TY - JOUR A1 - Ahmadi, Samim A1 - Thummerer, G. A1 - Breitwieser, S. A1 - Mayr, G. A1 - Lecompagnon, Julien A1 - Burgholzer, P. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Multi-dimensional reconstruction of internal defects in additively manufactured steel using photothermal super resolution combined with virtual wave based image processing JF - IEEE transactions on industrial informatics N2 - We combine three different approaches to greatly enhance the defect reconstruction ability of active thermographic testing. As experimental approach, laser-based structured illumination is performed in a step-wise manner. As an intermediate signal processing step, the virtual wave concept is used in order to effectively convert the notoriously difficult to solve diffusion-based inverse problem into a somewhat milder wavebased inverse problem. As a final step, a compressed-sensing based optimization procedure is applied which efficiently solves the inverse problem by making advantage of the joint sparsity of multiple blind measurements. To evaluate our proposed processing technique, we investigate an additively manufactured stainless steel sample with eight internal defects. The concerted super resolution approach is compared to conventional thermographic reconstruction techniques and shows an at least four times better spatial resolution. KW - Active thermography KW - Additive manufacturing KW - Stainless steel KW - ADMM KW - Block regularization KW - Internal defects KW - Joint sparsity KW - Laser excitation KW - Multi-dimensional reconstruction KW - Photothermal super resolution KW - Virtual waves PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-525330 DO - https://doi.org/10.1109/tii.2021.3054411 SN - 1551-3203 SN - 1941-0050 VL - 17 IS - 11 SP - 7368 EP - 7378 PB - IEEE CY - New York, NY AN - OPUS4-52533 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jonietz, Florian A1 - Myrach, Philipp A1 - Suwala, H. A1 - Ziegler, Mathias T1 - Examination of Spot Welded Joints with Active Thermography JF - Journal of Nondestructive Evaluation N2 - The method described here allows to determine the size of the thermal contact between two metal sheets joined by spot welding. This size is a measure for the size of the weld nugget, i.e. the zone melted during the welding process, and thus the quality of the welded joint. The method applies active thermography in transmission or reflection setup. Especially the reflection setup offers an attractive possibility for non-destructive testing when components can be accessed from one side only. The spot weld region is optically heated by laser or flash light radiation. The weld nugget provides the mechanical joint, but also constitutes a thermal bridge between the two welded sheets. The latter will be exploited in this method. The better thermal contact at the weld Nugget contrasts with the surrounding material, where the heat transfer between the two sheets is comparatively low. A major advantage of the described method is the applicability on sheets without any surface treatment. This is achieved by a proper normalization of the data, allowing for a correction of the varying surface emissivity. KW - Active thermography KW - Spot weld KW - Automotive industry PY - 2016 UR - http://link.springer.com/article/10.1007/s10921-015-0318-4?wt_mc=internal.event.1.SEM.ArticleAuthorIncrementalIssue DO - https://doi.org/10.1007/s10921-015-0318-4 VL - 35:1 SP - 1 EP - 14 PB - Springer CY - New York AN - OPUS4-35480 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maierhofer, Christiane A1 - Krankenhagen, Rainer A1 - Röllig, Mathias A1 - Schlichting, Joachim A1 - Schiller, M. A1 - Seidl, T. A1 - Mecke, R. A1 - Kalisch, U. A1 - Hennen, C. A1 - Meinhardt, J. T1 - Investigating historic masonry structures with a combination of active thermography and 3D laser scanner JF - QIRT Journal N2 - Methods for the combination (i. e. comparison and overlay) and data fusion (i. e. integration of all data in one data set, replacement of data) of active thermography and D laser scanner (light section method) have been developed. Systematic investigations for quantification of damage in historic structures are presented using both techniques. A case study shows that reproducible investigations at regular time intervals are very well suited for structural monitoring. KW - Active thermography KW - 3D laser scanner KW - Data fusion KW - Historic masonry KW - Monitoring PY - 2011 SN - 1768-6733 VL - 8 IS - 1 SP - 115 EP - 118 PB - Lavoisier CY - Cachan Cedex AN - OPUS4-24300 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maierhofer, Christiane A1 - Röllig, Mathias A1 - Gower, M. A1 - Lodeiro, M. A1 - Baker, G. A1 - Monte, C. A1 - Adibekyan, A. A1 - Gutschwager, B. A1 - Knazowicka, L. A1 - Blahut, A. T1 - Evaluation of different techniques of active thermography for quantification of artificial defects in fiber-reinforced composites using thermal and phase contrast data analysis JF - International Journal of Thermophysics N2 - For assuring the safety and reliability of components and constructions in energy applications made of fiber-reinforced polymers (e.g., blades of wind turbines and tidal power plants, engine chassis, flexible oil and gas pipelines) innovative non-destructive testing methods are required. Within the European Project VITCEA complementary methods (shearography, microwave, ultrasonics and thermography) have been further developed and validated. Together with partners from the industry, test specimens have been constructed and selected on-site containing different artificial and natural defect artefacts. As base materials, carbon and glass fibers in different orientations and layering embedded in different matrix materials (epoxy, polyamide) have been considered. In this contribution, the validation of flash and lock-in thermography to these testing problems is presented. Data analysis is based on thermal contrasts and phase evaluation techniques. Experimental data are compared to analytical and numerical models. Among others, the influence of two different types of artificial defects (flat bottom holes and delaminations) with varying diameters and depths and of two different materials (CFRP and GFRP) with unidirectional and quasi-isotropic fiber alignment is discussed. KW - Active thermography KW - CFRP KW - GFRP KW - Delaminations KW - Flash excitation KW - Lock-in excitation PY - 2018 DO - https://doi.org/10.1007/s10765-018-2378-z SN - 0195-928X SN - 1572-9567 VL - 39 IS - 5 SP - Article 61, 1 EP - 37 PB - Springer AN - OPUS4-44687 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maierhofer, Christiane A1 - Röllig, Mathias A1 - Krankenhagen, Rainer T1 - Integration of active thermography into the assessment of cultural heritage buildings JF - Journal of modern optics N2 - Applications of infrared thermography in civil engineering are not limited to the identification of heat losses in building envelopes. Active infrared thermography methods enable structural investigations of building elements with one-sided access up to a depth of about 10 cm. Masonry and especially historical masonry has a very heterogeneous structure containing several different materials (brick, stone, mortar, plaster, wood, metal, etc.) with various thermal properties. As many classes of damage originate from defects that are close to the surface, active thermography is in general very well suited to assessing different test problems in cultural heritage buildings. In this paper, the physical background, equipment, environmental influences and material properties are discussed. Several application results are presented. It is shown how active thermography can be integrated into a holistic approach for the assessment of historical structures. KW - Active thermography KW - Impulse KW - Lock-in KW - Historical structure KW - Thermal properties PY - 2010 DO - https://doi.org/10.1080/09500341003703497 SN - 0950-0340 VL - 57 IS - 18 SP - 1790 EP - 1802 PB - Taylor & Francis CY - Abingdon AN - OPUS4-22608 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maierhofer, Christiane A1 - Röllig, Mathias A1 - Steinfurth, Henrik A1 - Meinhardt, J. A1 - Arnold, T. T1 - Untersuchung sicherheitsrelevanter Ablösungen von Fassadenelementen mit aktiver Thermografie JF - Bautechnik N2 - Die Bewertung des Zustandes und der Haftung von Putz und Fassadenelementen auf den darunterliegenden Bauwerksstrukturen ist eine häufig auftretende Fragestellung bei der Erhaltung und Instandsetzung von Bauwerken und Baudenkmälern. Hier müssen nicht nur wirtschaftliche und denkmalpflegerische, sondern auch sicherheitsrelevante Aspekte berücksichtigt werden. Fehlstellen und Ablösungen können, auch wiederholend, mit hoher Nachweisempfindlichkeit mit aktiven Thermografieverfahren geortet und unter bestimmten Voraussetzungen quantitativ bewertet werden. Dazu wird der zu untersuchende Bereich zunächst kurzzeitig (mehrere Minuten lang) erwärmt und anschließend die Abkühlung mit einer Infrarotkamera aufgezeichnet. Systematische Untersuchungen an Probekörpern mit einer Vielzahl unterschiedlicher Fehlstellen unterhalb von Kalkputz, Fliesen und Klinkerriemchen zeigen, dass die Fehlstellen sowohl mittels künstlicher Erwärmung durch einen Infrarotstrahler als auch mittels natürlicher Erwärmung durch die Sonne detektiert und charakterisiert werden können. --------------------------------------------------------------------------------------------------------------------------------------- The evaluation of condition and adhesion of plaster and façade elements to the underlying building structure is a common issue in the maintenance and repair of buildings and monuments. Here not only economic and preservation, but also safety relevant aspects have to be considered. Voids and delaminations can be detected repeatedly with high sensitivity using active thermography methods. Under certain conditions, also a quantitative evaluation is possible. The area under investigation has to be heated up for a short time (up to several minutes). Subsequently, the cooling down is recorded using an infrared camera. Systematic studies on test specimens with a variety of defects below lime plaster, tiles and brick tiles show that the defects can be detected and even characterized both by means of artificial heating using an infrared heater, as well as by natural solar heating. KW - Zerstörungsfreie Prüfung KW - Aktive Thermografie KW - Sonnenerwärmung KW - Fassade KW - Putz KW - Klinkerriemchen KW - Fliese KW - Fehlstelle KW - Ablösung KW - Non-destructive testing KW - Active thermography KW - Heating using solar radiation KW - Facade KW - Plaster KW - Brick tile KW - Tile KW - Void KW - Delamination KW - Bauwerkserhaltung/Sanierung KW - Maintenance and Repair KW - Neue Verfahren/Versuchstechnik KW - New Processes/Experimental Techniques KW - Qualitätssicherung KW - Quality assurement PY - 2015 DO - https://doi.org/10.1002/bate.201500050 SN - 0932-8351 SN - 1437-0999 SN - 0005-6820 SN - 0341-1052 SN - 0932-6359 VL - 92 IS - 10 SP - 1 EP - 6 PB - Ernst & Sohn CY - Berlin AN - OPUS4-34527 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maierhofer, Christiane A1 - Röllig, Mathias A1 - Steinfurth, Henrik A1 - Ziegler, Mathias A1 - Kreutzbruck, Marc A1 - Scheuerlein, C. A1 - Heck, S. T1 - Non-destructive testing of Cu solder connections using active thermography JF - NDT & E international N2 - Impulse and lock-in thermography have been applied to detect delaminations of prototype solder joints, similar to those to be produced between Cu shunts and Cu busbar stabilisers at the Large Hadron Collider (LHC) at CERN. Two infrared cameras with different detector materials and with different spectral ranges and two excitation techniques have been tested and compared for their ability to detect delaminations behind 2 and 3 mm thick Cu shunts. We have analyzed the signal to noise ratio (SNR) for each detected defect and are able to detect defects down to a nominal edge length of 4 mm behind 2 mm thick Cu shunts by using fast impulse thermography and a camera with a microbolometer array. For the 3 mm thick Cu shunt, on the other hand, the nominal 4 mm defect is only visible in the lock-in thermography phase images and the highest SNR has been achieved with a cooled InSb-based camera. In addition, numerical simulations show the influence of the minimum detectable defect size on the shunt thickness and that the developed on-site testing technique is sufficient to find all defects that are detectable theoretically. KW - Active thermography KW - Solder joint KW - Copper KW - FFT KW - Signal-to-noise-ratio PY - 2012 DO - https://doi.org/10.1016/j.ndteint.2012.07.010 SN - 0963-8695 VL - 52 SP - 103 EP - 111 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-27575 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Metz, Christian A1 - Franz, Philipp A1 - Fischer, C. A1 - Wachtendorf, Volker A1 - Maierhofer, Christiane T1 - Active thermography for quality assurance of 3D-printed polymer structures JF - Quantitative InfraRed Thermography Journal N2 - Additively manufactured test specimens made of polyamide 12 (PA 12) by Laser Sintering as well as of acrylonitrile butadiene styrene (ABS) by Fused Layer Modelling, were characterised with active thermography directly after manufacturing and after artificial weathering. For this, two different excitation methods (flash and pulse heating) were used and compared, regarding their suitability for the detection of constructed and imprinted defects