Određivanje dijagrama granične deformacije elektrogalvansko pocinčanih čeličnih limova

Forming limit curves (FLC) of deep drawing steel sheets have been determined experimentally and calculated on the base of the material tensile properties following the Hill, Swift, Marciniak-Kuczyński and Sing-Rao methods. Only the FLC modeled from a singly linear forming limit stress curve exhibits good consistence with experimental curve. It was established that a linearized limit stress locus describes adequately the actual localized neck conditions for the material chosen in this study. The quantitative X-ray microanalysis of the Fe contents in the sheet surface layer composition was used to determine cracking limit curve (CLC) of electro-galvanized steel sheet. The change in zinc layer (and base sheet metal) thickness was used as a criteria in calculation of the CLC.Krivulje graničnih deformacija (KGD) pri dubokom izvlačenju čeličnih limova su ustrojene eksperimentalno a također su proračunate na temelju svojstava čvrstoće materijala po metodama Hill, Swift, Marciniak-Kuczyński i Sing-Rao. Dobra podudarnost s eksperimentalnom KGD daje jedino KGD dobivena na temelju modela krivulje graničnih deformacija. Utvrđeno je da linearizirano granično naprezanje dovoljno točno opisuje uvjete lokalnog progiba za materijale rabljene u ovom radu. Za određivanje krivulje graničnog prijeloma (KGP) na površini elektrogalvaniziranih cinkom čeličnih limova rabljena je kvantitativna X-zrakama mikroanaliza sadržaja Fe. Izmjene debljine sloja cinka (i osnovnog metala lima) je rabljena kao krivulja za proračun KGP

On Finite Element Computations of Contact Problems in Micropolar Elasticity

Within the linear micropolar elasticity we discuss the development of new finite element and its implementation in commercial software. Here we implement the developed 8-node hybrid isoparametric element into ABAQUS and perform solutions of contact problems. We consider the contact of polymeric stamp modelled within the micropolar elasticity with an elastic substrate. The peculiarities of modelling of contact problems with a user defined finite element in ABAQUS are discussed. The provided comparison of solutions obtained within the micropolar and classical elasticity shows the influence of micropolar properties on stress concentration in the vicinity of contact area

On strength analysis of highly porous materials within the framework of the micropolar elasticity

We discuss the finite element approach to modelling of static deformations of porous materials such as foams, beam lattices, and others within the linear micropolar elasticity. It is known that the micropolar elasticity may be used for microstructured solids and fluids since it can forecast size-effect near geometrical singularities such as holes, notches, small contact areas of two solids. Within the micropolar elasticity the translational and rotational interactions of the material particles can be taken into account. Here we present the recent developments in the theory of finite elements calculations for micropolar solids in order to capture the stress behaviour in the vicinity of geometric singularities such as holes, notches, imperfections or contact areas. The fundamental equations of the micropolar continuum are presented. The FEM implementation in micropolar elasticity is given. The new 8-node hybrid micropolar isoparametric element and its implementation in ABAQUS are introduced. The solutions of few 3D benchmark problems of the micropolar elasticity are given. Among them are analysis of stresses and couple stresses near notches and holes, contact problem of parabolic stamp and half space. The main attention is paid to modelling of interaction between a biodegradable porous implant and a trabecular bone. Comparison of classical and micropolar solutions is carefully discussed. Comparison of classical and micropolar solutions is discussed. Numerical tests have shown that couple stress appears almost in the vicinity of geometrical singularities. It is shown that micropolar elasticity allows to obtain better results for domains with microstructures and singularities than classical theory of elasticity

Modal Analysis of the Turbine Blade at Complex Thermomechanical Loads

The results of modal analysis of the turbine blade were presented. The turbine blade during the operation of the engine is subjected to complex thermomechanical loads induced by centrifugal forces of the rotating blade and a nonuniform thermal field. These loads have a great influence on the natural frequencies of the blade. In the first section of the study, modal analysis of the blade was performed using the vibration system. As a result, the resonant frequencies of the real blade were obtained. In order to check the effect of the rotational engine speed and the thermal field on the natural frequencies of the blade, the finite element method was employed. At the first stage of computations static analysis was conducted for the blade subjected to mechanical and thermal loads. Then modal analysis was used to isolate the natural frequencies and vibration modes of the blade. In modal analysis the stress state from the first stage was considered as preliminary conditions. Several results of numerical calculations and experimental analysis were compared to detect the relative error of natural frequency estimate

Facilitation and the niche: Implications for coexistence, range shifts and ecosystem functioning

Viewing facilitation through the lens of the niche concept is one way to unify conceptual and empirical advances about the role of facilitation in community ecology. We clarify conceptually and through examples from marine and terrestrial environments how facilitation can expand species' niches and consider how these interactions can be scaled up to understand the importance of facilitation in setting a species' geographic range. We then integrate the niche-broadening influence of facilitation into current conceptual areas in ecology, including climate change, diversity maintenance and the relationship between diversity and ecosystem functioning. Because facilitation can influence the range of physical conditions under which a species can persist, it has the potential to mitigate the effects of climate change on species distributions. Whereas facilitation has mostly been considered as a diversity-promoting interaction by ameliorating abiotic stresses, if facilitated species' niches expand and become less distinct as a result of habitat amelioration, the forces that maintain diversity and promote coexistence in regions or habitats dominated by the facilitator could be reduced (i.e. the sign of the effects of facilitation on populations could be species-specific). Finally, shifting or broadening ecological niches could alter the relationship between diversity and ecosystem functioning. A niche-based perspective on the effects of facilitation can foster a greater mechanistic understanding of the role played by facilitation in regulating species coexistence, range shifts and ecosystem functioning in a changing world

Linear Micropolar Elasticity Analysis of Stresses in Bones under Static Loads

We discuss the finite element modeling of porous materials such as bones using the linear micropolar elasticity. In order to solve static boundary-value problems, we developed new finite elements, which capture the micropolar behavior of the material. Developed elements were implemented in the commercial software ABAQUS. The modeling of a femur bone with and without implant under various stages of healing is discussed in details.Рассматривается моделирование таких пористых материалов, как кость, методом конечных элементов с помощью линейной микрополярной теории упругости. Для решения статических краевых задач разработаны новые конечные элементы, которые воспринимают микрополярное поведение этого материала. Разработанные элементы были реализованы в коммерческом программном комплексе ABAQUS. Рассматривается моделирование бедренной кости с имплантатом и без него на различных стадиях заживлени

Effect of Grinding Parameters on the Surface Quality of Cutting Tools Made of High-Speed Low-Alloy Steels

The occurrence of defects caused by sharpening leads to the considerable variation of lifetime of cutting tools under identical process conditions. The loss of cutting ability of cutting tools or the change of the blade original geometry influences the quality of the surface finish as well as both dimensional and shape accuracy of workpieces. The effect of the grinding parameters on the surface finish of selected high-speed steels has been investigated. The influence of the grinding parameters has been defined especially for surface roughness, grinding forces and grinding ratio with a wide range of grinding parameters. It is found that the value of average roughness (Ra ) parameter decreases together with an increase in the grinding depth and the feed length. Furthermore, the value of Ra increases proportionally to the grinding depth. To increase the efficiency of sharpening, it is required to increase the feed length other than the grinding depth

Investigation of frictional conditions of steel sheets using pin-on-disk tribometer

This paper presents a method of determining the anisotropic friction model for sheet metal forming processes based on experimental data obtained from the pin-on-disk tribometer test. Friction coefficient value was measured as a function of angular position with respect to the rolling direction of the sheet metal. The frictional investigations presented in this work were conducted for deep drawing quality cold-rolled steel sheet with a sheet thickness of 1 mm

Facilitation and the niche: Implications for coexistence, range shifts and ecosystem functioning

Viewing facilitation through the lens of the niche concept is one way to unify conceptual and empirical advances about the role of facilitation in community ecology. We clarify conceptually and through examples from marine and terrestrial environments how facilitation can expand species' niches and consider how these interactions can be scaled up to understand the importance of facilitation in setting a species' geographic range. We then integrate the niche-broadening influence of facilitation into current conceptual areas in ecology, including climate change, diversity maintenance and the relationship between diversity and ecosystem functioning. Because facilitation can influence the range of physical conditions under which a species can persist, it has the potential to mitigate the effects of climate change on species distributions. Whereas facilitation has mostly been considered as a diversity-promoting interaction by ameliorating abiotic stresses, if facilitated species' niches expand and become less distinct as a result of habitat amelioration, the forces that maintain diversity and promote coexistence in regions or habitats dominated by the facilitator could be reduced (i.e. the sign of the effects of facilitation on populations could be species-specific). Finally, shifting or broadening ecological niches could alter the relationship between diversity and ecosystem functioning. A niche-based perspective on the effects of facilitation can foster a greater mechanistic understanding of the role played by facilitation in regulating species coexistence, range shifts and ecosystem functioning in a changing world

Combining x-ray real and reciprocal space mapping techniques to explore the epitaxial growth of semiconductors

In the present work, the importance of determining the strain states of semiconductor compounds with high accuracy is demonstrated. For the matter in question, new software titled LAPAs, the acronym for LAttice PArameters is presented. The lattice parameters as well as the chemical composition of Al1-xInxN and Ge1-xSnx compounds grown on top of GaN- and Ge-buffered c-Al2O3 and (001) oriented Si substrates, respectively, are calculated via the real space Bond's method. The uncertainties in the lattice parameters and composition are derived, compared and discussed with the ones found via x-ray diffraction reciprocal space mapping. Broad peaks lead to increased centroid uncertainty and are found to constitute up to 99% of the total uncertainty in the lattice parameters. Refraction correction is included in the calculations and found to have an impact of 0.001 angstrom in the lattice parameters of both hexagonal and cubic crystallographic systems and below 0.01% in the quantification of the InN and Sn contents. Although the relaxation degrees of the nitride and tin compounds agree perfectly between the real and reciprocal-spaces methods, the uncertainty in the latter is found to be ten times higher. The impact of the findings may be substantial for the development of applications and devices as the intervals found for the lattice match the condition of Al1-xInxN grown on GaN templates vary between similar to 1.8% (0.1675-0.1859) and 0.04% (0.1708-0.1712) if derived via the real- and reciprocal spaces methods.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Plurianual Strategic Funding UID/FIS/50010/2019. FO acknowledges the FCT PhD Grant and thanks the Institut fuer Halbleitertechnik, Universitaet Stuttgart for hospitality. The authors acknowledge Professor I Watson and Professor F Schulze from the Universities of Strathclyde, Scotland, United Kingdom, and Stuttgart, Germany for the growth of the nitrides and tin compounds, respectively