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Publications in other journals ranked by Ministry of Science and Higher Education
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Affiliation to IPPT PAN

1.Grzywacz H., Milczarek M., Jenczyk P., Dera W., Michałowski M., Jarząbek D.M., Quantitative measurement of nanofriction between PMMA thin films and various AFM probes, MEASUREMENT, ISSN: 0263-2241, DOI: 10.1016/j.measurement.2020.108267, Vol.168, pp.108267-1-13, 2020
Grzywacz H., Milczarek M., Jenczyk P., Dera W., Michałowski M., Jarząbek D.M., Quantitative measurement of nanofriction between PMMA thin films and various AFM probes, MEASUREMENT, ISSN: 0263-2241, DOI: 10.1016/j.measurement.2020.108267, Vol.168, pp.108267-1-13, 2020

Abstract:
This study reports the quantitative, precise and accurate results of nanoscale friction measurements with the use of an Atomic Force Microscope calibrated with a precise nanoforce sensor. For this purpose, three samples of spin-coated thin Polymethylmethacrylate (PMMA) films were prepared with the following thicknesses: 235, 343, and 513 nm. Three different AFM probes were used for the friction measurements: with diamond-like carbon (DLC) tip with a small (15 nm) or big (2 µm) tip radius, and a reference silicon tip with a small (8 nm) radius. The results show that in all of the studied cases, the coefficient of friction strongly depends on the applied load, being much higher for a lower load. Furthermore, a strong relation of the friction force on the cantilever's geometry, the scanning velocity, and the film thickness was observed.

Keywords:
lateral force microscopy, friction, thin PMMA films, atomic force microscope, DLC coatings, adhesion

2.Ryś M., Forest S., Petryk H., A micromorphic crystal plasticity model with the gradient-enhanced incremental hardening law, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/j.ijplas.2019.102655, Vol.128, pp.102655-1-21, 2020
Ryś M., Forest S., Petryk H., A micromorphic crystal plasticity model with the gradient-enhanced incremental hardening law, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/j.ijplas.2019.102655, Vol.128, pp.102655-1-21, 2020

Abstract:
A model of crystal plasticity is developed in which the effects of plastic flow non-uniformity are described through the full dislocation density tensor. The micromorphic approach is used in which the dislocation density tensor is represented by the curl of an independent constitutive variable called microdeformation. The microdeformation tensor is enforced by an energetic penalty term to be close to the actual plastic distortion tensor. The curl of microdeformation tensor enters the constitutive model in two independent but complementary ways. First, it is an argument of the free energy density function, which describes the kinematic-type hardening in cyclic non-uniform deformation. Second, its rate influences the rates of critical resolved shear stresses, which corresponds to additional isotropic hardening caused by incompatibility of the plastic flow rate. The latter effect, missing in the standard slip-system hardening rule, is described in a simple manner that does not require any extra parameter in comparison to the non-gradient theory. In the proposed model there are two independent internal length scales whose interplay is examined by means of 1D and 2D numerical examples of plastic shearing of a single crystal.

Keywords:
gradient theory, crystal plasticity, dissipation, length scale, cyclic deformation, numerical regularization

3.Majewski M., Hołobut P., Kursa M., Kowalczyk-Gajewska K., Packing and size effects in elastic-plastic particulate composites: micromechanical modelling and numerical verification, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103271, Vol.151, pp.103271-1-18, 2020
Majewski M., Hołobut P., Kursa M., Kowalczyk-Gajewska K., Packing and size effects in elastic-plastic particulate composites: micromechanical modelling and numerical verification, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103271, Vol.151, pp.103271-1-18, 2020

Abstract:
The issue of applicability of the Morphologically Representative Pattern (MRP) approach to elastic-plastic composites is addressed. The extension to the regime of non-linear material behaviour is performed by employing the concept of incremental linearization of the material response in two basic variants: tangent and secant. The obtained predictions are evaluated through comparison with the outcomes of numerical analyses. Finite Element simulations are carried out using periodic unit cells with cubic arrangements of spherical particles and representative volume elements (RVE) with 50 randomly placed inclusions. In addition to the analysis of the packing effect in two-phase composites, the size effect is also studied by assuming an interphase between the matrix and inclusions. It is concluded that the MRP approach can be used as an effective predictive alternative to computational homogenization, not only in the case of linear elasticity but also in the case of elastic-plastic composites.

Keywords:
particulate composites, elastoplasticity, micromechanics, size effect, packing effect, morphologically representative pattern

4.Darban H., Luciano R., Caporale A., Fabbrocino F., Higher modes of buckling in shear deformable nanobeams, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103338, Vol.154, pp.103338-1-18, 2020
Darban H., Luciano R., Caporale A., Fabbrocino F., Higher modes of buckling in shear deformable nanobeams, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103338, Vol.154, pp.103338-1-18, 2020

Abstract:
The size-dependent buckling instability of shear deformable nanobeams rested on a two-parameter elastic foundation is studied through the stress-driven nonlocal theory of elasticity and the kinematic assumptions of the Timoshenko beam theory. The small-scale size effects are taken into account by nonlocal constitutive relationships, which define the strains at each point as integral convolutions in terms of the stresses in all the points and a kernel. In this manner, the nonlocal elasticity formulation is well-posed and does not include inconsistencies usually arising using other nonlocal models. The size-dependent governing differential equations in terms of the transverse displacement and the cross-sectional rotation are decoupled, and closed form solutions are presented for the displacement functions. Proper boundary conditions are imposed and the buckling problem is reduced to finding roots of a determinant of a matrix, whose elements are given explicitly for different classical edge conditions. The closed form treatment of the problem avoids the numerical instabilities usually occurring within numerical techniques, and allows to find also higher buckling loads and shape modes. Several nanobeams rested on the Winkler or Pasternak elastic foundations and characterized by different boundary conditions, shear deformability, and nonlocality are considered and the critical loads and shape modes are presented, including those for the higher modes of buckling. Excellent agreements are found with the available approximate numerical results in the literature and novel insightful findings are presented and discussed, which are in accordance with experimental observations.

Keywords:
nanobeam, buckling, elastic foundation, closed form solution, nonlocal elasticity, size effect

5.Darban H., Fabbrocino F., Luciano R., Size-dependent linear elastic fracture of nanobeams, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103381, Vol.157, pp.103381-1-13, 2020
Darban H., Fabbrocino F., Luciano R., Size-dependent linear elastic fracture of nanobeams, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103381, Vol.157, pp.103381-1-13, 2020

Abstract:
A nonlocal linear elastic fracture formulation is presented based on a discrete layer approach and an interface model to study cracked nanobeams. The formulation uses the stress-driven nonlocal theory of elasticity to account for the size-dependency in the constitutive equations, and the Bernoulli-Euler beam theory to define the kinematic field. Two fundamental mode I and mode II fracture nanospecimens with applications in Engineering Science are studied to reveal principal characteristics of the linear elastic fracture of beams at nanoscale. The domains are discretized both through the transverse and longitudinal directions and the field variables are derived by solving systems of the nonlocal equilibrium equations subjected to the variationally consistent and constitutive boundary and continuity conditions. The energy release rates of the fracture nanospecimens are calculated both from the global energy consideration and from the localized fields at the tip of the crack, i.e. the cohesive forces and the displacement jumps. The results are shown to be the same, proving the capability of the interface model to predict localized fields at the crack tip which are important for the cohesive fracture problems. It is found that the nanospecimens with higher nonlocality have higher fracture resistance and load bearing capacity due to higher energy absorptions and lower energy release rates. The crack propagation in the nanospecimens are also studied and load-displacement curves are presented. The nonlocality considerably increases the stiffness of the initial linear response of the nanospecimens. The fracture model is also able to capture the non-linear post-peak response and the unstable crack propagation, the snap-back instability, which is more intense for nanospecimens with higher nonlocality.

Keywords:
cracked nanobeams, nonlocal fracture, energy release rate, cohesive, crack propagation

6.Kowalczyk-Gajewska K., Maździarz M., Elastic properties of nanocrystalline materials of hexagonal symmetry: the core-shell model and atomistic estimates, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103393, Vol.157, pp.103393-1-21, 2020
Kowalczyk-Gajewska K., Maździarz M., Elastic properties of nanocrystalline materials of hexagonal symmetry: the core-shell model and atomistic estimates, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2020.103393, Vol.157, pp.103393-1-21, 2020

Abstract:
Anisotropic core-shell model of a nano-grained polycrystal is extended to estimate the effective elastic stiffness of several metals of hexagonal crystal lattice symmetry. In the approach the bulk nanocrystalline material is described as a two-phase medium with different properties for a grain boundary zone and a grain core. While the grain core is anisotropic, the boundary zone is isotropic and has a thickness defined by the cutoff radius of a corresponding atomistic potential for the considered metal. The predictions of the proposed mean-field model are verified with respect to simulations performed with the use of the Large-scale Atomic/Molecular Massively Parallel Simulator, the Embedded Atom Model, and the molecular statics method. The effect of the grain size on the overall elastic moduli of nanocrystalline material with random distribution of orientations is analyzed.

Keywords:
molecular statics, elasticity, polycrystal, effective medium, hexagonal symmetry

7.Jarząbek D.M., Milczarek M., Nosewicz S., Bazarnik P., Schift H., Size effects of hardness and strain rate sensitivity in amorphous silicon measured by nanoindentation, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, ISSN: 1073-5623, DOI: 10.1007/s11661-020-05648-w, Vol.51, No.4, pp.1625-1633, 2020
Jarząbek D.M., Milczarek M., Nosewicz S., Bazarnik P., Schift H., Size effects of hardness and strain rate sensitivity in amorphous silicon measured by nanoindentation, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, ISSN: 1073-5623, DOI: 10.1007/s11661-020-05648-w, Vol.51, No.4, pp.1625-1633, 2020

Abstract:
In this work, dynamic mechanical properties of amorphous silicon and scale effects were investigated by the means of nanoindentation. An amorphous silicon sample was prepared by plasma-enhanced chemical vapor deposition (PECVD). Next, two sets of the samples were investigated: as-deposited and annealed in 500 °C for 1 hour. A three-sided pyramidal diamond Berkovich's indenter was used for the nanoindentation tests. In order to determine the strain rate sensitivity (SRS), indentations with different loading rates were performed: 0.1, 1, 10, 100 mN/min. Size effects were studied by application of maximum indentation loads in the range from 1 up to 5 mN (penetrating up to approximately one-third of the amorphous layer). The value of hardness was determined by the Oliver-Pharr method. An increase of hardness with decrease of the indentation depth was observed for both samples. Furthermore, the significant dependence of hardness on the strain rate has been reported. Finally, for the annealed samples at low strain rates a characteristic "elbow" during unloading was observed on the force-indentation depth curves. It could be attributed to the transformation of (β-Sn)-Si to the PI (pressure-induced) a-Si end phase.

8.Węglewski W., Pitchai P., Bochenek K., Bolzon G., Konetschnik R., Sartory B., Ebner R., Kiener D., Basista M., Experimental and numerical investigation of the deformation and fracture mode of microcantilever beams made of Cr(Re)/Al2O3 metal–matrix composite, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, ISSN: 1073-5623, DOI: 10.1007/s11661-020-05687-3, Vol.51, No.5, pp.2377-2390, 2020
Węglewski W., Pitchai P., Bochenek K., Bolzon G., Konetschnik R., Sartory B., Ebner R., Kiener D., Basista M., Experimental and numerical investigation of the deformation and fracture mode of microcantilever beams made of Cr(Re)/Al2O3 metal–matrix composite, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, ISSN: 1073-5623, DOI: 10.1007/s11661-020-05687-3, Vol.51, No.5, pp.2377-2390, 2020

Abstract:
This work presents a combined experimental and computational study of the deformation and fracture of microcantilever specimens made of chromium(rhenium)-alumina metal–matrix composite (MMC), with a particular focus on the failure properties of the metal–ceramic interfaces. The obtained experimental results show that the bending strength of microcantilevers containing alumina particles in critical cross-sections near specimen's fixed end is considerably higher than that of unreinforced chromium(rhenium) samples. Brittle cracking along chromium–alumina interfaces is the dominant fracture mode of the composite microcantilevers. The interface characteristics are determined in an indirect way by numerical simulations of the experiment with account of the actual specimen microstructure from the scanning electron microscope (SEM) images. A parametric study demonstrates that the overall material response may be reproduced by different sets of model parameters, whereas the actual failure mode permits to discriminate among the possible alternatives. Using this approach, the in situ values of the chromium–alumina interface cohesive strength and the fracture energy are estimated.

9.Alvi S., Jarząbek D.M., Kohan M.G., Hedman D., Jenczyk P., Natile M.M., Vomiero A., Akhtar F., Synthesis and mechanical characterization of a CuMoTaWV high-entropy film by magnetron sputtering, ACS Applied Materials and Interfaces, ISSN: 1944-8244, DOI: 10.1021/acsami.0c02156, Vol.12, No.18, pp.21070-21079, 2020
Alvi S., Jarząbek D.M., Kohan M.G., Hedman D., Jenczyk P., Natile M.M., Vomiero A., Akhtar F., Synthesis and mechanical characterization of a CuMoTaWV high-entropy film by magnetron sputtering, ACS Applied Materials and Interfaces, ISSN: 1944-8244, DOI: 10.1021/acsami.0c02156, Vol.12, No.18, pp.21070-21079, 2020

Abstract:
Development of high-entropy alloy (HEA) films is a promising and cost-effective way to incorporate these materials of superior properties in harsh environments. In this work, a refractory high-entropy alloy (RHEA) film of equimolar CuMoTaWV was deposited on silicon and 304 stainless-steel substrates using DC-magnetron sputtering. A sputtering target was developed by partial sintering of an equimolar powder mixture of Cu, Mo, Ta, W, and V using spark plasma sintering. The target was used to sputter a nanocrystalline RHEA film with a thickness of ~900 nm and an average grain size of 18 nm. X-ray diffraction of the film revealed a body-centered cubic solid solution with preferred orientation in the (110) directional plane. The nanocrystalline nature of the RHEA film resulted in a hardness of 19 ± 2.3 GPa and an elastic modulus of 259 ± 19.2 GPa. A high compressive strength of 10 ± 0.8 GPa was obtained in nanopillar compression due to solid solution hardening and grain boundary strengthening. The adhesion between the RHEA film and 304 stainless-steel substrates was increased on annealing. For the wear test against the E52100 alloy steel (Grade 25, 700-880 HV) at 1 N load, the RHEA film showed an average coefficient of friction (COF) and wear rate of 0.25 (RT) and 1.5 (300 °C), and 6.4 × 10^–6 mm^3/N m (RT) and 2.5 × 10^–5 mm^3/N m (300 °C), respectively. The COF was found to be 2 times lower at RT and wear rate 10^2 times lower at RT and 300 °C than those of 304 stainless steel. This study may lead to the processing of high-entropy alloy films for large-scale industrial applications.

Keywords:
high-entropy alloys, magnetron sputtering, spark plasma sintering, mechanical properties, wear

10.Ceroni F., Darban H., Luciano R., Analysis of bond behavior of injected anchors in masonry elements by means of finite element modeling, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2020.112099, Vol.241, pp.112099-1-18, 2020
Ceroni F., Darban H., Luciano R., Analysis of bond behavior of injected anchors in masonry elements by means of finite element modeling, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2020.112099, Vol.241, pp.112099-1-18, 2020

Abstract:
Injected anchors made of steel bars embedded in masonry elements by means of cement-based grout represented in the past a wide solution for avoiding out-of-plane mechanisms. Corrosion phenomena in steel bars reduced the effectiveness of such type of intervention over time. Innovative materials, as the Fiber Reinforced Plastic ones, can represent a suitable alternative to increase durability and performance of injected anchors. Since the effectiveness of injected anchors is strictly related to bond behaviour along both the bar-grout and the grout-masonry interfaces, a detailed analysis by means of a Finite Element model was developed for different types of bars embedded in masonry elements. The numerical model was firstly calibrated on some experimental results of pull-out tests available in literature and, then, is used for investigating the effects of several parameters on both local and global behaviour. Load-displacement curves and local distributions of shear stresses are examined in detail. The numerical analyses evidenced that the maximum tensile force in the anchor mainly depends on the shear strength of the bar-grout and the grout-masonry interfaces and on the embedded length, but for very long embedded length, it can be limited by the tensile failure in the anchor or in the masonry.

Keywords:
masonry, FRP bars, injected anchors, bond, pull-out test, FE model

11.Lewandowski-Szewczyk M.J., Stupkiewicz S., Non-standard contact conditions in generalized continua: microblock contact model for a Cosserat body, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/j.ijsolstr.2020.07.001, Vol.202, pp.881-894, 2020
Lewandowski-Szewczyk M.J., Stupkiewicz S., Non-standard contact conditions in generalized continua: microblock contact model for a Cosserat body, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/j.ijsolstr.2020.07.001, Vol.202, pp.881-894, 2020

Abstract:
Generalized continuum theories involve non-standard boundary conditions that are associated with the additional kinematic variables introduced in those theories, e.g., higher gradients of the displacement field or additional kinematic degrees of freedom. Accordingly, formulation of a contact problem for such a continuum necessarily requires that adequate contact conditions are formulated for the additional kinematic variables and/or for the respective generalized tractions. In this paper, we address several related open problems, namely, how to enhance the classic contact conditions to include the effects of the additional kinematic variables, how to link the enhanced contact model to the underlying microstructure of the solid, and how to do it in a consistent manner. As a first step towards a new class of contact models for generalized continua, a microblock contact model is derived for a Cosserat solid based on simple micromechanical considerations. To illustrate the non-trivial effects introduced by the non-standard boundary conditions, the problem of compression of an infinite strip with nonaligned microblocks is considered, and the analytical solution is derived for the corresponding boundary layers. A Hertz-like contact problem is also solved numerically with the focus on non-standard features of the solution and on the related size effects.

Keywords:
microstructure, contact problems, size effects, boundary layers, Cosserat continuum

12.Lengiewicz J., Souza M., Lahmar M.A., Courbon C., Dalmas D., Stupkiewicz S., Scheibert J., Finite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/j.jmps.2020.104056, Vol.143, pp.104056-1-19, 2020
Lengiewicz J., Souza M., Lahmar M.A., Courbon C., Dalmas D., Stupkiewicz S., Scheibert J., Finite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/j.jmps.2020.104056, Vol.143, pp.104056-1-19, 2020

Abstract:
Solid contacts involving soft materials are important in mechanical engineering or biomechanics. Experimentally, such contacts have been shown to shrink significantly under shear, an effect which is usually explained using adhesion models. Here we show that quantitative agreement with recent high-load experiments can be obtained, with no adjustable parameter, using a non-adhesive model, provided that finite deformations are taken into account. Analysis of the model uncovers the basic mechanisms underlying anisotropic shear-induced area reduction, local contact lifting being the dominant one. We confirm experimentally the relevance of all those mechanisms, by tracking the shear-induced evolution of tracers inserted close to the surface of a smooth elastomer sphere in contact with a smooth glass plate. Our results suggest that finite deformations are an alternative to adhesion, when interpreting a variety of sheared contact experiments involving soft materials.

Keywords:
contact mechanics, friction, contact area, elastomer, full-field measurement

13.Bochenek K., Węglewski W., Morgiel J., Maj M., Basista M., Enhancement of fracture toughness of hot-pressed NiAl-Re material by aluminum oxide addition, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2020.139670, Vol.790, pp.139670-1-6, 2020
Bochenek K., Węglewski W., Morgiel J., Maj M., Basista M., Enhancement of fracture toughness of hot-pressed NiAl-Re material by aluminum oxide addition, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2020.139670, Vol.790, pp.139670-1-6, 2020

Abstract:
In the search for a remedy to increase the fracture toughness of NiAl, the effect of rhenium and aluminum oxide addition is explored. Using a powder metallurgy processing route an optimum composition of NiAl-Re-Al2O3 material is found which manifests KIC over two times higher than as-received NiAl sintered under the same conditions.

Keywords:
fracture behavior, stress/strain measurements, intermetallics, composites, powder metallurgy, grains and interfaces

14.Maj M., Nowak M., Musiał S., Płociński T., Experimental analysis of material, lattice and plastic rotation during deformation of aluminium multicrystal, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2020.139725, Vol.790, pp.139725-1-5, 2020
Maj M., Nowak M., Musiał S., Płociński T., Experimental analysis of material, lattice and plastic rotation during deformation of aluminium multicrystal, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2020.139725, Vol.790, pp.139725-1-5, 2020

Abstract:
This paper focuses on the experimental determination of the distribution of material, lattice and plastic rotation during deformation of crystalline aggregate. The proposed methodology uses standard electron backscattering diffraction technique combined with 3D digital image correlation data. The presented approach is used for analysis of rotations during deformation of aluminium multicrystal.

Keywords:
image analysis, electron backscattering diffraction, plastic deformation, misorientation, plastic rotation

15.Szymczyk M., Nowak M., Sumelka W., Plastic strain localization in an extreme dynamic tension test of steel sheet in the framework of fractional viscoplasticity, Thin-Walled Structures, ISSN: 0263-8231, DOI: 10.1016/j.tws.2019.106522, Vol.149, pp.106522-1-11, 2020
Szymczyk M., Nowak M., Sumelka W., Plastic strain localization in an extreme dynamic tension test of steel sheet in the framework of fractional viscoplasticity, Thin-Walled Structures, ISSN: 0263-8231, DOI: 10.1016/j.tws.2019.106522, Vol.149, pp.106522-1-11, 2020

Abstract:
The paper considers the plastic strain localization phenomenon in the framework of the fractional viscoplasticity. As an illustrative example, full spatial modelling of a tension test under extreme dynamic conditions is presented. The modelling assumes adiabatic conditions including isotropic work hardening-softening effects induced by plastic strains, temperature and damage (scalar). Special attention is paid to additional, compared to the classical Perzyna viscoplasticity, model parameters resulting from application of fractional calculus in the evolution law for plastic strains. It is shown that the proposed formulation allows for high flexibility of modelling of the localization zone with a limited number of model parameters.

Keywords:
fractional viscoplasticity, strain localization, extreme dynamics

16.Golasiński K.M., Pieczyska E.A., Maj M., Staszczak M., Świec P., Furuta T., Kuramoto S., Investigation of strain rate sensitivity of gum metal under tension using digital image correlation, ARCHIVES OF CIVIL AND MECHANICAL ENGINEERING, ISSN: 1644-9665, DOI: 10.1007/s43452-020-00055-9, Vol.20, No.2, pp.53-1-14, 2020
Golasiński K.M., Pieczyska E.A., Maj M., Staszczak M., Świec P., Furuta T., Kuramoto S., Investigation of strain rate sensitivity of gum metal under tension using digital image correlation, ARCHIVES OF CIVIL AND MECHANICAL ENGINEERING, ISSN: 1644-9665, DOI: 10.1007/s43452-020-00055-9, Vol.20, No.2, pp.53-1-14, 2020

Abstract:
Mechanical behavior of a multifunctional titanium alloy Gum Metal was investigated by conducting tensile tests at various strain rates and applying digital image correlation (DIC) technique. Stress–strain curves confirmed low Young's modulus and high strength of the alloy. The determined values of yield strength had a tendency to increase, whereas the elongation to the specimen rupture tended to decrease with increasing strain rate. True stress versus strain curves were analyzed using selected lengths of virtual extensometer (VE) placed in the strain localization area. When the initial length of the VE was the same as the gauge length, work hardening was observed macroscopically at lower strain rates, and a softening was seen at higher strain rates. However, the softening effect was not observed at the shorter VE lengths. Evolution of the Hencky strain and rate of deformation tensor component fields were analyzed for various strain rates at selected stages of Gum Metal loading. The DIC analysis demonstrated that for lower strain rates the deformation is macroscopically uniform up to the higher average Hencky strains, whereas for higher strain rates the strain localization occurs at the lower average Hencky strains of the deformation process and takes place in the smaller area. It was also found that for all strain rates applied, the maximal values of Hencky strain immediately before rupture of Gum Metal samples were similar for each of the applied strain rates, and the maximal local values of deformation rate were two orders higher when compared to applied average strain rate values.

Keywords:
titanium alloy, gum metal, strain rate sensitivity, strain localization, digital image correlation, full-field deformation analysis

17.Magliulo M., Lengiewicz J., Zilian A., Beex L.A.A., Non-localised contact between beams with circular and elliptical cross-sections, COMPUTATIONAL MECHANICS, ISSN: 0178-7675, DOI: 10.1007/s00466-020-01817-1, Vol.65, No.5, pp.1247-1266, 2020
Magliulo M., Lengiewicz J., Zilian A., Beex L.A.A., Non-localised contact between beams with circular and elliptical cross-sections, COMPUTATIONAL MECHANICS, ISSN: 0178-7675, DOI: 10.1007/s00466-020-01817-1, Vol.65, No.5, pp.1247-1266, 2020

Abstract:
The key novelty of this contribution is a dedicated technique to efficiently determine the distance (gap) function between parallel or almost parallel beams with circular and elliptical cross-sections. The technique consists of parametrizing the surfaces of the two beams in contact, fixing a point on the centroid line of one of the beams and searching for a constrained minimum distance between the surfaces (two variants are investigated). The resulting unilateral (frictionless) contact condition is then enforced with the Penalty method, which introduces compliance to the, otherwise rigid, beams' cross-sections. Two contact integration schemes are considered: the conventional slave-master approach (which is biased as the contact virtual work is only integrated over the slave surface) and the so-called two-half-pass approach (which is unbiased as the contact virtual work is integrated over the two contacting surfaces). Details of the finite element formulation, which is suitably implemented using Automatic Differentiation techniques, are presented. A set of numerical experiments shows the overall performance of the framework and allows a quantitative comparison of the investigated variants.

Keywords:
beams, contact, circular and elliptical cross-sections, rigid cross-sections, single-pass algorithm, two-half-pass algorithm

18.Ustrzycka A., Skoczeń B., Nowak M., Kurpaska Ł., Wyszkowska E., Jagielski J., Elastic–plastic-damage model of nano-indentation of the ion-irradiated 6061 aluminium alloy, INTERNATIONAL JOURNAL OF DAMAGE MECHANICS, ISSN: 1056-7895, DOI: 10.1177/1056789520906209, pp.1-35, 2020
Ustrzycka A., Skoczeń B., Nowak M., Kurpaska Ł., Wyszkowska E., Jagielski J., Elastic–plastic-damage model of nano-indentation of the ion-irradiated 6061 aluminium alloy, INTERNATIONAL JOURNAL OF DAMAGE MECHANICS, ISSN: 1056-7895, DOI: 10.1177/1056789520906209, pp.1-35, 2020

Abstract:
The paper presents experimental and numerical characterization of damage evolution for ion-irradiated materials subjected to plastic deformation during nano-indentation. Ion irradiation technique belongs to the methods where creation of radiation-induced defects is controlled with a high accuracy (including both, concentration and depth distribution control), and allows to obtain materials having a wide range of damage level, usually expressed in terms of displacements per atom (dpa) scale. Ion affected layers are usually thin, typically less than 1 micrometer thick. Such a low thickness requires to use nano-indentation technique to measure the mechanical properties of the irradiated layers. The He or Ar ion penetration depth reaches approximately 150 nm, which is sufficient to perform several loading-partial-unloading cycles at increasing forces. Damage evolution is reflected by the force-displacement diagram, that is backed by the stress–strain relation including damage. In this work the following approach is applied: dpa is obtained from physics (irradiation mechanisms), afterwards, the radiation-induced damage is defined in the framework of continuum damage mechanics to solve the problem of further evolution of damage fields under mechanical loads. The nature of radiation-induced damage is close to porosity because of formation of clusters of vacancies. The new mathematical relation between radiation damage (dpa) and porosity parameter is proposed. Deformation process experienced by the ion irradiated materials during the nano-indentation test is then numerically simulated by using extended Gurson–Tvergaard– Needleman (GTN) model, that accounts for the damage effects. The corresponding numerical results are validated by means of the experimental measurements. It turns out, that the GTN model quite successfully reflects closure of voids, and increase of material density during the nano-indentation.

Keywords:
radiation-induced damage, evolution of vacancy clusters, nano-indentation test, ion irradiation, radiation hardening

19.Gupta A., Jain A., Tripathi S., Structural and electrochemical studies of bromide derived ionic liquid-based gel polymer electrolyte for energy storage application, Journal of Energy Storage, ISSN: 2352-152X, DOI: 10.1016/j.est.2020.101723, Vol.32, pp.101723-1-7, 2020
Gupta A., Jain A., Tripathi S., Structural and electrochemical studies of bromide derived ionic liquid-based gel polymer electrolyte for energy storage application, Journal of Energy Storage, ISSN: 2352-152X, DOI: 10.1016/j.est.2020.101723, Vol.32, pp.101723-1-7, 2020

Abstract:
In the present studies, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), ionic liquid {1-Ethyl-3-methylimidazolium bromide} (EMIM)(Br), and magnesium perchlorate Mg(ClO4)2 as salt were used to synthesize free standing electrolyte films by using solution cast technique. The prepared electrolyte films were investigated by using various structural and electrochemical techniques like scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) as well as ionic and temperature dependence studies. It has been observed that addition of ionic liquid significantly increases the properties like ionic conductivity, thermal stability, transparency etc. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 2.05 × 10^−2 S cm^−1 which is suitable for device fabrication point of view. The optimized electrolyte films are suitable for supercapacitor application.

Keywords:
gel polymer electrolytes, ionic liquid, solution cast technique, supercapacitors

20.Magliulo M., Lengiewicz J., Zilian A., Beex L.A.A., Beam-inside-beam contact: mechanical simulations of slender medical instruments inside the human body, Computer Methods and Programs in Biomedicine, ISSN: 0169-2607, DOI: 10.1016/j.cmpb.2020.105527, Vol.196, pp.105527-1-14, 2020
Magliulo M., Lengiewicz J., Zilian A., Beex L.A.A., Beam-inside-beam contact: mechanical simulations of slender medical instruments inside the human body, Computer Methods and Programs in Biomedicine, ISSN: 0169-2607, DOI: 10.1016/j.cmpb.2020.105527, Vol.196, pp.105527-1-14, 2020

Abstract:
This contribution presents a rapid computational framework to mechanically simulate the insertion of a slender medical instrument in a tubular structure such as an artery, the cochlea or another slender instrument.

Keywords:
surgical simulation, contact mechanics, beam-inside-beam, artery, cochlea

21.Krajewski M., Liou S.C., Chiou W.A., Tokarczyk M., Małolepszy A., Płocińska M., Witecka A., Lewińska S., Ślawska-Waniewska A., Amorphous FexCo1–x wire-like nanostructures manufactured through surfactant-free magnetic-field-induced synthesis, Crystal Growth and Design, ISSN: 1528-7483, DOI: 10.1021/acs.cgd.0c00070, Vol.20, No.5, pp.3208-3216, 2020
Krajewski M., Liou S.C., Chiou W.A., Tokarczyk M., Małolepszy A., Płocińska M., Witecka A., Lewińska S., Ślawska-Waniewska A., Amorphous FexCo1–x wire-like nanostructures manufactured through surfactant-free magnetic-field-induced synthesis, Crystal Growth and Design, ISSN: 1528-7483, DOI: 10.1021/acs.cgd.0c00070, Vol.20, No.5, pp.3208-3216, 2020

Abstract:
So far, it has been proven that the magnetic-field-induced (MFI) synthesis is a process which mainly leads to the formation of magnetic metallic one-dimensional nanostructures. Taking advantage of this method, the new procedures which allow manufacture of the magnetic bimetallic iron–cobalt wire-like nanochains with Fe0.75 Co0.25, Fe0.50 Co0.50, and Fe0.25 Co0.75 compositions are demonstrated in this work. They were produced through a simple one-step magnetic-field-induced (MFI) chemical co-reduction of three different mixtures containing a proper amount of Fe2+ and Co2+ ions with aqueous sodium borohydride solution as the reducing agent. The synthesis process was carried out at room temperature without the use of templates, surfactants, complexing agents, and organic solvents. The morphological and structural studies indicated that all as-prepared materials were amorphous, and they were composed of nanoparticles aligned in almost straight chains. Moreover, they revealed the core–shell structures with bimetallic alloy cores containing desired iron-to-cobalt ratios and very thin oxide shells. Furthermore, the obtained nanostructures behaved as ferromagnetic materials. Their magnetic properties were correlated with their structural properties and chemical compositions. It was observed that their saturation magnetization decreased significantly with increasing content of cobalt in the chains, whereas the variation of their coercivity was less pronounced.

22.Jarząbek D.M., Harvey C., Levintant-Zayonts N., Wojciechowski T., Gniadek M., Krajewski M., Pathak S., Enhancement of mechanical properties of vertically aligned carbon nanotube arrays due to N+ ion irradiation, NANOTECHNOLOGY, ISSN: 0957-4484, DOI: 10.1088/1361-6528/ab8665, Vol.31, No.28, pp.285703-1-9, 2020
Jarząbek D.M., Harvey C., Levintant-Zayonts N., Wojciechowski T., Gniadek M., Krajewski M., Pathak S., Enhancement of mechanical properties of vertically aligned carbon nanotube arrays due to N+ ion irradiation, NANOTECHNOLOGY, ISSN: 0957-4484, DOI: 10.1088/1361-6528/ab8665, Vol.31, No.28, pp.285703-1-9, 2020

Abstract:
In this work we apply N+ ion irradiation on vertically aligned carbon nanotube (VACNT) arrays in order to increase the number of connections and joints in the CNT network. The ions energy was 50 keV and fluence 5 × 10^17 ions cm^−2. The film was 160 μm thick. SEM images revealed the ion irradiation altered the carbon bonding and created a sponge-like, brittle structure at the surface of the film, with the ion irradiation damage region extending ~4 μm in depth. TEM images showed the brittle structure consists of amorphous carbon forming between nanotubes. The significant enhancement of mechanical properties of the irradiated sample studied by the cyclic nanoindentation with a flat punch indenter was observed. Irradiation on the VACNT film made the structure stiffer, resulted in a higher percentage recovery, and reduced the energy dissipation under compression. The results are encouraging for further studies which will lead to create a class of materials - ion-irradiated VACNT films - which after further research may find application in storage or harvesting energy at the micro/nanoscale.

Keywords:
vertically aligned carbon nanotubes, ion irradiation, nanoindentation

23.Lee B.Y., Chu C.T., Krajewski M., Michalska M., Lin J.Y., Temperature-controlled synthesis of spinel lithium nickel manganese oxide cathode materials for lithium-ion batteries, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2020.05.124, Vol.46, No.13, pp.20856-20864, 2020
Lee B.Y., Chu C.T., Krajewski M., Michalska M., Lin J.Y., Temperature-controlled synthesis of spinel lithium nickel manganese oxide cathode materials for lithium-ion batteries, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2020.05.124, Vol.46, No.13, pp.20856-20864, 2020

Abstract:
In this work, we successfully synthesized series of LiNi0.5Mn1.5O4 (LNMO) cathode materials with spinel structure by using a facile sol-gel method and then calcined at various temperature ranging from 600 to 1000 °C. The application of different calcination temperatures significantly influenced the surface morphology, stoichiometry and crystalline nature of the as-synthesized LNMO material. According to the results of physical characterizations, the LNMO materials calcined at various temperatures mainly revealed the stoichiometric disordered Fd-3m structure with a small amount of well-ordered P4332 phase. The structural analysis also exhibited that the control of the calcination temperature contributed to the higher crystalline nature. Moreover, the morphological investigations indicated that the increasing calcination temperatures caused the formation of large micron-sized LNMO material. In turn, the electrochemical evaluations revealed the impact of the calcination temperatures on enhancing the electrochemical performances of the LNMO electrode materials up to 900 °C. The LNMO electrode calcined at 900 °C exhibited an impressive initial discharge specific capacity of ca. 142 mAh g^−1 between 3.5 and 4.9 V vs. Li/Li+, and remarkably improved capacity retention of 97% over 50 cycles. Those excellent electrochemical properties were associated with the presence of the dominant Fd-3m phase over the P4332 phase. Additionally, the results of the corrosion and dissolution tests which were performed for all calcined LNMO materials in order to estimate the amount of manganese and nickel ions leached from them, proved that the micro-sized LNMO calcined at 900 °C was the most stable.

Keywords:
spinel LiNi0.5Mn1.5O4, sol-gel synthesis, calcination temperature, cathode material, lithium-ion batteries

24.Mościcki T., Psiuk R., Słomińska H., Levintant-Zayonts N., Garbiec D., Pisarek M., Bazarnik P., Nosewicz S., Chrzanowska-Giżyńska J., Influence of overstoichiometric boron and titanium addition on the properties of RF magnetron sputtered tungsten borides, SURFACE AND COATINGS TECHNOLOGY, ISSN: 0257-8972, DOI: 10.1016/j.surfcoat.2020.125689, Vol.390, pp.125689-1-12, 2020
Mościcki T., Psiuk R., Słomińska H., Levintant-Zayonts N., Garbiec D., Pisarek M., Bazarnik P., Nosewicz S., Chrzanowska-Giżyńska J., Influence of overstoichiometric boron and titanium addition on the properties of RF magnetron sputtered tungsten borides, SURFACE AND COATINGS TECHNOLOGY, ISSN: 0257-8972, DOI: 10.1016/j.surfcoat.2020.125689, Vol.390, pp.125689-1-12, 2020

Abstract:
In this work, (W,Ti)B2 films with different stoichiometric ratio Ti/W deposited on silicon and 304 stainless steel by radio frequency magnetron sputtering are presented. The coatings were deposited from plasma spark sintered targets obtained from the mixture of pure boron, tungsten and titanium powders. It is shown that during plasma spark sintering process using overstoichiometric boron and a low content of titanium change the WB2 to WB4 phase with almost no secondary phases. Subsequently, the impact of titanium content on the films properties is investigated systematically, including the chemical and phase composition, crystalline structure, surface and cross-section morphology. Simultaneously, nano-indentation test and ball-on-disk tribometery are performed to analyse the hardness and tribological properties of the films. It is shown that deposited films with titanium content of 3.6 and 5.5 at.% are formed in the zone T of the Thornton's Structural Zone Model. In opposite to α-WB2 magnetron sputtered coatings they are more flexible and hard nanocomposite coatings. The results show that the addition of titanium is apparently changing the film structure from nanocrystalline columnar to amorphous, very dense and compact structure with the addition of TiB2 phase. That films are simultaneously hard (H > 37.5 GPa), have high hardness to effective Young's modulus ratio values (H/E* > 0.1) and elastic recovery (We > 60%) appropriate for tough and resistant to cracking materials. The presented (W,Ti)B2 films exhibit also tribological and corrosion properties better than unalloyed coatings.

Keywords:
superhard films, ternary tungsten borides, RF magnetron sputtering, wear resistance, corrosion

25.Luciano R., Caporale A., Darban H., Bartolomeo C., Variational approaches for bending and buckling of non-local stress-driven Timoshenko nano-beams for smart materials, Mechanics Research Communications, ISSN: 0093-6413, DOI: 10.1016/j.mechrescom.2019.103470, Vol.103, pp.103470-1-7, 2020
Luciano R., Caporale A., Darban H., Bartolomeo C., Variational approaches for bending and buckling of non-local stress-driven Timoshenko nano-beams for smart materials, Mechanics Research Communications, ISSN: 0093-6413, DOI: 10.1016/j.mechrescom.2019.103470, Vol.103, pp.103470-1-7, 2020

Abstract:
In this work, variational formulations are proposed for solving numerically the problem of bending and buckling of Timoshenko nano-beams. The present work belongs to research branch in which the non-local theory of elasticity has been used for analysis of beam-like elements in smart materials, micro-electro-mechanical (MEMS) or nano-electro-mechanical systems (NEMS). In fact, the local beam theory is not adequate to describe the behavior of beam-like elements of smart materials at the nano-scale, so that different non-local models have been proposed in last decades for nano-beams. The nano-beam model considered in this work is a convex combination (mixture) of local and non-local phases. In the non-local phase, the kinematic entities in a point of the nano-beam are expressed as integral convolutions between internal forces and an exponential kernel. The aim is to construct a functional whose stationary condition provides the solution of the problem. Two different functionals are defined: one for the pure non-local model, where the local fraction of the mixture is absent, and the other for the mixture with both local and non-local phases. The Euler equations of the two functionals are derived; then, attention focuses on the mixture model. The functional of the mixture depends on unknown Lagrange multipliers and the Euler equations of the functional provide not only the governing equations of the problem but also the relationships between these Lagrange multipliers and the other variables on which the functional depends. In fact, approximations of the variables of the functional can not be chosen arbitrarily in numerical analyzes but have to satisfy suitable conditions. The Euler equations involving the Lagrange multipliers are essential in the numerical analyzes and suggest the correct approximations that have to be adopted for Lagrange multipliers and the other unknown variables of the functional. The proposed method is verified by comparing numerical solutions with exact solutions in bending problem. Finally, the method is used to determine the buckling load of Timoshenko nano-beams with mixture of phases.

Keywords:
non-local elasticity, variational methods, Timoshenko beam, buckling load, smart materials

26.Luciano R., Darban H., Bartolomeo C., Fabbrocino F., Scorza D., Free flexural vibrations of nanobeams with non-classical boundary conditions using stress-driven nonlocal model, Mechanics Research Communications, ISSN: 0093-6413, DOI: 10.1016/j.mechrescom.2020.103536, Vol.107, pp.103536-1-5, 2020
Luciano R., Darban H., Bartolomeo C., Fabbrocino F., Scorza D., Free flexural vibrations of nanobeams with non-classical boundary conditions using stress-driven nonlocal model, Mechanics Research Communications, ISSN: 0093-6413, DOI: 10.1016/j.mechrescom.2020.103536, Vol.107, pp.103536-1-5, 2020

Abstract:
Free flexural vibrations of nanobeams with non-rigid edge supports are studied by means of the stress-driven nonlocal elasticity model and Euler-Bernoulli kinematics. The elastic deformations of the supports are modelled by transversal and flexural springs, so that, in the limit conditions when the springs stiffnesses tend to zero or infinity, the classical free, pinned, and clamped boundary conditions may be recovered. An analytical procedure is used to derive the closed form solution of the spatial differential equation. The problem of finding the natural frequencies is then reduced to find the roots of the determinant of a matrix, whose elements are explicitly given. The proposed technique, then, avoids the numerical instabilities usually arising when the numerical techniques are used to obtain the solution. The effects of both non-rigid supports elastic deformations and nonlocal parameter on the natural frequencies are studied also for higher vibrations modes. The comparison between the solutions of the proposed model and those available in the literature shows an excellent agreement, and new insightful results and discussions are presented.

Keywords:
elastically constrained beam, nanostructures, natural frequency, size effects, well-posed nonlocal formulation

27.Muszalski J., Sankowska I., Kucharski S., Nanoindentation of GaAs/AlAs distributed bragg reflector grown on GaAs substrate, Materials Science in Semiconductor Processing, ISSN: 1369-8001, DOI: 10.1016/j.mssp.2020.104912, Vol.109, pp.104912-1-8, 2020
Muszalski J., Sankowska I., Kucharski S., Nanoindentation of GaAs/AlAs distributed bragg reflector grown on GaAs substrate, Materials Science in Semiconductor Processing, ISSN: 1369-8001, DOI: 10.1016/j.mssp.2020.104912, Vol.109, pp.104912-1-8, 2020

Abstract:
Nanoindentation was used to investigate the mechanical parameters of GaAs/AlAs Distributed Bragg Reflectors. Such heterostructures are commonly employed in surface-emitting optoelectronic devices as LED or lasers. The investigation was carried for fully pseudomorphic AlAs/GaAs heterostructures and compared with bulk GaAs. The nanoindentation tests with sharp (Vickers) and spherical tip were conducted, and pop-in events were observed. We show that below pop-in load, the response of both materials is similar i.e., elastic parameters of the heterostructure and GaAs are practically the same. However, the pop-in events take place at higher loads for heterostructures than for GaAs. This in turn indicates that the heterostructure has a higher resistance to damage. For both materials, the pop-in load depends on loading rate. The possible mechanisms of pop-in are discussed. In the elastic-plastic stage (after pop-in), the heterostructure exhibits lower stiffness and lower hardness than GaAs does. The surface cracks that are generated in the heterostructure during the indentation test continue to grow even when the load is removed.

28.Krajewski M., Tokarczyk M., Stefaniuk T., Słomińska H., Małolepszy A., Kowalski G., Lewińska S., Ślawska-Waniewska A., Magnetic-field-induced synthesis of amorphous iron-nickel wire-like nanostructures, MATERIALS CHEMISTRY AND PHYSICS, ISSN: 0254-0584, DOI: 10.1016/j.matchemphys.2020.122812, Vol.246, pp.122812-1-7, 2020
Krajewski M., Tokarczyk M., Stefaniuk T., Słomińska H., Małolepszy A., Kowalski G., Lewińska S., Ślawska-Waniewska A., Magnetic-field-induced synthesis of amorphous iron-nickel wire-like nanostructures, MATERIALS CHEMISTRY AND PHYSICS, ISSN: 0254-0584, DOI: 10.1016/j.matchemphys.2020.122812, Vol.246, pp.122812-1-7, 2020

Abstract:
Manufacturing process of wire-like binary or ternary metal nanoalloys applying the magnetic-field-induced (MFI) synthesis is still a challenging task. Hence, this work demonstrates for the first time how to produce the iron-nickel wire-like nanostruc-tures with Fe0.75Ni0.25, Fe0.5Ni0.5 and Fe0.25Ni0.75 compositions. In a contrary to the previously reported synthesis of the Fe-Ni wire-like nanomaterials, this process has been carried out at room temperature without employment of templates, surfactants, organic solvents, and other chemical additives. The as-prepared samples exhibit specific structures with the amorphous bimetallic alloy cores covered by thin amorphous oxide shells. Moreover, they are composed of nanoparticles which are aligned in nearly linear chains. The Fe-Ni samples are ferromagnetic materials. Their coercivity values and saturation magnetizations depend on chemical compositions and dimensions of the investigated chains. The highest saturation magnetization and the lowest coercivity is found for the material with the lowest content of nickel and vice versa.

Keywords:
amorphous materials, Fe–Ni chains, magnetic-field-induced synthesis, magnetic materials, wire-like nanostructure

29.Caporale R., Darban H., Luciano R., Exact closed-form solutions for nonlocal beams with loading discontinuities, MECHANICS OF ADVANCED MATERIALS AND STRUCTURES, ISSN: 1537-6494, DOI: 10.1080/15376494.2020.1787565, pp.1-11, 2020
Caporale R., Darban H., Luciano R., Exact closed-form solutions for nonlocal beams with loading discontinuities, MECHANICS OF ADVANCED MATERIALS AND STRUCTURES, ISSN: 1537-6494, DOI: 10.1080/15376494.2020.1787565, pp.1-11, 2020

Abstract:
A novel mathematical formulation is presented for the applications of the stress-driven nonlocal theory of elasticity to engineering nano-scale problems requiring longitudinal discretization. Specifically, a differential formulation accompanied with novel constitutive continuity conditions is provided for determining exact closed-form solutions of nonlocal Euler-Bernoulli beams with loading discontinuities, i.e. points of discontinuity for external loads and internal forces. Constitutive continuity conditions have to be satisfied in interior points where a loading discontinuity occurs and contain integral convolutions of the stress over suitable parts of the nonlocal beam. Several results show the effectiveness of the proposed method.

Keywords:
closed-form solutions, discretization, Euler-Bernoulli beams, nanobeams

30.Darban H., Fabbrocino F., Feo L., Luciano R., Size-dependent buckling analysis of nanobeams resting on two-parameter elastic foundation through stress-driven nonlocal elasticity model, MECHANICS OF ADVANCED MATERIALS AND STRUCTURES, ISSN: 1537-6494, DOI: 10.1080/15376494.2020.1739357, pp.1-9, 2020
Darban H., Fabbrocino F., Feo L., Luciano R., Size-dependent buckling analysis of nanobeams resting on two-parameter elastic foundation through stress-driven nonlocal elasticity model, MECHANICS OF ADVANCED MATERIALS AND STRUCTURES, ISSN: 1537-6494, DOI: 10.1080/15376494.2020.1739357, pp.1-9, 2020

Abstract:
The instability of nanobeams rested on two-parameter elastic foundations is studied through the Bernoulli-Euler beam theory and the stress-driven nonlocal elasticity model. The size-dependency is incorporated into the formulation by defining the strain at each point as an integral convolution in terms of the stresses in all the points and a kernel. The nonlocal elasticity problem in a bounded domain is well-posed and inconsistencies within the Eringen nonlocal theory are overcome. Excellent agreement is found with the results in the literature, and new insightful results are presented for the buckling loads of nanobeams rested on the Winkler and Pasternak foundations.

Keywords:
buckling, closed form solution, nanobeam, nonlocal elasticity, Pasternak foundation, stress-driven

31.Krajewski M., Tokarczyk M., Witecka A., Lewińska S., Ślawska-Waniewska A., Płocińska M., Towards magnetic bimetallic wire-like nanostructures ‒ magnetic field as growth parameter, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.137.59, Vol.137, No.1, pp.59-61, 2020
Krajewski M., Tokarczyk M., Witecka A., Lewińska S., Ślawska-Waniewska A., Płocińska M., Towards magnetic bimetallic wire-like nanostructures ‒ magnetic field as growth parameter, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.137.59, Vol.137, No.1, pp.59-61, 2020

Abstract:
The magnetically-assisted growth of the amorphous bimetallic iron–nickel wire-like nanostructures is presented in this work. The applied process is based on a simple reduction reaction of aqueous solutions containing Fe2+ and Ni2+ ions with NaBH4 in the presence of an external magnetic field of about 0.05 T. The morphology, chemical composition, and magnetic properties of as-prepared Fe–Ni nanostructures have been determined by means of scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry, and vibrating sample magnetometry. The obtained experimental data indicate that the as-prepared samples exhibit quite complex architectures i.e., they comprise of nanoparticles aligned in almost straight lines. In addition, they reveal the typical core-shell structures where the amorphous bimetallic alloy cores are covered by thin amorphous oxide shells. In turn, the magnetic measurements show that the Fe–Ni wire-like nanostructures behave as typical ferromagnetic nanomaterials and their magnetic parameters like saturation magnetizations and coercivities are strictly dependent on their sizes and chemical compositions.

Keywords:
amorphous materials, bimetallic nanostructures, magnetic-field-induced synthesis, magneticmaterials, wire-like nanostructures

32.Pęcherski R.B., Rusinek A., Frąś T., Nowak M., Nowak Z., Energy-based yield condition for orthotropic materials exhibiting asymmetry of elastic range, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.24425/amm.2020.132819, Vol.65, No.2, pp.771-778, 2020
Pęcherski R.B., Rusinek A., Frąś T., Nowak M., Nowak Z., Energy-based yield condition for orthotropic materials exhibiting asymmetry of elastic range, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.24425/amm.2020.132819, Vol.65, No.2, pp.771-778, 2020

Abstract:
The aim of the paper is to formulate physically well founded yield condition for initially anisotropic solids revealing the asymmetry of elastic range. The initial anisotropy occurs in material primarily due to thermo-mechanical pre-processing and plastic deformation during the manufacturing processes. Therefore, materials in the "as-received" state become usually anisotropic. After short account of the known limit criteria for anisotropic solids and discussion of mathematical preliminaries the energy-based criterion for orthotropic materials was formulated and confronted with experimental data and numerical predictions of other theories. Finally, possible simplifications are discussed and certain model of isotropic material with yield condition accounting for a correction of shear strength due to initial anisotropy is presented. The experimental verification is provided and the comparison with existing approach based on the transformed-tensor method is discussed.

Keywords:
energy-based yield condition, orthotropic solids, initial anisotropy, strength differential effect, numerical simulation