TY - CONF A1 - Srinivasan, Krishnanand A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Laser Metal Deposition of Rene 80 – Microstructure and Solidification Behaviour Modelling N2 - New developments in nickel-based superalloys and production methods, such as the use of additive manufacturing (AM), can result in innovative designs for turbines. It is crucial to understand how the material behaves during the AM process to advance industrial use of these techniques. An analytical model based on reaction-diffusion formalism is developed to better explain the solidification behavior of the material during laser metal deposition (LMD). The well-known Scheil-Gulliver theory has some drawbacks, such as the assumption of equilibrium at the solid-liquid interface, which is addressed by this method. The solidified fractions under the Scheil model and the pure equilibrium model are calculated using CALPHAD simulations. Differential scanning calorimeter is used to measure the heat flow during the solid-liquid phase transformation, the result of which is further converted to solidified fractions. The analytical model is compared with all the other models for validation. T2 - Lasers in Manufacturing Conference 2023 CY - Munich, Germany DA - 26.06.2023 KW - Additive manufacturing KW - Laser metal deposition KW - Solidification behaviour KW - Analytical model KW - Nickel-based superalloy PY - 2023 SP - 1 EP - 10 AN - OPUS4-58612 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bernegger, Raphael A1 - Maierhofer, Christiane A1 - Altenburg, Simon T1 - Quantification of delaminations in semitransparent solids using pulsed thermography and mathematical 1D models N2 - Material defects in fiber reinforced polymers such as delaminations can rapidly degrade the material properties or can lead to the failure of a component. Pulse thermography (PT) has proven to be a valuable tool to identify and quantify such defects in opaque materials. However, quantification of delaminations within semitransparent materials is extremely challenging. We present an approach to quantify delaminations within materials being semitransparent within the wavelength ranges of the optical excitation sources as well as of the infrared (IR) camera. PT experimental data of a glass fiber reinforced polymer with a real delamination within the material were reconstructed by one dimensional (1D) mathematical models. These models describe the heat diffusion within the material and consider semitransparency to the excitation source as well to the IR camera, thermal losses at the samples surfaces and a thermal contact resistance between the two layers describing the delamination. By fitting the models to the PT data, we were able to determine the depth of the delamination very accurately. Additionally, we analyzed synthetic PT data from a 2D simulation with our 1D-models to show how the thermal contact resistance is influenced by lateral heat flow within the material. KW - Pulsed thermography KW - Quantification KW - Numerical simulation KW - Analytical model KW - Semitransparent KW - GFRP KW - Delamination PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-505766 VL - 41 IS - 5 SP - Article number: 67 PB - Springer AN - OPUS4-50576 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 - JOUR A1 - Bernegger, Raphael A1 - Altenburg, Simon A1 - Roellig, Mathias A1 - Maierhofer, Christiane T1 - Applicability of a 1D analytical model for pulse thermography of laterally heterogeneous semitransparent materials N2 - Pulse thermography (PT) has proven to be a valuable non-destructive testing method to identify and quantify defects in fiber-reinforced polymers. To perform a quantitative defect characterization, the heat diffusion within the material as well as the material parameters must be known. The heterogeneous material structure of glass fiber-reinforced polymers (GFRP) as well as the semitransparency of the material for optical excitation sources of PT is still challenging. For homogeneous semitransparent materials, 1D analytical models describing the temperature distribution are available. Here, we present an analytical approach to model PT for laterally inhomogeneous semitransparent materials.We show the validity of the model by considering different configurations of the optical heating source, the IR camera, and the differently coated GFRP sample. The model considers the lateral inhomogeneity of the semitransparency by an additional absorption coefficient. It includes additional effects such as thermal losses at the samples surfaces, multilayer systems with thermal contact resistance, and a finite duration of the heating pulse. By using a sufficient complexity of the analytical model, similar values of the material parameters were found for all six investigated configurations by numerical fitting. KW - Absorption coefficient KW - Analytical model KW - GFRP KW - Heterogeneous KW - Pulse thermography KW - Semitransparent PY - 2018 U6 - https://doi.org/10.1007/s10765-018-2362-7 SN - 0195-928X SN - 1572-9567 VL - 39 IS - 3 SP - Article 39, ICPPP 19, 1 EP - 17 PB - Springer International Publishing AG AN - OPUS4-44003 LA - eng 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 - Altenburg, Simon A1 - Bernegger, Raphael A1 - Krankenhagen, Rainer T1 - Analytical modelling of semitransparent solids for flash thermography with absorption coefficient dispersion N2 - Pulse and flash thermography are experimental techniques which are widely used in the field of non-destructive evaluation for materials characterization and defect detection. We recently showed that it is possible to quantitatively determine the thickness of semitransparent polymeric solids by fitting of results of an analytical model to experimental flash thermography data, for both transmission and reflection geometry. However, depending on the chosen experimental geometry, different effective optical absorption coefficients (i.e., penetration depths of the heating light) had to be utilized in the model in order to properly fit the experimental data. Here we show that this effect is caused by the wavelength dependency of the absorption coefficient of the sample material. We present an extension of the analytical model to incorporate this dispersion. Even accounting for only two different values of the absorption coefficient, the experimental results from both measurement geometries can be fitted by a single set of absorption coefficients. Additionally, the deviations between experimental data and fit are reduced compared to a single optimized effective absorption coefficient. This work is part of the ZIM-project KF2201089AT4 and is funded by the German Federal Ministry for Economic Affairs and Energy due to an order of the German Bundestag. T2 - 19th International Conference on Photoacoustic and Photothermal Phenomena CY - Bilbao, Spain DA - 16.07.2017 KW - Analytical model KW - Semitransparency KW - Thermography PY - 2017 AN - OPUS4-41084 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Altenburg, Simon A1 - Krankenhagen, Rainer T1 - Energy density detector for optical heat sources in step-heating thermography N2 - In this work, we describe the extension of the applicability of a point-shaped energy density detector formerly only applicable for flash lamp excitation to optical heat sources for step-heating thermography, such as IR lamps or halogen lamps. Such continuous heat sources are often used in active thermography testing, when materials with low thermal diffusivity and specimens with large heat capacity are examined and large amounts of energy have to be deposited. Here, the temperature transient at the sensor surface is recorded by the infrared camera that is already present. The energy (power) input into the investigated specimen can be determined during the following data evaluation by fitting the results of an analytical model to the experimental data. T2 - IRS² 2017 CY - Nürnberg, Germany DA - 30.05.2017 KW - Analytical model KW - Energy detector KW - Thermography PY - 2017 AN - OPUS4-40470 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Altenburg, Simon A1 - Weber, H. A1 - Krankenhagen, Rainer T1 - Thickness determination of semitransparent solids using flash thermography and an analytical model N2 - As groundwork for thickness determination of polymeric surface protection systems for concrete, we present a method for measuring the thickness of isolated semitransparent solids using flash thermography both in transmission and reflection configuration. Since standard models do not capture semitransparency, an advanced analytical model by Salazar et al. is applied. Physical material parameters are deduced by fitting experimental data from samples of well-known thickness. Using those, the thickness of samples of the material can be obtained by fitting, as demonstrated for different semitransparent polymer materials. KW - Analytical model KW - Concrete KW - Semitransparency KW - Surface protection KW - Thermography KW - Thickness PY - 2017 U6 - https://doi.org/10.1080/17686733.2017.1331655 SN - 1768-6733 SN - 2116-7176 VL - 15 IS - 1 SP - 95 EP - 105 PB - Taylor and Francis CY - Abingdon, UK AN - OPUS4-40468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Altenburg, Simon A1 - Krankenhagen, Rainer A1 - Bavendiek, F. T1 - Thickness determination of polymeric multilayer surface protection systems for concrete by means of pulse thermography N2 - For thickness determination of polymer based surface protection systems for concrete surfaces, so far only destructive measurement techniques are available. Pulse thermography appears to be well suited for non-destructive thickness evaluation in these systems. Here, we present first results of the development of a respective measurement and analysis procedure. Since surface protection systems consist of a number of layers, a model for the calculation of the surface temperature of a multi-layer structure on a semi-infinite (concrete) substrate in pulse thermography setup was developed. It considers semitransparency of the upmost layer and thermal losses at the surface. It also supports the use of an arbitrary temporal shape of the heating pulse to properly describe the measurement conditions for different heat sources. Simulations for one and three layers on the substrate are presented and first results from fitting the model to experimental data for thickness determination and verification of the model are presented. T2 - QNDE conference 2016 - Review of progress in quantitative nondestructive evaluation CY - Atlanta, GA, USA DA - 18.07.2016 KW - Analytical model KW - Concrete KW - Semitransparency KW - Surface protection KW - Thermography KW - Thickness PY - 2017 SN - 978-0-7354-1474-7 U6 - https://doi.org/10.1063/1.4974669 SN - 0094-243X VL - 1806 IS - 1 SP - Article UNSP 100004, 1 EP - 10 PB - AIP Publishing AN - OPUS4-39300 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Altenburg, Simon A1 - Krankenhagen, Rainer A1 - Weber, H. T1 - Thickness determination of semitransparent isolated solids using the flash method and an analytical model N2 - As groundwork for thickness determination of polymeric surface protection systems for concrete, we present a method for measuring the thickness of isolated semitransparent solids using pulse thermography both in Transmission and reflection geometry. Since standard models do not capture semitransparency, an advanced analytical model by Salazar et al. is applied. Physical material parameters are deduced by fitting experimental data from samples of well-known thickness. Using those, the thickness of samples of the material can be obtained by fitting, as demonstrated for different semitransparent polymer materials. T2 - QIRT 2016 CY - Gdańsk, Poland DA - 04.07.2016 KW - Analytical model KW - Concrete KW - Flash thermography KW - Semitransparency KW - Surface protection KW - Thermography KW - Thickness PY - 2016 U6 - https://doi.org/10.21611/qirt.2016.001 SN - 2371-4085 VL - 2016 SP - 71 EP - 78 AN - OPUS4-37200 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -