TY - CONF A1 - Bernegger, Raphael A1 - Altenburg, Simon A1 - Maierhofer, Christiane T1 - Numerical 2D model to quantify defects in semitransparent materials by pulsed thermography N2 - Pulsed thermography is a well-known non-destructive testing technique and has proven to be a valuable tool for evaluation of material defects. Material defects are often simulated by flat-bottom holes (FBH) or grooves. Typically, analytical 1D models are used to determine the defect depth of FBHs, grooves or delaminations. However, these models cannot take into account lateral heat flows, or only to a limited extent (semi-empirical model). Their applicability is therefore limited by the FBHs aspect ratio (diameter to remaining wall thickness), to ensure that the heat flow above the defect can still be described one-dimensionally. Additionally, the surfaces of semi-transparent materials have to be blackened to absorb the radiation energy on the surface of the material. Without surface coatings, these models cannot be used for semi-transparent materials. Available 1D analytical models for determination of sample or layer thicknesses also do not take into account lateral heat flows. Here, we present an approach for quantitative determination of the geometry of FBHs or grooves in semi-transparent materials by considering lateral heat flow. For this purpose, the results of a numerical 2D model are fitted to experimental data, e.g., to determine simultaneously the defect depth of a FBH or groove and its diameter or width, respectively. The model considers semi-transparency of the sample within the wavelength range of the excitation source as well as of the IR camera and thermal losses at its surfaces. Heat transport by radiation within the sample is neglected. It supports the use of an arbitrary temporal shape of the heating pulse to properly describe the measurement conditions for different heat sources. T2 - Progress in Photoacoustic & Photothermal Phenomena CY - Erice, Italy DA - 06.09.2018 KW - Pulse thermography KW - Numerical modelling KW - 2D model KW - Data reconstruction KW - Flat bottom holes KW - Notches KW - Semitrasnparent materials PY - 2018 AN - OPUS4-46105 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bernegger, Raphael A1 - Altenburg, Simon A1 - Röllig, Mathias A1 - Maierhofer, Christiane T1 - Thickness determination in active thermography for one and multilayer semitransparent materials N2 - Flash thermography is a well-known non-destructive testing technique and has proven to be a valuable tool to examine material defects and to determine thermal material parameters and the thickness of test specimens. However, its application to semitransparent materials is quite new and challenging, especially for semitransparent multilayer materials like glass fiber reinforced polymer (GFRP). Here, in order to deduce the thickness of coated and uncoated semitransparent specimens as well as the depth of defects in such specimens by means of flash thermography, we apply an analytical model based on the quadrupole method by Maillet et al. to calculate the temperature development during the flash thermography experiment. The model considers semitransparency of the sample and thermal losses at its surface. It supports the use of an arbitrary temporal shape of the heating pulse to properly describe the measurement conditions for different heat sources. By fitting the results of the analytical model to experimental data it is possible to determine the thickness of the specimen, provided the thermal material parameters are known, e.g., by calibration experiments with samples of the same material with known thickness. We will show that thickness determination of semitransparent test specimens is possible both for transmission and reflection configuration, with and without a blackened sample surface at either front or back side of the sample. As an example, Figure 1 shows the experimentally obtained temperature differences of the surface of a blackened GFRP sample in transmission configuration with the coating facing the flash lamp (usual configuration, (a)) or the infrared camera (unusual configuration, (b)). Using the proposed method, the thickness of the sample can be determined for both configurations. T2 - 19th International Conference on Photoacoustic and Photothermal Phenomena CY - Bilbao, Spain DA - 16.07.2017 KW - Semitransparent KW - Pulse thermography KW - Absorption coefficient KW - GFRP KW - Heterogeneous KW - Analytical model PY - 2017 AN - OPUS4-43409 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bernegger, Raphael A1 - Altenburg, Simon A1 - Maierhofer, Christiane T1 - Iterative numerical 2D-modeling for quantification of material defects by pulsed thermography N2 - Pulsed thermography is a well-known non-destructive testing technique and has proven to be a valuable tool for examination of material defects. Typically, analytical 1D models are used to determine the defect depth of flat-bottom holes (FBH), grooves or delamination. However, these models cannot take into account lateral heat flows, or only to a limited extent. They are therefore limited by the FBHs aspect ratio (diameter to remaining wall thickness), to ensure that the heat flow above the defect can still be described one-dimensionally. Here, we present an approach for quantitative determination of the geometry for FBH or grooves. For this purpose, the results of a numerical 2D model are fitted to experimental data, e.g., to determine simultaneously the defect depth of a groove or FBH and its diameter of width. The model takes lateral heat flows into account as well as thermal losses. Figure 1 shows the temperature increase of a pulsed thermography measurement at three different locations on the sample. The numerical model is fitted to the experimental data (red lines) to quantify the groove. The numerical simulation matches the experimental data well. T2 - 45th Annual Review of Progress in Quantitative Nondestructive Evaluation CY - Burlington, VT, USA DA - 15.07.2018 KW - Opaque materials KW - Pulse thermography KW - Numerical modelling KW - 2D model KW - Data reconstruction KW - Flat bottom holes KW - Notches PY - 2018 AN - OPUS4-46353 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bernegger, Raphael A1 - Altenburg, Simon A1 - Maierhofer, Christiane T1 - Pulsed thermography on semitransparent materials - what has to be considered? N2 - Pulsed thermography is a well-known non-destructive testing technique and has proven to be a valuable tool for examination of material defects, to determine thermal material parameters, and the thickness of test specimens through calibration or mathematical models. However, the application to semitransparent materials is quite new and demanding, especially for semitransparent materials like epoxy, polyamide 12, or glass fiber reinforced polymers with epoxy or polyamide matrix. In order to describe the temporal temperature evolution in such materials, which are recorded with an infrared camera during pulse thermography experiments, much more influences have to be considered, compared to opaque materials: - The wavelength of the excitation source and the spectral range of the infrared camera - The angles between the specimen, the excitation source and the infrared camera - The area behind the specimen - The roughness of the material surface - The scattering mechanism within the material Here, we will consider all these influences and describe how they can be treated mathematically in analytical or numerical models (using COMSOL Multiphysics software). These models describe the temperature development during the pulse thermography experiment in reflection and transmission configuration. By fitting the results of the mathematical models to experimental data it is possible to determine the thickness or the optical and thermal properties of the specimen. T2 - 20-th International Conference on Photoacoustic and Photothermal Phenomena CY - Moscow, Russia DA - 07.07.2019 KW - Numerical simulation KW - Pulsed thermography KW - Semitransparent KW - Analytical model KW - Delamination KW - GFRP PY - 2019 AN - OPUS4-49215 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bernegger, Raphael A1 - Altenburg, Simon A1 - Maierhofer, Christiane T1 - Analytisches Modell zur Bestimmung der Schichtdicke für opake und semitransparente Materialien mittels Impulsthermografie N2 - Impulsthermografie ist ein bekanntes zerstörungsfreies Prüfverfahren, welches sehr gut geeignet ist, um geometrische Eigenschaften von Materialfehler, thermische Materialparameter sowie die Dicke von Objekten zu bestimmen. Die Anwendung auf semitransparente Materialien ist jedoch recht neu und anspruchsvoll, insbesondere für semitransparente Mehrschichtmaterialien wie glasfaserverstärkte Kunststoffe (GFK). Um die Dicke beschichteter und unbeschichteter semitransparenten Proben mittels Impuls-Thermografie bestimmen zu können, verwenden wir ein analytisches Modell, welches auf der Quadrupol-Methode basiert. Unser 1D-Modell berücksichtigt: • die Semitransparenz der Probe, • die Wärmeverluste an den Seitenflächen, • beliebige zeitlichen Form des Heizimpulses (um die Messbedingungen für verschiedene Wärmequellen korrekt zu beschreiben), • mögliche Flächenabsorption an der Vorder- oder Rückseite (für beschichtete Proben), • und Mehrschichtsysteme. Durch Anpassung der Ergebnisse des analytischen Modells an experimentelle Daten ist es möglich, die Dicke der Probe zu bestimmen, sofern die thermischen Materialparameter bekannt sind. Diese können z.B. durch Kalibrierungsmessungen an Proben desselben Materials mit bekannter Dicke bestimmt werden. T2 - Physikalisch-Technische Bundesanstalt CY - Berlin, Germany DA - 06.12.2017 KW - Schichtdicke KW - Analytisches Modell KW - Impulsthermografie KW - 1D-Modell KW - Semitransparent PY - 2017 AN - OPUS4-43410 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -