Comparison of fatigue criteria for combined bending-torsion loading of nitrided and virgin specimens

This work deals with fatigue life of plasma-nitrided and virgin specimens made of a low-alloy high strength steel. Specimens were subjected to an in-phase combined bending-torsion loading. The plasma-nitrided specimens exhibited a significantly improved fatigue resistance. The criterion proposed by McDiarmid was found to be the most precise in the fatigue life prediction fo r virgin specimens. On the other hand, the Matake criterion was the most successful fo r nitrided specimens.Исследована усталостная долговечность азотированных в плазме образцов и исходных образцов из низколегированной высокопрочной стали. Испытания образцов проводились при синфазном совмещенном изгибе с кручением. Показано, что азотированные в плазме образцы обладают более высокой усталостной стойкостью. Установлено, что для образцов в исходном состоянии наибольшая точность прогнозирования усталостной долговечности обеспечивается при использовании критерия, предложенного Мак-Диармидом. С другой стороны, для азотированных образцов наиболее подходящим оказался критерий Матаке

Elastic properties of B19’ structure of NiTi alloy under uniaxial and hydrostatic loading from first principles

The uniaxial and hydrostatic deformations of martensitic structure B19’ of NiTi shape memory alloy are studied using first-principles calculations. The bulk and Young’s moduli and the theoretical strength under uniaxial tension and hydrostatic loading are computed from crystal response to applied deformations. The behavior of angle β of the B 19’ structure was investigated along the whole deformation path. The computed values of Young’s moduli are compared with available experimental results. The results obtained complement and extend the already known characteristics of NiTi alloy.Проведено исследование одноосной и гидростатической деформаций мартенситной структуры B19’ сплава с памятью формы NiTi по методу расчетов ab initio. Величины объемного модуля упругости, модуля Юнга и теоретической прочности при одноосном растяжении и гидростатическом нагружении рассчитаны по реакции кристалла на приложенные деформации. Изучен характер изменения угла β структуры B19’ по всей траектории деформации. Выполнено сопоставление расчетных значений модуля Юнга с имеющимися экспериментальными результатами. Полученная информация дополняет и расширяет уже известные данные о характеристиках сплава NiTi

Effects of microstructure and crystallography on crack path and intrinsic resistance to shear-mode fatigue crack growth

The paper focuses on the effective resistance and the near-threshold growth mechanisms in theferritic-pearlitic and the pure pearlitic steel. The influence of microstructure on the shear-mode fatigue crackgrowth is divided here into two factors: the crystal lattice type and the presence of different phases.Experiments were done on ferritic-pearlitic steel and pearlitic steel using three different specimens, for whichthe effective mode II and mode III threshold values were measured and fracture surfaces were reconstructed inthree dimensions using stereophotogrammetry in scanning electron microscope. The ferritic-pearlitic andpearlitic steels showed a much different behaviour of modes II and III cracks than that of the ARMCO iron.Both the deflection angle and the mode II threshold were much higher and comparable to the austenitic steel.Mechanism of shear-mode crack behaviour in the ARMCO iron, titanium and nickel were described by themodel of emission of dislocations from the crack tip under a dominant mode II loading. In other testedmaterials the cracks propagated under a dominance of the local mode I. In the ferritic-pearlitic and pearliticsteels, the reason for such behaviour was the presence of the secondary-phase particles (cementite lamellas),unlike in the previously austenitic steel, where the fcc structure and the low stacking fault energy were the mainfactors. A criterion for mode I deflection from the mode II crack-tip loading, which uses values of the effectivemode I and mode II thresholds, was in agreement with fractographical observations

The Influence of synthetic strigolactones and plant extracts on the morphological parameters of onion (Allium cepa)

In recent years there has been frequent reference to the significance of strigolactones as a new group of hormones which might have a significant effect on horticultural production. The aim of this work was to find an ideal combination of stable synthetic strigolactones and plant extracts with potential effects on onion plants. The synthetic strigolactone Fenyl 7 (dihydro-3-[[2,5- dihydro-4-methyl-5-oxo-2-furanyl)oxy]-methylene]-5-phenyl-2(3H)-furanone) was tested in a carrot macerate, with citric acid and with salicylic acid. From the results it was confirmed that increasing the pH of the preparation leads to improving the stability of Fenyl 7. Evaluation has repeatedly confirmed the effect of the preparation, combining synthetic strigolactone and a macerate of carrot in a mixture of surfactants with added citric acid. In all the experiments this combination showed a statistically demonstrable influence on leaf weight (increased by 12-31%) and length (increased by 6-13%) in comparison with the controls.

Plasma-sprayed thermal barrier coatings: numerical study on damage localization and evolution

Thermal barrier coatings (TBCs) are advanced material systems used to enhance performance and in-service life of components operated at high temperatures in gas turbines and other power-generation devices. Because of complexity, numerical methods became important tools both for design of these coatings and for in-service life estimations and optimization. In this contribution, two main features that affect the TBCs’ performance, namely the roughness of the bond coat and the microstructure of the ceramic top coat, are discussed based on Finite Element Method (FEM) and Finite Element Microstructure MEshfree (FEMME) simulations that were used to calculate stresses and assess damage within the coating. Roughness data obtained from plasma-sprayed CoNiCrAlY + YSZ coated samples are supplemented to discuss assumptions and results of employed numerical models

Demography and Dispersal Ability of a Threatened Saproxylic Beetle: A Mark-Recapture Study of the Rosalia Longicorn (Rosalia alpina)

The Rosalia longicorn or Alpine longhorn (Coleoptera: Cerambycidae) is an endangered and strictly protected icon of European saproxylic biodiversity. Despite its popularity, lack of information on its demography and mobility may compromise adoption of suitable conservation strategies. The beetle experienced marked retreat from NW part of its range; its single population survives N of the Alps and W of the Carpathians. The population inhabits several small patches of old beech forest on hill-tops of the Ralska Upland, Czech Republic. We performed mark-recapture study of the population and assessed its distribution pattern. Our results demonstrate the high mobility of the beetle, including dispersal between hills (up to 1.6 km). The system is thus interconnected; it contained ∼2000 adult beetles in 2008. Estimated population densities were high, ranging between 42 and 84 adult beetles/hectare a year. The population survives at a former military-training ground despite long-term isolation and low cover of mature beech forest (∼1%). Its survival could be attributed to lack of forestry activities between the 1950s and 1990s, slow succession preventing canopy closure and undergrowth expansion, and probably also to the distribution of habitat patches on conspicuous hill-tops. In order to increase chances of the population for long term survival, we propose to stop clear-cuts of old beech forests, increase semi-open beech woodlands in areas currently covered by conifer plantations and active habitat management at inhabited sites and their wider environs