Small crack initiation and growth behavior of IN738LC at low cycle fatigue and thermal fatigue.
It is significant to study the difference between thermal fatigue behavior and high temperature low cycle fatigue, in order to understand the fracture mechanism of metals.In this study, thermal fatigue tests (the upper temperature 800°C, the lower temperature 400°C) and low cycle fatigue tests at 800°C were carried out for super alloy IN738LC, and the initiation of a short crack and its propagation behavior were observed.The results of these fatigue tests showed that the difference in fatigue life between them were caused by the differences in crack initiation life and crack propagation rate during the time of the short crack (2a≤2.0mm).On the other hand, it was observed that the fatigue crack propagation behavior was affected largely by the fracture resistance of grain boundary and cell boundary in crystal grains at high temperatures.
We present what is to our knowledge the most complete 1-D numerical analysis of the evolution and the propagation ::: dynamics of an ultrashort laser pulse in a Ti:Sapphire laser oscillator. This study confirms the dispersion ::: managed model of mode-locking, and emphasizes the role of the Kerr nonlinearity in generating mode-locked ::: spectra with a smooth and well-behaved spectral phase. A very good agreement with experimental measurements ::: of pulse energy, spectrum, and temporal width of extracavity compressed pulses is found.