint kinematics and biomechanics has still not been studied. In this paper, a three-dimensional finite element model of an intact tibiofemoral joint was reconstructed. Three ACL constitutive models were compared under different joint loads (such as anterior tibial force, varus tibial torque, and valgus tibial torque) to investigate the effect of the change of the ACL constitutive model. The three constitutive models corresponded to an isotropic hyperelasticity model, a transversely isotropic hyperelasticity model with neo-Hookean ground substance description, and a transversely isotropic hyperelastic model with nonlinear ground substance description. Although the material properties of these constitutive equations were fitted on the same uniaxial tension stress-strain curve, the change of the ACL material constitutive model was found to induce altered joint kinematics and biomechanics. The effect of different ACL constitutive equations on joint kinematics depended on both deformation direction and load type. The variation in the ACL constitutive models would influence the joint kinematic results greatly in both the anterior and internal directions under anterior tibial force as well as some other deformations such as the anterior and medial tibial translations under valgus tibial torque, and the medial tibial translation and internal rotation under varus torque. It was revealed that the transversely isotropic hyperelastic model with nonlinear ground substance description (FE model III) was the best representation of the realistic ACL property by a linear regression between the simulated and the experiment deformation results. But the comparison of the predicted and experiment force of ligaments showed that all the three ACL constitutive models represented similar force results. The stress value and distribution of ACL were also altered by the change in the constitutive equation. In brief, although different ACL constitutive models have been fitted using the same uniaxial tension curve and have the similar longitudinal material property, the ACL constitutive equation should still be carefully chosen to investigate joint kinematics and biomechanics due to the different transverse material behavior.

Lagrangian Explicit Finite Element Modeling for Spin-Rolling Contact

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Xiangyun Deng ◽  
Zhiwei Qian ◽  
Rolf Dollevoet
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Fatigue Behavior ◽  
Rolling Contact ◽  
Material Behavior ◽  
Elastoplastic Material ◽  
Fe Model ◽  
New Approach ◽  
Explicit Finite Element ◽  
Deep Groove

Spin in frictional rolling contact can cause significant stress, which is the key to understanding and predicting the wear and fatigue behavior of contact components, such as wheels, rails, and rolling bearings. The lateral creep force arising from spin influences the kinematics of a wheelset and thus of vehicles. The solution that is currently employed in the field of elasticity and continuum statics was developed by Kalker and uses a boundary element method (BEM). In this paper, a new approach based on Lagrangian explicit finite element (FE) analysis is employed. This approach is able to consider arbitrary geometric profiles of rails and wheels, complex material behavior and dynamic effects, and some other factors. The new approach is demonstrated using a three-dimensional (3D) model of a wheel with a coned profile rolling along a quarter cylinder and can be easily adapted to apply to wheels and rails of arbitrary profiles. The 3D FE model is configured with elastic material properties and is used to obtain both normal and tangential solutions. The results are compared with those of the Hertz theory and the Kalker's model. The 3D FE model is then configured with elastoplastic material properties to study the spin-rolling contact with plasticity. The continuum dynamics phenomenon is captured by the FE model, which enhances the ability of the model to mimic reality. This improvement considerably extends the applicability of the FE model. The model can be applied to fatigue and wear analyses at gauge corners or rails as well as to deep groove bearings, where a large geometrical spin is present and plastic deformation may be of importance.

Finite Element Modelling of Cochlear Electrode Arrays

2021 ◽  
Vol 49 ◽  
pp. 47-52
Author(s):  
Jamal M. Al Samri ◽  
Abdulaziz S. Alaboodi
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Finite Element Modeling ◽  
Material Properties ◽  
Finite Element Modelling ◽  
Medical Surgery ◽  
Electrode Arrays ◽  
Element Modelling ◽  
Significant Difference ◽  
Good Agreement

The implant of cochlear electrode arrays is standard nowadays as a result of the improvement of medical surgery, equipment, and material properties. In this paper, the finite element modeling FEM will be utilized to characterize the mechanical properties of the electrode arrays. The results show that a good agreement between the finite element results and the experimental. Besides, it shows that no significant difference between the tapered and uniform correctional electrodes.

