Patient-Specific Finite-Element Analyses of the Proximal Femur with Orthotropic Material Properties Validated by Experiments

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Nir Trabelsi ◽  
Zohar Yosibash
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Orthotropic Material ◽  
High Order ◽  
Patient Specific ◽  
Pronounced Difference ◽  
Quantitative Computer Tomography ◽  
Fresh Frozen ◽  
Orthotropic Properties

Patient-specific high order finite-element (FE) models of human femurs based on quantitative computer tomography (QCT) with inhomogeneous orthotropic and isotropic material properties are addressed. The point-wise orthotropic properties are determined by a micromechanics (MM) based approach in conjunction with experimental observations at the osteon level, and two methods for determining the material trajectories are proposed (along organs outer surface, or along principal strains). QCT scans on four fresh-frozen human femurs were performed and high-order FE models were generated with either inhomogeneous MM-based orthotropic or empirically determined isotropic properties. In vitro experiments were conducted on the femurs by applying a simple stance position load on their head, recording strains on femurs’ surface and head’s displacements. After verifying the FE linear elastic analyses that mimic the experimental setting for numerical accuracy, we compared the FE results to the experimental observations to identify the influence of material properties on models’ predictions. The strains and displacements computed by FE models having MM-based inhomogeneous orthotropic properties match the FE-results having empirically based isotropic properties well, and both are in close agreement with the experimental results. When only the strains in the femoral neck are being compared a more pronounced difference is noticed between the isotropic and orthotropic FE result. These results lay the foundation for applying more realistic inhomogeneous orthotropic material properties in FEA of femurs.

A CT-Based High-Order Finite Element Analysis of the Human Proximal Femur Compared to In-vitro Experiments

2006 ◽  
Vol 129 (3) ◽  
pp. 297-309 ◽  
Author(s):  
Zohar Yosibash ◽  
Royi Padan ◽  
Leo Joskowicz ◽  
Charles Milgrom
Keyword(s):  
Finite Element ◽  
Proximal Femur ◽  
Mechanical Response ◽  
Clinical Importance ◽  
High Order ◽  
Patient Specific ◽  
In Vitro Experiments ◽  
Element Analysis ◽  
Bone Response

The prediction of patient-specific proximal femur mechanical response to various load conditions is of major clinical importance in orthopaedics. This paper presents a novel, empirically validated high-order finite element method (FEM) for simulating the bone response to loads. A model of the bone geometry was constructed from a quantitative computerized tomography (QCT) scan using smooth surfaces for both the cortical and trabecular regions. Inhomogeneous isotropic elastic properties were assigned to the finite element model using distinct continuous spatial fields for each region. The Young’s modulus was represented as a continuous function computed by a least mean squares method. p-FEMs were used to bound the simulation numerical error and to quantify the modeling assumptions. We validated the FE results with in-vitro experiments on a fresh-frozen femur loaded by a quasi-static force of up to 1500N at four different angles. We measured the vertical displacement and strains at various locations and investigated the sensitivity of the simulation. Good agreement was found for the displacements, and a fair agreement found in the measured strain in some of the locations. The presented study is a first step toward a reliable p-FEM simulation of human femurs based on QCT data for clinical computer aided decision making.

Predicting the yield of the proximal femur using high-order finite-element analysis with inhomogeneous orthotropic material properties

2010 ◽  
Vol 368 (1920) ◽  
pp. 2707-2723 ◽  
Author(s):  
Zohar Yosibash ◽  
David Tal ◽  
Nir Trabelsi
Keyword(s):  
Finite Element ◽  
Proximal Femur ◽  
Material Properties ◽  
Orthotropic Material ◽  
Isotropic Material ◽  
High Order ◽  
Principal Strain ◽  
Fe Model ◽  
Yield Criteria ◽  
Maximum Principal Strain

High-order finite-element (FE) analyses with inhomogeneous isotropic material properties have been shown to predict the strains and displacements on the surface of the proximal femur with high accuracy when compared with in vitro experiments. The same FE models with inhomogeneous orthotropic material properties produce results similar to those obtained with isotropic material properties. Herein, we investigate the yield prediction capabilities of these models using four different yield criteria, and the spread in the predicted load between the isotropic and orthotropic material models. Subject-specific high-order FE models of two human femurs were generated from CT scans with inhomogeneous orthotropic or isotropic material properties, and loaded by a simple compression force at the head. Computed strains and stresses by both the orthotropic and isotropic FE models were used to determine the load that predicts ‘yielding’ by four different ‘yield criteria’: von Mises, Drucker–Prager, maximum principal stress and maximum principal strain. One of the femurs was loaded by a simple load until fracture, and the force resulting in yielding was compared with the FE predicted force. The surface average of the ‘maximum principal strain’ criterion in conjunction with the orthotropic FE model best predicts both the yield force and fracture location compared with other criteria. There is a non-negligible influence on the predictions if orthotropic or isotropic material properties are applied to the FE model. All stress-based investigated ‘yield criteria’ have a small spread in the predicted failure. Because only one experiment was performed with a rather simplified loading configuration, the conclusions of this work cannot be claimed to be either reliable or sufficient, and future experiments should be performed to further substantiate the conclusions.

Fracture Prediction for the Proximal Femur Using Finite Element Models: Part I—Linear Analysis

1991 ◽  
Vol 113 (4) ◽  
pp. 353-360 ◽  
Author(s):  
J. C. Lotz ◽  
E. J. Cheal ◽  
W. C. Hayes
Keyword(s):  
Finite Element ◽  
Fracture Risk ◽  
Strain Gage ◽  
Proximal Femur ◽  
Material Properties ◽  
The United States ◽  
Nonlinear Material ◽  
Finite Element Models ◽  
Model Predictions

Over 90 percent of the more than 250,000 hip fractures that occur annually in the United States are the result of falls from standing height. Despite this, the stresses associated with femoral fracture from a fall have not been investigated previously. Our objectives were to use three-dimensional finite element models of the proximal femur (with geometries and material properties based directly on quantitative computed tomography) to compare predicted stress distributions for one-legged stance and for a fall to the lateral greater trochanter. We also wished to test the correspondence between model predictions and in vitro strain gage data and failure loads for cadaveric femora subjected to these loading conditions. An additional goal was to use the model predictions to compare the sensitivity of several imaging sites in the proximal femur which are used for the in vivo prediction of hip fracture risk. In this first of two parts, linear finite element models of two unpaired human cadaveric femora were generated. In Part II, the models were extended to include nonlinear material properties for the cortical and trabecular bone. While there was poor correspondence between strain gage data and model predictions, there was excellent agreement between the in vitro failure data and the linear model, especially using a von Mises effective strain failure criterion. Both the onset of structural yielding (within 22 and 4 percent) and the load at fracture (within 8 and 5 percent) were predicted accurately for the two femora tested. For the simulation of one-legged stance, the peak stresses occurred in the primary compressive trabeculae of the subcapital region. However, for a simulated fall, the peak stresses were in the intertrochanteric region. The Ward’s triangle (basicervical) site commonly used for the clinical assessment of osteoporosis was not heavily loaded in either situation. These findings suggest that the intertrochanteric region may be the most sensitive site for the assessment of fracture risk due to a fall and the subcapital region for fracture risk due to repetitive activities such as walking.

scholarly journals Inverse Calculation of Timber-CFRP Composite Beams Using Finite Element Analysis

2020 ◽  
Author(s):  
Khaled Saad ◽  
András Lengyel
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Material Properties ◽  
Orthotropic Material ◽  
Material Model ◽  
Flexural Behavior ◽  
Fiber Reinforced Polymers ◽  
Element Analysis ◽  
Linear Elastic ◽  
Timber Beams

This study focuses on the flexural behavior of timber beams externally reinforced using carbon fiber-reinforced polymers (CFRP). Linear and non-linear finite element analysis were proposed and validated by experimental tests carried out on 44 timber beams to inversely determine the material properties of the timber and the CFRP. All the beams have the same geometrical properties and were loaded under four points bending. In this paper the general commercial software ANSYS was used, and three- and two-dimensional numerical models were evaluated for their ability to describe the behavior of the solid timber beams. The linear elastic orthotropic material model was assumed for the timber beams in the linear range and the 3D nonlinear rate-independent generalized anisotropic Hill potential model was assumed to describe the nonlinear behavior of the material. As for the CFRP, a linear elastic orthotropic material model was introduced for the fibers and a linear elastic isotropic model for the epoxy resin. No mechanical model was introduced to describe the interaction between the timber and the CFRP since failure occurred in the tensile zone of the wood. Simulated and measured load-mid-span deflection responses were compared and the material properties for timber-CFRP were numerically determined.

Different Finite Element Strategies to Satisfy Clinical and Engineering Requirements in Modeling a Novel Percutaneous Device

2012 ◽  
Author(s):  
Claudio Capelli ◽  
Giovanni Biglino ◽  
Lorenza Petrini ◽  
Francesco Migliavacca ◽  
Philipp Bonhoeffer ◽  
...  
Keyword(s):  
Finite Element ◽  
Right Ventricular Outflow Tract ◽  
Patient Specific ◽  
In Vitro Tests ◽  
Loading Conditions ◽  
Modeling Tools ◽  
Transcatheter Heart Valve ◽  
Specific Loading ◽  
Valve Implantation

By taking into account patient-specific properties, finite element (FE) models can aid in the optimization of the devices’ mechanical performances, accelerating the time of development and reducing testing costs. Patient-specific cardiovascular modeling can also drive the development of novel devices [1], by means of anatomical elements that are more representative than animal surrogates [2], and integrating standard in vitro tests with patient-specific loading conditions [3]. Transcatheter heart valve implantation can particularly benefit from a modeling approach. In the field of treatment of valve dysfunctions, percutaneous techniques are relatively new or under development, and modeling tools can contribute to improve these procedures (e.g. design modifications or different routes for device insertion) and increase patient safety in the early introduction of new devices into clinical practice. For a feasible clinical application, computational methods need to be fully validated against physical data, to take into account patient-specific properties, and to provide results in a short time. Instead, from an engineering perspective, models can cost-effectively aid the design phase by improving preclinical testing with more realistic loading conditions for accurate simulation of mechanical behaviour and prediction of durability. This study aims to identify optimal modeling strategies to respond to both clinical and engineering requirements. As a case study, simulations were conducted on a new percutaneous pulmonary valve implantation (PPVI) device [4] tested within a patient-specific right ventricular outflow tract model.

A high-order control volume finite element method for thermoelastic analysis of functionally graded solids with mixed grids

2018 ◽  
Vol 233 (11) ◽  
pp. 3994-4013
Author(s):  
Qi Liu ◽  
Yan Yu ◽  
Pingjian Ming
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Material Properties ◽  
Control Volume ◽  
Functionally Graded ◽  
High Order ◽  
Shape Functions ◽  
Quadrilateral Element ◽  
Thermoelastic Analysis ◽  
Control Volume Finite Element

In this article, a new two-dimensional control volume finite element method has been developed for thermoelastic analysis in functionally graded materials. A nine-node quadrilateral element and a six-node triangular element are employed to deal with the mixed-grid problem. The unknown variables and material properties are defined at the node. The high-order shape functions of six-node triangular and nine-node quadrilateral element are employed to obtain the unknown variables and their derivatives. In addition, the material properties in functionally graded structure are also modeled by applying the high-order shape functions. The capabilities of the presented method to heat conduction problem, elastic problem, and thermoelastic problem have been validated. First, the defined location of material properties is found to be important for the accuracy of the numerical results. Second, the presented method is proven to be efficient and reliable for the elastic analysis in multi-phase materials. Third, the presented method is capable of high-order mixed grids. The memory and computational costs of the presented method are also compared with other numerical methods.

Analysis for Tire Mold Design

1974 ◽  
Vol 2 (3) ◽  
pp. 195-210 ◽  
Author(s):  
R. A. Ridha
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Shell Element ◽  
Structural Behavior ◽  
Temperature History ◽  
Small Displacement ◽  
Toroidal Shell ◽  
Mold Design ◽  
Orthotropic Properties ◽  
Element Technique

Abstract An analysis is presented for determining tire deformation due to shrinkage. The analysis uses composite theory and the finite element technique in modeling the material properties and the structural behavior. The constant strain toroidal shell element developed by Wilson for small displacement and isotropic properties is modified for orthotropic properties which depend on the element location. Temperature history and the buildup of shrink forces during cure are determined experimentally. The shrink forces are represented by a set of equivalent loads applied at the nodes. Good correlation is obtained between calculated and experimental displacements. The analysis is applied in relating the mold shape to the final shape of the tire.

Development and Validation of Patient-Specific Finite Element Models of the Hemipelvis Generated From a Sparse CT Data Set

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Vickie B. Shim ◽  
Rocco P. Pitto ◽  
Robert M. Streicher ◽  
Peter J. Hunter ◽  
Iain A. Anderson
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Patient Data ◽  
Ct Scans ◽  
Patient Specific ◽  
Data Sets ◽  
Fe Model ◽  
Data Set ◽  
Spatially Varying ◽  
Ct Slices

To produce a patient-specific finite element (FE) model of a bone such as the pelvis, a complete computer tomographic (CT) or magnetic resonance imaging (MRI) geometric data set is desirable. However, most patient data are limited to a specific region of interest such as the acetabulum. We have overcome this problem by providing a hybrid method that is capable of generating accurate FE models from sparse patient data sets. In this paper, we have validated our technique with mechanical experiments. Three cadaveric embalmed pelves were strain gauged and used in mechanical experiments. FE models were generated from the CT scans of the pelves. Material properties for cancellous bone were obtained from the CT scans and assigned to the FE mesh using a spatially varying field embedded inside the mesh while other materials used in the model were obtained from the literature. Although our FE meshes have large elements, the spatially varying field allowed them to have location dependent inhomogeneous material properties. For each pelvis, five different FE meshes with a varying number of patient CT slices (8–12) were generated to determine how many patient CT slices are needed for good accuracy. All five mesh types showed good agreement between the model and experimental strains. Meshes generated with incomplete data sets showed very similar stress distributions to those obtained from the FE mesh generated with complete data sets. Our modeling approach provides an important step in advancing the application of FE models from the research environment to the clinical setting.

Fatigue Analysis for the Lower Assembly of a U-Tube Steam Generator

2019 ◽  
Author(s):  
Moli J. Cao
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Steam Generator ◽  
Material Properties ◽  
Orthotropic Material ◽  
Element Model ◽  
Fatigue Analysis ◽  
Temperature Fields ◽  
Flat Bottom ◽  
Primary Channel

Abstract The lower assembly of a U-tube steam generator consists of a hemispherical primary channel head with a flat bottom, a perforated tubesheet, a partition plate, and a portion of lower shell. The partition plate divides the primary channel head into two halves. Each half contains a primary nozzle and a manway opening. The fatigue analysis of the lower assembly of a U-tube steam generator can be a challenge due to the complexities of the geometry and loading conditions. In this paper, the development of a global finite element model including all important features and several submodels to cover the effects of all these features is described. The tubesheet is simulated using equivalent solid properties with orthotropic material properties. The thermal loads from the inner surfaces of the tubes embedded in the tubesheet are implemented using surface elements. The submodeling technique is utilized to evaluate the local small features, such as tube holes at primary and secondary faces of the tubesheet, with the constraints at the cut-boundaries and the temperature fields of the submodel being extracted from the global model.

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