PSI - Issue 42

Jürgen Bär et al. / Procedia Structural Integrity 42 (2022) 1061–1068 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1068

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place. Along the crack tip under tension loading no dissipative temperature changes are visible, with increasing compression loading a temperature rise due to sliding of the crack flanks takes place. This temperature increase disappears during the unloading of the specimen.

3000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Temperature change by dissipation [K]

far away from the crack tip crack flanks crack tip near crack tip Force

2000

R=-1

1000

0

Force [N]

-1000

-2000

-0.2 -0.1

-3000

0.00

0.25

0.50

0.75

1.00

Cycle time [1/T]

Fig. 9. Dissipative temperature changes at different positions on the ligament.

4. Conclusions The investigations clearly show that a description of the temperature changes using an LI decomposition of the signal is not perfectly possible, even if more than the usual 2 modes are used for the description. Thus, the decomposition of the signal into the E- and D-mode does not provide quantitatively correct values for the thermoelastic effect and the temperature changes caused by dissipative effects. The position-time-diagram introduced in this work provides in a simple way the real temperature changes at different positions on the ligament. A determination of the dissipative temperature changes can be done by a compensation of the thermoelastic effect, but because of the crack it requires a separate compensation for tension and compression loading and is therefore difficult and cannot be realized fully automatically. Other effects like delayed crack opening or crack closer can complicate the direct linking from load change to local stress change. References Bär, J.; L. Seilnacht, L.; Urbanek, R.; Determination of dissipated energies during fatigue tests on Copper and AA7475 with Infrared Thermography, Procedia Structural Integrity 17 (2019) 308-315, DOI: 10.1016/j.prostr.2019.08.041 Bär, J.; Urbanek, R.; 2019. Determination of dissipated Energy in Fatigue Crack Propagation Experiments with Lock-In Thermography, Frattura ed Integrità Strutturale 13 , 563-570. DOI: 10.3221/IGF-ESIS.48.54. Brémond, P.; 2007. New developments in Thermo Elastic Stress Analysis by Infrared Thermography. IV Pan-American Conference for Non Destructive Testing. Fargione, G.; Geraci, A.; La Rosa, G.; Risitano, A.; Rapid determination of the fatigue curve by the thermographic method. International Journal of Fatigue 24 (2002) 11 – 19. DOI: 10.1016/S0142-1123(01)00107-4. Luong, M.P.; 1995. Infrared Thermographic scanning of fatigue in metals. Nuclear Engineering and Design 158 , 363–373. DOI: 10.1016/0029 5493(95)01043-H. Meneghetti, G.; 2007. Analysis of the fatigue strength of a stainless steel based on the energy dissipation. International Journal of Fatigue 29 , 81 94. DOI: 10.1016/j.ijfatigue.2006.02.043. Robinson, A. F.; Dulieu-Barton, J. M.; Quinn, S.; Burguete, R. L. (2010): Paint coating characterization for thermoelastic stress analysis of metallic materials. In: Meas. Sci. Technol. 21 (8), S. 85502. DOI: 10.1088/0957-0233/21/8/085502. Sakagami, T.; Kubo, S.; Tamura, E.; Nishimura, T.; Identification of plastic-zone based on double frequency lock-in thermographic temperature measurement, In: ICF11 Italy, 2005. Thomson, W.; 1853. On the Dynamical Theory of Heat, with numerical results deduced from Joule's equivalent of a Thermal Unit. Transactions of the Royal Society of Edingburgh 20 , 261-288. Urbanek, R., Bär, J.; 2017. Lock-In Thermographic Stress Analysis of notched and unnotched specimen under alternating loads. Procedia Structural Integrity 5 , 785-792. DOI: 10.1016/j.prostr.2017.07.170. Urbanek, R, Bär, J.; 2017a. Influence of motion compensation on lock-In thermographic investigations of fatigue crack propagation. Engineering Fracture Mechanics 183, 13–25. DOI: 10.1016/j.engfracmech.2017.03.043.