Issue 21

A. Yu Fedorova et alii, Frattura ed Integrità Strutturale, 21 (2012) 46-53; DOI: 10.3221/IGF-ESIS.21.06 50 s – unknown specific power of the heat source (W/m 3 ), τ – a constant related to the losses of heat by heat exchange with the surroundings (10 3 J/(m 3 ·K)). The resulting value of the specific power of heat source was integrated over the time during which the plastic zone was observed. The profile of the specific heat dissipated during plastic deformation is plotted in Fig. 5. a) b) Figure 5 : Specific heat (J/m 3 ) dissipated during plastic deformation (a) and its profile in the direction of crack propagation (b) . The developed algorithm allows us to study a time evolution of temperature evolution and heat dissipation processes at the crack tip. The plots of the temperature increment, heat and stress of two types of experiments are presented in Fig. 6. At the beginning of cycling, the thermoelastic effect leads to emergence of cooling zone at crack tip, the local transition through the yields stress leads to temperature increase caused by the formation of a plastic deformation zone. When the stress decreases, the heat dissipation at the crack tip continues the heat dissipation rises and the temperature reaches a maximum at the falling load. At the beginning of the next cycle, the temperature again decreases due to the thermoelastic effect and the process repeats. a) b) Figure 6 : Heat source evolution (1), loads (2) and the temperature increment (3) at the crack tip during the loading. Loading frequency is 5 Hz (a) , loading frequency - 10 Hz (b) . The Fig. 7 presents the detail analysis of the temperature evolution near fatigue crack tip in the direction of the crack propagation. The legends indicate the time of temperature distribution. The data corresponds to the test presented with stress amplitude 250 MPa and frequency 10 Hz.