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Results for “Finite Element Analysis”

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At least 343 records · Page 19Linked to original sources

PubMed1993

Finite element analysis of four-abutment Hader bar designs.

Three-dimensional finite element analyses were conducted on the four-abutment Hader bar to determine mechanical properties with respect to bar length, stiffener height, and material properties. Three stiffener heights (1, 2, and 3 mm) were analyzed representing a clinical range of usage. Three material types were studied which represent a selection of alloys commonly used clinically. The model consisted of a representative Hader bar of 1.8-mm diameter with a 1-mm inferior stiffener. The ends of the bar were fixed to a 5-mm diameter coping which was attached to a 3.8-mm root form-type implant fixed in a representative block of bone. The bone was modeled as fixed at its distal end to eliminate rigid body motion. A 200 Newton occlusal force was imposed on the mesial bar and a 450 Newton force on the distal bar for the three stiffener heights. The results of these analyses predicted yielding and fracture (failure) for all 1-mm stiffener height and type IV gold alloy cases studied. Stiffener height was found to play a strong role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffness tested. Factors of safety with respect to static yield strength ranged from 1.44 to 2.12 on the distal portion.

Chromium Alloys↗

PubMed1989

Visualization and finite element analysis of pulsatile flow in models of the abdominal aortic aneurysm.

Pulsatile flows in glass models simulating fusiform and lateral saccular aneurysms were investigated by a flow visualization method. When resting fluid starts to flow, the initial fluid motion is practically irrotational. After a short period of time, the flow began to separate from the proximal wall of the aneurysm. Then the separation bubble or vortex grew rapidly in size and filled the whole area of the aneurysm circumferentially. During this period of time, the center of the vortex moved from the proximal end to the distal point of the aneurysm. The transient reversal flow, for instance, which may occur at the end of the ejection period, passed between the wall of the aneurysm and the centrally located vortex. When the rate and pulsatile frequency of flow were high, the vortex broke down into highly disturbed flow (or turbulence) at the distal portion of the aneurysm. The same effect was observed when the length of the aneurysm was increased. A reduction in pulsatile amplitude made the flow pattern close to that in steady flow. A finite element analysis was made to obtain velocity and pressure fields in pulsatile flow through a tube with an axisymmetric expansion. Calculations were performed with the pulsatile flows used in the visualization experiment in order to study the effects of change in the pulsatile wave form by keeping the time-mean Reynolds number and Womersley's parameter unchanged. Calculated instantaneous patterns of velocity field and stream lines agreed well with the experimental results. The appearance and disappearance of the vortex in the dilated portion and its development resulted in complex distributions of pressure and shear fields. Locally minimum and maximum values of wall shear stress occurred at points just upstream and downstream of the distal end of the expansion when the flow rate reached its peak.

Aorta, Abdominal↗

PubMed2000

Three-dimensional finite element analysis of the human temporomandibular joint disc.

A three-dimensional finite element model of the articular disc of the human temporomandibular joint has been developed. The geometry of the articular cartilage and articular disc surfaces in the joint was measured using a magnetic tracking device. First, polynomial functions were fitted through the coordinates of these scattered measurements. Next, the polynomial description was transformed into a triangulated description to allow application of an automatic mesher. Finally, a finite element mesh of the articular disc was created by filling the geometry with tetrahedral elements. The articulating surfaces of the mandible and skull were modeled by quadrilateral patches. The finite element mesh and the patches were combined to create a three-dimensional model in which unrestricted sliding of the disc between the articulating surfaces was allowed. Simulation of statical joint loading at the closed jaw position predicted that the stress and strain distributions were located primarily in the intermediate zone of the articular disc with the highest values in the lateral part. Furthermore, it was predicted that considerable deformations occurred for relatively small joint loads and that relatively large variations in the direction of joint loading had little influence on the distribution of the deformations.

Aged↗

PubMed1996

Finite element analysis and experimental studies on the thickness resonance of piezocomposite transducers.

Finite element method (FEA) has been used to calculate the thickness resonance frequency and electromechanical coupling coefficient kt for 2-2 piezocomposite transducers. The results are compared with that of the effective medium theory and also verified by experiments. It is shown that the predicted resonance frequencies from the effective medium theory and the unit cell modeling using FEA deviate from the experimental observations for composite systems with a ceramic aspect ratio (width/length) more than 0.4. For such systems, full size FEA modeling is required which can provide accurate predictions of the resonance frequency and thickness coupling constant kt.

Equipment Design↗

PubMed2005

Dynamic finite element analysis of the human maxillary incisor under impact loading in various directions.

The aim of this study was to investigate fracture patterns occurring when a human upper central incisor is subjected to impact loadings at various angles. A two-dimensional finite element (FE) model of the maxillary incisor and surrounding tissues was established. The structural damping factor for the tooth was then calculated and assigned to the model. Dynamic FE analysis was performed to stimulate the associated impacts. Time-dependent traumatic forces at 0 degrees, 45 degrees, and 90 degrees labially to the long axis of the tooth were applied to the model. Von Mises's equivalent stress contours within the FE models were calculated. Our results indicated that tooth damping lagged behind peak stress by 0.05 ms. In addition, we found that impact direction played an important role in terms of outcome for the fractured incisor. These results can, in part, explain the mechanisms underlying the alternative outcomes when upper incisors are subjected to impact.

Bite Force↗

PubMed2003

Finite element analysis of the initial stability of ankle arthrodesis with internal fixation: flat cut versus intact joint contours.

OBJECTIVE: Qualitative comparison of the initial stability provided by two joint preparation techniques and various screw configurations in ankle arthrodesis, using the finite element method.Design. A three-dimensional model of a healthy ankle was developed from computed tomography images. Two groups of models were built, one with the joint contours resected to produce flat surfaces, and the second with the joint contours preserved. In each case, a variety of screw orientations were examined. BACKGROUND: Despite the improved results of ankle arthrodesis, failure rates due to non-union are still reported. The initial stability of the arthrodesis construct seems important in the final outcome of the fusion. METHODS: Non-linear contact finite element analyses were performed in the arthrodesis constructs subjected to internal/external torsion and dorsiflexion. Micromotions at the bone-to-bone interface were calculated for frictionless and Coulomb friction contact, and compared for the two joint preparation techniques and screw configurations. RESULTS: Overall lower peak micromotions were predicted when preserving the joint contours both in torsion and dorsiflexion. For both preparation techniques, the lowest micromotions tended to occur with the screws inserted at 30 degrees with respect to the long axis of the tibia, crossing above the fusion site. Inclusion of friction in the models caused a general decrease on the magnitude of the micromotions as compared to the frictionless case, but did not affect the ranking of the models. CONCLUSIONS: The finite element method can be used as a qualitative tool to study the initial stability of ankle arthrodesis, overcoming the difficulties of measuring bone-to-bone interface micromotions experimentally. Better initial stability was predicted for ankle arthrodesis when the joint contours were preserved rather than resected. Crossing the screws above the fusion site at a steeper angle also tended to increase the stability at the fusion site. RELEVANCE: Finite element analyses can help during the pre-operative planning of ankle arthrodesis. When bone density is not compromised, preserving the joint contour and inserting the screws at less than 45 degrees to the long axis of the tibia, crossing over the arthrodesis site, may offer better initial stability.

Ankle Joint↗

PubMed2004

[The three-dimensional nonlinear finite element analysis of force system of the "rocking-chair archwire"].

OBJECTIVE: The purpose of this study was to qualitatively and quantitatively analyze the initial force system of "rocking-chair archwire" on every tooth. METHODS: Three-dimensional finite element model of "rocking-chair archwire" was set up, and nonlinear method was used to analyze the force system. RESULTS: The archwire exerted intruding force, labial force, lingual-root torque and mesial-labial moment on incisors; Extruding force, lingual-root torque and mesial-labial moment were applied on canines and premolars; The archwire also created intruding force, buccal force, buccal-root torque and mesial-labial moment on molars. CONCLUSIONS: "rocking-chair archwire" produced a complicated force system. While intruding incisors, molars and extruding premolars. It has a tendency to induce tooth rotation and tipping.

