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Results for “Finite Element Analysis”

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PubMed1995

Axisymmetric finite element analysis of hip replacements possessing an elastomeric layer: the effects of clearance and Poisson's ratio.

A finite element analysis has been performed for a hip replacement incorporating an elastomeric surface layer. The effects of assuming the elastomer as incompressible have been examined for imposed loads, by comparing the incompressible solution to that using accurately measured values for Poisson's ratio, and while deflections were found to be significantly different, the changes in maximum pressure in the contact, maximum shear stress, contact angle and angular position to maximum shear stress were all small (less than 10 per cent). Comparisons have also been made between the finite element results for ABAQUS and an asymptotic solution, and it was found to be important to use the numerical model particularly at small values of clearance.

Hip Prosthesis↗

PubMed2006

Three-dimensional finite-element analysis investigating the biomechanical effects of human mandibular reconstruction with autogenous bone grafts.

PURPOSE: To investigate the biomechanics of the mandible following reconstruction with autogenous bone grafts. MATERIAL: Computerized tomography scan images of a human mandible, fibula and iliac crest were collected and used to build models on a PC. METHODS: Four finite-element analysis (FEA) models of mandibles reconstructed with autogenous bone were created. The principal stresses of marked points, the Von Mises stresses at anatomical index regions, and the force values of temporo-mandibular joints and masticatory muscles were calculated. RESULTS: Compared with the normal mandible, the one repaired with a fibula had greater Von Mises stresses on the grafted bone; the one repaired with iliac crest bone had the similar distribution of the Von Mises stresses as in the normal mandible. The principal stresses in the autograft varied between tensile and compressive stresses from the right graft/bone binding interface to the left in all reconstructed mandibles. On the whole, the maximum Von Mises stress was greater on the mandible reconstructed with fibula than that reconstructed with iliac crest. CONCLUSION: Mandibles repaired with iliac crest grafts have more mechanical properties similar to normal than those repaired with fibula grafts.

Adult↗

PubMed2003

Finite element analysis and strain-gauge studies of vertical root fracture.

Vertical root fracture seems to result from stresses generated within the root canal and typically occurs in a buccolingual direction through the thickest part of dentin. Because stresses in the canal wall are difficult to measure experimentally, we have attempted to correlate stress patterns derived from finite element models of maxillary and mandibular incisors with strain measurements on the root surfaces of extracted teeth. Finite element analysis indicated that circumferential tensile stresses were concentrated on the buccal and lingual surfaces of the canal wall, corresponding to areas of greatest canal wall curvature. Surface stresses were much lower and were consistently tensile on the proximal root surfaces but variable on the buccal and lingual surfaces. The measurement of root surface stresses does not provide a reliable picture of internal stresses in the root. Canal wall curvature is a major factor in stress concentration and hence in the pattern of fracture.

Compressive Strength↗

PubMed2003

Finite element analysis of the temperature and thermal stress in a postrestored tooth.

The finite element method was used to calculate temperature and thermal stress distribution as a result of hot/cold liquid in the mouth. This numerical study was carried out using axisymmetric finite element models and the tooth model was endodontically treated restored with cast post and cores. The two tooth models evaluated were Ti-Ti alloy and NiCr-AuPd alloy as post material and crown material with porcelain. First, temperature changes on the restored tooth as a result of hot/cold liquid in the mouth were calculated and then the thermal stress as a result of temperature changes were carried out. A fortran computer program was developed for this study. The tooth was assumed isotropic, homogenous, elastic and symmetrical. The distribution of temperature and thermal stress versus time were plotted for four critical points.

Dental Amalgam↗

PubMed2006

Three-dimensional finite element analysis of strain and stress distributions in endodontically treated maxillary central incisors restored with different post, core and crown materials.

OBJECTIVES: The present comparative analysis aimed at evaluating which combination of restorative materials resulted in the most homogeneous stress and strain distributions. METHODS: A three-dimensional finite element analysis was performed. All the nodes on the external surface of the root were constrained in all directions. Eighteen experimental models with different material properties and configurations were simulated. An arbitrary load of 10N was applied at 60 degrees angle with tooth longitudinal axis on the palatal surface of the crown. Von Mises (equivalent stresses) energetic criterion was chosen. RESULTS: In all the models the values of both strain and stress recorded at the middle third of the buccal aspect of the root surface were at their maxima. On the contrary, the minimum values were noticed at level of both the apical portion of the post and the root apex. The maximum stresses were evidenced at level of the cemento-enamel junction (CEJ) on both the buccal and palatal aspects of root cement and dentin. Stress progressively decreased from the outer to the inner part of the root and from the CEJ towards the incisal margin of the crown as well. SIGNIFICANCE: The results of the present study would allow clinicians to make an informed choice from among available materials to restore endodontically treated teeth.

Cementation↗

PubMed2006

A finite-element analysis model of orbital biomechanics.

To reach a better understanding of the suspension of the eye in the orbit, an orbital mechanics model based upon finite-element analysis (FEA) has been developed. The FEA model developed contains few prior assumptions or constraints (e.g., the position of the eye in the orbit), allowing modeling of complex three-dimensional tissue interactions; unlike most current models of eye motility. Active eye movements and forced ductions were simulated and showed that the supporting action of the orbital fat plays an important role in the suspension of the eye in the orbit and in stabilization of rectus muscle paths.

Adipose Tissue↗

PubMed2004

Thermal residual stresses near the interface between plasma-sprayed hydroxyapatite coating and titanium substrate: finite element analysis and synchrotron radiation measurements.

Plasma-sprayed hydroxyapatite (HA) coatings on titanium alloy are often used in prosthetic implants. The metallic substrate gives the implant good mechanical strength which is combined with good biocompatibility and osteointegration of the ceramic coating. However, the interface between the HA coating and titanium alloy substrate is an area of critical weakness when compared with the interlamellar cohesive strength of the HA coating structure. Knowledge of the stresses in materials near the interface seems to be an important step in understanding why failure occurs. Synchrotron radiation, using Beamline BM16 at the European Synchrotron Radiation Facility (Grenoble, France), has been used to determine local stresses near the interface, down to 10 microm in resolution, between a plasma-sprayed HA coating and a titanium alloy substrate. This experimental determination of residual stresses is compared with the results found by a finite element analysis modeling the thermal effects of the plasma-spraying process. Residual stresses have been found in deposited ceramic near the interface due to a thermal properties mismatch of the materials. If the plane stress state is assumed, meaning the perpendicular component of residual stress is ignored (sigma(z) = 0), then the synchrotron residual stress measurements should be interpreted as mainly compressive in the ceramic coating. This is in contradiction with the coefficient of thermal expansion mismatch; therefore, the simplified plane stresses assumption seems to be inappropriate for the deposited morphology characterized by pores and a network of microcracks. The detailed finite element analysis model, taking into account the real morphology of the coating and the real three-dimensional stress field distribution, allowed the estimation of sigma(z), leading to a more accurate interpretation of synchrotron measurements, which is validated by the experimental results.

Algorithms↗

PubMed2003

The effect of prosthesis design on vibration of the reconstructed ossicular chain: a comparative finite element analysis of four prostheses.

HYPOTHESIS: It was hypothesized that the differences in the bioacoustic performance of ossicular replacement prosthesis designs, and insertion positions, could be quantified using finite element analysis. BACKGROUND: Many designs of prosthesis are available for middle ear surgery. The materials used, and the shape of the implants, differ widely. Advances in computer simulation technologies offer the possibility of replicating the in vivo behavior of the different prostheses. If this can be achieved, insight into the design attributes required for improved biofunctionality may be gained. METHODS: Micro-computed tomography and nuclear magnetic resonance imaging were used to obtain geometric information that was translated into a finite element model of the outer and middle ear. The forced frequency response across the hearing range of the normal middle ear was compared with the middle ear reconstructed with partial and total ossicular replacement prostheses. RESULTS: The amplitude of vibration of the footplate was more similar to that of the normal ear when a Kurz total ossicular replacement prosthesis was implanted than when a Xomed total ossicular replacement prosthesis was implanted. This may be attributed to the latter's titanium link. Partial ossicular replacement prostheses were stiffest and had lower umbo vibrations and higher stapedial footplate vibrations. In all cases but one, the vibration of the prostheses had resonances that caused the vibration of the stapes footplate to be noticeably different from normal. CONCLUSION: The authors confirmed the hypothesis that finite element modeling can be used to predict the differences in the response of ossicular replacement prostheses. This study shows that computer simulation can potentially be used to test or optimize the vibroacoustic characteristics of middle ear implants.

Acoustic Impedance Tests↗

PubMed2003

Severe aortic insufficiency and normal systolic function: determining regional left ventricular wall stress by finite-element analysis.

BACKGROUND: Because severe aortic insufficiency in the setting of preserved left ventricular function is often associated with a long asymptomatic period and unpredictable course on medical therapy, sensitive indices of left ventricular systolic performance are necessary for the optimal direction of therapeutic intervention. Because myocardial wall stress is closely related to both pathologic cardiac remodeling and ultimately to left ventricular decompensation, an accurate description of regional wall stress distribution may improve our ability to clinically manage these patients appropriately. The objectives of this study were (1) to define sensitive, noninvasive indices of left ventricular systolic performance to assist the clinician in the serial evaluation and early detection of increased left ventricular wall stress and, therefore, inadequate left ventricular remodeling and subsequent myocardial decompensation of patients with aortic insufficiency, and (2) to quantify differences in instantaneous global and regional end-systolic wall stress between normal subjects and patients. METHODS: Magnetic resonance imaging was performed on 23 normal volunteers and 19 patients with aortic insufficiency and normal systolic function (ejection fraction, 57% +/- 6%). Finite-element analysis was used to estimate global and regional end-systolic stress. RESULTS: End-systolic stress was significantly higher in the patient group globally (154,700 +/- 31,711 versus 96,781 +/- 23,185 dyne/cm(2); p < 0.001) and regionally (p < 0.001 in all segments) despite normal systolic function and similar end-systolic pressures. CONCLUSIONS: End-systolic stress as determined by magnetic resonance imaging and finite-element analysis may have considerable potential as a noninvasive, clinically applicable index of regional left ventricular function that may help in the serial evaluation, optimal management, and early identification of left ventricular decompensation in patients with aortic insufficiency.

Adult↗

PubMed2006

Three-dimensional finite element analysis of weakened roots restored with different cements in combination with titanium alloy posts.

BACKGROUND: It is very difficult and relatively unpredictable to preserve and restore severely weakened pulpless roots. To provide much needed benefit basis for clinical practice, this study was carried out to analyze the stress distribution in weakened roots restored with different cements in combination with titanium alloy posts. Finite element analysis (FEA) was employed in the study. METHODS: A pseudo three-dimensional model of a maxillary central incisor with flared root canal, theoretically restored with titanium alloy posts in combination with different cements, was established. The analysis was performed by use of ANSYS software. The tooth was assumed to be isotropic, homogenous and elastic. A load of 100 N at an angle of 45 degrees to the longitudinal axis was applied at the palatal surface of the crown. The distributions of stresses in weakened roots filled with cements of different elastic modulus were analyzed by the three-dimensional FEA model. RESULTS: Several stress trends were observed when the stress cloud atlas obtained in the study was analyzed. With the increase of the elastic modulus of cements from 1.8 GPa to 22.4 GPa, the stress values in dentin decreased from 39.58 MPa to 31.43 MPa and from 24.51 MPa to 20.76 MPa (respectively, for maximum principle stress values and Von Mises stress values). When Panavia F and zinc phosphate cement were used, the stress peak values in dentin were very small with no significant difference observed, and the Von Mises stress values were 20.87 MPa and 20.76 MPa respectively. On the other hand, maximum principle stress value and Von Mises stress value in cement layer increased with the increase of the elastic modulus of cements. CONCLUSIONS: The result of this study demonstrated that elastic modulus was indeed one of the important parameters to evaluate property of the cements. Our three-dimensional FEA model study also found that the cement with elastic modulus similar to that of dentin could reinforce weakened root and reduce the stress in dentin. Thus, it may be a better choice for the restoration of weakened roots in clinical practice.

Adult↗

PubMed1993

Finite element analysis of quasistatic and fatigue failure of post and cores.

Finite element (FE) analysis of the mechanical behaviour of materials and structures facilitates the investigation of their internal stress distributions. However, the validity of the model is not always ascertained. In this study a three-dimensional (3D) FE model was developed, representing a laboratory set-up of direct post and core restored upper premolars. These restorations, using either composite or amalgam for core material, have been the subject of study in previous quasistatic and fatigue strength tests. The aim of this study was to validate the FE model for prefailure and failure modelling, by comparing the computational results with the laboratory observations and failure results. Two failure criteria were selected for investigation: Modified Von Mises and Drücker-Prager equivalent stress. Four model variations were carried out, representing different conditions at the core-tooth interface. Prefailure modelling was found to be adequate. The calculated failure results could only partly be fitted to the quasistatic tests. The best fit was effected with a model using partial bonding of the core, for the composite core. Fatigue failure was reproduced somewhat better by a model using no bonding at all, again to a higher degree for the composite core. Calculations of post stress using a model simulating increased core mobility supported an observation made previously (M. C. D. N. J. M. Huysmans et al., in press; Int. Endodont. J. XX, XXX-XXX), implying that a composite core raises the demands made on the post. The conclusion is made that validation of FE calculations is essential. A 3D model as presented here shows a satisfactory fit to fatigue data but not to quasistatic results.(ABSTRACT TRUNCATED AT 250 WORDS)

Alloys↗

PubMed2000

Finite element analysis of stress relaxation in soft denture liner.

To gather knowledge related to establishing criteria for selecting soft denture liners for individual patients, the effects of certain properties of soft denture liners on stress distribution were evaluated by two-dimensional finite element analysis. A partial mandibular edentulous ridge crest was modelled. Six combinations of thickness (mucosa: 1 or 2 mm; soft denture liner: 1, 2, or 3 mm) and 18 combinations of Young's modulus (mucosa: three kinds; soft denture liner: six kinds) were analysed. The ratio of maximum to minimum stress in the mucosa (stress ratio) was calculated to estimate stress concentration. In the case of thin mucosa (1 mm thickness), the lower the Young's modulus of the soft denture liner, the lower the stress ratio. However, if the soft denture liner had a lower Young's modulus than the mucosa, stress concentrated adversely. These results suggest that the elasticity of the soft denture liner should match the elasticity of the mucosa to obtain the optimum cushioning effect.

Dental Stress Analysis↗

PubMed1990

Incorporation of spinal flexibility measurements into finite element analysis.

This technical note demonstrates two methods of incorporating the experimental stiffness of spinal motion segments into a finite element analysis of the spine. The first method is to incorporate the experimental data directly as a stiffness matrix. The second method approximates the experimental data as a beam element.

Elasticity↗

PubMed2002

Finite element analysis of imposing femtonewton forces with micropipette aspiration.

A novel technique of imposing femtonewton forces with micropipette aspiration [i.e., the extended micropipette aspiration technique (EMAT)] is proposed, and an axisymmetric finite element analysis of this technique is provided. The EMAT is experimentally based upon a micropipette manipulation system and is theoretically based upon hydrodynamics. Any spherical object such as a human neutrophil or a latex bead can be employed as the force transducer, so cell-cell interactions can be directly studied. Our computational analysis shows that femtonewton forces can indeed be imposed. The force magnitude is sensitive to the radius of the micropipette and the micropipette-transducer distance, but it is much less sensitive to other parameters including the radius of the transducer, the substrate curvature, and the thickness of the micropipette wall. Combining the EMAT and the previously developed micropipette aspiration technique will allow us to impose an unprecedented range of forces, from a few femtonewtons to a few hundred piconewtons on single molecules or receptor-ligand bonds.

Cell Adhesion↗

PubMed2005

Measurement of pharyngeal cross-sectional area by finite element analysis.

A noninvasive measurement of pharyngeal cross-sectional area (CSA) during sleep would be advantageous for research studies. We hypothesized that CSA could be calculated from the measured pharyngeal pressure and flow by finite element analysis (FEA). The retropalatal airway was visualized by using a fiber-optic scope to obtain the measured CSA (mCSA). Flow was measured with a pneumotachometer, and pharyngeal pressure was measured with a pressure catheter at the palatal rim. FEA was performed as follows: by using a three-dimensional image of the upper airway, a mesh of finite elements was created. Specialized software was used to allow the simultaneous calculation of velocity and area for each element by using the measured pressure and flow. In the development phase, 677 simultaneous measurements of CSA, pressure, and flow from one subject during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep were entered into the software to determine a series of equations, based on the continuity and momentum equations, that could calculate the CSA (cCSA). In the validation phase, the final equations were used to calculate the CSA from 1,767 simultaneous measurements of pressure and flow obtained during wakefulness, NREM, and REM sleep from 14 subjects. In both phases, mCSA and cCSA were compared by Bland-Altman analysis. For development breaths, the mean difference between mCSA and cCSA was 0.0 mm2 (95% CI, -0.1, 0.1 mm2). For NREM validation breaths, the mean difference between mCSA and cCSA was 1.1 mm2 (95% CI 1.3, 1.5 mm2). Pharyngeal CSA can be accurately calculated from measured pharyngeal pressure and flow by FEA.

Anatomy, Cross-Sectional↗

PubMed2006

Intra-articular contact stress distributions at the ankle throughout stance phase-patient-specific finite element analysis as a metric of degeneration propensity.

A contact finite element (FE) formulation is introduced, amenable to patient-specific analysis of cumulative cartilage mechano-stimulus attributable to habitual functional activity. CT scans of individual human ankles are segmented to delineate bony margins. Each bone surface is projected outward to create a second surface, and the intervening volume is then meshed with continuum hexahedral elements. The tibia is positioned relative to the talus into a weight-bearing apposition. The articular members are first engaged under light preload, then plantar-/dorsi-flexion kinematics and resultant loadings are input for serial FE solutions at 13 instants of the stance phase of level walking gait. Cartilage stress histories are post-processed to recover distributions of cumulative stress-time mechano-stimulus, a metric of degeneration propensity. Consistency in computed contact stress exposures presented for seven intact ankles stood in contrast to the higher magnitude and more focal exposures in an incongruously reduced tibial plafond fracture. This analytical procedure provides patient-specific estimates of degeneration propensity due to various mechanical abnormalities, and it provides a platform from which the mechanical efficacy of alternative surgical interventions can be estimated.

Ankle Injuries↗

PubMed2007

Contact stress assessment of conventional and highly crosslinked ultra high molecular weight polyethylene acetabular liners with finite element analysis and pressure sensitive film.

Stress magnitude and distribution of both conventional polyethylene versus a crosslinked polyethylene in the liner of a total hip replacement (THR) were examined using finite element analysis and pressure sensitive film. Both types of polyethylene were assessed against head sizes of 22 and 28 mm with 5-mm thick polyethylene liners and head sizes of 28, 38, and 46 mm with 3-mm thick polyethylene liners. Liners with 5-mm conventional polyethylene represented successful combinations with long track records. Our hypothesis was that although the combination of the large head and the lower modulus of the highly crosslinked polyethylene would lead to lower stresses, the stresses would be excessive if the liner was extremely thin at 3 mm. Von Mises stresses at the articulating surface of the highly crosslinked liners were lower, when compared to conventional polyethylene, in every THR size examined. Specifically, however, the 38- and 46-mm inner diameter (ID) highly crosslinked polyethylene even at the extreme of only 3-mm thick had lower stresses than the 22-mm ID conventional liner of 5-mm thickness. These data indicate that the use of a large head against highly crosslinked material even at 3-mm thickness results in lower stresses than in an existing conventional 22-mm head and 5-mm thick combination. Obviously, other considerations will influence the minimum thickness to be recommended.

Acetabulum↗

PubMed1998

A finite element analysis of factors influencing total hip dislocation.

A previously validated three-dimensional finite element model was used to study how several total hip component design and surgical placement variables contribute to resisting the propensity for posterior dislocation in the case of leg crossing in an erectly seated position. The computational formulation incorporated treatments of polyethylene material nonlinearity and large displacement sliding contact. The primary outcome measures were the peak intrinsic moment developed to resist dislocation, and the ranges of motion before neck on lip impingement and before frank dislocation. Modifications of the acetabular linear design (chamfer bevel angle, lip breadth, head center inset) involved trading off improved peak resisting moment for compromised range of motion and vice versa. Increases of head size led to substantial improvements in peak resisting moment, but if the head to neck diameter ratio was held constant, had almost no influence on the component range of motion. For the leg crossing event studied, increased component anteversion, and even more so increased tilt (less net abduction), achieved improvements in range of motion and in peak resisting moment, but these changes imply diminished resistance to anterior dislocation from extension and adduction motion inputs.

Arthroplasty, Replacement, Hip↗