Constitutive Equations and Finite Element Implementation of Isochronous Nonlinear Viscoelastic Behavior

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Hossein Sepiani ◽  
Maria Anna Polak ◽  
Alexander Penlidis
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Constitutive Relations ◽  
Viscoelastic Behavior ◽  
Material Behavior ◽  
Constitutive Law ◽  
Nonlinear Viscoelastic ◽  
Nonlinear Viscoelastic Behavior ◽  
Stress Dependent

We present a phenomenological three-dimensional (3D) nonlinear viscoelastic constitutive model for time-dependent analysis. Based on Schapery's single integral constitutive law, a solution procedure has been provided to solve nonlinear viscoelastic behavior. This procedure is applicable to 3D problems and uses time- and stress-dependent material properties to characterize the nonlinear behavior of material. The equations describing material behavior are chosen based on the measured material properties in a short test time frame. This estimation process uses the Prony series material parameters, and the constitutive relations are based on the nonseparable form of equations. Material properties are then modified to include the long-term response of material. The presented model is suitable for the development of a unified computer code that can handle both linear and nonlinear viscoelastic material behavior. The proposed viscoelastic model is implemented in a user-defined material algorithm in abaqus (UMAT), and the model validity is assessed by comparison with experimental observations on polyethylene for three uniaxial loading cases, namely short-term loading, long-term loading, and step loading. A part of the experimental results have been conducted by (Liu, 2007, “Material Modelling for Structural Analysis of Polyethylene,” M.Sc. thesis, University of Waterloo, Waterloo, ON Canada), while the rest are provided by an industrial partner. The research shows that the proposed finite element model can reproduce the experimental strain–time curves accurately and concludes that with proper material properties to reflect the deformation involved in the mechanical tests, the deformation behavior observed experimentally can be accurately predicted using the finite element simulation.

scholarly journals Influence of Annular Dynamics and Material Behavior in Finite Element Analysis of Barlow’s Mitral Valve Disease

2021 ◽  
Author(s):  
Hans Martin Aguilera ◽  
Stig Urheim ◽  
Bjørn Skallerud ◽  
Victorien Prot
Keyword(s):  
Finite Element ◽  
Mitral Valve ◽  
Mitral Regurgitation ◽  
Boundary Conditions ◽  
Material Properties ◽  
Material Behavior ◽  
Patient Specific ◽  
Healthy Human ◽  
Barlow’S Disease ◽  
Annular Dilation

AbstractBarlow’s disease affects the entire mitral valve apparatus, by altering several of the fundamental mechanisms in the mitral valve which ensures unidirectional blood flow between the left atrium and the left ventricle. In this paper, a finite element model of a patient diagnosed with Barlow’s disease with patient-specific geometry and boundary conditions is presented. The geometry and boundary conditions are extracted from the echocardiographic assessment of the patient prior to surgery. Material properties representing myxomatous, healthy human and animal mitral valves are implemented and computed response are compared with each other and the echocardiographic images of the patient. This study shows that the annular dilation observed in Barlow’s patients controls several aspects of the mitral valve behavior during ventricular systole. The coaptation of the leaflets is observed to be highly dependent on annular dilation, and the coaptation area reduces rapidly at the onset of mitral regurgitation. Furthermore, the leaflet material implementation is important to predict lack of closure in the FE model correctly. It was observed that using healthy human material parameters in the Barlow’s diseased FE geometry gave severe lack of closure from the onset of mitral regurgitation, while myxomatous material properties showed a more physiological leakage.

Determination of Charge Coefficient of Piezoelectric Films Using a Combined Finite Element Model and Dynamic Loading Technique

2020 ◽  
Vol 835 ◽  
pp. 229-242
Author(s):  
Oboso P. Bernard ◽  
Nagih M. Shaalan ◽  
Mohab Hossam ◽  
Mohsen A. Hassan
Keyword(s):  
Finite Element ◽  
Dynamic Loading ◽  
Material Properties ◽  
Accurate Determination ◽  
Substrate Material ◽  
Experimental Results ◽  
Piezoelectric Composite ◽  
Piezoelectric Film ◽  
Piezoelectric Charge

Accurate determination of piezoelectric properties such as piezoelectric charge coefficients (d33) is an essential step in the design process of sensors and actuators using piezoelectric effect. In this study, a cost-effective and accurate method based on dynamic loading technique was proposed to determine the piezoelectric charge coefficient d33. Finite element analysis (FEA) model was developed in order to estimate d33 and validate the obtained values with experimental results. The experiment was conducted on a piezoelectric disc with a known d33 value. The effect of measuring boundary conditions, substrate material properties and specimen geometry on measured d33 value were conducted. The experimental results reveal that the determined d33 coefficient by this technique is accurate as it falls within the manufactures tolerance specifications of PZT-5A piezoelectric film d33. Further, obtained simulation results on fibre reinforced and particle reinforced piezoelectric composite were found to be similar to those that have been obtained using more advanced techniques. FE-results showed that the measured d33 coefficients depend on measuring boundary condition, piezoelectric film thickness, and substrate material properties. This method was proved to be suitable for determination of d33 coefficient effectively for piezoelectric samples of any arbitrary geometry without compromising on the accuracy of measured d33.

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