Departamento de Ingeniería Mecánica y Minera
URI permanente para esta comunidadhttps://hdl.handle.net/10953/41
En esta Comunidad se recogen los documentos generados por el Departamento de Ingeniería Mecánica y Minera y que cumplen los requisitos de Copyright para su difusión en acceso abierto.
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Examinando Departamento de Ingeniería Mecánica y Minera por Autor "Díaz, Francisco"
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Ítem An alternative approach for improving DIC by using out-of-plane displacement information(Elsevier, 2020-05-01) Siegmann, Philip; Felipe-Sesé, Luis; Díaz, FranciscoA new approach to perform 2D Digital Image Correlation (DIC) on objects that are subjected to large out-of-plane displacements is presented. It employs out-of-plane information to distort the speckle images of the reference and the deformed surface, increasing their similarity and therefore their sub-set cross-correlation peaks. The new approach is implemented using the combined Fringe Projection and 2D-DIC technique on two experiments: The buckling of an initial flat plate, and the rotation of the reference surface towards the camera from 0° to 60°. In both cases large speckle distortions are produced due to two issues, the lens magnification and the surface tilting. The first speckle distortion is applied to the deformed image to perform the lens magnification correction, and the second speckle distortion is applied to the reference image. The obtained distorted speckle images become very similar, allowing to successfully compute corresponding pixels between both images in a simple way (i.e. without nonlinear minimization processes). For this propose, an analytical iterative equation is derived to determine pixel displacements due to out-of-plane surface tilting. The resulting displacements are compared with those obtained by the conventional procedure, applying 2D-DIC (using open source Ncorr software) on the non-distorted speckle images and then making the lens magnification correction. The novel procedure proposed makes it possible to successfully find the corresponding pixels at the reference surface for out-of-plane rotations of 55° and 60° for which Ncorr failed. 3D-DIC (using commercial VIC software) is also employed to validate the results.Ítem Evaluation of modal identification under base motion excitation using vision techniques(ELSEVIER, 2022-11) Molina-Viedma, Ángel; Felipe-Sesé, Luis; Pastor-Cintas, Manuel; López-Alba, Elías; Díaz, FranciscoIn certain situations, employing a movable base acting as the excitation of a mechanical system is the best or even the only way to determine the response model for modal analysis. However, the obtained transmissibility functions must be modified prior to modal identification with a conventional procedure based on frequency response functions. Moreover, when employing vision techniques, the response curves are noisier and even poorly defined as the sensitivity is significantly lower than traditional sensors. Using the right model for curve-fitting is particularly relevant in this case. The current study performs an analysis of the adaptation of transmissibility functions, obtained by a vision technique, to improve the accuracy of the modal data estimation with conventional procedures. Two sets of transmissibility functions were evaluated: the originally obtained in the experiment, and the adapted one. After modal identification, significant differences were found concerning mode shapes and curve synthesis. The adaptation improved the accuracy of the identification in all the measurement points, proved by statistical indicators of the curve-fitting procedure like the correlation coefficient and the error between the synthesised and the experimental curves.Ítem Exploiting phase-based motion magnification for the measurement of subtle 3D deformation maps with FP+ 2D-DIC(Elsevier, 2022-05-31) Felipe-Sesé, Luis; Molina-Viedma, Ángel J.; Pastor-Cintas, Manuel; López-Alba, Elías; Díaz, FranciscoPhase-Based Motion Magnification (PBMM) is an effective methodology to visualise imperceptible phenomena based on magnifying periodic subtle movements on image sequences. Moreover, the integration of the optical techniques Fringe Projection and 2D Digital Image Correlation (FP + 2D-DIC) make it possible to obtain 3D displacement maps employing a single camera. In this study, the integration of PBMM with FP + 2D-DIC is exploited for the determination of subtle 3D displacements. An initial solid-rigid test validates of the combination of those techniques. A later test, employing a cantilever beam, demonstrates its correct performing in the determining of Operational Deflection Shapes. In both cases, the results are compared with those obtained with 3D-DIC and Scanning Laser Doppler Vibrometer (SLDV) to evaluate the relation between the magnification factor and the result obtained. Finally, the potential of the proposed integration for the determination of complex mode shapes is demonstrated by obtaining the ODSs of an industrial component.Ítem Full-field 3D displacement and strain analysis during low energy impact tests employing a single-camera system(Elsevier, 2020) Felipe-Sesé, Luis; López-Alba, Elías; Díaz, FranciscoCharacterising materials behaviour during dynamics events such as impact require several features related to monitoring and instrumentation which find in full-field techniques one of the main responses due to high spatial and, nowadays, also temporal resolution. 3D-Digital Image Correlation has provided an interesting tool to evaluate the material response during impact testing. It contributes with displacement and strain fields at high frame rates, which represents enormous potential for subsequent analysis. However, 3D-DIC also presents some issues which may condition the experimentation. The first of them is the requirement of a stereoscopic optical system, which lead to important economic issues if high speed cameras are required. Secondly, certain impact arrangements have limited space which make complicated to dispose of a proper stereoscopic system observing an area of interest with a suitable angle that makes it possible r a successful processing. In this work, a recent procedure combining Fringe projection and 2D-DIC is presented as an alternative for impact testing analysis. As main characteristic, the optical arrangement is simplified to only one high speed camera and an additional simple LCD projector which makes it easier the experimentation, reducing significantly the setup cost. To demonstrate that capabilities of FP+2D-DIC as a simpler approach with results comparable to those obtained with 3D-DIC, in this work it was analysed 2, 3, 4, and 5 mm thickness aluminium plates under low speed impacts with different energy levels. Impacts were performed employing an impact tower with a hemispherical impactor, connected to a load cell. During the impact, displacement and strain maps were measured at the non-impacted face of the specimen, using a single camera system implementing the combination of FP and 2D-DIC techniques. Permanent displacement and strain maps were validated with those obtained with a 3D-DIC system, supporting the potential of this FP+2D-DIC approach for impact testing.Ítem On the fracture behaviour of fibre-reinforced gypsum using micro and macro polymer fibres(Elsevier, 2020-05-30) Suárez Guerra, Fernando; Felipe-Sesé, Luis; Díaz, Francisco; Galvez, Jaime; García-Alberti, Marcos GarcíaGypsum is the most widely used material as interior lining in buildings due to its low cost and good habitability conditions. The use of fibres as randomly distributed reinforcement of quasibrittle matrices, such as gypsum, remarkably improve the material behaviour under tensile stresses. In this work, the fracture behaviour of gypsum specimens reinforced with several types of polymer fibres was assessed, for one of them three fibre lengths were studied. Three types of polymer fibres were employed, with one of them being of microscopic scale and the other two of macroscopic scale. The mechanical behaviour of each mix was studied by means of three-point bending tests and compression tests that were analysed using a digital image correlation system. To study the influence of the fibre length, pull-out tests were also performed. The size, surface finishing and length of the fibres strongly affect the material properties and the way that the fracture mechanisms are developed.