PSI - Issue 18

Andrzej Katunin et al. / Procedia Structural Integrity 18 (2019) 20–27 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The third case occurs when q d = q c (see Fig.1), i.e. when  ( t ) =  k , where  k is the critical temperature of the self heating (see Fig. 2, curve no. 3). In fact, this case is unstable because any slight increase of the temperature  ( t ) causes that the thermodynamic equilibrium of the cyclically loaded composite structure turns into the second case, i.e. the case where q d > q c . The unstable thermal equilibrium is characterized by the interval  k ( L ) –  k ( H ) .

Fig. 2. Diagram of temperature increase for different cases of heat removal by means of air cooling.

3. Preliminary experimental verification The preliminary experiments were performed on the glass/epoxy composite specimens purchased from Izo Erg S.A. The specimens were tested on the test rig, which is shown in Fig. 3. A tested specimen was clamped in a specimen holder and excited by the electrodynamic shaker through a stinger with a specimen holder connected to the force sensor at the end.

Fig. 3. Views of the experimental test rig used in the study.

The excitation signal was measured by the accelerometer. A velocity of vibration of the specimen was measured on its surface near the clamp using the single point laser Doppler vibrometer (LDV). In order to detect damage initiation in the structure due to the self-heating effect, besides measuring the surface temperature and excitation parameters, acoustic emission (AE) measurement system was used. In particular, the AE sensor, the AE signal preamplifier, the dual channel AE signal processor board and the dedicated software for AE signal acquisition and processing were used. The AE sensor was glued with a silicone glue to the specimen at its ending was fixed in the