A new displacement measurement technique is proposed in a stereovision setup, which uses the object of interest as the support of the correlation process. This procedure leads to a global approach to stereocorrelation. The method is presented in its general formulation and is then particularized to the case of non uniform rational B-splines (NURBS). The displacement field is directly measured as a 3D field expressed in a NURBS basis consistent with the existing geometric model. The kinematic measurements are validated against prescribed displacements of a machined Bezier patch. The feasibility in an industrial context is shown with the analysis of 3D displacement fields of a 2- m2 automotive roof panel during a welding operation.

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CAD-based Displacement Measurements with Stereo-DIC

Since the turn of the century experimental solid mechanics has undergone major changes with the generalized use of images. The number of acquired data has literally exploded and one of today’s challenges is related to the saturation of mining procedures through such big data sets. With respect to digital image/volume correlation one of tomorrow’s pathways is to better control and master this data flow with procedures that are optimized for extracting the sought information with minimum uncertainties and maximum robustness. In this paper emphasis is put on various hierarchical identification procedures. Based on such structures a posteriori model/data reductions are performed in order to ease and make the exploitation of the experimental information far more efficient. Some possibilities related to other model order reduction techniques like the proper generalized decomposition are discussed and new opportunities are sketched.

/pdf/big-data-in-experimental-mechanics-and-model-order-reduction-3onwd8c18a.pdf

Big Data in Experimental Mechanics and Model Order Reduction: Today’s Challenges and Tomorrow’s Opportunities

It is proposed to develop a multiview framework to perform stereocorrelation by resorting to isogeometric descriptions of the observed three-dimensional surfaces. Once the three-dimensional surface...

/pdf/shape-displacement-and-mechanical-properties-from-38s5rkod29.pdf

Shape, displacement and mechanical properties from isogeometric multiview stereocorrelation

Stereo digital image correlation (stereo-DIC) is in wide-spread use for full-field shape, motion and deformation-measurements. However there are very few papers investigating the influence of the setup on the measurement uncertainty. This is mainly due to the highly non-linear measurement chain involving both optical and numerical aspects, making it difficult to investigate how error sources are propagated through the stereo-DIC chain. Indeed, it is impossible to separate all the error sources that are present during a physical measurement. This paper tries to investigate a selection of error sources that are present during experiments. This is based on a simulator introduced in a previous article (Balcaen et al., Exp Mech, 1–16 2017) and briefly reviewed here. Based on these simulations we suggest some “best-practices” guidelines of optimal stereo-DIC setups.

/pdf/stereo-dic-uncertainty-quantification-based-on-simulated-264pssuz3g.pdf

Stereo-DIC Uncertainty Quantification based on Simulated Images

The use of Finite Element meshes in Digital Image Correlation (FE-DIC) is now widespread in experimental mechanics. Up to now FE have been much less used in Stereo-DIC. The first goal of this paper is to explain in details how to use FE in Stereo-DIC using a formulation in the physical coordinate system. More precisely, it is shown how to perform the calibration of possibly nonlinear models, shape and displacement measurement based on a FE mesh. In addition it is shown that with such a framework it is possible to regularise the measurement with a FE model based on the same mesh. For instance, using this technique, it is shown that it is possible to measure the rotation field of a bending plate in addition to its displacement.

/pdf/finite-element-stereo-digital-image-correlation-framework-210d12ncar.pdf

Finite Element Stereo Digital Image Correlation: Framework and Mechanical Regularization

A new calibration procedure is proposed for a stereovision setup It uses the object of interest as the calibration target, provided the observed surface has a known definition (eg, its CAD model) In a first step, the transformation matrices needed for the calibration of the setup are determined assuming that the object conforms to its CAD model Then the 3D shape of the surface of interest is evaluated by deforming the a priori given freeform surface These two steps are performed via an integrated approach to stereoDIC The measured 3D shape of a machined Bezier patch is validated against data obtained by a coordinate measuring machine The feasibility of the calibration method’s application to large surfaces is shown with the analysis of a 2-m2 automotive roof panel

/pdf/cad-based-calibration-and-shape-measurement-with-stereodic-16dwsbrdao.pdf

CAD-based calibration and shape measurement with stereoDIC

The aim of this study is to measure the (complex) shape of an object by using a priori information given by its CAD representation in a 3D-DIC framework. In order to follow a 3D object during its deformation and to determine 3D surface displacement fields, a first measurement of the object shape is necessary. The main goal of the present method is to obtain a CAD representation of this measurement by updating the CAD reference via a global approach to 3D-DIC. Although in the majority of the shape measurement methods a cloud of points is obtained and subsequently interpolated to create a continuous description of the surface, CAD-based stereoDIC is devised to directly measure a 3D shape described by NURBS. This approach allows a direct link to be established between the theoretical CAD model and its true geometry thereby yielding the metrology of the measured surface in the CAD language.

B. Beaubier

Papers

CAD-based calibration and shape measurement with stereoDIC

Shape Measurement Using CAD-Based Stereo-DIC