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This paper describes a series of physically-based crystal plasticity finite element method (CPFEM) simulations of long-term creep and creep rupture of Grade 91 steel. It is Part 2 of a two part series of papers. Part 1 describes the simulation framework; this part focuses on specific simulations and on how the predicted long-term creep properties of Grade 91 compare to the assumptions used in current high temperature design practices. This work extends the model developed in Part 1 to look at creep properties at different temperatures, principal stresses, and multiaxial stress states. The simulations show that empirically extrapolating creep rupture stresses from short-term experimental data may substantially over predict the actual long-term creep properties of Grade 91. Additionally, the CPFEM calculations predict a transition from notch strengthening creep behavior for high values of maximum principal stress and moderate notch severity to notch weakening behavior for low principal stresses and more severe notches. The latter regime better categorizes conditions in engineering components designed for long term elevated temperature use, which implies Grade 91 may be a notch weakening material in actual service. This would have a significant impact on high temperature design practices, though confirmatory test data on long-life, low stress notched specimens is difficult to obtain. Finally, one advantage of the physically-based modeling approach adopted here is that the simulation results also elucidate the microstructural mechanisms causing the macroscopic trends in engineering properties predicted by the simulations. This paper shows that the detailed micromechanical mechanisms predicted by the CPFEM simulations can be abstracted with a simple micromechanical model that can be used to both explain the detailed results and make improved predictions of engineering properties from experimental data. [ABSTRACT FROM AUTHOR]

The laser-induced plume is an essential physical phenomenon during high power fiber laser welding. Its physical nature can be investigated by diagnosing its temperature. In order to overcome the lack of sufficient line spectra in the temperature diagnosis, the continuous spectrum method (based on the continuous spectrum and Wien’s displacement law) is thus developed in this research. The optical spectra emitted by the plume or plasma were detected by using a SP-2500i spectrometer during bead-on-plate welding with an IPG YLS-6000 fiber laser or fiber laser-arc hybrid. The rationality of the continuous spectrum method was evaluated by comparing the plasma temperatures diagnosed by applying the continuous spectrum and line spectra. The results reveal that the continuous spectrum method used in temperature diagnosis is rational. When the line spectra cannot be detected due to an increase in detected height, the plume temperature can be still obtained by using the continuous spectrum method. [ABSTRACT FROM AUTHOR]