Dental Stress Analysis↗

PubMed2001

Three-dimensional finite element analysis of the facial skeleton on simulated occlusal loading.

Development of predictive models of occlusal loading of the facial skeleton will be of value for prosthetic design in oral rehabilitation. A 3-D finite element (FE) model of a human skull, based on CT scans, was constructed to analyse strain and stress distribution in the facial skeleton caused by simulated occlusal loading. Vertical loads were applied simulating loading of the full maxillary arch and unilateral single point occlusal loading of maxillary molar, pre-molar, canine and incisor sites. Strain and stress regimes from Von Mises (VM) failure criteria and extension and compression diagrams showed even distribution of strain following loading of the full maxillary arch throughout the facial elements. For individual points, the highest VM concentrations were consistently located on the facial aspect several mm above the loading site. Strain trajectories divided into a 'V-shaped' pattern, from the loading point into medial and lateral branches with higher VM values in the medial. As the same load was applied from the posterior to anterior region, VM values increased on all facial areas. Strain patterns were less symmetric and there was an increase in strain in the alveolar arch and around the rim of the nasal cavity. The overall picture of the facial skeleton is of a vertical plate enabling it to withstand occlusal stresses by in-plane loading and bending in its own plane. The most efficient distribution of load was on maxillary full arch loading with the most unfavourable strain concentrations occurring on loading in the anterior region.

Adult↗

PubMed2004

[A three-dimensional finite element analysis of stress distribution in mandibular FPDs with different length pontics].

OBJECTIVE: To investigate the stress distribution in the mandibular fixed partial denture (FPD) by changing the length of pontics. METHODS: Based on a 3-DFE model of the mandibular FPD, we analyzed the stress distribution in the mandibular FPDs by loading the same level force at pontics with different lengths that were 2 to 4 times of normal length. RESULTS: The distribution trends of the stresses in the mandibular FPDs with differently elongated pontics were similar, but the highest von Mises stress in the bridge was enlarged. CONCLUSION: Damages may develop in the mandibular FDP, when the length of the pontic is longer than 3 times of normal length.

Dental Stress Analysis↗

PubMedDate not supplied

Finite element analysis of a three unit fixed partial denture cast with nickel-chromium alloy.

A two dimensional mathematical model was generated, representing a three unit fixed-fixed partial denture and its supporting structures. Second premolar and second molar were used as abutments with first molar as pontic. A load of 1 kg was applied to the occlusal surface of the casting. Stresses and displacement developed at various regions were analyzed with STAAD III/ISDS program. Maximum stresses were developed in the pontic and connectors with distal connector experiencing the maximum stresses. Stresses transmitted to the dentin were comparatively lower and more of compressive in nature. The underying bone experienced moderate amount of both compressive and tensile stresses but the displacement in this tissue were minimal compared to the rest.

Chromium Alloys↗

PubMed2004

Scoliosis of the cranial base: radiological and mathematical analysis using finite elements system analysis (FESA) of a case.

INTRODUCTION AND PROPOSED STUDY: Numerous deforming syndromes of the craniofacial complex involve also the symmetry of the cranial base. This study considers a particular alteration, that of 'scoliosis', in which the line Nasion-Sella-Basion-Inion is not rectilinear but curved, due to a torsion of the cranial base in the horizontal plane. MATERIALS: Plagiocephaly was studied in one patient, which was probably caused by altered timing or mechanism of closure of the cranial sutures. METHODS: This study was carried out using CT images of the patient's craniofacial complex, using standard neuroradiological points. In order to study the forces that operated in the various complexes, a mathematical analysis was applied namely, a finite element system analysis (FESA). RESULTS: From this mathematical study, which has enabled us to evaluate the forces that operate in determining the deformity, it has been possible to locate two sites of force concentration. They were located at different levels and on opposite sides. CONCLUSION: This finding could explain why the middle and lower thirds of the face were also involved.

Biomechanical Phenomena↗

PubMed2005

Changes in orthodontic cephalometric reference points on application of orthopedic force to jaw: three-dimensional finite element analysis.

The present study investigated the effects of two orthodontic appliances on changes in the cephalometric reference planes using the three-dimensional finite element method. We simulated the use of a headgear and an orthopedic facial mask, two devices for the application of orthodontic force to the jaw. Using a finite element model of the skull, orthodontic force was applied to the maxillary first molar in a posterior or anterior direction. Changes in the maxilla, mandible and cephalometric reference planes were ascertained by the three-dimensional finite element method. The results showed that posterior force caused a slight posterior displacement and clockwise rotation of the reference planes, while anterior force caused anterior displacement and counterclockwise rotation. Since the maxilla was displaced and rotated in the same direction, the degrees of cephalometric displacement and rotation of the maxilla were smaller than the actual values.

Biomechanical Phenomena↗

PubMed2002

Parametric finite element analysis and closed-form solutions in orthodontics.

The goal and clinical relevance of this work was the development of closed formulas that are correct and simple enough for a fast decision making by the orthodontist in the daily praxis. This paper performs a parametric three-dimensional finite element linear analysis on a maxillary central incisor with a root of paraboloidal shape, which is subjected to typical orthodontic force-systems. Parameters of most importance, such as the tooth mobility in translation and in pure moment rotation including orthodontic centers, as well as the stresses inside the periodontal ligament are calculated for a large variety of over four hundred different couples of root lengths and root diameters around a nominal value. Regression analysis is afterwards performed and establishes closed-form solutions, which are also explained in terms of analytical strain energy and hydrostatic stress considerations within the periodontal ligament characterised by a small compressibility. The obtained expressions include both the root length as well as the root diameter.

Computer Simulation↗

PubMed1992

Finite-element analysis of arterial anastomoses with vein, Dacron and PTFE grafts.

A finite-element simulation of an end-to-end artery/graft anastomosis has been presented in this study to evaluate the distribution of compliance and stresses in the vicinity of the anastomosis due to any mismatch in compliance characteristics. The arterial wall was assumed to be made of linear isotropic elastic material in this simplified model and a static analysis was performed with a mean arterial pressure loading of the artery-graft model. Anastomoses to vein grafts and both Dacron and polytetrafluoroethylene (PTFE) grafts were studied. The results suggested the presence of a hypercompliant zone on the arterial side and a region of high tensile stresses in the wall on the graft side of the anastomosis. The presence of a hypercompliant zone has been reported from previous in vivo studies. The hypercompliance was larger with Dacron and PTFE grafts compared with that with the vein graft. However, larger tensile stresses were present in the wall of the vein graft compared with the synthetic grafts. The analysis further showed that increasing the diameter of the graft compared with the host artery to increase flow through the implant will result in a significant increase in the hypercompliance on the arterial side. Such simulation studies may prove valuable in studying the effects of compliance mismatch and suggest ways to improve the design of small diameter vascular grafts.

Anastomosis, Surgical↗

PubMed2000

Finite element analysis of brain contusion: an indirect impact study.

The mechanism of brain contusion has been investigated using a series of three-dimensional (3D) finite element analyses. A head injury model was used to simulate forward and backward rotation around the upper cervical vertebra. Intracranial pressure and shear stress responses were calculated and compared. The results obtained with this model support the predictions of cavitation theory that a pressure gradient develops in the brain during indirect impact. Contrecoup pressure-time histories in the parasagittal plane demonstrated that an indirect impact induced a smaller intracranial pressure (-53.7 kPa for backward rotation, and -65.5 kPa for forward rotation) than that caused by a direct impact. In addition, negative pressures induced by indirect impact to the head were not high enough to form cavitation bubbles, which can damage the brain tissue. Simulations predicted that a decrease in skull deformation had a large effect in reducing the intracranial pressure. However, the areas of high shear stress concentration were consistent with those of clinical observations. The findings of this study suggest that shear strain theory appears to better account for the clinical findings in head injury when the head is subjected to an indirect impact.

