José Viriato Araújo dos Santos | Instituto Superior Técnico (original) (raw)

Papers by José Viriato Araújo dos Santos

Research paper thumbnail of On the use of finite differences for vibration-based damage localization in laminated composite plates

Purpose-Laminated composite materials are a staple of modern material development, with extremely... more Purpose-Laminated composite materials are a staple of modern material development, with extremely strong fibers being combined with resins to form versatile and efficient engineering structures. However, the advancements in material development must be accompanied by equally advanced methods for damage detection, localization and quantification, as these materials develop inherently unique failure modes. This paper aims to further the study of the use of modal shapes and their spatial derivatives to localize damage in laminated composite rectangular plates. Exploring different damage scenarios and models, as well as different orders of mode shape derivatives of laminated plates.

Design/methodology/approach-ANSYS® Parametric Design Language (APDL) is used to perform finite element analysis of plates with several damage scenarios and damage mechanics models. MATLAB® is used to post-process these simulation results, namely by calculating the derivatives using finite differences, applying three distinct sets of damage indices, including one that is presently proposed. To mimic experimental conditions and test the resilience of the derivative orders, different noise levels are introduced into the results of the finite element analysis. A quality index is employed to quantitatively evaluate the solutions, mainly regarding the response to the introduced noise.

Findings-The results show that the applied damage localization methods have comparable results in terms of quality. These results also show that the quality of the damage localizations is higher when the damaged areas coincide with high displacement/curvature areas of the mode shapes and that higher noise levels have a more noticeable negative impact when employing higher-order derivatives.

Originality/value-Exploring different damage scenarios and models, as well as different orders of mode shape derivatives of laminated plates. The influence of a specific damage layer on the order of derivatives of modal response is evaluated, showing promising results concerning its identification.

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Research paper thumbnail of Damage Identification in Beams by Post-processing Modal Displacements and Rotations with Haar Wavelet

Lecture Notes in Civil Engineering, 2021

A study on the post-processing of modal displacements and modal rotations with the Haar wavelet i... more A study on the post-processing of modal displacements and modal rotations with the Haar wavelet is presented in this paper. A free-free aluminum beam is chosen as a structure to be analyzed and its modal displacements and rotations in both undamaged and multiple damagedstates are computed with the finite element method. Three sets of damageindicators are proposed: (1) wavelet transform of damaged modal displacements or modalrotations, (2) wavelet transform of differences in modal displacements or modal rotations, and (3) ratio of wavelet transform of differences in modal displacements or modal rotations to wavelet transform of undamaged modal displacements or modal rotations. The study shows that post-processing modal displacements with the Haar wavelet leads to poor damageidentifications. On the other hand, if one applies the same type of wavelet to modalrotations, the damage indicators (2) and (3) clearly pinpoints the location of the damage. Although the set of damage indicators (1) and (2) are prone to the boundary effect, where high values of wavelets coefficients are present, the third set of damageindicators does not present this problem. Furthermore, for large values of damage, this damage indicators shows the presence of damagein all scales of the wavelet scalogram. The present study clearly shows that by post-processing modalrotations with the simplest wavelet one can obtain reliable identifications of multiple damage.

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Research paper thumbnail of Improvement on modal curvatures methods for multiple damage identification in beams

Multidiscipline Modeling in Materials and Structures, 2021

PurposeThe purpose of this paper is to present a study on the application of four damage factors ... more PurposeThe purpose of this paper is to present a study on the application of four damage factors to several single and multiple damage scenarios of aluminium beams. Each one of these damage factors is defined by the information given by modal curvatures of the beams.Design/methodology/approachThe methodology consisted of a first experimental stage in which the modal rotations were measured with shearography and a subsequent numerical analysis in order to obtain the modal curvatures. To this end, three finite difference formulae were applied. The modal curvatures were then used to calculate the damage factors.FindingsIt was found that the profile of the damage factors varies according to the finite difference formula used. In view of the findings, the differences among the damage factors analysed are highlighted and some final recommendations to improve damage identifications via modal curvature-based are presented.Originality/valueTo the best of the authors’ knowledge, the applicati...

