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Affiliation to IPPT PAN

1.Jurczak G., Dłużewski P., Finite element modelling of threading dislocation effect on polar GaN/AlN quantum dot, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, ISSN: 1386-9477, DOI: 10.1016/j.physe.2017.08.018, Vol.95, pp.11-15, 2018
Jurczak G., Dłużewski P., Finite element modelling of threading dislocation effect on polar GaN/AlN quantum dot, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, ISSN: 1386-9477, DOI: 10.1016/j.physe.2017.08.018, Vol.95, pp.11-15, 2018

Abstract:
In this paper the effect of adjacent threading dislocation at the edge of the GaN/AlN quantum dot is analysed by use of the finite element analysis. Elastic as well electric effects related to dislocation core are taken into account. Two types of threading dislocations: edge- and screw-type, common for III-nitride epitaxial layers, are considered. Also, three different QD geometries are considered to estimate the impact of the threading dislocation on the quantum heterostructure. It is demonstrated that the local elastic and electric fields around dislocation affect local piezoelectric fields built-in the quantum dot. Local lattice deformation near the dislocation core reduce residual strains in the quantum dot. It is prominent in the case of edge-type dislocation. The presence of an electric charge along dislocation line provides significant shift of the total potential towards the negative values. However, estimated difference in band-to-band transition energy for edge- and screw-type dislocations are rather small, what suggest low sensitivity to the charge density along dislocation line. Unexpectedly, local strain field around the edge-type dislocation, slightly compensate the negative affect of the electrostatic potential.

Keywords:
Quantum dot, Threading dislocation, Piezoelectricity, Finite element modelling

2.Wiśniewski K., Turska E., Improved nine-node shell element MITC9i with reduced distortion sensitivity, COMPUTATIONAL MECHANICS, ISSN: 0178-7675, DOI: 10.1007/s00466-017-1510-4, pp.1-25, 2017
Wiśniewski K., Turska E., Improved nine-node shell element MITC9i with reduced distortion sensitivity, COMPUTATIONAL MECHANICS, ISSN: 0178-7675, DOI: 10.1007/s00466-017-1510-4, pp.1-25, 2017

Abstract:
The 9-node quadrilateral shell element MITC9i is developed for the Reissner-Mindlin shell inematics, the extended potential energy and Green strain. The following features of its formulation ensure an improved behavior: 1. The MITC technique is used to avoid locking, and we propose improved ransformations for bending and transverse shear strains, which render that all patch tests are passed for the regular mesh, i.e. with straight element sides and middle positions of midside nodes and a central node. 2. To reduce shape distortion effects, the so-called corrected shape functions of Celia and Gray (Int J Numer Meth Eng 20:1447–1459, 1984) are extended to shells and used instead of the standard ones. In effect, all patch tests are passed additionally for shifts of the midside nodes along straight element sides and for arbitrary shifts of the central node. 3. Several extensions of the corrected shape functions are proposed to enable computations of non-flat shells. In particular, a criterion is put forward to determine the shift parameters associated with the central node for non-flat elements. Additionally, the method is presented to construct a parabolic side for a shifted midside node, which improves accuracy for symmetric curved edges. Drilling rotations are included by using the drilling Rotation Constraint equation, in a way consistent with the additive/multiplicative rotation update scheme for large rotations. We show that the corrected shape functions reduce the sensitivity of the solution to the regularization parameter γ of the penalty method for this constraint. The MITC9i shell element is subjected to a range of linear and non-linear tests to show passing the patch tests, the absence of locking, very good accuracy and insensitivity to node shifts. It favorably compares to several other tested 9-node elements.