Brain Injuries↗

PubMed2006

Determination of lamb wave dispersion data in lossy anisotropic plates using time domain finite element analysis. Part I: theory and experimental verification.

A theoretical and experimental approach for extraction of guided wave dispersion data in plate structures is described. Finite element modeling is used to calculate the surface displacement data (in-plane and out-of-plane) when the plate is subject to either symmetrical or antisymmetrical impulsive force stimulation at one or both of the parallel faces. Fourier transformation of the resultant space-time displacement histories is then employed to obtain phase velocity as a function of frequency. Experimental verification in the case of antisymmetrical stimulation is provided by means of a high-power Q-switched laser source that is used to excite guided waves in the plate. The subsequent out-of-plane displacement data were then obtained by means of a scanning laser vibrometer, and good agreement between theory and experiment is demonstrated. Examples of dispersion data are provided for aluminum, and excellent correlation between the data sets and conventional Rayleigh-Lamb theory for plate structures was obtained. This was then extended to lossy polymeric plates, in addition to both unpolarized and polarized piezoelectric ceramic plates, again with good agreement between the finite element modeling and optical experiments. The last set of results prepares the way for a detailed investigation of the nonhomogeneous piezoelectric composite waveguides described in a companion paper (Part II).

Anisotropy↗

PubMed1980

Load transmission through the proximal femur of the growing child: a finite element analysis.

Growth-related variations in the distribution of mechanical stress in the normal juvenile proximal femur are explored using a computer-based finite element stress analysis technique. Input data for the model are obtained from serial patient roentgenograms and from laboratory compression tests of fresh autopsy material. The results for the limiting case of epiphyseal closure (18-year-old male) are in substantive agreement with previous experimental and mathematical studies of the adult proximal femur. The computational results for the juvenile hip show that in spite of the complex morphological alterations occurring during growth, the basic mechanisms of load transmission at first ambulation are still operational at skeletal maturity. Foremost among these are the distally-concentrated weight bearing compressive stresses in the primary trabeculation system, the abductor-induced tensile stresses in the greater trochanter, and the large longitudinal stresses within the proximal femoral cortices. As growth advances, however, the importance of transverse compressive stresses in the proximal lateral metaphysis progressively diminishes, while shearing stresses in the plane of the epiphyseal plate increase markedly. These two major growth-related changes results largely from decreases in the neck-shaft angle, and if excessive, may be implicated in development coxa vara or slipped capital femoral epiphysis.

Adolescent↗

PubMed2004

Three-dimensional finite element analysis in distal en masse movement of the maxillary dentition with the multiloop edgewise archwire.

The purpose of this study was to compare the effects of a multiloop edgewise archwire (MEAW) on distal en masse movement with a continuous plain ideal archwire (IA). Three-dimensional finite element models (FEM) of the maxillary dentition in which the second permanent molars had been extracted were constructed to include the periodontal membrane, alveolar bone, standard edgewise bracket (0.018 x 0.025 inch), stainless steel IA (0.016 x 0.022 inch), and MEAW (0.016 x 0.022 inch). The stress distribution and displacement of the maxillary dentition were analysed when Class II intermaxillary elastics (300 g/side) and 5 degree tip-back bends were applied to the IA and MEAW for distal en masse movement of the maxillary dentition. Compared with the IA, the MEAW showed that the discrepancy in the amount of tooth displacement was lower and individual tooth movement was more uniform and balanced. There was minimal vertical displacement or rotation of the teeth using the MEAW when compared with the IA. The MEAW seems to have advantages for distal en masse movement of the maxillary dentition.

Alveolar Process↗