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

1.Kowalczyk-Gajewska K., Maździarz M., Effective stiffness tensor of nanocrystalline materials of cubic symmetry: The core-shell model and atomistic estimates, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2019.103134, Vol.144, pp.103134-1-24, 2019
Kowalczyk-Gajewska K., Maździarz M., Effective stiffness tensor of nanocrystalline materials of cubic symmetry: The core-shell model and atomistic estimates, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2019.103134, Vol.144, pp.103134-1-24, 2019

Abstract:
Anisotropic core-shell model of a nano-grained polycrystal, proposed recently for nanocrystalline copper, is applied to estimate elastic effective properties for a set of crystals of cubic symmetry. Materials selected for analysis differ in the lattice geometry (face-centered cubic vs. body-centered cubic) as well as the value of a Zener factor: a ratio of two shear moduli defining elastic anisotropy of a cubic crystal. The predictions are verified by means of the atomistic simulations. The dependence of the overall bulk and shear moduli on the average grain diameter is analysed. In the mean-field approach the thickness of the shell is specified by the cutoff radius of a corresponding atomistic potential, while the grain shell is isotropic and its properties are identified by molecular simulations performed for very small grains with approximately all atoms belonging to the grain boundary zone. It is shown that the core-shell model provides predictions of satisfactory qualitative and quantitative agreement with atomistic simulations. Performed study indicates that the variation of the bulk and shear moduli with the grain size changes qualitatively when the Zener anisotropy factor is smaller or greater than one.

Keywords:
Molecular statics, Elasticity, Polycrystal, Effective medium, Cubic symmetry

2.Madan N., Rojek J., Nosewicz S., Convergence and stability analysis of the deformable discrete element method, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.6014, Vol.118, No.6, pp.320-344, 2019
Madan N., Rojek J., Nosewicz S., Convergence and stability analysis of the deformable discrete element method, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.6014, Vol.118, No.6, pp.320-344, 2019

Abstract:
This work investigates numerical properties of the algorithm of the discrete element method employing deformable circular discs presented in an earlier authors' publication. The new formulation, called the deformable discrete element method (DDEM) enhances the standard discrete element method (DEM) by introducing an additional (global) deformation mode caused by the stresses in the particles induced by the contact forces. An accurate computation of the contact forces would require an iterative solution of the implicit relationship between the contact forces and particle displacements. In order to preserve efficiency of the DEM, the new formulation has been adapted to the explicit time integration. It has been shown that the explicit DDEM algorithm is conditionally stable and there are two restrictions on its stability. Except for the limitation of the time step as in the standard DEM, the stability in the DDEM is governed by the convergence criterion of the iterative solution of the contact forces. The convergence and stability limits have been determined analytically and numerically for selected regular and irregular configurations. It has also been found out that the critical time step in DDEM remains unchanged with respect to standard DEM.

Keywords:
discrete element method; deformable particles; iterative solution; convergence criterion;explicit scheme; stability

3.Tauzowski P., Błachowski B., Lógó J., Functor-oriented topology optimization of elasto-plastic structures, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2019.102690, Vol.135, pp.102690-1-11, 2019
Tauzowski P., Błachowski B., Lógó J., Functor-oriented topology optimization of elasto-plastic structures, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2019.102690, Vol.135, pp.102690-1-11, 2019

Abstract:
The paper deals with a novel approach to development of optimality criteria based finite element code for topology optimization of elasto-plastic structures. The novelty of this work is related to the concept of function object called functor and its application to efficient FE code development. First, the general problem of topology optimization under stress constraints is briefly formulated. Then, the programming aspects of topology optimization using traditional object-oriented and functor based programming are discussed. The advantages of the functor based approach are related to simplicity of designing the FE code architecture and reusability of this code. In particular the metric known as 'Lack of cohesion of methods' is useful in comparing these two different paradigms. Finally, the paper is also illustrated with numerical examples of topology optimization using the proposed methodology.

Keywords:
Topology optimization, Function object, Functor programming, Optimal design, Elasto-plastic structures, Finite element programming

4.Postek E., Sadowski T., Impact model of WC/Co composite, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2019.01.084, Vol.213, pp.231-242, 2019
Postek E., Sadowski T., Impact model of WC/Co composite, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2019.01.084, Vol.213, pp.231-242, 2019

Abstract:
WC/Co composite is a standard hard material used for the production of cutting tools. It has both very good thermo-mechanical and wear properties. During the cutting, process tools are subjected to impact loading and gradual degradation due to high-stress concentrations. This loading induced deterioration is complex process still not well investigated and explained.Up till now the dynamic response of the WC/Co composite was analysed under dynamic impulse compressive loading [1]. However, the behaviour of the above two-phase composite under impacts conditions was not investigated in details. In the presented micromechanical approach the real material structure geometry of the internal structure can be performed including spatial distribution of: (1) WC grains and their dimensions, (2) volume content of plastic Co binder with their thickness, (3) system of grain/binder interfaces and (4) cracks initiated and developed during impulse loading, (5) possible brittle grains rotation.The results reveal the dependence of the microcracking processes and the stress distribution on impact velocity and presence of discontinuities in the Co binder and the interface zone between the binders and the grains. The microcracks system was evaluated by the damage parameter according to Kachanov, 1986 [62].

Keywords:
Cermet; Impact load; Microcracking; Cohesive elements; Numerical modelling;

5.Maździarz M., Comment on ‘The Computational 2D Materials Database: high-throughput modeling and discovery of atomically thin crystals’, 2D Materials, ISSN: 2053-1583, DOI: 10.1088/2053-1583/ab2ef3, Vol.6, No.4, pp.048001-1-3, 2019
Maździarz M., Comment on ‘The Computational 2D Materials Database: high-throughput modeling and discovery of atomically thin crystals’, 2D Materials, ISSN: 2053-1583, DOI: 10.1088/2053-1583/ab2ef3, Vol.6, No.4, pp.048001-1-3, 2019

Abstract:
Recently Haastrup et al 2018 (2D Mater. 5 042002) introduced the Computational 2D Materials Database (C2DB), which organises a variety of structural, thermodynamic, elastic, electronic, magnetic, and optical properties of around 1500 two-dimensional materials distributed over more than 30 different crystal structures. Unfortunately, the work contains serious and fundamental flaws in the field of elasticity and mechanical stability tests that make it unreliable.

Keywords:
ab initio calculations; elastic stability; 2D materials; materials discovery

6.Meissner M., Wiśniewski K., Influence of room modes on low-frequency transients: Theoretical modeling and numerical predictions, JOURNAL OF SOUND AND VIBRATION, ISSN: 0022-460X, DOI: 10.1016/j.jsv.2019.02.012, Vol.448, pp.19-33, 2019
Meissner M., Wiśniewski K., Influence of room modes on low-frequency transients: Theoretical modeling and numerical predictions, JOURNAL OF SOUND AND VIBRATION, ISSN: 0022-460X, DOI: 10.1016/j.jsv.2019.02.012, Vol.448, pp.19-33, 2019

Abstract:
In the low-frequency range, a sound reproduction in enclosures is strongly influenced by excited room modes. While the spectral impact of acoustic modes on a room response is well recognized, there is no sufficient knowledge on how these modes affects transients. In the paper this issue has been examined theoretically and numerically for a room excited by a tone burst by using a modal expansion method supported by a computer implementation. To quantify a temporal accuracy of a sound reproduction, the new metrics referred to as the tone burst reproduction error was introduced. The basis for determining this quantity was a deviation between the tone burst amplitude and the amplitude of a sound pressure computed via the Hilbert transform. A numerical simulation was performed for an irregularly shaped enclosure having a form of two-room coupled system. Calculation results have proved that a high inaccuracy of a tone burst reproduction occurs at receiving points corresponding to sharp dips in a distribution of the steady-state sound pressure level. This is because in these points an amplitude of transient sound is much bigger than a tone burst amplitude. It was discovered that strong narrow peaks in the tone burst reproduction error are located at centers of vortices in the active sound intensity vector field. An influence of a sound damping in a room on a reproduction of a tone burst was also examined and it was found that a substantial increase in a wall sound absorption does not significantly improves a tone burst reproduction because it does not eliminate sharp dips in a distribution of the steady-state sound pressure level.

