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Detection, characterisation and measurement of weld defects by active thermography and macro-photogrammetry.

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There are many types of defects in welded joints, each of them is different and differ in their effects and dangerousness, and can produce different types of failures under certain mechanical stresses. For this reason, a new non-destructive testing (NDT) procedure to detect and characterise these defects is proposed, which is part of the research line led jointly by the Applied Geotechnology Group of the University of Vigo (http://geotech.webs.uvigo.es/) and the TIDOP Group of the University of Salamanca.

With the use of active thermography, cracks in welds can be detected and classified. Image 1 shows the implementation of the procedure used to detect a “toe crack”. These types of crack are characterised by incisions that penetrate into the interior of the material volume and this characteristic makes it possible to distinguish them from other types of crack. The procedure ends with a 3D thermal graph in which the thermal profile of the defect and the existence of the aforementioned incisions (peaks) can be seen.

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On the other hand, the crack is analysed using a photogrammetric procedure consisting of the construction of point clouds from standard photographic images and their subsequent meshing. With this procedure, the study of its different zones and depths can be carried out; with this, it is possible to take measurements with an accuracy of tenths of a millimetre and also to export the solid model to a Finite Element Method (FEM) software that allows a more in-depth study to predict the failure from the point of view of the strength of materials.

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However, the use of this procedure is not limited to the detection, characterisation and measurement of cracks; it can also be used to assess many other types of defects in welded joints against quality standards.