scholarly journals A closed-form formulation for the conformal articulation of metal-on-polyethylene hip prostheses: Contact mechanics and sliding distance

2018 ◽  
Vol 232 (12) ◽  
pp. 1196-1208 ◽  
Author(s):  
Ehsan Askari ◽  
Michael S Andersen
Keyword(s):  
Finite Element ◽  
Closed Form ◽  
Contact Mechanics ◽  
Contact Pressure ◽  
Contact Point ◽  
Contact Stresses ◽  
Computational Time ◽  
Physiological Loading ◽  
Sliding Distance ◽  
Inertia Forces

Using Hertz contact law results in inaccurate outcomes when applied to the soft conformal hip implants. The finite element method also involves huge computational time and power. In addition, the sliding distance computed using the Euler rotation method does not incorporate tribology of bearing surfaces, contact mechanics and inertia forces. This study, therefore, aimed to develop a nonlinear dynamic model based on the multibody dynamic methodology to predict contact pressure and sliding distance of metal-on-polyethylene hip prosthesis, simultaneously, under normal walking condition. A closed-form formulation of the contact stresses distributed over the articulating surfaces was derived based upon the elastic foundation model, which reduced computational time and cost significantly. Three-dimensional physiological loading and motions, inertia forces due to hip motion and energy loss during contact were incorporated to obtain contact properties and sliding distance. Comparing the outcomes with that available in the literature and a finite element analysis allowed for the validation of our approach. Contours of contact stresses and accumulated sliding distances at different instants of the walking gait cycle were investigated and discussed. It was shown that the contact point at each instant was located within the zone with the corresponding highest accumulated sliding distance. In addition, the maximum contact pressure and area took place at the stance phase with a single support. The stress distribution onto the cup surface also conformed to the contact point trajectory and the physiological loading.

THE EFFECT OF ASPHERICITY OF ACETABULAR BEARING SURFACE ON CONTACT MECHANICS OF UHMWPE TOTAL HIP IMPLANTS BY FINITE ELEMENT ANALYSIS

2017 ◽  
Vol 17 (01) ◽  
pp. 1750011 ◽  
Author(s):  
XUAN ZHANG ◽  
LING WANG ◽  
XIFENG PENG ◽  
DICHEN LI ◽  
JIANKANG HE ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Contact Mechanics ◽  
Contact Pressure ◽  
Surface Profile ◽  
Surface Measurement ◽  
Element Analysis ◽  
Actual Surface ◽  
Total Hip ◽  
Measuring Machine

Asphericity and out-of-roundness are generally used to evaluate the manufacturing quality of ultra-high molecular weight polyethylene (UHMWPE) cup inner surfaces, which can potentially affect initial clinical wear and contribute to osteolysis of total hip arthroplasty. This study measured the location and magnitude of asphericity and the out-of-roundness value for four UHMWPE cups in a single set, and then investigated the effects of the asphericity on the contact mechanics of UHMWPE cups. A co-ordinate measuring machine (CMM) was used for the surface measurement and finite element analysis (FEA) was adopted for contact mechanics study. The results demonstrated that the asphericity varied between cups with the maximum value as 0.088[Formula: see text][Formula: see text][Formula: see text]0.004[Formula: see text]mm. Although such a value met the ISO specification, large difference of volume appeared for the asphericity above 0.060[Formula: see text]mm. Actual surface profile accounting for the asphericity was found to affect the value of contact pressure and contact area by around 12%. The inferior asphericity resulted in a nonsmoothly distributed contact pressure, which had a negative effect on the contact mechanics of UHMWPE cups and the edge loading was predicted to occur for the sample with a large asphericity. In conclusion, the asphericity of UHMWPE cup could affect the contact mechanics of the articular bearings and may subsequently contribute to initial wear during bedding-in phase.

Effect of microseparation on contact mechanics in ceramic-on-ceramic hip joint replacements

2002 ◽  
Vol 216 (6) ◽  
pp. 403-408 ◽  
Author(s):  
M M Mak ◽  
A A Besong ◽  
Z M Jin ◽  
J Fisher
Keyword(s):  
Femoral Head ◽  
Contact Mechanics ◽  
Contact Pressure ◽  
Contact Area ◽  
Three Dimensional ◽  
Contact Stresses ◽  
Radial Clearance ◽  
Acetabular Cup ◽  
Edge Contact ◽  
Ceramic On Ceramic

The contact mechanics in ceramic-on-ceramic hip implants are investigated in this study under the microseparation condition where the edge contact occurs between the superolateral rim of the acetabular cup and the femoral head. A three-dimensional finite element model is developed to examine the effect of the microseparation distance between the femoral head and the acetabular cup on the contact area and contact stresses between the bearing surfaces. It is shown that microseparation leads to edge contact and elevated contact stresses, and these are mainly dependent on the magnitude of separation, the radial clearance between the femoral head and the acetabular cup, and the cup inclination angle. For a small microseparation distance (less than the diametrical clearance), the contact occurs within the acetabular cup, and consequently an excellent agreement of the predicted contact pressure distribution is obtained between the present three-dimensional anatomical model and a simple two-dimensional axisymmetric model adopted in a previous study [5]. However, as microsegregation is increased further, edge contact between the superolateral rim and the femoral head occurs. Consequently, the predicted contact pressure is significantly increased. The corresponding contact area resembles closely the stripe wear pattern observed on both clinically retrieved and simulator-tested ceramic femoral heads [8, 9, 11]. Furthermore, introducing a fillet radius of 2.5 mm at the mouth of the acetabular cup is shown to reduce the contact stress due to edge contact, but only under relatively large microseparation distances.

On the Analytical Determination of the Nominal Stresses in Dovetail Attachments

2020 ◽  
Author(s):  
Glenn Sinclair
Keyword(s):  
Finite Element ◽  
Closed Form ◽  
Contact Region ◽  
Essential Elements ◽  
Contact Stresses ◽  
Physical Models ◽  
Analytical Determination ◽  
Bending Stress ◽  
Attachment Model

Abstract Simple physical models are developed for the nominal contact stresses in dovetail attachments. These nominal stresses include the pressure, the shear traction, and the bending stress in the contact region, both during loading up and unloading. The models furnish closed-form expressions for these stresses. For a specific dovetail attachment, model values are compared with verified finite element values. As a result of the simplifications introduced to make the models tractable, model values only approximately equal finite element values. Nonetheless, the models capture the essential elements of the response of nominal stresses in dovetail attachments.

Contact-Point Response for Modal Identification of Bridges by a Moving Test Vehicle

2018 ◽  
Vol 18 (05) ◽  
pp. 1850073 ◽  
Author(s):  
Y. B. Yang ◽  
Bin Zhang ◽  
Yao Qian ◽  
Yuntian Wu
Keyword(s):  
Finite Element ◽  
Closed Form ◽  
Frequency Response Function ◽  
Contact Point ◽  
Modal Identification ◽  
Mode Shapes ◽  
Test Vehicle ◽  
Closed Form Solutions ◽  
Road Surfaces ◽  
Vehicle Response

The response of the contact point of the vehicle with the bridge, rather than the vehicle itself, is proposed for modal identification of bridges by a moving test vehicle. To begin, approximate closed-form solutions were derived for the vehicle and contact-point responses, and they were verified by finite element solutions. The contact-point acceleration is born to be free of the vehicle frequency, an annoying effect that may overshadow the bridge frequencies in case of rough surface. From the frequency response function (FRF) of the vehicle with respect to the contact point, it was shown that the contact-point response generally outperforms the vehicle response in extracting the bridge frequencies because it could identify more frequencies. In the numerical simulations, the contact-point response was compared with the vehicle response for various scenarios. It is concluded that in each case, say, for varying vehicle speeds or frequencies, for smooth or rough road surfaces, with or without existing traffic, the contact-point response outperforms the vehicle response in extracting either the frequencies or mode shapes of the bridge.

Computationally Efficient, Explicit Finite Element Model for Evaluation of Patellofemoral Mechanics

2007 ◽  
Author(s):  
Mark A. Baldwin ◽  
Paul J. Rullkoetter
Keyword(s):  
Finite Element ◽  
Contact Mechanics ◽  
Probabilistic Approach ◽  
Element Model ◽  
Relevant Information ◽  
Composite Fiber ◽  
Computational Time ◽  
Patient Specific ◽  
Fe Model ◽  
Explicit Finite Element

Patient-specific finite element (FE) models can provide clinically relevant information about contact mechanics and kinematics that may be difficult or infeasible to obtain otherwise, and have potential to guide pre-operative planning. However, substantial uncertainty in model variables exists in patient-specific modeling, and suggests a probabilistic approach. Although efficient probabilistic methodology has been recently developed, multiple analyses are still required, and computational time for a fully deformable FE model throughout a flexion cycle has typically made this impractical. Therefore, the goal of the present study was to develop an explicit FE model of the patellofemoral joint with deformable cartilage and deformable, wrapping extensor tendons, and to compare kinematic and contact mechanics results with a model modified for computational efficiency. The efficient model incorporated rigid femoral and patellar cartilage representation with an optimized contact pressure–surface overclosure relationship, and composite-fiber tendons.

Predicting Finite Element Submodel Boundary Conditions for Contact Models Using Richardson Extrapolation

2019 ◽  
Author(s):  
Michael W. Sracic ◽  
William J. Elke
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Richardson Extrapolation ◽  
Global Model ◽  
Computational Time ◽  
Analytical Prediction ◽  
Contact Models ◽  
Relationship Of ◽  
Future Work ◽  
Maximum Contact

Abstract This paper considers an efficient way to apply submodeling methods to finite element models using Richardson Extrapolation. A problem is considered where a rigid cylindrical indenter contacts an elastic half plane (RCEHP). A submodeling method is introduced where the errors of the displacements on the boundaries of the submodel are controlled by employing a best-fit Richardson Extrapolation curve. Specifically, the curve is fit to the convergence relationship of various estimates of submodel boundary displacements. The method is tested on the RCEHP problem, and the results of the model predictions for maximum contact pressure are compared to an analytical and converged global model result. The submodeling method predicted the maximum contact pressure of the RCEHP contact interface to be about 7% higher than the analytical prediction and 5% higher than the converged global model prediction. The error is likely due to the selection of the global and submodel domains, the numerical algorithm used to estimate the Richardson Extrapolation Curve Fits, and the mesh refinements used for the various models. The proposed method solved in about 42.6 minutes while the converged global model solved in 11.19 hours. Future work will aim to provide best practices to reduce error and maximize computational time savings when using the method.

Comparison of Deformable and Elastic Foundation Finite Element Simulations for Predicting Knee Replacement Mechanics

2005 ◽  
Vol 127 (5) ◽  
pp. 813-818 ◽  
Author(s):  
Jason P. Halloran ◽  
Sarah K. Easley ◽  
Anthony J. Petrella ◽  
Paul J. Rullkoetter
Keyword(s):  
Finite Element ◽  
Rigid Body ◽  
Contact Pressure ◽  
Elastic Foundation ◽  
Knee Replacement ◽  
Contact Area ◽  
Contact Model ◽  
Computational Time ◽  
Loading Conditions ◽  
Pressure Surface