Keywords:
room acoustics, room modes, transients, tone burst, discrete Hilbert transform, sound intensity vector field

7.Bazarnik P., Nosewicz S., Romelczyk-Baishya B., Chmielewski M., Strojny-Nędza A., Maj J., Huang Y., Lewandowska M., Langdon T.G., Effect of spark plasma sintering and high-pressure torsion on the microstructural and mechanical properties of a Cu–SiC composite, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2019.138350, Vol.766, pp.138350-1-11, 2019
Bazarnik P., Nosewicz S., Romelczyk-Baishya B., Chmielewski M., Strojny-Nędza A., Maj J., Huang Y., Lewandowska M., Langdon T.G., Effect of spark plasma sintering and high-pressure torsion on the microstructural and mechanical properties of a Cu–SiC composite, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2019.138350, Vol.766, pp.138350-1-11, 2019

Abstract:
This investigation examines the problem of homogenization in metal matrix composites (MMCs) and the methods of increasing their strength using severe plastic deformation (SPD). In this research MMCs of pure copper and silicon carbide were synthesized by spark plasma sintering (SPS) and then further processed via high-pressure torsion (HPT). The microstructures in the sintered and in the deformed materials were investigated using Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM). The mechanical properties were evaluated in microhardness tests and in tensile testing. The thermal conductivity of the composites was measured with the use of a laser pulse technique. Microstructural analysis revealed that HPT processing leads to an improved densification of the SPS-produced composites with significant grain refinement in the copper matrix and with fragmentation of the SiC particles and their homogeneous distribution in the copper matrix. The HPT processing of Cu and the Cu–SiC samples enhanced their mechanical properties at the expense of limiting their plasticity. Processing by HPT also had a major influence on the thermal conductivity of materials. It is demonstrated that the deformed samples exhibit higher thermal conductivity than the initial coarse-grained samples.

Keywords:
Copper, Silicon carbide, High-pressure torsion, Spark plasma sintering, Thermal conductivity

8.Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Discrete Element Modeling of Intermetallic Matrix Composite Manufacturing by Powder Metallurgy, Materials, ISSN: 1996-1944, DOI: 10.3390/ma12020281, Vol.12, No.2, pp.281-1-18, 2019
Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Discrete Element Modeling of Intermetallic Matrix Composite Manufacturing by Powder Metallurgy, Materials, ISSN: 1996-1944, DOI: 10.3390/ma12020281, Vol.12, No.2, pp.281-1-18, 2019

Abstract:
This paper presents a numerical and experimental analysis of manufacturing of intermetallic ceramic composites by powder metallurgy techniques. The scope of the paper includes the formulation and development of an original numerical model of powder metallurgy of two-phase material within the framework of the discrete element method, simulations of powder metallurgy processes for different combinations of process parameters, and a verification of the numerical model based on own experimental results. Intermetallic-based composite NiAl–Al2O3 has been selected as representative material for experimental and numerical studies in this investigation. Special emphasis was given to the interactions between the intermetallic and ceramic particles by formulating the special model for adhesive contact bond. In order to properly represent a real microstructure of a two-phase sintered body, a discrete element specimen was generated using a special algorithm. Numerical validation showed the correct numerical representation of a sintered two-phase composite specimen. Finally, micromechanical analysis was performed to explain the macroscopic behavior of the sintered sample. The evolution of the coordination number, a number of equilibrium contacts, and the distribution of the cohesive neck size with respect to time are presented.

Keywords:
powder metallurgy; sintering; discrete element method; modeling; intermetallic matrix composites

9.Postek E., Sadowski T., Temperature Effects during Impact Testing of a Two-Phase Metal-Ceramic Composite Material, Materials, ISSN: 1996-1944, DOI: 10.3390/ma12101629, Vol.12, No.10, pp.1629-1-13, 2019
Postek E., Sadowski T., Temperature Effects during Impact Testing of a Two-Phase Metal-Ceramic Composite Material, Materials, ISSN: 1996-1944, DOI: 10.3390/ma12101629, Vol.12, No.10, pp.1629-1-13, 2019

Abstract:
Metal-ceramic composite (MCC) materials can be used for manufacturing high-responsibility structures such as jet engines or cutting tools. One example of these materials is a two-phase wolfram carbide (WC) and cobalt (Co) composite. This MCC is a combination of hard WC grains with a Co metallic ductile binder. The resulting microstructure is a combination of two phases with significantly different mechanical behaviors. In this study, we investigate impact conditions, starting with an illustrative example of the Taylor impact bar where—although the process is very rapid—the equivalent plastic strain and temperature are higher in the adiabatic solution than those in the coupled solution. On exposing the WC/Co composite with a metallic binder to impact loading, heat is generated by plastic deformation. If the process is fast enough, the problem can be treated as adiabatic. However, a more common situation is that the process is slower, and the heat is generated in the ductile metallic binders. As a result, the associated grains are heated due to the conduction effect. Consequently, the process should be treated as coupled. When the impact is applied over a short time period, maximum temperatures are significantly lower if the process is analyzed as coupled rather than as adiabatic. The grains are immediately affected by temperature increase in the binders. Therefore, the heat conduction effect should not be omitted

Keywords:
metal-ceramic composite, impact, coupled problem, thermomechanics

10.Nosewicz S., Rojek J., Wawrzyk K., Kowalczyk P., Maciejewski G., Maździarz M., Multiscale modeling of pressure-assisted sintering, COMPUTATIONAL MATERIALS SCIENCE, ISSN: 0927-0256, DOI: 10.1016/j.commatsci.2018.10.001, Vol.156, pp.385-395, 2019
Nosewicz S., Rojek J., Wawrzyk K., Kowalczyk P., Maciejewski G., Maździarz M., Multiscale modeling of pressure-assisted sintering, COMPUTATIONAL MATERIALS SCIENCE, ISSN: 0927-0256, DOI: 10.1016/j.commatsci.2018.10.001, Vol.156, pp.385-395, 2019

Abstract:
This report presents the modeling of pressure-assisted sintering within the framework of a multiscale approach. Three individual numerical methods have been collectively applied to predict the behavior of a sintering body at three different scales. The appropriate solutions to connect each model/scale have been proposed. Molecular dynamics have been employed to evaluate the grain boundary diffusion coefficient at the atomistic scale. The obtained results of diffusive parameters have been transferred to the micromechanical model of sintering. Here, the discrete element method was used to represent the sintered material properties at the microscopic scale. Micromechanical based results have been validated by own experimental data of material density evolution, indicating the required coincidence. The transfer from micro- to the macroscopic model has been realized by determining the macroscopic viscous moduli from discrete element simulations and subsequently applying them to the continuum model of sintering. The numerical results from finite element simulations at the macroscopic scale have been compared with discrete element ones.

Keywords:
Sintering; Multiscale modeling; Discrete element method; Molecular dynamics; Finite element method

11.Rojek J., Lumelskyj D., Nosewicz S., Romelczyk-Baishya B., Numerical and experimental investigation of an elastoplastic contact model for spherical discrete elements, Computational Particle Mechanics, ISSN: 2196-4378, DOI: 10.1007/s40571-018-00219-8, Vol.6, No.3, pp.383-392, 2019
Rojek J., Lumelskyj D., Nosewicz S., Romelczyk-Baishya B., Numerical and experimental investigation of an elastoplastic contact model for spherical discrete elements, Computational Particle Mechanics, ISSN: 2196-4378, DOI: 10.1007/s40571-018-00219-8, Vol.6, No.3, pp.383-392, 2019

Abstract:
A contact model for the normal interaction between elastoplastic spherical discrete elements has been investigated in the present paper. The Walton–Braun model with linear loading and unloading has been revisited. The main objectives of the research have been to validate the applicability of the linear loading and unloading models and estimate the loading and unloading stiffness parameters. The investigation has combined experimental tests and finite element simulations. Both experimental and numerical results have proved that the interaction between the spheres subjected to a contact pressure inducing a plastic deformation can be approximated by a linear relationship in quite a large range of elastoplastic deformation. Similarly, the linear model has been shown to be suitable for the unloading. It has been demonstrated that the Storåkers model provides a good evaluation of the loading stiffness for the elastoplastic contact and the unloading stiffness can be assumed as varying linearly with the deformation of the contacting spheres. The unloading stiffness can be expressed in a convenient way as a function of the Young’s modulus and certain scaling factor dependent on the dimensionless parameter defining the level of the sphere deformation.

Keywords:
Contact; Discrete element method; Elastoplastic; Spheres; Unloading

12.Łażewski J., Jochym P.T., Piekarz P., Sternik M., Parlinski K., Cholewiński J., Dłużewski P., Krukowski S., DFT modelling of the edge dislocation in 4H-SiC, JOURNAL OF MATERIALS SCIENCE, ISSN: 0022-2461, DOI: 10.1007/s10853-019-03630-5, Vol.54, No.15, pp.10737-10745, 2019
Łażewski J., Jochym P.T., Piekarz P., Sternik M., Parlinski K., Cholewiński J., Dłużewski P., Krukowski S., DFT modelling of the edge dislocation in 4H-SiC, JOURNAL OF MATERIALS SCIENCE, ISSN: 0022-2461, DOI: 10.1007/s10853-019-03630-5, Vol.54, No.15, pp.10737-10745, 2019

Abstract:
We have presented ab initio study, based on density functional theory methods,
of full-core edge dislocation impact on basic properties of 4H-SiC semiconductor.
To enable calculations in periodic boundary conditions, we have proposed
geometry with two dislocations with opposite Burgers vectors. For this
geometry, which determines the distance between dislocations, we have estimated
the creation energy per unit length of a single-edge dislocation. The
radial distribution function has been used to assess the effect of the dislocations
on the local crystal structure. The analysis of the electronic structure reveals
mid-gap p states induced by broken atomic bonds in the dislocation core. The
maps of charge distribution and electrostatic potential have been calculated, and
the significant decrease in the electrostatic barriers in the vicinity of the dislocation
cores has been quantified. The obtained results have been discussed in
the light of previous findings and calculations based mainly on phenomenological
models.

13.Chmielewski M., Nosewicz S., Wyszkowska E., Kurpaska Ł., Strojny-Nędza A., Piątkowska A., Bazarnik P., Pietrzak K., Analysis of the micromechanical properties of copper-silicon carbide composites using nanoindentation measurements, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2019.01.257, Vol.45, No.7A, pp.9164-9173, 2019
Chmielewski M., Nosewicz S., Wyszkowska E., Kurpaska Ł., Strojny-Nędza A., Piątkowska A., Bazarnik P., Pietrzak K., Analysis of the micromechanical properties of copper-silicon carbide composites using nanoindentation measurements, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2019.01.257, Vol.45, No.7A, pp.9164-9173, 2019

Abstract:
The study presents a detailed analysis of the impact of the coating type of silicon carbide particles and its share by volume on the microstructure and micromechanical properties of Cu-SiC composites. In order to protect the carbide from decomposition during the manufacturing of the composites, the surface of SiC was modified via a plasma vapour deposition technique with a layer of metals (W, Cr, Ti and Ni). Composites with a variable share of the ceramic phase (10–50 %vol.) were obtained at a temperature of 950 °C using spark plasma sintering. An analysis of the structures of the composites, especially in the metal-ceramic boundary region, was conducted with the use of scanning and transmission electron microscopy. The mechanical properties of the composites in the Cu-interface-SiC system were studied via a nanoindentation technique. The comparison of the results of hardness and Young's modulus studies were completed in relation to the actual structures of the materials, which in turn made it possible to determine the impact of the interfacial structure on the global properties of the composite materials.

Keywords:
Copper-silicon carbide composites; Nanoindentation; SPS; Interface study

14.Colabella L., Cisilino A.P., Fachinotti V., Kowalczyk P., Multiscale design of elastic solids with biomimetic cancellous bone cellular microstructures, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-019-02229-3, Vol.60, No.2, pp.639-661, 2019
Colabella L., Cisilino A.P., Fachinotti V., Kowalczyk P., Multiscale design of elastic solids with biomimetic cancellous bone cellular microstructures, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-019-02229-3, Vol.60, No.2, pp.639-661, 2019

Abstract:
Natural (or biological) materials usually achieve outstanding mechanical performances. In particular, cancellous bone presents a high stiffness/strength toweight ratio, so its structure inspires the development of novel ultra-light cellularmaterials.Amultiscale method for the design of elastic solids with a cancellous bone parameterized biomimetic microstructure is introduced in this work. The method combines a finite element model to evaluate the stiffness of the body at the macroscale with a gradient-based nonlinear constrained optimization solver to obtain the optimal values of themicroparameters andmicrostructure orientation over the body domain. The most salient features of the implementation are an offline response surface methodology for the evaluation of the microstructure elastic tensor in terms of the microparameters, an adjoint method for the computation of the sensitivity of the macroscopic stiffness to the microparameters, a quasi-Newton approximation for the evaluation of the Hessian matrix of the nonlinear optimizer, and a distanceweighted filter of the microparameters to remediate checkerboard effects. The settings of the above features, the optimizer termination options, and the initial values of the microparameters are investigated for the best performance of the method. The effectiveness of the method is demonstrated for several examples, whose results are compared with the reference solutions calculated using a SIMP method. The method shows to be effective; it attains results coherent with SIMP approaches in terms of stiffness and spatial material distribution. The good performance of themultiscalemethod is attributed to the capability of the parameterized mimeticmicrostructure to attain bulk and shear moduli that are close to the Hashin-Shtrikman upper bounds over the complete solid volume fraction range.

Keywords:
Multiscale optimization, Cancellous bone, Parameterized microstructure, Interior-point optimizer, Biomimetic materials

15.Zaremba D., Błoński S., Marijnissen M.J., Korczyk P.M., Fixing the direction of droplets in a bifurcating microfluidic junction, MICROFLUIDICS AND NANOFLUIDICS, ISSN: 1613-4982, DOI: 10.1007/s10404-019-2218-x, Vol.23, pp.55-1-18, 2019
Zaremba D., Błoński S., Marijnissen M.J., Korczyk P.M., Fixing the direction of droplets in a bifurcating microfluidic junction, MICROFLUIDICS AND NANOFLUIDICS, ISSN: 1613-4982, DOI: 10.1007/s10404-019-2218-x, Vol.23, pp.55-1-18, 2019

Abstract:
We present a novel type of microfluidic bifurcating junctions which fixes the droplet’s route. Unlike in regular junctions, where a droplet chooses one of two outputs depending on the (often instantaneous) flow distribution, our modifications direct droplets only to one preferred outlet. As we show, this solution works properly regardless of the variations of flow distribution in a wide range of its amplitude. Such modified junctions allow for the encoding of the droplet’s traffic in the geometry of the device. We compare in a series of experiments different junctions having channels of uniform square cross section. Our observations revealed that a small, local modification of the junction in the form of an additional shallow slit imposes a significant consequence for the flow of droplets at an entire microfluidic network’s scale. Another interesting and helpful feature of these new junctions is that they keep the integrity of long droplets, unlike regular junctions, which tend to split long droplets. Our experimental investigations revealed a complex transformation of the long droplet during its transfer through the modified junction. We show that this transformation resembles the Baker’s transform and can be used for the enhancement of mixing inside the droplets. Finally, we show two examples of microfluidic devices where the deterministic character of these modified junctions is utilized to obtain new, non-trivial functionalities. This approach can be used for the engineering of microfluidic devices with embedded procedures replacing active elements like valves or magnetic/electric fields.

Keywords:
Droplet, Microfluidics, Two-phase, Manipulations

16.Jurczak G., Maździarz M., Dłużewski P., Dimitrakopulos G.P., Komninou Ph., Karakostas T., On the applicability of elastic model to very thin crystalline layers, JOURNAL OF PHYSICS: CONFERENCE SERIES, ISSN: 1742-6588, DOI: 10.1088/1742-6596/1190/1/012017, No.1190, pp.012017-1-5, 2019
Jurczak G., Maździarz M., Dłużewski P., Dimitrakopulos G.P., Komninou Ph., Karakostas T., On the applicability of elastic model to very thin crystalline layers, JOURNAL OF PHYSICS: CONFERENCE SERIES, ISSN: 1742-6588, DOI: 10.1088/1742-6596/1190/1/012017, No.1190, pp.012017-1-5, 2019

Abstract:
Elastic model of continuum material is often used to simulate the relaxation of crystalline heterostructures. There are many reports on the successful application of the theory of elasticity to nano-sized crystalline heterostructures, even if the continuum condition for them is hardly fulfilled. On the other hand, progress in epitaxial growth allows for the preparation of stable ultra-thin layers with thickness of few monolayers. For such ultra-thin layers, results provided by continuum model and molecular statics/dynamics calculations become diverging. The key problem seems to be located at the modelling of the interface between layers, which is problematic in the continuum approach. By applying a step-wise substitutive compositional interfacial function, it is possible to obtain good agreement with molecular dynamics calculations, even for a single monolayer heterostructure. We propose another approach that uses composition as an extra parameter during finite element calculations, along with classical nodal displacements. Such an approach creates a chemo-elastic coupling that allows to interpolate the composition much like in the case of atomistic calculations.

Keywords:
ultra-thin layers, elastic relaxation, molecular statics, finite elemenet modelling

17.Nowak Z., Nowak M., Pęcherski R.B., Wiśniewski K., Widłaszewski J., Kurp P., Computational modeling of thermoplastic behavior of inconel 718 in application to laser-assisted bending of thin-walled tubes, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, Vol.17, No.3, pp.317-338, 2019
Nowak Z., Nowak M., Pęcherski R.B., Wiśniewski K., Widłaszewski J., Kurp P., Computational modeling of thermoplastic behavior of inconel 718 in application to laser-assisted bending of thin-walled tubes, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, Vol.17, No.3, pp.317-338, 2019

Abstract:
Laser-assisted tube bending is a promising manufacturing process which enables production of forms and shapes that cannot be obtained by purely mechanical bending. It is particularly suitable for high hardness and brittle materials, such as nickel alloys, ceramics and cast iron. In the current paper, mechanical loading and simultaneous heating by a moving laser beam are used in a controlled manner to obtain the required deformation. Experimental investigation of the Inconel 718 (IN718) alloy provides the basis for identification of parameters of two constitutive models, which encompass softening phenomena and the coupling of temperature and strains. Numerical simulations are conducted to provide more insight into the laser-assisted bending process of the IN718 thin-walled tubes. Temperature, stress and deformation fields are determined in sequentially coupled thermomechanical analyses using the FE code ABAQUS. Laser beam is modeled as a surface heat flux using the dedicated DFLUX procedure. The temperature field is used as a thermal load in the static general step, together with an external mechanical load. The process of tube bending is controlled by the displacement of the piston rod of the actuator, while the thrust force is the resulting value.

Keywords:
laser-assisted bending of tubes, identification of material parameters, numerical simulations

18.Romelczyk-Baishya B., Lumelskyj D., Stępniewska M., Giżyński M., Pakieła Z., The mechanical properties at room and low temperature of p110 steel characterised by means of small punch test, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.24425/amm.2019.126232, Vol.64, No.1, pp.159-165, 2019
Romelczyk-Baishya B., Lumelskyj D., Stępniewska M., Giżyński M., Pakieła Z., The mechanical properties at room and low temperature of p110 steel characterised by means of small punch test, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.24425/amm.2019.126232, Vol.64, No.1, pp.159-165, 2019

Abstract:
In this paper, small punch test (SPT) which is one of miniaturized samples technique, was employed to characterize the mechanical properties of carbon steel P110. The tests were carried out in the range of –175°C to RT. Results obtained for SPT were compared to those calculated for tensile and Charpy impact test. Based on tensile and SPT parameters numerical model was prepared. 8 mm in diameter and 0.8 mm in height (t) discs with and without notch were employed in this research. The specimens had different depth notch (a) in the range of 0.1 to 0.4 mm. It was estimated that α factor for comparison of Tsp and DBTT for carbon steel P110 is 0.55 and the linear relation is DBTT = 0.55TSPT. The numerical model fit with force – deflection curve of SPT. If the factor of notch depth and samples thickness is higher than 0.3 the fracture mode is transformed from ductile to brittle at –150°C.

Keywords:
small punch test, carbon steel P110, small samples, low temperature, mechanical properties

19.Postek E., Pęcherski R.B., Nowak Z., Peridynamic simulation of crushing processes in copper open-cell foam, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, Vol.64, No.4, pp.1603 -1610, 2019
Postek E., Pęcherski R.B., Nowak Z., Peridynamic simulation of crushing processes in copper open-cell foam, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, Vol.64, No.4, pp.1603 -1610, 2019

Abstract:
In the last 20 years, a new meshless computational method has been developed that is called peridynamics. The method is based on the parallelized code. The subject of the study is the deformation of open-cell copper foams under dynamic compression. The computational model of virtual cellular material is considered. The skeleton structure of such a virtual cellular material can be rescaled according to requirements. The material of the skeleton is assumed as the oxygen free high conductivity (OFHC) copper. The OFHC copper powder can be applied in additive manufacturing to produce the open-cell multifunctional structures, e.g., crush resistant heat exchangers, heat capacitors, etc. In considered peridynamic computations the foam skeleton is described with the use of an elastic-plastic model with isotropic hardening. The dynamic process of compression and crushing with different impact velocities is simulated.

Keywords:
virtual cellular material, metallic foams, OFHC copper, elastic-plastic model, numerical methods, peridynamics, crushing process