Browsing by Author "Guedes, Rui M."
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- An improved mixed numerical-experimental method for stress field calculationPublication . Lopes, Hernani; Guedes, Rui M.; Vaz, M.A.P.In this work a numerical-experimental method is used to study the dynamic behavior of an aluminum plate subjected to a small mass impact.The out-of-plane displacements,due to transient bending wave propagation,were assessed for successive time instants,using double pulse TV-holography,also known as pulsed ESPI.
- An improved numerical-experimental method for damage location in structuresPublication . Lopes, Hernani; Santos, J.V. Araújo; Soares, C.M. Mota; Guedes, Rui M.; Vaz, M.A.P.An improvement of a curvature based numerical-experimental method for damage location in structures [1] is presented. The Mach-Zehnder shearography interferometer is used to measure the rotations field or the out-of-plane first order derivatives of mode shapes displacement field [2, 3]. The curvatures or second order derivatives are computed by a numerical method [4]. An aluminum beam with two small transversal cuts was tested for damaged location. The experimental results show a high correlation between the curvatures discontinuities field and the damages position. This study also demonstrates the superior performance of the curvature method using measured rotations field instead of measured displacements field.
- An improved sherography technique for spatial differentiationPublication . Lopes, Hernani; Guedes, Rui M.; Vaz, M.A.P.In this work we describe a new device designed to obtain a high quality experimental measurement with shearography. With this setup the spatial differentiation, up to the third order of out-of-plane displacements can be directly obtained. A compact setup with a high resolution camera was developed to capture the spatial derivatives. The quantitative measurements are obtained from the phase maps computed with four images phase shift technique. Good quality measurements of the higher order spatial differentiation were obtained by optical and digital means without the need of advance post processing. The border problem is also discussed and the results up to the third order are compared with the analytical solution.
- Buckling resistance of partially encased columns embedded on walls under fire from one sidePublication . Piloto, P.A.G.; Gonçales, Nathália; Rigobello, Ronaldo; Vaz, Mário; Guedes, Rui M.; Baptista, João S.Partially encased columns (PEC) have better fire resistance when compared to bare steel columns, due to the existence of concrete between the flanges. The aim of this study is to develop a new proposal for the calculation of the buckling strength of partially encased columns, embedded on walls, under fire conditions. This proposal is based on the current calculation method proposed in Annex G of EN 1994-1-2. This study uses the finite element method to calculate the average temperature of seven components. The average temperature is then used to find the buckling resistance of composite columns when submitted to fire from one side. This solution method is carried out using 30 different cross sections. All cross sections are exposed to the standard fire curve ISO834 from one side, assuming the specific fire rating of 30, 60, 90 and 120 min.
- Direct measurement of the plate bending stresses using michelson shearography interferometerPublication . Lopes, Hernani; Ribeiro, J.E.; Guedes, Rui M.; Vaz, M.A.P.This work presents a new approach to achieve the third order spatial derivatives of out-of-plane displacements field using a full field technique. The Michelson Shearography technique is used to obtain the first order derivatives. The second and third orders are computed using multiple exposed Shearography technique with digital superposed method. An experimental procedure is proposed for the measurement of the first order derivatives. A steel clamped plate loaded with a uniform pressure was tested for internal stresses calculation. A good agreement between the experimental results and analytical solution is presented.
- Estudo das técnicas de processamento de imagem dedicadas ao tratamento dos mapas de fasePublication . Lopes, Hernani; Ribeiro, J.E.; Guedes, Rui M.; Vaz, M.A.P.As técnicas ópticas, em conjunto com as ferramentas de processamento digital de imagem, têm encontrado um interesse cada vez maior na investigação laboratorial. No âmbito da mecânica experimental, as técnicas ópticas de interferometria Speckle são utilizadas para a medição do campo de deslocamentos de estruturas sob solicitação. A informação é gravada na forma de mapas de fase, os quais estão contaminados por ruído de Speckle e apresentam descontinuidades na fase. Estes deverão ser posteriormente tratados por ferramentas dedicadas de processamento de imagem de forma a eliminar o ruído sem destruir a informação de fase. Neste trabalho descrevem-se as principais técnicas de processamento de imagem dedicadas à análise de padrões de interferometria Speckle, como são, por exemplo, as técnicas de filtragem de fase e de padrões de intensidade, métodos de desembrulhar da fase. A partir de simulações numéricas é realizada uma análise comparativa da eficácia e robustez de diversas técnicas na remoção do ruído e eliminação das descontinuidades de fase. A partir pela minimização do valor eficaz do erro são determinados os parâmetros óptimos de cada técnica.
- Estudo das técnicas de processamento de imagem dedicadas ao tratamento dos mapas de fasePublication . Lopes, Hernani; Ribeiro, J.E.; Guedes, Rui M.; Vaz, M.A.P.As técnicas ópticas, em conjunto com as ferramentas de processamento digital de imagem, têm encontrado um interesse cada vez maior na investigação laboratorial. No âmbito da mecânica experimental, as técnicas ópticas de interferometria Speckle são utilizadas para a medição do campo de deslocamentos de estruturas sob solicitação. A informação é gravada na forma de mapas de fase, os quais estão contaminados por ruído de Speckle e apresentam descontinuidades na fase. Estes deverão ser posteriormente tratados por ferramentas dedicadas de processamento de imagem de forma a eliminar o ruído sem destruir a informação de fase. Neste trabalho descrevem-se as principais técnicas de processamento de imagem dedicadas à análise de padrões de interferometria Speckle, como são, por exemplo, as técnicas de filtragem de fase e de padrões de intensidade, métodos de desembrulhar da fase. A partir de simulações numéricas é realizada uma análise comparativa da eficácia e robustez de diversas técnicas na remoção do ruído e eliminação das descontinuidades de fase. A partir pela minimização do valor eficaz do erro são determinados os parâmetros óptimos de cada técnica.
- A hybrid technique for damage detection on laminated platesPublication . Lopes, Hernani; Santos, J.V. Araújo; Guedes, Rui M.; Vaz, M.A.P.This work presents an experimental/numerical technique for delamination damage detection on thin laminated composite plates. The delamination is identified using a technique based on the curvature differences of the plate modes shapes measured before and after impact damage. The natural frequencies are extracted from Frequency Response Functions. A double pulse TV holography is used for no-contact and accurate measurement of the amplitude mode shapes. The curvature is obtained by applying an improved differentiation /smoothing technique to the experimental data. Finally, the curvatures of each mode are subtracted and the damage is located.
- New improvements in shearography techniquesPublication . Lopes, Hernani; Vaz, M.A.P.; Guedes, Rui M.; Gomes, J.F. SilvaShearography is a non-contact full field technique used in the assessment of spatial gradient of displacements through a preset direction, Hung and Taylor [1]. The optical set-up can be based on a Michelson interferometer scheme, for static or quasi-static measurements, and on the Mach- Zehnder interferometer if dynamic measurements have to be performed, Santos et al [2]. In both set-ups a speckle pattern, obtained from a rough surface, is laterally shifted to create the interference and the light used for the interferometer arms have a common path between the object and the set-up. So, this interferometric technique can be used with low coherence lasers and is almost insensitive to rigid body motion. The fringe patterns obtained with shearography result from the interference between two speckled wave fronts and have lower contrast that the ones obtained with specular reference interferometers.
- A numerical-experimental method for damage location based on rotation fields spatial differentiationPublication . Lopes, Hernani; Santos, J.V. Araújo; Soares, C.M. Mota; Guedes, Rui M.; Vaz, M.A.P.This paper presents a structural damage location method that decreases the number of spatial differentiations needed to compute modal curvature fields. The method is numerically and experimentally applied to isotropic and laminated rectangular plates, respectively. A speckle shear interferometer is used to measure the rotation fields of the laminated plate, while the isotropic plate is analysed by finite elements. It was found that the Gaussian differentiation is the most suited technique to compute the curvature fields. It is also demonstrated the superior performance of the curvature method using measured rotation fields instead of measured displacement fields.