Browsing by Author "Monteiro, Jaime M."
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- Aplicação da interferometria holografia subaquática para análise de estruturasPublication . Monteiro, Jaime M.; Lopes, Hernani; Valin Rivera, Jose Luis; Vaz, M.A.P.Pretende-se com este trabalho estudar a aplicação das técnicas de interferometria holográfica à análise estrutural em ambiente subaquático. Estas técnicas estão hoje bem divulgadas e com aplicações em diversas áreas. No entanto, a sua aplicação em ambientes subaquáticos, apresenta alguns desafios. Neste trabalho estuda-se a aplicação de duas técnicas, ESPI e holografia digital, comparando-as e apresentando vantagens e desvantagens de cada uma delas. Faz-se um breve estudo sobre a influência das instabilidades resultantes da turbulência das águas e da presença de partículas em suspensão bem como possíveis soluções para minimizar estes problemas.
- Assessment of the displacement field along a surface crack in a flat plate using optical techniquesPublication . Ribeiro, J.E.; Vaz, M.A.P.; Lopes, Hernani; Melo, F.J.M.Q. de; Monteiro, Jaime M.Structural components may contain cracks, and for these components a crack tip represents a highly singular stress. The evaluation of the associated strain gradient is difficult to achieve with experimental discrete methods. An efficient alternative are the optical techniques which are non-contact, and so delivering continuous information of the displacement fields and associated derivatives for strain evaluation. This paper describes some experimental methods to fully characterize the displacement field near a crack tip existing in flat plates. Three optical field techniques based on image analysis were used in the present work; respectively, Electronic Speckle Pattern Interferometry, Moir ´e Interferometry, and Digital Image Correlation. These methods allow different resolutions which can be adjusted according to the expected strain gradient. While the first method depends on the laser wavelength and position of the illumination sources, the second depends on the grating pitch and the last on the surface texture or painted speckle. Algorithms to derivate and filtering the displacement field are developed to compute the strain field and will be used for further works.
- Caracterização do campo de deslocamentos em tecidos hiperelásticosPublication . Ribeiro, J.E.; Martins, Pedro; Monteiro, Jaime M.; Vaz, M.A.P.; Lopes, HernaniNeste trabalho pretende-se caracterizar, por um lado, o campo de deslocamentos em tecidos hiper-elásticos e, por outro, avaliar a aplicação da técnica de Correlação Digital de Imagem neste tipo de materiais. Para o efeito, implementou-se um ensaio de tracção de um tecido com propriedades mecânicas hiper-elásticas (tecidos da mucosa vaginal humana) e, recorrendo ao equipamento de Correlação Digital de Imagem, Aramis, da GOM, fez-se uma análise global do campo de deslocamentos ocorrido na superfície do provete.
- Damage characterization in laminated plates using digital SherographyPublication . Lopes, Hernani; Monteiro, Jaime M.; Vaz, M.A.P.In this work we describe the experimental characterization of the delimitation in a carbon fibre plate based on the measurement of displacement gradient for different loading conditions. The Michelson shearing arrangement with time modulation technique was used in quasi-static measurements and Mach-Zehnder shearing with spatial modulation technique for the dynamic measurements. The objective of the experimental procedure was to investigate the best technique for the identification of two different sizes delaminations in the carbon fibre plate. Another objective of this study was to compare the results from static and dynamic loads.
- Digital holography using a photographic cameraPublication . Monteiro, Jaime M.; Lopes, Hernani; Vaz, M.A.P.In this work an experimental device for surface deformation assessment on components and structures is presented. The system is based in a holographic interferometric technique and benefits from all the advantages associated with these techniques such as: high resolution, full field, non contact and the possibility of post processing the obtained numerical data. To perform measurements the proposed device uses digital holograms recorded with a standard digital photographic camera. In order to test and validate the system proposed some experimental results are presented and discussed.
- Displacement full-fiel measurement at crack root using the interferometric Moiré techniquePublication . Ribeiro, J.E.; Lopes, Hernani; Monteiro, Jaime M.; Vaz, M.A.P.This paper presents the measurement of displacement field at the crack root of test specimens using the interferometric Moiré technique. The assessment of the displacement field is obtained from the standard test method for plain-strain, ASTM E399-90. The Moiré grating is replicated on specimen surface and the double LASER illumination allows the non-contact full-field measurement of the displacement field with high resolution down to a tenth of the wave length. The time phase modulation technique is used for increasing the spatial resolution of this method. The global displacement field is obtained by dedicated image processing technique. Finally, a comparison of the experimental results and the numerical calculations is presented.
- Estudo do comportamento mecânico dos compósitos de restauro dentário utilizando técnicas ópticasPublication . Monteiro, Jaime M.; Lopes, Hernani; Vaz, M.A.P.; Campos, L.M.; Vasconcelos, Mário; Campos, J.C. ReisOs materiais compósitos são hoje em dia cada vez mais utilizados no restauro dentário. Estes materiais substituíram as tradicionais amálgamas que apresentavam alguns inconvenientes. Apesar das vantagens no uso destes novos materiais existem ainda alguns problemas a resolver, nomeadamente a sua contracção durante o processo de cura. Desta forma surgem tensões nos dentes restaurados, podendo originar dano estrutural. Pretende-se com este trabalho estudar o processo de contracção dos compósitos dentários utilizando as técnicas ópticas, holografia digital, ESPI e correlação de imagem que demonstraram estar bem adaptadas a este estudo. É ainda apresentado um estudo comparativo utilizando diferentes materiais compósitos, bem como um estudo numérico com simulação por elementos finitos.
- Experimental measurement of the displacement field on a mandible in vitroPublication . Lopes, Hernani; Ribeiro, J.E.; Piloto, P.A.G.; Viriato, Nuno; Monteiro, Jaime M.; Campos, J.C. Reis; Vaz, M.A.P.This paper presents an attempt to obtain the displacement field produced in a human mandible during the mastication. This information is of crucial importance in the stress estimation. Rubber bands fixed on mandible bone are used to simulate muscles and tendons being the load applied at the incisive teeth and controlled by a load cell. The temporomandibular joint and ligaments are implemented through the fixation of the mandible to a mechanic rig. The global boundary conditions were defined according to the anatomic model. The in-plane ESPI (Electronic Speckle Pattern interferometry) technique [1] is used for the measurement of flue global displacement field at mandible surface. The numerical simulation of the 3D modal mandible [2], which includes the cortical and spongeous bone, is performed using a commercial finite element method code, Ansys® [3J. The figure 1 shows the experimental results with ESPI and the numerical simulation.
- Improvements in damage detection using modal strain fields measured by digital shearographyPublication . Lopes, Hernani; Santos, J.V. Araújo; Monteiro, Jaime M.; Ribeiro, J.E.In this paper we present a novel approach for damage detection based on discontinuities analysis of experimental modal strain fields. These fields are extracted from the combination of two rotation fields and they are measured using digital shearography with stroboscopic double illumination. The rotation fields of a damaged laminated plate are frozen by the synchronization between the LASER illumination and the modal vibration of the object. The quantitative evaluation is performed for each digital shearogram using a time modulation technique. The evaluation of a delamination damage on composite plates is performed by using dedicate image processing techniques. Finally, a comparative analysis of damage detections using the experimental measurement of rotation and deformation fields and their spatial derivatives is presented.
- Measurement of residual stresses with optical techniquesPublication . Ribeiro, J.E.; Monteiro, Jaime M.; Vaz, M.A.P.; Lopes, Hernani; Piloto, P.A.G.The goal of this work was the development of other experimental techniques to measure residual stresses, as an alternative to the hole-drilling method with strain gauges. The proposed experimental techniques are based on the use of Moiré interferometry and in-plane electronic speckle pattern interferometry (ESPI). Both are field techniques allowing the assessment of in-plane displacements without contact and high resolution. Grating replication techniques were developed to record high-quality diffraction gratings onto the specimen's surfaces. An optical set-up of laser interferometry was developed to generate the master grating (virtual). An in-plane ESPI set-up was also designed and implemented to measure displacements in one direction. The stress relaxation was promoted by the blind hole-drilling and the obtained fringe patterns (Moiré and speckle) were video-recorded. Image processing techniques were applied to assess the in-plane strain field. A finite-element code (ansys®) was used to simulate the stress relaxation process, whose values were compared with the experimental data, and to calculate the hole-drilling calibration constants.