J. Bär et alii, Frattura ed Integrità Strutturale, 34 (2015) 456-465; DOI: 10.3221/IGF-ESIS.34.51 456 Focussed on Crack Paths Combined lock-in thermography and heat flow measurements for analysing heat dissipation during fatigue crack propagation J. Bär University of the Federal Armed Forces Munich, Institute for Materials Science, 85577 Neubiberg, Germany A. Vshivkov, O. Plekhov Institute of continuous media mechanics UB RAS, 614013 Perm, Russia A BSTRACT . During fatigue crack propagation experiments with constant force as well as constant stress intensity lock in thermography and heat flow measurements with a new developed peltier sensor have been performed. With lock in thermography space resolved measurements are possible and the evaluation allows to distinguish between elastic and dissipated energies. The specimens have to be coated with black paint to enhance the emissivity. The thickness of the coating influences the results and therefore quantitative measurements are problematic. The heat flow measurements are easy to perform and provide quantitative results but only integral in an area given by the used peltier element. To get comparable results the values measured with thermography were summarized in an area equivalent to that of the peltier element. The experiments with constant force show a good agreement between the thermography and the heat flow measurements. In case of the experiments with a constant stress intensity some differences become visible. Whereas the thermography measurements show a linear decrease of the signal with rising crack length, the heat flow measurements show a clearly nonlinear dependency. Obviously the measured energies in thermography and peltier based heat flow measurement are not comparable. K EYWORDS . Fatigue; Crack propagation; Thermography; Heat dissipation. I NTRODUCTION ock-in thermography is widely used to gather information about the deformation behavior of metallic materials under cyclic loading. Besides elastic stress fields [1] also dissipated energies [2, 3] can be determined with this method. Therefore it can be used for crack detection [3] or for determining deformation areas around fatigue cracks [5]. Quantitative measurements are complicated due to the need of a calibration of the system and reproducible paints on the surface of the investigated specimens. A method for quantitative heat flow measurement during fatigue experiments based on Peltier elements was developed by Prokhorov et al. [6] and optimized by Vshivkov et al. [7] This method allows a simple measurement of the integral heat flow within an area specified by the dimensions of the used peltier element. L