Browsing by Author "Soares, C.M. Mota"
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- 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.
- Combined numerical-experimental model for the identification of mechanical properties of laminated structuresPublication . Araújo, A.L.; Soares, C.M. Mota; Freitas, M.J.M.; Pedersen, P.; Herskovits, J.A combined numerical-experimental method for the identification of six elastic material modulus of generally thick composite plates is proposed in this paper. This technique can be used in composite plates made of different materials and with general stacking sequences. It makes use of experimental plate response data, corresponding numerical predictions and optimisation techniques. The plate response is a set of natural frequencies of flexural vibration. The numerical model is based on the finite element method using a higher-order displacement field. The model is applied to the identification of the elastic modulus of the plate specimen through optimisation techniques, using analytical sensitivities. The validity, efficiency and potentiality of the proposed technique is discussed through test cases.
- Damage localization in laminated composite plates using double pulse-electronic holographic interferometryPublication . Santos, J.V. Araújo; Lopes, Hernani; Vaz, M.A.P.; Soares, C.M. Mota; Freitas, M.J.M.One method for the damage localization of impact damage in laminated composite plates, based on their vibrational characteristics, is presented in this paper. This method uses double pulse-electronic holographic interferometry for mode shapes acquisition and the differences in curvatures. The rotations and curvatures are numerically obtained. The method is applied to a carbon fibre reinforced epoxy rectangular plate, free in space, subjected to two cases of impact damage. It is shown that the method based on curvatures allows for the localization of both cases of damage, which can be undetected by visual, X-ray or C-Scan inspections. The best localizations are achieved by selecting and applying the method to the most changed mode.
- Damage localization in laminated composite plates using mode shapes measured by pulsed TV holographyPublication . Santos, J.V. Araújo; Lopes, Hernani; Vaz, M.A.P.; Soares, C.M. Mota; Freitas, M.J.M.Three methods for the damage localization of impact damage in laminated composite plates, based on their vibrational characteristics, are presented in this paper. These methods use double pulse TV holography with acoustic excitation for mode shapes acquisition and the differences in translations, rotations and curvatures. The rotations and curvatures are obtained by numerical differentiation of mode shapes translations using a differentiation/smoothing technique. The methods are applied to a carbon fiber reinforced epoxy rectangular plate, free in space, subjected to two cases of impact damage. It is shown that the method based on curvatures allows the localization of both cases of damage, which can be undetected by visual, X-ray or C-scan inspections. The best localizations are achieved by selecting and applying the method to the most changed mode.
- Identificação de parâmetros elásticos e piezoelétricos em estruturas activas tipo placa : técnicas de optimização clássica versus redes neuronais artificiaisPublication . Araújo, A.L.; Lopes, Hernani; Vaz, M.A.P.; Soares, C.M. Mota; Herskovits, J.Neste trabalho são apresentados dois métodos não destrutivos para a identificação de parâmetros elásticos e piezoeléctricos em estruturas laminadas activas do tipo placa, com sensores/actuadores de superfície. O primeiro destes métodos resolve o problema inverso através de métodos de optimização clássica, minimizando a diferença entre frequências naturais experimentais e as fornecidas por um modelo de elementos finitos. O segundo método baseia-se na construção de um “meta-modelo” do problema inverso, recorrendo a Redes Neuronais Artificiais. Os dois métodos são comparados recorrendo a resultados experimentais de uma placa em vibração livre.
- 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.
- Parameter estimation in active plate structuresPublication . Araújo, A.L.; Lopes, Hernani; Vaz, M.A.P.; Soares, C.M. Mota; Herskovits, J.; Pedersen, P.In this paper two non-destructive methods for elastic and piezoelectric parameter estimation in active plate structures with surface bonded piezoelectric patches are presented. These methods rely on experimental undamped natural frequencies of free vibration. The first solves the inverse problem through gradient based optimization techniques, while the second is based on a metamodel of the inverse problem, using artificial neural networks. A numerical higher order finite element laminated plate model is used in both methods and results are compared and discussed through a simulated and an experimental test case.