Filtern
Dokumenttyp
Sprache
- Englisch (2)
Referierte Publikation
- ja (2) (entfernen)
Schlagworte
- Flat bottom holes (2) (entfernen)
Organisationseinheit der BAM
Iterative numerical 2D-modelling for quantification of material defects by pulsed thermography
(2019)
This paper presents a method to quantify the geometry of defects such as flat bottom holes (FBH) and notches in opaque materials by a pulse thermography (PT) experiment and a numerical model. The aim was to precisely describe PT experiments in reflection configuration with a simple and fast numerical model in order to use this model and a fit algorithm to quantify defects within the material. The algorithm minimizes the difference between the time sequence of a line shaped region of interest (ROI) on the surface (above the defect) from the PT experiment and the numerical data. Therefore, the experimental data can be reconstructed with the numerical model. In this way, the defect depth of a notch or FBH and its width or diameter was determined simultaneously. A laser was used for heating which was widened to a top hat spatial profile to ensure homogeneous illumination (rectangular impulse profile in time). The numerical simulation considers heating conditions and takes thermal losses due to convection and radiation into account. We quantified the geometry of FBH and notches in steel and polyvinyl chloride plasticized (PVC-U) materials with an accuracy of < 5 %.
Lockin thermography as well as flash thermography are very well suited for non-destructive testing and characterisation of inhomogeneities and damage in CFRP structures. Both methods are applied more and more in research and industry, but until know it is not clear which are the advantages of one method against the other. In
this paper, results of two research projects concerning the validation and standardisation of both methods are presented. Three different types of CFRP test specimens consisting of well-defined flat bottom holes, of artificial delaminations made of PTFE plates embedded in CFRP and of real impact damage have been investigated systematically with flash and lockin excitation. Here, the phase images of both methods are compared qualitatively as well as quantitatively.