Cortical Bone Viscoelasticity and Fixation Strength of Press-Fit Femoral Stems: A Finite Element Model

2005 ◽  
Vol 128 (1) ◽  
pp. 7-12 ◽  
Author(s):  
T. R. Shultz ◽  
J. D. Blaha ◽  
T. A. Gruen ◽  
T. L. Norman
Keyword(s):  
Finite Element ◽  
Stress Relaxation ◽  
Finite Element Model ◽  
Cortical Bone ◽  
Coefficient Of Friction ◽  
Viscoelastic Behavior ◽  
Element Model ◽  
Press Fit ◽  
Initial Fixation ◽  
Push Out

Many cementless implant designs rely upon a diaphyseal press-fit in conjunction with a porous coated implant surface to achieve primary or short term fixation, thereby constraining interface micromotion to such a level that bone ingrowth and consequent secondary or long-term fixation, i.e., osseointegration, can occur. Bone viscoelasticity, however, has been found to affect stem primary stability by reducing push-out load. In this investigation, an axisymmetric finite element model of a cylindrical stem and diaphyseal cortical bone section was created in order to parametrically evaluate the effect of bone viscoelasticity on stem push-out while controlling coefficient of friction (μ=0.15, 0.40, and 1.00) and stem-bone diametral interference (δ=0.01, 0.05, 0.10, and 0.50mm). Based on results from a previous study, it was hypothesized that stem-bone interference (i.e., press-fit) would elicit a bone viscoelastic response which would reduce the initial fixation of the stem as measured by push-out load. Results indicate that for all examined combinations of μ and δ, bone viscoelastic behavior reduced the push-out load by a range of 2.6–82.6% due to stress relaxation of the bone. It was found that the push-out load increased with μ for each value of δ, but minimal increases in the push-out load (2.9–4.9%) were observed as δ was increased beyond 0.10mm. Within the range of variables reported for this study, it was concluded that bone viscoelastic behavior, namely stress relaxation, has an asymptotic affect on stem contact pressure, which reduces stem push-out load. It was also found that higher levels of coefficient of friction are beneficial to primary fixation, and that an interference “threshold” exists beyond which no additional gains in push-out load are achieved.

A Finite Element Model for Direction-Dependent Mechanical Response to Nanoindentation of Cortical Bone Allowing for Anisotropic Post-Yield Behavior of the Tissue

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
D. Carnelli ◽  
D. Gastaldi ◽  
V. Sassi ◽  
R. Contro ◽  
C. Ortiz ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Cortical Bone ◽  
Yield Stress ◽  
Bone Tissue ◽  
Mechanical Response ◽  
Experimental Studies ◽  
Element Model ◽  
Yield Behavior ◽  
Constitutive Parameters

A finite element model was developed for numerical simulations of nanoindentation tests on cortical bone. The model allows for anisotropic elastic and post-yield behavior of the tissue. The material model for the post-yield behavior was obtained through a suitable linear transformation of the stress tensor components to define the properties of the real anisotropic material in terms of a fictitious isotropic solid. A tension-compression yield stress mismatch and a direction-dependent yield stress are allowed for. The constitutive parameters are determined on the basis of literature experimental data. Indentation experiments along the axial (the longitudinal direction of long bones) and transverse directions have been simulated with the purpose to calculate the indentation moduli and the tissue hardness in both the indentation directions. The results have shown that the transverse to axial mismatch of indentation moduli was correctly simulated regardless of the constitutive parameters used to describe the post-yield behavior. The axial to transverse hardness mismatch observed in experimental studies (see, for example, Rho et al. [1999, “Elastic Properties of Microstructural Components of Human Bone Tissue as Measured by Nanoindentation,” J. Biomed. Mater. Res., 45, pp. 48–54] for results on human tibial cortical bone) can be correctly simulated through an anisotropic yield constitutive model. Furthermore, previous experimental results have shown that cortical bone tissue subject to nanoindentation does not exhibit piling-up. The numerical model presented in this paper shows that the probe tip-tissue friction and the post-yield deformation modes play a relevant role in this respect; in particular, a small dilatation angle, ruling the volumetric inelastic strain, is required to approach the experimental findings.

Cortical Bone Viscoelasticity and Fixation Strength of Press-Fit Femoral Stems: An In-Vitro Model

2005 ◽  
Vol 128 (1) ◽  
pp. 13-17 ◽  
Author(s):  
T. L. Norman ◽  
E. S. Ackerman ◽  
T. S. Smith ◽  
T. A. Gruen ◽  
A. J. Yates ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Viscoelastic Behavior ◽  
Fixation Strength ◽  
Viscoelastic Response ◽  
Press Fit ◽  
Initial Stability ◽  
Vitro Model ◽  
Stem Stability ◽  
Push Out

Cementless total hip femoral components rely on press-fit for initial stability and bone healing and remodeling for secondary fixation. However, the determinants of satisfactory press-fit are not well understood. In previous studies, human cortical bone loaded circumferentially to simulate press-fit exhibited viscoelastic, or time dependent, behavior. The effect of bone viscoelastic behavior on the initial stability of press-fit stems is not known. Therefore, in the current study, push-out loads of cylindrical stems press-fit into reamed cadaver diaphyseal femoral specimens were measured immediately after assembly and 24h with stem-bone diametral interference and stem surface treatment as independent variables. It was hypothesized that stem-bone interference would result in a viscoelastic response of bone that would decrease push-out load thereby impairing initial press-fit stability. Results showed that push-out load significantly decreased over a 24h period due to bone viscoelasticity. It was also found that high and low push-out loads occurred at relatively small amounts of stem-bone interference, but a relationship between stem-bone interference and push-out load could not be determined due to variability among specimens. On the basis of this model, it was concluded that press-fit fixation can occur at relatively low levels of diametral interference and that stem-bone interference elicits viscoelastic response that reduces stem stability over time. From a clinical perspective, these results suggest that there could be large variations in initial press-fit fixation among patients.

Axial Strength of Tube-to-Tubesheet Joints: Finite Element and Experimental Evaluations

2001 ◽  
Vol 124 (1) ◽  
pp. 22-31 ◽  
Author(s):  
M. Allam ◽  
A. Bazergui
Keyword(s):  
Finite Element ◽  
Analytical Solution ◽  
Finite Element Model ◽  
Experimental Testing ◽  
Element Model ◽  
Axial Strength ◽  
Pull Out ◽  
Push Out ◽  
Pull Out Strength ◽  
The Finite Element Model

Because of their importance for the integrity of heat exchangers, the strength of tube-to-tubesheet joints, and particularly their axial strength, is of special interest. A finite element model of an expanded tube-to-tubesheet joint is proposed and examined experimentally with the objective of determining numerically its axial strength. Simplified analytical methods that were previously proposed by many authors to predict the joint axial strength are also used in this investigation. Experimental testing shows that the finite element model is highly accurate for calculating the joint axial strength. The experimental investigation also proves that the pull-out strength is overestimated when calculated using a simple analytical solution. A parametric analysis using the finite element results indicates that the pull-out force is normally lower than the push-out load and that both are lower than the estimations of the analytical solution. The results indicate that the pull-out force as given by the finite element model is generally 35 percent lower than that evaluated by the analytical solution. A difference of as much as 10 percent is also found between the push-out and pull-out loads.

Evaluating a NiTi Implant Under Realistic Loads: A Simulation Study

2016 ◽  
Author(s):  
Amirhesam Amerinatanzi ◽  
Narges Shayesteh Moghaddam ◽  
Hamdy Ibrahim ◽  
Mohammad Elahinia
Keyword(s):  
Finite Element ◽  
Additive Manufacturing ◽  
Finite Element Model ◽  
Cortical Bone ◽  
Reconstructive Surgery ◽  
Stress Shielding ◽  
Element Model ◽  
Patient Specific ◽  
Porous Niti ◽  
Biocompatible Alloys

Additive manufacturing (i.e. 3D printing) has only recently be shown as a well-established technology to create complex shapes and porous structures from different biocompatible metal powder such as titanium, nitinol, and stainless steel alloys. This allows for manufacturing bone fixation hardware with patient-specific geometry and properties (e.g. density and mechanical properties) directly from CAD files. Superelastic NiTi is one of the most biocompatible alloys with high shock absorption and biomimetic hysteresis behavior. More importantly, NiTi has the lowest stiffness (36–68 GPa) among all biocompatible alloys [1]. The stiffness of NiTi can further be reduced, to the level of the cortical bone (10–31.2 GPa), by introducing engineered porosity using additive manufacturing [2–4]. The low level of fixation stiffness allows for bone to receive a stress profile close to that of healthy bone during the healing period. This enhances the bone remodeling process (Wolf’s Law) which primarily driven by the pattern of stress. Also, this match in the stiffness of bone and fixation mitigates the problem of stress shielding and detrimental stress concentrations. Stress shielding is a known problem for the currently in-use Ti-6Al-4V fixation hardware. The high stiffness of Ti-6Al-4V (112 GPa) compared to bone results in the absence of mechanical loading on the adjacent bone that causes loss of bone mass and density and subsequently bone/implant failure. We have proposed additively manufactured porous NiTi fixation hardware with a patient-specific stiffness to be used for the mandibular reconstructive surgery (MRS). In MRS, the use of metallic fixation hardware and double barrel fibula graft is the standard methodology to restore the mandible functionality and aesthetic. A validated finite element model was developed from a dried cadaveric mandible using CT scan data. The model simulated a patient’s mandible after mandibular reconstructive surgery to compare the performance of the conventional Ti-6Al-4V fixation hardware with the proposed one (porous superelastic NiTi fixation plates). An optimized level of porosity was determined to match the NiTi equivalent stiffness to that of a resected bone, then it was imposed to the simulated fixation plates. Moreover, the material property of superelastic NiTi was simulated by using a validated customized code. The code was calibrated by using DSC analysis and mechanical tests on several prepared bulk samples of Ni-rich NiTi. The model was run under common activities such as chewing by considering different levels of the applied fastening torques on screws. The results show a higher level of stress distribution on mandible cortical bone in the case of using NiTi fixation plates. Based on wolf’s law it can lead to a lower level of stress shielding on the grafted bone and over time bone can remodel itself. Moreover, the results suggest an optimum fastening torque for fastening the screws for the superelastic fixations causes more normal distribution of stress on the bone similar to that for the healthy mandible. Finally, we successfully fabricated the stiffness-matched porous NiTi fixation plates using selective laser melting technique, and they were mounted on the dried cadaveric mandible used to create the finite element model.

Dependence of Elastic Properties of Human Femoral Cortical Bone on Porosity

2015 ◽  
Author(s):  
Maryam Khosroshahi ◽  
Fred Barez ◽  
Amer El-Hage ◽  
James Kao
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Finite Element Model ◽  
Cortical Bone ◽  
Elastic Properties ◽  
Transversely Isotropic ◽  
Element Model ◽  
Element Analysis ◽  
Age Related ◽  
The Finite Element Model