inside the test specimens. To increase the quality of the thermograms, data processing methods like thermal signal reconstruction (TSR) and Fourier Transformation after TSR were applied. To further investigate the long-term stability of the additively manufactured test specimens towards environmental stress, like UV radiation, heat, humidity, water contact and frost with active thermography, an artificial weathering test over 2000 hours (~3 months) was applied to the specimens. The monitoring of the changes in the optical properties of the weathered plastics was supplemented by spectral reflectance and UV/VIS spectroscopy. KW - Additive manufacturing KW - Polymers KW - Artificial weathering KW - Active thermography KW - UV/VIS spectroscopy PY - 2019 DO - https://doi.org/10.1080/17686733.2019.1686896 SN - 1768-6733 (Print) 2116-7176 (Online) VL - 18 IS - 1 SP - 50 EP - 72 PB - Taylor & Francis AN - OPUS4-49817 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Müller, Jan P. A1 - Götschel, S. A1 - Maierhofer, Christiane A1 - Weiser, M. T1 - Determining the Material Parameters for the Reconstruction of Defects in Carbon Fiber Reinforced Polymers from Data Measured by Flash Thermography JF - AIP Conference Proceedings N2 - Flash thermography is a fast and reliable non-destructive testing method for the investigation of defects in carbon fiber reinforced polymer (CFRP) materials. In this paper numerical simulations of transient thermography data are presented, calculated for a quasi-isotropic flat bottom hole sample. They are compared to experimental data. These simulations are one important step towards the quantitative reconstruction of a flaw by assessing thermographic data. The applied numerical model is based on the finite-element method, extended by a semi-analytical treatment of the boundary of the sample, which is heated by the flash light. A crucial part for a reliable numerical model is the prior determination of the material parameters of the specimen as well as of the experimental parameters of the set-up. The material parameters in plane and in depth diffusivity are measured using laser line excitation. In addition, the absorption and heat transfer process of the first layers is investigated using an IR microscopic lens. The performance of the two distinct components of CFRP during heating – epoxy resin and carbon fibers – is examined. Finally, the material parameters are optimized by variation and comparison of the simulation results to the experimental data. The optimized parameters are compared to the measured ones and further methods to ensure precise material parameter measurements are discussed. T2 - 43rd Review of Progress in Quantitative Nondestructive Evaluation CY - Atlanta, GA, USA DA - 17.07.2016 KW - Aktive Thermografie KW - Thermische Diffusivität KW - Zerstörungsfreie Prüfung KW - Kohlenstofffaserverstärkter Kunststoff KW - CFK KW - Active thermography KW - Thermal diffusivity KW - Non-Destructive testing KW - Carbon fiber reinforced polymer KW - CFRP PY - 2017 SN - 978-0-7354-1474-7 DO - https://doi.org/10.1063/1.4974671 SN - 0094-243X VL - 1806 IS - 1 SP - UNSP 100006-1 EP - 11 PB - AIP Publishing CY - Melville, NY, USA AN - OPUS4-39332 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Richter, U. A1 - Mischke, R. A1 - Röllig, Mathias A1 - Maierhofer, Christiane A1 - Eigenfeld, K. T1 - Porosity detection in high pressure die castings - Part 2 - Non-destructive characterization of pores in HPD castings using active thermpography: numerical simulation and experimental validation JF - Gießereiforschung N2 - Ever larger high pressure die castings (HPDC) with ever thinner walls raise the issue of casting defects. Properties of components are often strongly influenced by inner porosity. In the case of high pressure die castings, shrinkage and gas porosity occur. Two possibilities of characterizing porosity - by microscopy and acitve thermography - are dealt with in two articles. In the previous article, the microscopic investigations are presented. In this article, first the feasibility of thermographic detection will be discussed based on simulations and, thereafter, the experimental determination of porosity with active thermography will be described. KW - Porosity KW - Aluminium KW - HPD casting KW - Active thermography KW - Flash KW - Numerical simulation PY - 2015 SN - 0046-5933 VL - 67 IS - 2 SP - 38 EP - 47 PB - Gießerei-Verl. CY - Düsseldorf AN - OPUS4-34283 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -