Instytut Podstawowych Problemów Techniki

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We present a facile and green approach to produce crystalline TiO2 nanoparticles on a surface of different carbonaceous materials derived from lignocellulosic biomass such as STARBON-800® obtained by carbonization at 800 °C and biochar-SWP700 (Soft Wood Pellets (SWP) obtained by pyrolysis at 700 °C) via novel low-temperature ultrasound-promoted green methodology coupled with citric acid as a cross-linking agent. In comparison to other methods, the developed method has several significant benefits such as simplicity, great ability to get crystalline TiO2 particles (elimination of high-temperature treatment (material calcination at >300 °C) needed in the conventional sol-gel method, which is extremely important in transforming amorphous TiO2 into a photoactive crystalline phase) elimination of risky chemicals and oxidizing agent, and also ability to change some parameters (e. g. ultrasound intensity). Prepared materials were characterized by XRD, DR UV−vis, N2 physisorption, HR-XPS, XRF, HR-TEM, FT-IR and subsequently tested for their photocatalytic activities both in photocatalytic phenol degradation (in water) and oxidation of methanol (in air) under UV and visible light irradiation.

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In this paper the results of numerical simulations and experimental studies are presented which describe potential and limitation of applications of single-layer (SLG) and multi-layer (MLG) graphene for thermal conductivity enhancement (TCE) of copper. A series of composite structures were studied which are representative of most widely used systems. The influence of structural parameters on the macroscopic thermal conductivity was analyzed, both experimentally and by numerical simulations. Analytical and Finite Element Method modeling were carried out to investigate a wide range of phenomena, including the effect of copper-MLG interface, copper grain size, volume fraction, thickness and orientation of MLG platelets as well as spatial distribution of MLG defined by percolation factor. Both modeling and the experimental results show that the volume fraction of MLG regions, their size, orientation and spatial distribution may significantly affect the thermal conductivity of metal matrix composites. TCE can be obtained for the laminate-like structure or particulate composites with highly aligned MLG regions. The thermal conductivity of such composites is strongly anisotropic and enhanced in the direction perpendicular to the layers. The results obtained in this study predict that SLG will have a negative effect on the thermal conductivity of copper matrix composites.

Słowa kluczowe:

Thermal conductivity, Composites, Graphene, Finite element method

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The paper presents the results of studies on the structure and properties of the AlNi type diffusion layers fabricated on the IN 740 nickel alloy by chemical vapor deposition using aluminium chloride (AlCl3), introduced into a hydrogen atmosphere. The layers were examined by light microscopy and scanning electron microscopy. Their chemical composition was examined by EDS, and the phase composition - using a Bruker D8 X-ray diffractometer with CuKa radiation. Fatigue tests were carried out in Inconel 740 sample, in the initial state and covered with the diffusion intermetallic AlNi layers. The strength under dynamic load was examined using a MTS 858 testing machine using symmetric load cycles repeated at a frequency of 20 Hz. The stress amplitude was 550 MPa. Corrosion resistance tests were performed employing potentiodynamic methods, in 0.1M Na2SO4 solution, at ambient temperature. It is shown that the layers improve the fatigue resistance and corrosion resistance of the Inconel 740 substrate.

Słowa kluczowe:

Inconel 740, CVD, Aluminide layer, High-cycle fatigue, corrosion resistance

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Material and magnetic degradation on the edges of electromagnetic silicon steel sheets is usually neglected in designing electro-mechanical equipment. Magnetic changes at the sheet edges are insignificantly small in the case of transformers. In the electric machines they can produce significant losses, amounting to 0.5 % when the losses due to the magneto-elastic and reverse phenomena (Joule and Villari) are taken into account. In this context the paper presents the results of laboratory and simulation studies of the influence of various production technologies on the material structure and magnetic properties at edges of elements for electro-mechanical devices.

Słowa kluczowe:

magneto-elastic and elasto-magnetic effects, plastic strains, changes of magnetic parameters, changes of magnetic hysteresis loop of electromagnetic steel sheet

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Our numerical approach to modeling elastic-plastic deformation comes back to the idea of the time-independent plasticity developed here at the molecular-statics level. We use a constitutive atomic model based on the second-moment approximation of the tight-binding potential coupled to a linear theory of elasticity solved simultaneously within the finite element method. Our model is applied to the nanoindentation problem for copper in which the indenter is represented by the equations of a sphere. For convenience the time-dependency of the nanoindentation problem is reduced to a quasi-static adiabatic scheme. A recurring theme in this paper is to determine the response of the proposed model for two differing systems: mono and polycrystalline copper. This paper discusses the force-depth response in terms of atomic bond-lengths, elastic-plastic deformations, and the instantaneous stiffness of the material. We report on an increased instantaneous stiffness of polycrystalline copper compared to that of its monocrystalline counterpart. From both a distinct and a comparative analysis of both systems, based on the relaxed positions of the atoms in the structure during the simulation, we deduce that plastic deformations at grain-boundaries are responsible for this change in the overall instantaneous stiffness of the material.

Słowa kluczowe:

linear elasticity, material science, molecular statics, nanoindentation, quasicontinuum methods

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Problem of locally disordered atomic structure is solved by using a hybrid formulation in which nonlinear elastic finite elements are linked with discrete atomic interaction elements. The continuum approach uses nonlinear hyperelasticity based upon the generalized strain while the atomistic approach employs the Tight-Binding Second-Moment Approximation potential to create new type of elements. The molecular interactions yielding from constitutive models of TB-SMA were turned into interactions between nodes to solve a boundary value problem by means of finite element solver.
In this paper we present a novel way of modelling materials behaviour where both discrete (molecular dynamics) and continuum (nonlinear finite element) methods are used. As an example, the nanoindentation of a copper sample is modelled numerically by applying a hybrid formulation. Here, the central area of the sample subject to a nanoindentation operation is discretised by an atomic net where the remaining area of the sample far from indenters tip is discretised by the use of a nonlinear finite element mesh.

Słowa kluczowe:

Nanostructure, Nanoindentation, Molecular statics, Finite element modelling

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