Issue34

J. Bär et alii, Frattura ed Integrità Strutturale, 34 (2015) 456-465; DOI: 10.3221/IGF-ESIS.34.51 460 Specimen Peltier (measure) Peltier (cooling) Copper plate Resin Resin Thermocouple Figure 5 : Schematic drawing of the peltier sensor. R ESULTS he thermography measurement as well as the heat flow measurements were performed on force as well as stress intensity controlled experiments. The thermography measurements were performed in intervals of 60 s, i.e. 1200 cycles. For the heat flow measurement for each cycle a minimum and maximum value was acquired. To get comparable results the thermographic images were quantified by summarizing the values of all pixels in a rectangle area with size and location equivalent to that of the peltier sensor as shown in Fig. 6. Figure 6 : Evaluation of the thermographic measurements. Summation of the values of all pixels in a rectangular section of 10x10 mm. Constant Force In Fig. 7 the evaluation of fatigue crack propagation experiments with a constant force of 8.5 (left hand side) and 8.8 kN right hand side) are shown. The results of the thermography measurements are drawn by symbols, the heat flow measurement is given as a solid line. It should be mentioned that in the case of the thermography measurement the assignment of the crack length to the individual measurements is not perfect, because the both measuring devices are not linked. Especially at higher crack length, i.e. higher crack propagation rates deviations may be possible although the crack length was checked with the thermography images. In the thermography measurements, the summarized E-amplitude (blue squares) plays the dominant role. The summarized D-amplitude (red circles) is about one magnitude lower. This also reflects in the addition of the both values (black triangle) which shows nearly the same values as the E-Mode. The values of the E-mode as well as the D-mode are rising with the crack length. The only exception is the last recorded E-mode value in case of the loading with F max =8.8 kN. This value is significant lower compared to all values determined before. On the contrary the value of the T