Issue34

J. Bär et alii, Frattura ed Integrità Strutturale, 34 (2015) 456-465; DOI: 10.3221/IGF-ESIS.34.51 459 image also the plastic zone is clearly visible. Along the crack path also a region with a higher signal level can be seen. The latter is also visible in the D-mode phase image. Figure 4 : Evaluation of the Lock-In measurements. Left side: Amplitude pictures, right side: phase images. Upper pictures E-Mode, lower pictures D-Mode. Heat Flow Measurements The heat flow measurements were performed with a new developed peltier sensor. A drawing of this sensor is given in Fig. 5. The heat flow is measured by a peltier element directly attached to the specimen. To get a constant temperature on the backside of this peltier element a second peltier element is used. This second peltier element is regulated to the temperature of the chamber controlled by a thermocouple between the two peltier elements. A copper plate on the cooling peltier element ensures a good heat flow to the environment. To fix the peltier elements and the thermocouple the complete device was molded into a resin. The sensor is pressed on the backside of the specimen (Fig. 1). To enhance the heat flow, a heat-conductive paste was applicated between the sensor and the specimen. When the temperature of the specimen is changing, the corresponding temperature difference at the measurering peltier element generates a current. This current leads to a voltage at a resistor that is integrated into the electric circuit. The voltage is measured using an amplifier of the EDC 580 control electronics and is registered by the control software. The system was calibrated with a flat resistor applicated on a plastic specimen installed into the grips. By knowledge of the voltage and the current, the power at the resistor is defined and the system can be calibrated directly to the heat flow [7].