PSI - Issue 5

O. Plekhov et al. / Procedia Structural Integrity 5 (2017) 438–445 A. Vshivkov et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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The sensitivity of the heat flux sensor was verified during the fatigue crack propagation with the constant amplitude of loading. In this experiment the heat flux sensor was located at a distance from the crack tip. The results of such measurements qualitatively correspond to the case of the direct location of the sensor over the top of the fatigue crack tip. This effect is a consequence of the high thermal conductivity of the material. Measurement results are presented in figure 3

Fig. 3. Direct measurement of the heat flux at the crack tip and measurement at the distance.

There are three sections on the heat flux curve under the mixed loading. Short initial increasing part corresponds to starting of crack propagation (part 1). The second part with constant heat flux corresponds to the regime of short crack propagation (part 2). The last part of the plot (part 3) is characterized by sharp increasing of heat dissipation. During this part we observe the long crack propagation process. The last part is finished by specimen failure. The evolution of the temperature field was recorded by infrared camera FLIR SC 5000. The spectral range of the camera is 3-5 µm. The maximum frame size is 320×256 pixels; the spatial resolution is 10-4 meters. The temperature sensitivity is 25 mK at 300 K. Calibration of the camera was made based on the standard calibration table. It was used FLIR SC5000 MW G1 F/3.0 close-up lens (distortion is less than 0.5%) to investigate the plastic zone in details.

Fig. 4. Schematic of the measured equipment.