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This paper describes the way in which a specialized validation set intended for quick validation of new multiaxial fatigue strength estimation models in the high‐cycle fatigue regime was prepared. The rules established for accepting various data sets into the complete FatLim database are briefly described. This final FatLim database contained 282 data items at the moment this paper was written. The paper describes how FatLim has been reduced to a smaller validation set, marked as AMSD25. The criteria used for accepting the data items for this small‐scale test set are based on evaluating the mean and the standard deviation of the fatigue index errors obtained for each data item on the basis of 18 different prediction criteria. The items that got into the AMSD25 validation set are described, and potential issues are noted. The comparison between the original FatLim validation set and the shortened AMSD25 data set is presented. It shows that the in‐phase load cases without any mean stress effect are generally well mastered by most criteria, and they can be excluded as insignificant from any such analysis. However, the mean stress effect is generally poorly incorporated. Future multiaxial fatigue strength criteria should focus on load cases including mean stresses. [ABSTRACT FROM AUTHOR]

This paper presents an assessment of the performance of a set of multi-axial high-cycle fatigue criteria on the basis of a series of fretting fatigue experiments. We carried out tests on a creep-resistant chromium steel material used for steam-turbine blades. The first type of experiment employed the classical cylinder-on-flat geometry with flat dog-bone specimens. The second set of experiments adopted dovetail geometry. Various loads were applied in order to capture a wide range of contact slip amplitudes. A set of eight plain multi-axial fatigue criteria was applied to the numerically simulated stress response in the contacts during a single load cycle. Methods, which originated in the so-called theory of critical distances, were used for correcting the results in order to take the stress gradient effect into account. A simple factor based on slip amplitudes is introduced in order to consider the surface damage and is calibrated for the McDiarmid method. This criterion provided the best estimates of the most probable cracking sites. [ABSTRACT FROM AUTHOR]

We report investigation of carrier recombination and diffusivity in bulk diamonds of different crystalline structure - microcrystalline (MC) CVD-grown and single crystalline HPHT diamonds. Presence of neutral and positively charged nitrogen and hydrogen defects was determined from NIR and UV-IR absorption spectra. Carrier injection into 1-mm thick bulk layers was realized by two-photon absorption at 351 nm wavelength. Carrier lifetimes of 150-330 ns in IIa type HPHT crystals correlated with N density, while the lifetimes in CVD crystal exhibited very fast (80 ps), slower one (3-8 ns), and µs-duration thermally-activated (∼1.5 eV) decay components. The initial two components correlated with the grain size at the front and backsides of the MC diamond. Linearly increasing with injection carrier recombination rates were observed in both CVD and HPHT samples at 800 K, and fitted with effective recombination coefficient B = 3-4 × 10−9 cm3/s. Ambipolar mobility and thermal diffusivity parameters in CVD and HPHT bulk crystals were measured by light-induced free carrier and thermal grating techniques. [ABSTRACT FROM AUTHOR]

In this article, theoretical interpretation and prediction of the optical properties of nanodiamond (ND) particles', containing various luminescence centers, was made. Particularly, nitrogen, and chromium atoms embedded into the diamond crystal lattice were modeled. In the case of nitrogen centers containing ND particles, the effect of various surface terminations (hydrogen and/or oxygen, fluorine) was also studied. To get a qualitative better understanding of the complicated and specific process of ND particles, luminescence using density functional theory, were modeled processes and states influencing the luminescence of ND particles. [ABSTRACT FROM AUTHOR]