Photoelastic analisys in the lower region of vertebral body L4

OBJETIVO: Analisar as tensões geradas no corpo vertebral L4 quando submetida à força de compressão, utilizando a técnica da fotoelasticidade de transmissão. MÉTODOS: Doze modelos fotoelásticos foram utilizados e divididos em três grupos, sendo cada grupo formado por quatro modelos, de acordo com a localização do corte sagital nas vértebras L4-L5 (cortes A, B e C). A simulação foi realizada utilizando uma força compressão de 15 N e as ordens de franjas foram avaliadas no corpo vertebral L4 utilizando o método de compensação de Tardy. RESULTADOS: A análise fotoelástica mostrou que em geral, as tensões se distribuíram de forma homogênea nos corpos vertebrais. As tensões no corte C foram maiores que no B, que por sua vez foram maiores que no corte A. CONCLUSÃO: A região posterior do corpo vertebral L4, principalmente no corte C, apresentou maiores concentrações de tensões, sendo assim, é a área mais susceptível à fratura vertebral e à espondilolistese. Análises econômicas e de decisão. Desenvolvimento de modelo econômico ou de decisão, Nível de evidência I

System's dynamic modelling through of component modal synthesis

Orientador: Paulo Roberto Gardel KurkaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Uma das principais técnicas de modelagem mixta de sistemas complexos ou de grande porte é a técnica de síntese modal. Os vários métodos de síntese modal propostos são formulados sob dois pontos de vista distintos, ou seja, considerando-se o sistema sem amortecimento ou com amortecimento geral. Além disso, surgem inerentes dificuldades na aplicação da metodologia de síntese modal na análise experimental. Neste trabalho é proposto uma técnica de síntese modal generalizada aplicada em sistemas sem amortecimento ou com amortecimento geral. O método utiliza um superconjunto modal de flexibilidade residual, cuja principal aplicação é na síntese modal experimental. O método utiliza um processo de remontagem das subestruturas que otimiza as equações finais da síntese. Propõe-se, também, um novo procedimento, definido como critério de eliminação automática de modos (CEA), que define um índice de qualidade para os modos das subestruturas, indicando quais serão aqueles mais apropriados para serem mantidos nas bases modais. Todas as metodologias propostas no trabalho foram implementadas em um software denominado Programa STRUCT. O método foi testado através de quatro exemplos de simulação. Foi feita uma validação experimental através de uma estrutura construída em escala reduzida, que visa representar um modelo esquemático e simplificado de uma asa de avião com um tanque de combustível fixado em sua extremidade. Além disso, foi também construído o modelo de elementos finitos da estrutura, com a finalidade de ajustar os modelos analítico e experimentalAbstract: Modal Synthesis is one of the main techniques for the modelling of complex or large sized system's. Two approaches for modal synthesis might be formulated those which considers the behaviour of undamped system's and those where the effects of generalized damping is apprised. Further to those consideration comes the application of the modal synthesis techniques in experimental modal analysis. The present work proposes a generalized modal synthesis procedure for damped and undamped system's. The method uses a residual flexibility superset which is applied to the experimental modal analysis. A methodology for assembling adjacent substructures is also proposed which represents an important step towards the obtention of more accurate final results. Another important procedure introduced is that of automatic selection of modes to be kept in the modal base of the residual flexibility superset, defining a quality index for the modes of each substructure. AlI methodologies have been implemented in the form of the STRUCT software. Results of four numerical simulation and a practical application have been included to illustrate the performance of the methodologies. Finite element models have also been developed for the practical application (Combination of aircraft wing and fuel tank models) for performance comparison purposesDoutoradoMecanica dos SolidosDoutor em Engenharia Mecânic

Photoelastic evaluation of pathological axis deviation of the femur in the frontal plane

The objective of this study is to evaluate the repercussions of the pathological deviation of the coxa brevis, femur, and tibia without the pathological deviation of the axis in the femoral or tibial frontal plane. The stress distribution in the proximal and distal joints was evaluated in relation to the deviations using transmission photoelasticity. Two-dimensional femur and tibia models were developed from frontal panoramic radiographs, which were later used to fabricate molds and photoelastic models. A force of 8 N was applied to the top of the femoral head. For the deviation of the coxa brevis and for the femur and tibia without pathological deviation, the stresses were more critical in the calcar region of the proximal femur. In the distal femur and proximal and distal tibia, the stress distributions were in accordance with the models, the proposed fixation conditions, and the long bone geometries. The most important conclusion of this investigation was that joint deviation also alters the stress on all primary joints of the lower extremities. From this study, it will be possible to develop better correction criteria for angular deviations and discharges of bone and joint forces of the lower extremities and to provide refinements to prostheses

Análise fotoelástica da região inferior do corpo vertebral L4

Objective: To analyze the shear forces on the vertebral body L4 when submitted to a compression force by means of transmission photoelasticity. Methods: Twelve photoelastic models were divided into three groups, with four models per group, according to the positioning of the sagittal section vertebrae L4-L5 (sections A, B and C). The simulation was performed using a 15N compression force, and the fringe orders were evaluated in the vertebral body L4 by the Tardy compensation method. Results: Photoelastic analysis showed, in general, a homogeneous distribution in the vertebral bodies. The shear forces were higher in section C than B, and higher in B than A. Conclusion: The posterior area of L4, mainly in section C, showed higher shear concentrations, corresponding to a more susceptible area for bone fracture and spondylolisthesis. Economic and Decision Analyses Development of an Economic or Decision Model. Level IObjetivo: Analisar as tensões geradas no corpo vertebral L4 quando \ud submetida à força de compressão, utilizando a técnica da fotoelasticidade de transmissão. Métodos: Doze modelos fotoelásticos foram \ud utilizados e divididos em três grupos, sendo cada grupo formado por \ud quatro modelos, de acordo com a localização do corte sagital nas vértebras L4-L5 (cortes A, B e C). A simulação foi realizada utilizando uma \ud força compressão de 15 N e as ordens de franjas foram avaliadas no \ud corpo vertebral L4 utilizando o método de compensação de Tardy. Resultados: A análise fotoelástica mostrou que em geral, as tensões se \ud distribuíram de forma homogênea nos corpos vertebrais. As tensões \ud no corte C foram maiores que no B, que por sua vez foram maiores \ud que no corte A. Conclusão: A região posterior do corpo vertebral L4, \ud principalmente no corte C, apresentou maiores concentrações de \ud tensões, sendo assim, é a área mais susceptível à fratura vertebral e à \ud espondilolistese. Análises econômicas e de decisão. Desenvolvimento \ud de modelo econômico ou de decisão, Nível de evidência I.FAPESPFAPESPCAPESCAPE

THE PHOTOELASTIC ANALISYS OF VERTEBRAL FIXATION SYSTEM SCREWS

Introduction: The photoelasticity is used for assessing the tensions/deformations involved in photoelastic materials when submitted to a given load by the observation of optical effects. The screw performance and mechanical functions are directly associated to the quality of the screws fixation in the vertebrae. Photoelasticity is an important tool to perform comparative studies of this nature. Objective: The aim of this study was to compare, by using photoelasticity, internal stresses produced by the screw with an external diameter of 6 mm, when submitted to two different pullout strengths. Materials and Methods: For this, four photoelastic models were produced. The simulation was conducted by using two pullout strengths: 0.75 and 1.50 kgf. The maximum shear stresses were calculated on 19 points around the screws, using the Tardy compensation method. Results:The values of maximum shear stress were higher with the load of 1.50 kgf. Conclusion: Thus, the screw will be more susceptible to pullout when heavier loads are applied. According to our analysis, we also found that the site with the highest maximum shear stress was found to be at the peak of creast, particularly near the tips of the screws, regardless of the load employed.FAPESPCAPE

BIOMECHANICAL BEHAVIOR OF THE SYSTEM PROSTHESIS/DENTAL IMPLANT: ANALYSIS BY THE PHOTOELASTICITY METHOD

One of the main reasons for the failure in dental implant treatments is the overload, which can cause bone resorption and later, the osseointegration loss in the implant. Therefore, the aim of this study was to analyze the tension generated around dental implants in the rehabilitation of three mandible posterior teeth, varying the connection type, the disposal, and the quantity of implants. The photoelasticity method was used in order to accomplish it. Through photoelasticity, the quantity and localization of the tensions around the implants in the different studied groups were compared (three straight line implants, three offset placement implants, two implants with a mesial cantilever, and two implants with a pontic). The results showed that the tension quantity and disposition around the dental implants of the connection external hexagon and internal hexagon were similar in all groups. In the group where the cantilever was used, an increase of the tension around the implant, adjacent to the cantilever, was observed. From the results it is concluded that the type of connection used in this study did not influence the tension quantity and distribution around the implants; however, the prosthetic configuration with the cantilever use, led to an increase of the tension around the implant, adjacent to the cantilever