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Research paper thumbnail of Application of spline interpolation to speckle shearography measurements for damage identification

Procedia Structural Integrity, 2019

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Research paper thumbnail of Identification of multiple damage using modal rotation obtained with shearography and undecimated wavelet transform

Mechanical Systems and Signal Processing, 2019

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Research paper thumbnail of A Review and Study on Ritz Method Admissible Functions with Emphasis on Buckling and Free Vibration of Isotropic and Anisotropic Beams and Plates

Archives of Computational Methods in Engineering, 2017

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Research paper thumbnail of Numerical study on damage identification using shearography with different shearing amounts

Procedia Structural Integrity, 2017

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Research paper thumbnail of Influence of shearing amount and vibration amplitude on noise in shearography

Procedia Structural Integrity, 2017

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Research paper thumbnail of A damage localisation method based on higher order spatial derivatives of displacement and rotation fields

Journal of Physics: Conference Series, 2011

ABSTRACT This paper presents the development of a damage localisation method based on low and hig... more ABSTRACT This paper presents the development of a damage localisation method based on low and higher order spatial derivatives of displacement and rotation fields. The method relies on the Timoshenko beam theory, the Hamilton's principle and the Ritz method, allowing the computation of an approximate analytical solution of natural frequencies, displacement and rotation fields. Since these fields are expressed analytically, through a series expansion, the spatial derivatives are also obtained analytically. Besides the usual curvature difference and damage index, which are based on comparisons of second order spatial derivative of the displacement field of a beam in the undamaged and damaged states, other damage indicators are proposed. These new indicators rely on spatial derivatives of rotation fields. The indicators are applied to the localisation of various cases of damages in beams and a comparison among them is carried out. It is found that, for relatively thick beams, the values of the indicators based on rotation fields spatial derivatives are, in general, lower than those based on displacement fields. It is also observed that these differences are negligible for beams with high length to thickness ratio.

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Research paper thumbnail of A new technique to optimize the use of mode shape derivatives to localize damage in laminated composite plates

Composite Structures, 2014

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Research paper thumbnail of Free Vibration and Buckling Analysis of Beams with a Modified Couple-Stress Theory

International Journal of Applied Mechanics, 2012

A model based on a modified couple stress theory for the free vibration and buckling analyses of ... more A model based on a modified couple stress theory for the free vibration and buckling analyses of beams is presented. The model also incorporates the Poisson's effect and allows the analysis of Timoshenko beams with any arbitrary end boundary condition. The natural frequencies and buckling loads are computed using the Ritz method. Parametric studies show that, while the natural frequencies and the buckling loads increase monotonically with the increase of the material length scale, they present a minimum in certain values of the Poisson's ratio. A study relating the classical elasticity and the couple stress strain energies is also presented. By establishing this relation, explicit formulas to obtain the natural frequencies and buckling loads, in which the couple stress and Poisson's effects are accounted for, in terms of the buckling loads of the classical elasticity are found. These formulas, which are valid when the shear strain and stress are zero, allow an expedite c...

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Research paper thumbnail of Nonlocal material properties of single-walled carbon nanotubes

International Journal of Smart and Nano Materials, 2012

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Research paper thumbnail of Damage Localisation in Beams using the Ritz Method and Speckle Shear Interferometry

Proceedings of the Tenth International Conference on Computational Structures Technology

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Research paper thumbnail of Efficiency assessment of wavelet transforms and wavelets for damage localization in beams using shearography

Diagnostyka

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Research paper thumbnail of Damage identification by wavelet analysis of modal rotation differences

In this paper, a novel damage identification approach based on differences in modal rotation fiel... more In this paper, a novel damage identification approach based on differences in modal rotation fields obtained from shearographic measurements of structures and post-processed with the 2D continuous wavelet transform-based algorithm is presented. It is shown that the baseline approach, which assumes analysis of differences in modal rotation fields, allows to improve the sensitivity of a method to damage, making it possible to identify smaller damage with respect to the baseline-free approach. Moreover, a new approach for the reduction of the boundary effect is presented, which allows for the improvement visualization of the resulting maps using the proposed damage identification method. The proposed method was tested with eight damage scenarios, which allowed to prove repeatability of the obtained results, as well as to define a detectability threshold which is on the level of 3.5% of the thickness reduction.

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Research paper thumbnail of Improvement in Damage Localisation using Speckle Shearography

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Research paper thumbnail of Enhancement of shearography-based damage identification using best tree wavelet packet analysis

MATEC Web of Conferences

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Research paper thumbnail of Improvement in Damage Localisation using Speckle Shearography

Proceedings of the Eleventh International Conference on Computational Structures Technology, 2012

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Research paper thumbnail of Damage Identification in Beams by Post-processing Modal Displacements and Rotations with Haar Wavelet

A study on the post-processing of modal displacements and modal rotations with the Haar wavelet i... more A study on the post-processing of modal displacements and modal rotations with the Haar wavelet is presented in this paper. A free-free aluminum beam is chosen as a structure to be analyzed and its modal displacements and rotations in both undamaged and multiple damagedstates are computed with the finite element method. Three sets of damageindicators are proposed: (1) wavelet transform of damaged modal displacements or modalrotations, (2) wavelet transform of differences in modal displacements or modal rotations, and (3) ratio of wavelet transform of differences in modal displacements or modal rotations to wavelet transform of undamaged modal displacements or modal rotations. The study shows that post-processing modal displacements with the Haar wavelet leads to poor damageidentifications. On the other hand, if one applies the same type of wavelet to modalrotations, the damage indicators (2) and (3) clearly pinpoints the location of the damage. Although the set of damage indicators (1) and (2) are prone to the boundary effect, where high values of wavelets coefficients are present, the third set of damageindicators does not present this problem. Furthermore, for large values of damage, this damage indicators shows the presence of damagein all scales of the wavelet scalogram. The present study clearly shows that by post-processing modalrotations with the simplest wavelet one can obtain reliable identifications of multiple damage.

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Research paper thumbnail of Optimal Finite Difference Schemes for Multiple Damage Identification in Beams

This paper presents an experimental and numerical study on multiple damage localization in a beam... more This paper presents an experimental and numerical study on multiple damage localization in a beam. The modal rotations of an aluminum beam were measured with shearography and post-processed to obtain the modal curvatures. The modal curvatures, which are computed by finite differences, are used as damage indicators. In most approaches available in the literature, the modal curvatures are defined from the modal displacements, requiring the computation of the second order derivate. In the present approach, since the modal rotations are available, the curvatures are obtained by computing only the first order derivative, reducing the propagation of measurement errors. Optimal samplings for both the forward and the central finite difference schemes, the latter with three and five points formulas, are derived. The results of applying these three finite difference formulas are compared, showing that both central finite differences allow for a better representation of the experimental modal curvature. Therefore, the perturbations on the modal curvatures are better identified, thus clearly indicating the damage presence.

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Research paper thumbnail of On the use of finite differences for vibration-based damage localization in laminated composite plates

Purpose-Laminated composite materials are a staple of modern material development, with extremely... more Purpose-Laminated composite materials are a staple of modern material development, with extremely strong fibers being combined with resins to form versatile and efficient engineering structures. However, the advancements in material development must be accompanied by equally advanced methods for damage detection, localization and quantification, as these materials develop inherently unique failure modes. This paper aims to further the study of the use of modal shapes and their spatial derivatives to localize damage in laminated composite rectangular plates. Exploring different damage scenarios and models, as well as different orders of mode shape derivatives of laminated plates.

Design/methodology/approach-ANSYS® Parametric Design Language (APDL) is used to perform finite element analysis of plates with several damage scenarios and damage mechanics models. MATLAB® is used to post-process these simulation results, namely by calculating the derivatives using finite differences, applying three distinct sets of damage indices, including one that is presently proposed. To mimic experimental conditions and test the resilience of the derivative orders, different noise levels are introduced into the results of the finite element analysis. A quality index is employed to quantitatively evaluate the solutions, mainly regarding the response to the introduced noise.

Findings-The results show that the applied damage localization methods have comparable results in terms of quality. These results also show that the quality of the damage localizations is higher when the damaged areas coincide with high displacement/curvature areas of the mode shapes and that higher noise levels have a more noticeable negative impact when employing higher-order derivatives.

Originality/value-Exploring different damage scenarios and models, as well as different orders of mode shape derivatives of laminated plates. The influence of a specific damage layer on the order of derivatives of modal response is evaluated, showing promising results concerning its identification.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Damage Identification in Beams by Post-processing Modal Displacements and Rotations with Haar Wavelet

Lecture Notes in Civil Engineering, 2021

A study on the post-processing of modal displacements and modal rotations with the Haar wavelet i... more A study on the post-processing of modal displacements and modal rotations with the Haar wavelet is presented in this paper. A free-free aluminum beam is chosen as a structure to be analyzed and its modal displacements and rotations in both undamaged and multiple damagedstates are computed with the finite element method. Three sets of damageindicators are proposed: (1) wavelet transform of damaged modal displacements or modalrotations, (2) wavelet transform of differences in modal displacements or modal rotations, and (3) ratio of wavelet transform of differences in modal displacements or modal rotations to wavelet transform of undamaged modal displacements or modal rotations. The study shows that post-processing modal displacements with the Haar wavelet leads to poor damageidentifications. On the other hand, if one applies the same type of wavelet to modalrotations, the damage indicators (2) and (3) clearly pinpoints the location of the damage. Although the set of damage indicators (1) and (2) are prone to the boundary effect, where high values of wavelets coefficients are present, the third set of damageindicators does not present this problem. Furthermore, for large values of damage, this damage indicators shows the presence of damagein all scales of the wavelet scalogram. The present study clearly shows that by post-processing modalrotations with the simplest wavelet one can obtain reliable identifications of multiple damage.

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Research paper thumbnail of Improvement on modal curvatures methods for multiple damage identification in beams

Multidiscipline Modeling in Materials and Structures, 2021

PurposeThe purpose of this paper is to present a study on the application of four damage factors ... more PurposeThe purpose of this paper is to present a study on the application of four damage factors to several single and multiple damage scenarios of aluminium beams. Each one of these damage factors is defined by the information given by modal curvatures of the beams.Design/methodology/approachThe methodology consisted of a first experimental stage in which the modal rotations were measured with shearography and a subsequent numerical analysis in order to obtain the modal curvatures. To this end, three finite difference formulae were applied. The modal curvatures were then used to calculate the damage factors.FindingsIt was found that the profile of the damage factors varies according to the finite difference formula used. In view of the findings, the differences among the damage factors analysed are highlighted and some final recommendations to improve damage identifications via modal curvature-based are presented.Originality/valueTo the best of the authors’ knowledge, the applicati...

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Research paper thumbnail of Application of spline interpolation to speckle shearography measurements for damage identification

Procedia Structural Integrity, 2019

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Research paper thumbnail of Identification of multiple damage using modal rotation obtained with shearography and undecimated wavelet transform

Mechanical Systems and Signal Processing, 2019

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Research paper thumbnail of A Review and Study on Ritz Method Admissible Functions with Emphasis on Buckling and Free Vibration of Isotropic and Anisotropic Beams and Plates

Archives of Computational Methods in Engineering, 2017

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Research paper thumbnail of Numerical study on damage identification using shearography with different shearing amounts

Procedia Structural Integrity, 2017

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Research paper thumbnail of Influence of shearing amount and vibration amplitude on noise in shearography

Procedia Structural Integrity, 2017

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Research paper thumbnail of A damage localisation method based on higher order spatial derivatives of displacement and rotation fields

Journal of Physics: Conference Series, 2011

ABSTRACT This paper presents the development of a damage localisation method based on low and hig... more ABSTRACT This paper presents the development of a damage localisation method based on low and higher order spatial derivatives of displacement and rotation fields. The method relies on the Timoshenko beam theory, the Hamilton's principle and the Ritz method, allowing the computation of an approximate analytical solution of natural frequencies, displacement and rotation fields. Since these fields are expressed analytically, through a series expansion, the spatial derivatives are also obtained analytically. Besides the usual curvature difference and damage index, which are based on comparisons of second order spatial derivative of the displacement field of a beam in the undamaged and damaged states, other damage indicators are proposed. These new indicators rely on spatial derivatives of rotation fields. The indicators are applied to the localisation of various cases of damages in beams and a comparison among them is carried out. It is found that, for relatively thick beams, the values of the indicators based on rotation fields spatial derivatives are, in general, lower than those based on displacement fields. It is also observed that these differences are negligible for beams with high length to thickness ratio.

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Research paper thumbnail of A new technique to optimize the use of mode shape derivatives to localize damage in laminated composite plates

Composite Structures, 2014

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Research paper thumbnail of Free Vibration and Buckling Analysis of Beams with a Modified Couple-Stress Theory

International Journal of Applied Mechanics, 2012

A model based on a modified couple stress theory for the free vibration and buckling analyses of ... more A model based on a modified couple stress theory for the free vibration and buckling analyses of beams is presented. The model also incorporates the Poisson's effect and allows the analysis of Timoshenko beams with any arbitrary end boundary condition. The natural frequencies and buckling loads are computed using the Ritz method. Parametric studies show that, while the natural frequencies and the buckling loads increase monotonically with the increase of the material length scale, they present a minimum in certain values of the Poisson's ratio. A study relating the classical elasticity and the couple stress strain energies is also presented. By establishing this relation, explicit formulas to obtain the natural frequencies and buckling loads, in which the couple stress and Poisson's effects are accounted for, in terms of the buckling loads of the classical elasticity are found. These formulas, which are valid when the shear strain and stress are zero, allow an expedite c...

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Research paper thumbnail of Nonlocal material properties of single-walled carbon nanotubes

International Journal of Smart and Nano Materials, 2012

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Research paper thumbnail of Damage Localisation in Beams using the Ritz Method and Speckle Shear Interferometry

Proceedings of the Tenth International Conference on Computational Structures Technology

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Research paper thumbnail of Efficiency assessment of wavelet transforms and wavelets for damage localization in beams using shearography

Diagnostyka

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Research paper thumbnail of Damage identification by wavelet analysis of modal rotation differences

In this paper, a novel damage identification approach based on differences in modal rotation fiel... more In this paper, a novel damage identification approach based on differences in modal rotation fields obtained from shearographic measurements of structures and post-processed with the 2D continuous wavelet transform-based algorithm is presented. It is shown that the baseline approach, which assumes analysis of differences in modal rotation fields, allows to improve the sensitivity of a method to damage, making it possible to identify smaller damage with respect to the baseline-free approach. Moreover, a new approach for the reduction of the boundary effect is presented, which allows for the improvement visualization of the resulting maps using the proposed damage identification method. The proposed method was tested with eight damage scenarios, which allowed to prove repeatability of the obtained results, as well as to define a detectability threshold which is on the level of 3.5% of the thickness reduction.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Improvement in Damage Localisation using Speckle Shearography

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Enhancement of shearography-based damage identification using best tree wavelet packet analysis

MATEC Web of Conferences

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Research paper thumbnail of Improvement in Damage Localisation using Speckle Shearography

Proceedings of the Eleventh International Conference on Computational Structures Technology, 2012

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Research paper thumbnail of Damage Identification in Beams by Post-processing Modal Displacements and Rotations with Haar Wavelet

A study on the post-processing of modal displacements and modal rotations with the Haar wavelet i... more A study on the post-processing of modal displacements and modal rotations with the Haar wavelet is presented in this paper. A free-free aluminum beam is chosen as a structure to be analyzed and its modal displacements and rotations in both undamaged and multiple damagedstates are computed with the finite element method. Three sets of damageindicators are proposed: (1) wavelet transform of damaged modal displacements or modalrotations, (2) wavelet transform of differences in modal displacements or modal rotations, and (3) ratio of wavelet transform of differences in modal displacements or modal rotations to wavelet transform of undamaged modal displacements or modal rotations. The study shows that post-processing modal displacements with the Haar wavelet leads to poor damageidentifications. On the other hand, if one applies the same type of wavelet to modalrotations, the damage indicators (2) and (3) clearly pinpoints the location of the damage. Although the set of damage indicators (1) and (2) are prone to the boundary effect, where high values of wavelets coefficients are present, the third set of damageindicators does not present this problem. Furthermore, for large values of damage, this damage indicators shows the presence of damagein all scales of the wavelet scalogram. The present study clearly shows that by post-processing modalrotations with the simplest wavelet one can obtain reliable identifications of multiple damage.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Optimal Finite Difference Schemes for Multiple Damage Identification in Beams

This paper presents an experimental and numerical study on multiple damage localization in a beam... more This paper presents an experimental and numerical study on multiple damage localization in a beam. The modal rotations of an aluminum beam were measured with shearography and post-processed to obtain the modal curvatures. The modal curvatures, which are computed by finite differences, are used as damage indicators. In most approaches available in the literature, the modal curvatures are defined from the modal displacements, requiring the computation of the second order derivate. In the present approach, since the modal rotations are available, the curvatures are obtained by computing only the first order derivative, reducing the propagation of measurement errors. Optimal samplings for both the forward and the central finite difference schemes, the latter with three and five points formulas, are derived. The results of applying these three finite difference formulas are compared, showing that both central finite differences allow for a better representation of the experimental modal curvature. Therefore, the perturbations on the modal curvatures are better identified, thus clearly indicating the damage presence.

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