Rigid body total knee replacement (TKR) models with tibiofemoral contact based on elastic foundation (EF) theory utilize simple contact pressure-surface overclosure relationships to estimate joint mechanics, and require significantly less computational time than corresponding deformable finite element (FE) methods. However, potential differences in predicted kinematics between these representations are currently not well understood, and it is unclear if the estimates of contact area and pressure are acceptable. Therefore, the objectives of the current study were to develop rigid EF and deformable FE models of tibiofemoral contact, and to compare predicted kinematics and contact mechanics from both representations during gait loading conditions with three different implant designs. Linear and nonlinear contact pressure-surface overclosure relationships based on polyethylene material properties were developed using EF theory. All other variables being equal, rigid body FE models accurately estimated kinematics predicted by fully deformable FE models and required only 2% of the analysis time. As expected, the linear EF contact model sufficiently approximated trends for peak contact pressures, but overestimated the deformable results by up to 30%. The nonlinear EF contact model more accurately reproduced trends and magnitudes of the deformable analysis, with maximum differences of approximately 15% at the peak pressures during the gait cycle. All contact area predictions agreed in trend and magnitude. Using rigid models, edge-loading conditions resulted in substantial overestimation of peak pressure. Optimal nonlinear EF contact relationships were developed for specific TKR designs for use in parametric or repetitive analyses where computational time is paramount. The explicit FE analysis method utilized here provides a unique approach in that both rigid and deformable analyses can be run from the same input file, thus enabling simple selection of the most appropriate representation for the analysis of interest.

scholarly journals Direct Validation of Human Knee-Joint Contact Mechanics Derived From Subject-Specific Finite-Element Models of the Tibiofemoral and Patellofemoral Joints

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Wei Gu ◽  
Marcus G. Pandy
Keyword(s):  
Finite Element ◽  
Knee Joint ◽  
Contact Mechanics ◽  
Contact Pressure ◽  
Weight Bearing ◽  
Human Knee ◽  
Human Knee Joint ◽  
Joint Contact ◽  
Joint Contact Pressure

Abstract The primary aim of this study was to validate predictions of human knee-joint contact mechanics (specifically, contact pressure, contact area, and contact force) derived from finite-element models of the tibiofemoral and patellofemoral joints against corresponding measurements obtained in vitro during simulated weight-bearing activity. A secondary aim was to perform sensitivity analyses of the model calculations to identify those parameters that most significantly affect model predictions of joint contact pressure, area, and force. Joint pressures in the medial and lateral compartments of the tibiofemoral and patellofemoral joints were measured in vitro during two simulated weight-bearing activities: stair descent and squatting. Model-predicted joint contact pressure distribution maps were consistent with those obtained from experiment. Normalized root-mean-square errors between the measured and calculated contact variables were on the order of 15%. Pearson correlations between the time histories of model-predicted and measured contact variables were generally above 0.8. Mean errors in the calculated center-of-pressure locations were 3.1 mm for the tibiofemoral joint and 2.1 mm for the patellofemoral joint. Model predictions of joint contact mechanics were most sensitive to changes in the material properties and geometry of the meniscus and cartilage, particularly estimates of peak contact pressure. The validated finite element modeling framework offers a useful tool for noninvasive determination of knee-joint contact mechanics during dynamic activity under physiological loading conditions.

Friction Effects on the Edge-of-Contact Stresses for Sliding Contact Between a Flat Punch With Rounded Corners and a Half Space

2017 ◽  
Vol 84 (12) ◽  
Author(s):  
G. B. Sinclair
Keyword(s):  
Closed Form ◽  
Half Space ◽  
Contact Pressure ◽  
Contact Stresses ◽  
Sliding Contact ◽  
Flat Punch ◽  
Title Problem

For the title problem, the punch is assumed to be pressed vertically into the horizontal upper surface of the half space, then slide horizontally sideways. A range of such configurations is identified that permit Shtaerman’s solution for the contact pressure for a rigid frictionless punch to be modified so that it applies to a deformable punch and also yields the contact stresses when the punch slides in the presence of friction. Closed-form expressions are obtained for the peak edge-of-contact stresses. These edge-of-contact stresses can fluctuate significantly with even modest amounts of sliding.

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