Browsing by Author "Gomes, J.F. Silva"
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- Damage identification using real time rotating field analysisPublication . Lopes, Hernani; Ribeiro, J.E.; Santos, J.V. Araújo; Vaz, M.A.P.; Gomes, J.F. SilvaThis paper proposes a real time damage identification method based on the perturbation analysis of the rotation field, which are measured using shearography technique. A particular case of phase modulation method is applied to the interference pattern in order to improve the spatial resolution of the rotation field. A program was developed in Matlab® platform for digital recording the information capture by CCD camera and post-processing the data using dedicated image techniques. The phase filter and unwrapping algorithms were optimized to allow the visualization at video rate the full-field rotations fields. For small internal damages in laminated composite plates, the results show a superior performance of the proposed technique in relation to the classical raw fringe analysis.
- Damage identification using real time rotating field analysisPublication . Lopes, Hernani; Ribeiro, J.E.; Santos, J.V. Araújo; Vaz, M.A.P.; Gomes, J.F. SilvaThis paper proposes a real time damage identification method based on the perturbation analysis of the rotation field, which are measured using shearography technique. A particular case of phase modulation method is applied to the interference pattern in order to improve the spatial resolution of the rotation field. A program was developed in Matlab® platform for digital recording the information capture by CCD camera and post-processing the data using dedicated image techniques. The phase filter and unwrapping algorithms were optimized to allow the visualization at video rate the full-field rotations fields. For small internal damages in laminated composite plates, the results show a superior performance of the proposed technique in relation to the classical raw fringe analysis.
- Displacement and strain field assessment of PDMS using digital image correlationPublication . Mendonça, Bebiana Alexandra Bragança; Ribeiro, J.E.; Lopes, Hernani; Martins, Pedro; Vaz, M.A.P.; Gomes, J.F. SilvaThe main goal of this work is the characterization of the hyper-elastic mechanical behaviour of PDMS. The special specimens of PDMS (Sylgard® 184) were tested in a bi-axial tensile machine. During the tensile test was used a commercial digital image correlation system (ARAMIS of GOM) to obtain de displacement and strain fields. These measurements are compared with numerical simulations which use the most popular algorithms of constitutive models.
- Displacement and strain field assessment of PDMS using digital image correlationPublication . Mendonça, Bebiana Alexandra Bragança; Ribeiro, J.E.; Lopes, Hernani; Martins, Pedro; Vaz, M.A.P.; Gomes, J.F. SilvaThe main goal of this work is to characterize the hyper-elastic mechanical behaviour of PDMS. For that, were made-up special specimens of PDMS (Sylgard® 184) for test them in bi-axial tensile machine. During the tensile test was used a commercial digital image correlation system (ARAMIS of GOM) to obtain de displacement and strain fields. These measurements are compared with numerical simulations which uses the more popular algorithms of constitutive models.
- 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.
- Numerical simulation of wall deformation in an aneurysm modelPublication . Ribeiro, J.E.; Lima, Rui A.; Lopes, Hernani; Vaz, M.A.P.; Gomes, J.F. SilvaThis work presents the numerical assessment of the deformation of an artery wall with and without an aneurism. The simulations consider the hyper-elastic behaviour of the artery tissues, taken in consideration the properties of polydimethylsiloxane (PDMS), which are more similar to the biological tissues. The numerical simulations were performed using the commercial finite element routines ANSYS®, by considering the inner the artery fluid flow and the consequent pressure is used to simulate the wall deformation.
- Numerical simulation of wall deformation in an aneurysm modelPublication . Ribeiro, J.E.; Lima, Rui A.; Lopes, Hernani; Vaz, M.A.P.; Gomes, J.F. SilvaThis work presents the numerical deformation of an artery wall with and without an aneurism. The simulations consider the hyper-elastic behaviour of the artery tissues, taken in consideration the properties of polydimethylsiloxane (PDMS), which are more similar to the biological tissues. The numerical simulations were performed using the commercial finite element method ANSYS®, by considering the inner the artery fluid flow and the consequent pressure is used to simulate the wall deformation.
- Unwrapping techniques for speckle phase maps: study and comparison of the performance of principal methodsPublication . Lopes, Hernani; Ribeiro, J.E.; Vaz, M.A.P.; Gomes, J.F. SilvaHolographic interferometry (HI) techniques are powerful tools for experimental mechanics which can be used to assess displacement fields on a loaded object surface. Used with no contact and high resolution HI can be combined with image methods for data analysis. Nevertheless, the speckle should be fully resolved by the image detector to digitally record an interferogram. This leads to a noisy recording which difficult it’s post-processing. Each measurement with HI ends normally in a phase map computation representing the object displacement. Phase calculation algorithms are based on spatial or temporal phase modulation and lead to wrapped phase maps. To obtain the continuous phase distribution several solutions have been implemented. This paper describes the main filtering and unwrapping algorithms available and compares it´s performance to solve discontinuities in noisy phase maps.