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"Distribuição de tensões em testes de cisalhamento e micro-cisalhamento mediante análise de elementos finitos" ; A finite element stress analysis of shear and micro-shear bond strength tests

Placido, Eliane
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/06/2006 Português
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Os objetivos deste estudo foram comparar, através de análise de elementos finitos, a distribuição de tensões em modelos que representam arranjos experimentais nor-malmente utilizados em testes de cisalhamento e micro-cisalhamento, verificar a tendência de variar o local de início e o modo de fratura em função de mudanças nos parâmetros dos ensaios e analisar a influência de dois modos de fixação do substrato sobre a concentração de tensões. Os modelos bidimensionais em estado plano de deformações representaram o compósito (híbrido ou flow) aderido à dentina através de uma camada de adesivo de 50 μm. Duas condições de fixação da dentina foram estabelecidas: na primeira (mais rígida), os deslocamentos foram restritos em todas as direções nos nós das arestas que representam as três superfícies livres de adesão e na segunda, a restrição foi colocada apenas na parte posterior da dentina. Foi aplicado um carregamento pontual a várias distâncias da interface dentina-adesivo, de modo a obter um tensão nominal constante de 4MPa. Foram analisadas as tensões máximas de tração e cisalhamento, a distribuição das tensões ao longo dos nós da interface dentina-adesivo e os vetores de tensão máxima principal...

Modelagem do comportamento dinâmico não linear de risers pelo método dos elementos finitos.; Modeling the behavior of nonlinear dynamic risers by finite element method.

Prado, Fabio Selleio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/03/2013 Português
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Mais recentemente a exploração offshore de petróleo e gás tem se intensificado na costa brasileira. Uma das características da exploração offshore no Brasil está ligada ao fato de os hidrocarbonetos se situarem a grandes profundidades no mar, frequentemente abaixo de uma espessa camada de sal, exigindo o desenvolvimento de novas tecnologias para vencer os desafios para sua prospecção e extração. A profundidade dos poços pode variar entre dois mil e sete mil metros abaixo da superfície do mar. Um dos grandes desafios é garantir uma boa conexão dos equipamentos de extração com a unidade de produção na superfície, o que se faz com risers. Há distintas configurações de risers, entre as quais os verticais, em catenária, lazy waves ou steep waves, sendo que o riser em catenária e o vertical, em particular, serão estudados aqui. Este trabalho visa a estudar os efeitos dinâmicos não lineares no riser, que, por ser extremamente esbelto, exige a consideração da não linearidade geométrica. Entre eles, destaca-se a possibilidade de ocorrência da ressonância paramétrica. Os carregamentos dinâmicos podem ser provenientes da movimentação da unidade flutuante, correntezas ou escoamento interno. Neste trabalho serão elaborados modelos em elementos finitos...

Platform Switching: Biomechanical Evaluation Using Three-Dimensional Finite Element Analysis

Tabata, Lucas Fernando; Rocha, Eduardo Passos; Ricardo Barao, Valentim Adelino; Assuncao, Wirley Goncalves
Fonte: Quintessence Publishing Co Inc Publicador: Quintessence Publishing Co Inc
Tipo: Artigo de Revista Científica Formato: 482-491
Português
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Purpose: The objective of this study was to evaluate, using three-dimensional finite element analysis (3D FEA), the stress distribution in peri-implant bone tissue, implants, and prosthetic components of implant-supported single crowns with the use of the platform-switching concept. Materials and Methods: Three 3D finite element models were created to replicate an external-hexagonal implant system with peri-implant bone tissue in which three different implant-abutment configurations were represented. In the regular platform (RP) group, a regular 4.1-mm-diameter abutment (UCLA) was connected to regular 4.1-mm-diameter implant. The platform-switching (PS) group was simulated by the connection of a wide implant (5.0 mm diameter) to a regular 4.1-mm-diameter UCLA abutment. In the wide-platform (WP) group, a 5.0-mm-diameter UCLA abutment was connected to a 5.0-mm-diameter implant. An occlusal load of 100 N was applied either axially or obliquely on the models using ANSYS software. Results: Both the increase in implant diameter and the use of platform switching played roles in stress reduction. The PS group presented lower stress values than the RP and WP groups for bone and implant. In the peri-implant area, cortical bone exhibited a higher stress concentration than the trabecular bone in all models and both loading situations. Under oblique loading...

Effect of Metal-Ceramic or All-Ceramic Superstructure Materials on Stress Distribution in a Single Implant-Supported Prosthesis: Three-Dimensional Finite Element Analysis

Gomes, Erica Alves; Ricardo Barao, Valentim Adelino; Rocha, Eduardo Passos; de Almeida, Erika Oliveira; Assuncao, Wirley Goncalves
Fonte: Quintessence Publishing Co Inc Publicador: Quintessence Publishing Co Inc
Tipo: Artigo de Revista Científica Formato: 1202-1209
Português
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Purpose: This three-dimensional finite element analysis study evaluated the effect of different material combinations on stress distribution within metal-ceramic and all-ceramic single implant-supported prostheses. Materials and Methods: Three-dimensional finite element models reproducing a segment of the maxilla with a missing left first premolar were created. Five groups were established to represent different superstructure materials: GP, porcelain fused to gold alloy; GR, modified composite resin fused to gold alloy; TP, porcelain fused to titanium; TR, modified composite resin fused to titanium; and ZP, porcelain fused to zirconia. A 100-N vertical force was applied to the contact points of the crowns. All models were fixed in the superior region of bone tissue and in the mesial and distal faces of the maxilla section. Stress maps were generated by processing with finite element software. Results: Stress distribution and stress values of supporting bone were similar for the GP, GR, TP, and ZP models (1,574.3 MPa, 1,574.3 MPa, 1,574.3 MPa, and 1,574.2 MPa, respectively) and different for the TR model (1,838.3 MPa). The ZP model transferred less stress to the retention screw (785 MPa) than the other groups (939 MPa for GP, 961 MPa for GR...

Implant Platform Switching: Biomechanical Approach Using Two-Dimensional Finite Element Analysis

Tabata, Lucas Fernando; Assuncao, Wirley Goncalves; Ricardo Barao, Valentim Adelino; Sousa, Edson Antonio Capello; Gomes, Erica Alves; Delben, Juliana Aparecida
Fonte: Lippincott Williams & Wilkins Publicador: Lippincott Williams & Wilkins
Tipo: Artigo de Revista Científica Formato: 182-187
Português
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In implant therapy, a peri-implant bone resorption has been noticed mainly in the first year after prosthesis insertion. This bone remodeling can sometimes jeopardize the outcome of the treatment, especially in areas in which short implants are used and also in aesthetic cases. To avoid this occurrence, the use of platform switching (PS) has been used. This study aimed to evaluate the biomechanical concept of PS with relation to stress distribution using two-dimensional finite element analysis. A regular matching diameter connection of abutment-implant (regular platform group [RPG]) and a PS connection (PS group [PSG]) were simulated by 2 two-dimensional finite element models that reproduced a 2-piece implant system with peri-implant bone tissue. A regular implant (prosthetic platform of 4.1 mm) and a wide implant (prosthetic platform of 5.0 mm) were used to represent the RPG and PSG, respectively, in which a regular prosthetic component of 4.1 mm was connected to represent the crown. A load of 100 N was applied on the models using ANSYS software. The RPG spreads the stress over a wider area in the peri-implant bone tissue (159 MPa) and the implant (1610 MPa), whereas the PSG seems to diminish the stress distribution on bone tissue (34 MPa) and implant (649 MPa). Within the limitation of the study...

Finite Element Stress Analysis of Edentulous Mandibles with Different Bone Types Supporting Multiple-Implant Superstructures

de Almeida, Erika Oliveira; Rocha, Eduardo Passos; Freitas, Amilcar Chagas; Martin, Manoel
Fonte: Quintessence Publishing Co Inc Publicador: Quintessence Publishing Co Inc
Tipo: Artigo de Revista Científica Formato: 1108-1114
Português
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 08/00209 9; Purpose The purpose of this study was to evaluate the influence of different types of bone on the stress distribution in the mandibular bone supporting a prefabricated bar type implant prosthesis using three dimensional finite element analysis Materials and Methods Four finite element models (M) of a completely edentulous mandibular arch were built The bone types varied from type I to type 4 (M1, M2, M3, M4) The arch was restored using a prefabricated bar system supported by four interforaminal implants for the protocol prosthesis Computer software was used to determine the stress fields Three unilateral posterior loads (L) of 150 N were exerted on the prosthesis L1, perpendicular to the prefabricated bar, L2, oblique (30 degrees) in the buccolingual direction, and L3, oblique (30 degrees) in the linguobuccal direction The maximum principal stress (sigma(max)) and the maximum principal strain (epsilon(max)) were obtained for cortical and trabecular bone Results Types 3 and 4 bone showed the highest sigma(max) (MPa) in the cortical bone (19 9 and 18 2 for L1, 34 6 and 31 3 for L2, and 3 88 and 24 4 for L3, respectively) The maximum principal strain (epsilon(max)) was observed in type 4 cortical bone for all loads (1 80 for L1...

Stress distribution in ceramic restorations over natural tooth using finite element analysis. lithium disilicate x aluminum oxide material

Freitas Jr., Amilcar Chagas; Rocha, Eduardo Passos; dos Santos, Paulo Henrique; de Almeida, Erika Oliveira; de Anchieta, Rodolfo Bruniera; Martín Jr., Manoel; Archangelo, Carlos Marcelo
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 43-55
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Background: Data on stress distribution in tooth-restoration interface with different ceramic restorative materials are limited. The aim of this chapter was to assess the stress distribution in the interface of ceramic restorations with laminate veneer or full-coverage crown with two different materials (lithium dissilicate and densely sintered aluminum oxide) under different loading areas through finite element analysis. Materials and Methods: Six two-dimensional finite element models were fabricated with different restorations on natural tooth: laminate veneer (IPS Empress, IPS Empress Esthetic and Procera AllCeram) or full-coverage crown (IPS e.max Press and Procera AllCeram). Two different loading areas (L) (50N) were also determined: palatal surface at 45° in relation to the long axis of tooth (L1) and perpendicular to the incisal edge (L2). A model with higid natural tooth was used as control. von Mises equivalent stress (σ vM) and maximum principal stress (σ max) were obtained on Ansys software. Results: The presence of ceramic restoration increased σ vM and σ max in the adhesive interface, mainly for the aluminum oxide (Procera AllCeram system) restorations. The full-coverage crowns generated higher stress in the adhesive interface under L1 while the same result was observed for the laminate veneers under L2. Conclusions: Lithium dissilicate and densely sintered aluminum oxide restorations exhibit different behavior due to different mechanical properties and loading conditions. © 2011 Nova Science Publishers...

Comparison of gunshot entrance morphologies caused by .40-caliber Smith & Wesson, .380-caliber, and 9-mm Luger bullets : a finite element analysis study = Comparação de morfologias de orifícios de entrada causados por projéteis de calibre .40 Smith & Wesson, calibre .380, e 9 mm Luger: estudo com análise de elementos finitos; MatComparação de morfologias de orifícios de entrada causados por projéteis de calibre .40 Smith & Wesson, calibre .380, e 9 mm Luger : estudo com análise de elementos finitos

Rodrigo Ivo Matoso
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/01/2014 Português
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Armas de fogo podem causar feridas fatais e serem identificadas pelos vestígios deixados no corpo ou em torno deste. Entretanto, há casos em que nem projétil e nem arma do delito estão dispostos no local de crime. Estudos balísticos envolvendo modelos de elementos finitos podem reproduzir condições biomecânicas computacionais, sem ferir princípios bioéticos, pois não ocorrem testes diretos em animais ou em seres humanos. O objetivo deste estudo é comparar as morfologias de orifícios de entrada causados por projéteis calibre .40 Smith & Wesson (S&W), calibre .380 e calibre 9x19 mm Luger. Um projétil .40 S&W encamisado total, um projétil .380 encamisado total e um projétil 9x19 mm Luger encamisado total foram computacionalmente disparados contra região de glabela do modelo de elementos finitos, à distância de 10 cm, com incidência perpendicular ao ponto do alvo. Os resultados apresentam diferentes morfologias nos orifícios de entrada produzidos pelos três projéteis, utilizando-se o mesmo modelo de crânio e na mesma distância de tiro. Os resultados e as características dos orifícios de entrada foram discutidos. Modelos de elementos finitos permitem pesquisas balísticas computacionais praticáveis, que podem ser úteis para peritos forenses quando da comparação e análise de dados relacionados a feridas por arma de fogo na região frontal do crânio.; Firearms can cause fatal wounds...

Mechanical and thermal response of enamel to IR radiation - a finite element mesoscopic model

Vila Verde, A.; Ramos, Marta M. D.
Fonte: SPIE Publicador: SPIE
Tipo: Artigo de Revista Científica
Publicado em //2005 Português
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We present finite element models of human dental enamel that account for water-pores known to exist in this material, and use them to assess the influence of these pores on the temperature and stress profiles during and after single Er:YAG (2.9 µm) and CO2 (10.6 µm) laser pulses of duration 0.35 µs. Our results indicate that the temperature maximum is reached at the water-pores at the end of the laser pulse; this maximum seems to be independent of pore size for the CO2 laser but appears to be strongly dependent of pore size for the Er:YAG laser. The pressure reached at the water pore seems to be directly related to the temperature at the pore and it is significantly higher that the stress levels reached throughout the modelled structure, which indicates that water pores should play a significant role in the ablation mechanisms, even before water vaporization takes place. These results suggest that researchers conducting enamel ablation by Er:YAG lasers - or other lasers with wavelengths for which the absorption coefficients of the mineral and the water differ significantly - may want to select their samples and analyse their results taking into account factors that may alter the degree of mineralization of a tooth, such as age or type of tooth.; Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência ...

Finite element and experimental cortex strains of the intact and implanted tibia

Completo, A.; Fonseca, F.; Simões, J. A.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Artigo de Revista Científica
Português
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Finite Element (FE) models for the simulation of intact and implanted-bone find their main purpose in accurately reproducing the associated mechanical behavior FE models can be used for preclinical testing of joint replacement implants, where some biomechanical aspects are difficult, if not possible, to simulate and investigate in vitro. To predict mechanical failure or damage, the model should accurately predict stresses and strains. Commercially available synthetic femur models have been extensively used to validate finite element models, but despite the vast literature available on the characteristics of synthetic tibia, numerical and experimental validation of the intact and implant assemblies of tibia are very limited or lacking. In the current study, four FE models of synthetic tibia, intact and reconstructed, were compared against experimental bone strain data, and an overall agreement within 10% between experimental and FE strains was obtained. Finite element and experimental (strain gauge) models of intact and implanted synthetic tibia were validated based on the comparison of cortex bone strains. The study also includes the analysis carried out on standard tibial components with cemented and noncemented stems of the RE C Sigma Modular Knee System. The overall agreement within 10% previously established was achieved...

Experimental validation of intact and implanted distal femur finite element models

Completo, A.; Fonseca, F.; Simões, J. A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
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Four finite element (FE) models of intact and distal femur of knee replacements were validated relative to measured bone strains. FE models of linear tetrahedrons were used. Femoral replacements with cemented stemless, cemented and noncemented femoral sterns of the PFC Sigma Modular Knee System were analyzed. Bone strains were recorded at ten locations on the cortex. The magnitude of the FE bone strains corresponded to the mean measured strains, with an overall agreement of 10%. Linear regression between the FE and mean experimental strains produced slopes between 0.94 and 1.06 and R, values between 0.92 and 0.99. RSME values were less than 12%. The FE models were able to adequately replicate the mechanical behavior of distal femur reconstructions.

Biomechanical analysis of total elbow replacement with unlinked iBP prosthesis: an in vitro and finite element analysis

Completo, A.; Pereira, J.; Fonseca, F.; Ramos, A.; Relvas, C.; Simões, J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
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888.2915%
Background: Numerous models of elbow prostheses are being used and can be divided into two categories: one being a semi-constrained, linked type; and the other being non-constrained, unlinked type. Recent reports of National Elbow Arthroplasty Registers reveal no significant differences in the survival rates between linked and unlinked prosthesis brands, and the main cause appointed for revision for both types is loosening. Some previous biomechanical studies confirm the presence of abnormal bone stresses for the linked type, which can be associated with the risk of loosening. However for the unlinked type, biomechanical studies are not available that corroborate a loosening risk. It seems, that issue has not yet been fully answered and requires further analysis. Methods: Cortex strains adjacent to the elbow joint were measured with strain gauges in synthetic humeri and ulnae, before and after replacement. To assess cancellous bone strains and cement stresses around the implant finite element models validated relative to measured strains were used. Findings: Bone strains adjacent to the implant tip increased several times in the humerus and ulna. At the epiphyseal regions a generalised cancellous bone strain reduction was observed for both humerus and ulna relatively to the intact bones. Interpretation: The unlinked elbow prostheses can be associated with the risk of bone fatigue failure by overload...

Biomechanical analysis of total elbow replacement with unlinked iBP prosthesis: an in vitro and finite element analysis

Completo, A.; Pereira, J.; Fonseca, F.; Ramos, A.; Relvas, C.; Simões, J.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
888.2915%
Background: Numerous models of elbow prostheses are being used and can be divided into two categories: one being a semi-constrained, linked type; and the other being non-constrained, unlinked type. Recent reports of National Elbow Arthroplasty Registers reveal no significant differences in the survival rates between linked and unlinked prosthesis brands, and the main cause appointed for revision for both types is loosening. Some previous biomechanical studies confirm the presence of abnormal bone stresses for the linked type, which can be associated with the risk of loosening. However for the unlinked type, biomechanical studies are not available that corroborate a loosening risk. It seems, that issue has not yet been fully answered and requires further analysis. Methods: Cortex strains adjacent to the elbow joint were measured with strain gauges in synthetic humeri and ulnae, before and after replacement. To assess cancellous bone strains and cement stresses around the implant finite element models validated relative to measured strains were used. Findings: Bone strains adjacent to the implant tip increased several times in the humerus and ulna. At the epiphyseal regions a generalised cancellous bone strain reduction was observed for both humerus and ulna relatively to the intact bones. Interpretation: The unlinked elbow prostheses can be associated with the risk of bone fatigue failure by overload...

Analysis of laminated adaptive plate structures using layerwise finite element models

Garção, José; Mota Soares, Cristóvão; Mota Soares, Carlos; Reddy, JN
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica Formato: 560570 bytes; application/pdf
Português
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A general finite element formulation using the layerwise theory is developed for the analysis of laminated plate structures with piezoelectric layers or patches. The formulation considers small deformations and linear elastic material behaviour, and includes full electromechanical coupling. Several approximations of the primary variables in the thickness direction and different interpolation schemes in the surface directions are considered. This study illustrates the importance of the thickness approximation and provides a comparison between layerwise theories with different along the thickness direction approximations for the problem variables. The predictions of the displacement components, electrical potential, stress components and electrical displacement components are compared with three-dimensional, closed-form solutions for two benchmark problems. A very good agreement is obtained for the models using cubic approximation in the thickness direction. The accuracy of these models in the prediction of layer stresses is fully illustrated.

Finite element analysis of rapid canine retraction through reducing resistance and distraction

XUE,Junjie; YE,Niansong; YANG,Xin; WANG,Sheng; WANG,Jing; WANG,Yan; LI,Jingyu; MI,Congbo; LAI,Wenli
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2014 Português
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Objective: The aims of this study were to compare different surgical approaches to rapid canine retraction by designing and selecting the most effective method of reducing resistance by a three-dimensional finite element analysis. Material and Methods: Three-dimensional finite element models of different approaches to rapid canine retraction by reducing resistance and distraction were established, including maxillary teeth, periodontal ligament, and alveolar. The models were designed to dissect the periodontal ligament, root, and alveolar separately. A 1.5 N force vector was loaded bilaterally to the center of the crown between first molar and canine, to retract the canine distally. The value of total deformation was used to assess the initial displacement of the canine and molar at the beginning of force loading. Stress intensity and force distribution were analyzed and evaluated by Ansys 13.0 through comparison of equivalent (von Mises) stress and maximum shear stress. Results: The maximum value of total deformation with the three kinds of models occurred in the distal part of the canine crown and gradually reduced from the crown to the apex of the canine; compared with the canines in model 3 and model 1, the canine in model 2 had the maximum value of displacement...

Novel mixed finite element models for nonlinear analysis of plates

Kim,Wooram; Reddy,J. N
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 Português
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In this study, mixed finite element models of plate bending are developed to include other variables (e.g., the membrane forces and shear forces) in addition to the generalized displacements to investigate their effect on nonlinear response. Various finite element models are developed using the weighted-residual statements of suitable equations. The classical plate theory and the first-order shear deformation plate theory are used in this study and the von Karman nonlinear strains are accounted for. Each newly developed model is examined and compared with displacement finite element models to evaluate their performance. Numerical results show that the new mixed models developed herein show better accuracy than existing displacement based models.

Dynamic analysis for different finite element models of beams with viscoelastic damping layer

Silva, Lucas de Haro; Santade, Fransber; Paupitz Gonçalves, Paulo José; Capello Sousa, Edson Antonio; Cunha, A.; Caetano, E.; Ribeiro, P.; Muller, G.
Fonte: European Assoc Structural Dynamics Publicador: European Assoc Structural Dynamics
Tipo: Conferência ou Objeto de Conferência Formato: 1769-1773
Português
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Many new viscoelastic materials have been developed recently to help improve noise and vibration levels in mechanical structures for applications in automobile and aeronautical industry. The viscoelastic layer treatment applied to solid metal structures modifies two main properties which are related to the mass distribution and the damping mechanism. The other property controlling the dynamics of a mechanical system is the stiffness that does not change much with the viscoelastic material. The model of such system is usually complex, because the viscoelastic material can exhibit nonlinear behavior, in contrast with the many available tools for linear dynamics. In this work, the dynamic behavior of sandwich beam is modeled by finite element method using different element types which are then compared with experimental results developed in the laboratory for various beams with different viscoelastic layer materials. The finite element model is them updated to help understand the effects in the damping for various natural frequencies and the trade-off between attenuation and the mass add to the structure.

Finite element modeling and simulation of thermomechanical processing of particle reinforced metal matrix composites

Gennick, Kendall
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
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Approved for public release; distribution is unlimited; During the consolidation phase, reinforcement particles of Metal Matrix Composites (MMC's) tend to be non uniformly distributed. The result is that the material properties of the composite materials are not as good as those originally desired. Through large amounts of straining, homogeneity can be achieved. Finite element models of MMC's undergoing different thermomechanical processes (TMP's) to true strains of approximately 1.2 were generated. The models consist of particle clusters within the particle-depleted matrix. The particle clusters were modeled by either a smeared model in which the particles refine the grains in the cluster, or a discrete model of the particles within clusters. The smeared and discrete models qualitatively agreed with each other. The results suggest that the best TMP to reach a state of reinforcement particle homogeneity was a hot worked, low strain rate TMP; http://archive.org/details/finiteelementmod00genn; Lieutenant, United States Navy

Application of artificial boundary conditions in sensitivity-based updating of finite element models

Mentzer, John R.
Fonte: Monterey California. Naval Postgraduate School Publicador: Monterey California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xiv, 95 p. ;
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In structural dynamics the ability of a finite element model, or (FEM), to accurately represent a structure's dynamic response (natural frequencies and mode shapes) determines its utility as a solution tool. Oftern the model needs to be updated or improved to better represent the structure it is modeling. An updated or improved model of an undamaged structure is often needed in order to identify damage in an in-service structure. A difficulty generally arises in trying to slove for this error because it is often represented by an underdetermined problem, as the number of parameters potentially in error in the FEM is typically much larger than the number of measured parameters. The method of Artifical Boundary Conditions (ABC) can help to resolve the problem and lead to an improved solution. The ABC systems provide the natural frequencies for the structure under test, under a variety of boundary conditions which are imposed computationally. Specifically, the use of ABC in sensitivity based updating will be investigated and its improvement on performance reviewed.; US Navy (USN) author.

Finite element analyses of the structural behaviour of pylons supporting an inclined coal conveyor

Perduh,M; Strasheim,J A v B
Fonte: Journal of the South African Institution of Civil Engineering Publicador: Journal of the South African Institution of Civil Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2015 Português
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As part of the coal conveyance system at Medupi Power Station, an inclined coal conveyor will transport coal from the stockyard to the coal transfer tower, and from there to the boilers. The conveyor is supported by concrete columns (pylons), in turn supporting the steel gantries on which the conveyor is located. The pylons can be considered as cantilever columns during the construction stage, while in the final operational stage with the steel gantries positioned in-between the pylons, a frame system will be formed. The gantries are connected to the pylons with custom-designed sliding joints, which allow limited movement of the gantries in the longitudinal direction of the conveyor. This paper describes how various finite element analyses of the structural behaviour of the pylons and the overall structure of the inclined coal conveyor were undertaken to assess wind and seismic actions. It focuses on modelling the behaviour of the concrete pylons during the construction period, a comparison between finite element models (FEMs) with different complexities and the implications of simplifying the FEMs. It will be shown that the simplified beam element models provide adequate modelling of the structural behaviour for this kind of structure. The modelling of non-linear connections between elements for static and dynamic conditions was also investigated...