Hip fracture is one of the most serious and common health problems among elderly which may lead to permanent disability or death. Hip fracture commonly occurs in the femoral bone, the major bone in the hip joint. Microscopic age-related changes in the structure of cortical bone is one of the factors that is considered to be partially responsible for the increase of fracture risk in elderly. It is of great interest to develop a predictable model of such fractures for the aging population in preparation of a suitable therapy. These micro structural changes influence mechanical properties and, therefore, behavior of bone and are critical to understand risk and mechanics of fracture of bone. Correlation between cortical bone strength and porosity, as a microscopic structural factor, has been examined frequently as a function of age and/or porosity. These studies have investigated the effect of porosity experimentally and have not studied the effect of porosity independently from other structural factors such as bone mineral density. In this study effect of porosity on elastic properties of human femoral cortical bone was studied independently using finite element analysis assuming transversely isotropic behavior in terms of elastic properties with the axis of elastic properties along the longitudinal axis of femur shaft. In this study, published standard mechanical tests for transversely isotropic materials were simulated using finite element computer simulation on models with different porosities. The developed finite element model utilized material properties based on the best fit regression in previously published articles. Pores’ size, shape and distribution were also modeled based on previous experimental studies. The finite element model, in general, predicted behavior of five independent elastic mechanical properties, namely, longitudinal Young’s modulus, transverse poisson’s ratio, transverse shear modulus, transverse Young’s modulus and longitudinal poisson’s ratio, as a function of porosity. Furthermore, effect of porosity on the elastic properties across various age groups was investigated using published data on age-related changes in bone porosity. Mathematical models based on Finite Element Analysis results have been developed using linear least square regression. These models show negative linear relationship between studied elastic properties of human femoral cortical bone and porosity. The Finite Element Analysis results compared well with the previously published experimental data. Furthermore, the results obtained show the elastic properties as functions of age for females and males. The predicted values for elastic properties are lower for men compared to women of age 20 to 40 years old. However, after the age of 44, elastic properties of femoral cortical bone for men are higher than women. The Finite Element Model developed in this study will help to create a clinical bone model for the prediction of fracture risk or the selection of suitable therapy in orthopedic surgery.

3D bending simulation and mechanical properties of the OLED bending area

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 397-407
Author(s):  
Liang Ma ◽  
Jinan Gu
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Stress Relaxation ◽  
Finite Element Model ◽  
3D Model ◽  
Simulation Models ◽  
Element Model ◽  
Uniaxial Tensile ◽  
Proposed Model ◽  
Stress Changes

AbstractDue to the poor mechanical properties of traditional simulation models of the organic light-emitting device (OLED) bending area, this article puts forward a finite element model of 3D bending simulation of the OLED bending area. During the model construction, it is necessary to determine the viscoelastic and hyperelastic mechanical properties, respectively. In order to accurately obtain the stress changes of material deformation during the hyperelasticity determination, a uniaxial tensile test and a shear test were used to obtain data and thus to characterize the hyperelastic properties. In order to measure the viscoelasticity, a stress relaxation test was used to draw the stress relaxation curve, so as to characterize the viscoelastic properties. Then, the plane or axisymmetric stress–strain analysis was achieved, and the material parameters of the 3D model of the OLED bending area were obtained. Finally, the 3D model was applied to the 3D bending of the OLED bending area. Combined with the axisymmetric finite element analysis method, the 3D bending simulation finite element model of the OLED bending area was constructed by dividing the finite element mesh. Experimental results show that the mechanical properties of the proposed model are better than those of traditional OLED bending simulation models. Meanwhile, the proposed model has stronger application advantages.

A Methodology for the Simulation of Surface-Contact Grinding Tool Topography

2009 ◽  
Vol 416 ◽  
pp. 519-523
Author(s):  
Guo Zhi Zhang ◽  
Xian Hua Zhang ◽  
Li Li Liu ◽  
Zeng Ju Wei
Keyword(s):  
Finite Element ◽  
Theoretical Model ◽  
Finite Element Model ◽  
Coefficient Of Friction ◽  
Surface Friction ◽  
Static Friction ◽  
Element Model ◽  
Friction Mechanism ◽  
Manufacturing Quality ◽  
The Coefficient Of Friction

Study on the effect of the surface manufacturing quality (roughness) to the friction between the surfaces. Based on the plastic theory of mechanism-based strain gradient (MSG) of the micro-plastic-mechanics and the contact theory, the theoretical model of the coefficient of friction between the rough surfaces and the non-linear finite element model between the grinding samples were established. Moreover, the surface stress distribution and the coefficient of friction were obtained through the sub-structure finite element method. The established model of static friction theoretical model and the accuracy of the finite element model were verified through comparing with the result of the static friction experiments between the grinding samples with different surface manufacturing quality. The study in the paper is important to the study on the surface friction mechanism.

Initial fixation of a finite element model of an AI-Hip cementless stem evaluated by micromotion and stress

2010 ◽  
Vol 15 (1) ◽  
pp. 132-139 ◽  
Author(s):  
Rina Sakai ◽  
Yusuke Sato ◽  
Moritoshi Itoman ◽  
Kiyoshi Mabuchi
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Cementless Stem ◽  
Initial Fixation

DYNAMIC STRESS DISTRIBUTION IN A MODEL OF IMPLANTED MANDIBLE: NUMERICAL ANALYSIS OF VISCOELASTIC BONE

2015 ◽  
Vol 15 (04) ◽  
pp. 1550050 ◽  
Author(s):  
H. MOTALLEBZADEH ◽  
M. TAFAZZOLI-SHADPOUR ◽  
M. M. KHANI
Keyword(s):  
Finite Element ◽  
Stress Distribution ◽  
Cortical Bone ◽  
Dynamic Loading ◽  
Viscoelastic Behavior ◽  
Element Model ◽  
Von Mises Stress ◽  
Dental Implantation ◽  
Trabecular Bones ◽  
Von Mises

To determine the success of dental implants, mechanical stress distribution in the implant-bone interface is considered to be a determinant. Many researchers have used finite element modeling of implant-bone through applying static loading on the implant; however, dynamic loading has not extensively been investigated specially considering viscoelastic behavior of the bone. The aim of this study is to analyze effects of viscoelasticity of bone and dynamic loading comparable to mastication conditions on stress distribution in an implanted mandible. A three-dimensional finite-element model of an implanted mandible in the first molar region was constructed from computerized tomography data. Effects of several parameters, such as material properties including viscoelastic behavior of the cortical and trabecular bones, load amplitude, duration and direction on the instantaneous and long-term von Mises stress distribution of an implanted mandible were evaluated. In all loading conditions, the maximum von Mises stress occurred in cortical bone surrounding the neck of implant. Stress distribution was not noticeably affected by viscoelastic behavior during the first loading cycles, however, after 100 s periodic loading, the differences between stress magnitudes (especially in the cortical bone) became noticeable. In addition, sensitivity analysis showed that both cortical and trabecular bones were more sensitive to axial load than buccalingual and mesiodistal forces. The results of this study contribute to analysis of parameters involved in success of dental implantation.

Experimental and Finite Element Comparaison of Various Joint Fixation Designs

1999 ◽  
Author(s):  
O. Patenaude ◽  
A. Shirazi-Adl ◽  
M. Dammak
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Bone Ingrowth ◽  
Element Model ◽  
Bone Implant ◽  
Combined Loads ◽  
Pull Out ◽  
Initial Fixation ◽  
Fixation Stability ◽  
Friction Models

Abstract The short- and long-term success of tibial cementless implants depends on the initial fixation stability provided primarily by posts and screws. Excessive relative motions at the bone-implant interface are known to inhibit bone ingrowth and, hence, biologic fixation. In this work, the performance of a number of fixation configurations under static and fatigue combined loads (i.e., compression plus shear) is investigated both experimentally and numerically. These results will permit both to compare different fixation types and to serve to validate a 3D finite element model that incorporates the measured nonlinear bone-implant friction and posts/screws pull-out tests. Once validated, the finite element model is also used to study the effect of different bone-implant friction models for porous coated posts and plate and of loading order of application on predictions.

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