TY - JOUR A1 - Thiel, Erik A1 - Ziegler, Mathias A1 - Studemund, Taarna T1 - Localization of subsurface defects in uncoated aluminum with structured heating using high-power VCSEL laser arrays JF - International Journal of Thermophysics N2 - We report on photothermal detection of subsurface defects by coherent superposition of thermal wave fields. This is made possible by structured heating using high-power VCSEL laser arrays whose individual emitter groups can be arbitrarily controlled. In order to locate the defects, we have developed a scanning method based on the continuous wavelet transformation with complex Morlet wavelet using the destructive interference effect of thermal waves. This approach can also be used for thermally very fast and highly reflective materials such as uncoated aluminum. We show that subsurface defects at an aspect ratio of defect width to defect depth down to 1/3 are still detectable in this material. KW - Thermography KW - Heat diffusion KW - Laser thermography KW - Structured heating KW - NDT KW - Subsurface defects KW - Thermal wave KW - VCSEL KW - Wavelet transformation PY - 2019 DO - https://doi.org/10.1007/s10765-018-2478-9 SN - 1572-9567 SN - 0195-928X VL - 40 IS - 2 SP - 17, 1 EP - 13 PB - Springer Science+Business Media, LLC, part of Springer Nature 2019 AN - OPUS4-47208 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer A1 - Worzewski, Tamara A1 - Doroshtnasir, Manoucher A1 - Röllig, Mathias A1 - Studemund, Taarna T1 - Inspecting rotor blades by thermographic monitoring from greater distances T2 - DEWEK 2015 N2 - The paper presents some of the results obtained within a project concerning the validation of the thermographic inspection method applied to rotor blades of wind turbines. Thermographic testing (TT) is a well established nondestructive testing method under laboratory conditions. It is suited to detect typical structural features and also faults and damages within the blade structure. However, the onsite application for wind turbines during Operation is not straightforward. Some resuits of non-rotating blades as well as of rotating blades are presented. The simultaneous recording of all blades in the rotating state allows the application of a reference method suppressing disturbing influences and leading to enhanced thermal contrasts. T2 - DEWEK 2015 CY - Bremen, Deutschland DA - 19.05.2015 PY - 2015 AN - OPUS4-33272 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -