Oxidation and low cycle fatigue life prediction

When a metallic material is exposed to a high temperature in an ambient atmosphere, oxidation takes place on the metallic surface. The formed oxides (both surface and grain boundary oxides) are mechanically brittle so that if the stress is high enough the oxides will be cracked. The grain boundary oxide formation in TAZ-8A nickel-base superalloy was studied. The effect of oxide crack nucleus on low cycle fatigue life will be analyzed. The TAZ-8A was subjected to high temperature oxidation tests in air under the stress-free condition. The oxidation temperatures were 600, 800, and 1000 C. The oxidation time varies from 10 to 1000 hours

Extracting and Stabilizing the Unstable State of Hysteresis Loop

A novel perturbation method for the stabilization of unstable intermediate states of hysteresis loop (i.e. S-shaped curve) is proposed. This method only needs output signals of the system to construct the perturbation form without delay-coordinate embedding technique, it is more practical for real-world systems. Stabilizing and tracking the unstable intermediate branch are demonstrated through the examples of a bistable laser system and delay feedback system. All the numerical results are obtained by simulating each of the real experimential conditions.Comment: 6 pages, REVTEX, 4 ps figure

Level Densities by Particle-Number Reprojection Monte Carlo Methods

A particle-number reprojection method is applied in the framework of the shell model Monte Carlo approach to calculate level densities for a family of nuclei using Monte Carlo sampling for a single nucleus. In particular we can also calculate level densities of odd-even and odd-odd nuclei despite a new sign problem introduced by the projection on an odd number of particles. The method is applied to level densities in the iron region using the complete $pf+g_{9/2}$-shell. The single-particle level density parameter $a$ and the backshift parameter $\Delta$ are extracted by fitting the microscopically calculated level densities to the backshifted Bethe formula. We find good agreement with experimental level densities with no adjustable parameters in the microscopic calculations. The parameter $a$ is found to vary smoothly with mass and does not show odd-even effects. The calculated backshift parameter $\Delta$ displays an odd-even staggering effect versus mass and is in better agreement with the experimental data than are the empirical values.Comment: To be published in the proceedings of the Tenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, S. Wender, ed., AIP Conference Proceedings (2000

Advances on creep–fatigue damage assessment in notched components

In this paper, the extended Direct Steady Cyclic Analysis method (eDSCA) within the Linear Matching Method Framework (LMMF) is combined with the Stress Modified Ductility Exhaustion method and the modified Cavity Growth Factor (CGF) for the first time. This new procedure is used to systematically investigate the effect of several load parameters including load level, load type and creep dwell duration on the creep–fatigue crack initiation process in a notched specimen. The results obtained are verified through a direct comparison with experimental results available in the literature demonstrating great accuracy in predicting the crack initiation life and the driving mechanisms. Furthermore, this extensive numerical study highlighted the possible detrimental effect of the creep–ratchetting mechanism on the crack growth process. This work has a significant impact on structural integrity assessments of complex industrial components and for the better understanding of creep–fatigue lab scale tests

Self-similarity in a system with short-time delayed feedback

Using the Poincar\'{e} section technique, we study in detail the dynamical behaviors of delay differential system and find a new type of solutions $S_i$ in short-time delay feedback. Our numerical results remind us to deny the opinion that there are no complex phenomena in short-time delay case. Many similarities between foundamental solution and the new type of solutions are found. We demonstrate that the scales of $S_i$ increase with exponential growth via $i$ in the direction of $\mu$, while decrease with exponential decays in the direction of $x$ or delay time $t_R$.Comment: 4 pages, REVTEX, 4 ps figures, to be published in Phys. Lett.