Keywords:
9-node shell element MITC9i, Two-level approximation of strains, Patch tests, Corrected shape functions, Node shift parameters, Coarse mesh accuracy, Drilling rotations

3.Colabella L., Cisilino A.P., Häiat G., Kowalczyk P., Mimetization of the elastic properties of cancellous bone via a parameterized cellular material, Biomechanics and Modeling in Mechanobiology, ISSN: 1617-7959, DOI: 10.1007/s10237-017-0901-y, Vol.16, No.5, pp.1485-1502, 2017
Colabella L., Cisilino A.P., Häiat G., Kowalczyk P., Mimetization of the elastic properties of cancellous bone via a parameterized cellular material, Biomechanics and Modeling in Mechanobiology, ISSN: 1617-7959, DOI: 10.1007/s10237-017-0901-y, Vol.16, No.5, pp.1485-1502, 2017

Abstract:
Bone tissue mechanical properties and trabecular microarchitecture are the main factors that determine the biomechanical properties of cancellous bone. Artificial cancellous microstructures, typically described by a reduced number of geometrical parameters, can be designed to obtain a mechanical behavior mimicking that of natural bone. In this work, we assess the ability of the parameterized microstructure introduced by Kowalczyk (Comput Methods Biomech Biomed Eng 9:135–147, 2006. doi:10.1080/10255840600751473) to mimic the elastic response of cancellous bone. Artificial microstructures are compared with actual bone samples in terms of elasticity matrices and their symmetry classes. The capability of the parameterized microstructure to combine the dominant isotropic, hexagonal, tetragonal and orthorhombic symmetry classes in the proportions present in the cancellous bone is shown. Based on this finding, two optimization approaches are devised to find the geometrical parameters of the artificial microstructure that better mimics the elastic response of a target natural bone specimen: a Sequential Quadratic Programming algorithm that minimizes the norm of the difference between the elasticity matrices, and a Pattern Search algorithm that minimizes the difference between the symmetry class decompositions. The pattern search approach is found to produce the best results. The performance of the method is demonstrated via analyses for 146 bone samples.

Keywords:
Cancellous bone, Parameterized microstructure, Elastic properties, Homogenization, Symmetry classes, Optimization

4.Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Discrete element modeling and experimental investigation of hot pressing of intermetallic NiAl powder, ADVANCED POWDER TECHNOLOGY, ISSN: 0921-8831, DOI: 10.1016/j.apt.2017.04.012, Vol.28, pp.1745-1759, 2017
Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Discrete element modeling and experimental investigation of hot pressing of intermetallic NiAl powder, ADVANCED POWDER TECHNOLOGY, ISSN: 0921-8831, DOI: 10.1016/j.apt.2017.04.012, Vol.28, pp.1745-1759, 2017

Abstract:
This paper presents the numerical and experimental analysis of hot pressing of NiAl powder with an emphasis on the best possible representation of its main stages: initial powder compaction and pressure-assisted sintering. The numerical study has been performed within the discrete element framework. In the paper, an original viscoelastic model of hot pressing has been used. In order to ensure that the applied values of material parameters in numerical simulations are appropriate, the reference literature has been reviewed. It produced the relations and equations to estimate the values of all required sintering material parameters of the considered viscoelastic model. Numerical simulations have employed the geometrical model of the initial dense specimen generated by a special algorithm which uses the real grain distribution of powder. The numerical model has been calibrated and validated through simulations of the real process of hot pressing of intermetallic NiAl material. The kinetics of compaction, sintering and cooling stage indicated by the evolution of density, shrinkage and densification rate have been studied. The comparison of numerical and experimental results has shown a good performance of the developed numerical model.

Keywords:
Powder metallurgy; Hot pressing; Sintering; Simulation; Discrete element method; Nickel aluminide

5.Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Lumelskyj D., Application of the Hertz formulation in the discrete element model of pressure-assisted sintering, GRANULAR MATTER, ISSN: 1434-5021, DOI: 10.1007/s10035-016-0699-9, Vol.19, No.1, pp.16-1-8, 2017
Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Lumelskyj D., Application of the Hertz formulation in the discrete element model of pressure-assisted sintering, GRANULAR MATTER, ISSN: 1434-5021, DOI: 10.1007/s10035-016-0699-9, Vol.19, No.1, pp.16-1-8, 2017

Abstract:
This paper presents the numerical modelling of initial powder compaction and pressure-assisted sintering performed by original viscoelastic discrete element model. The research is focused on the influence of the type of the model representing an elastic part of interparticle force. Two elastic contact models—linear and nonlinear Hertz model—have been implemented and used to analyse interaction of NiAl powder particles during compaction and sintering process. Numerical models have been validated using own experimental results. Microscopic effects (particle penetration) and macroscopic changes (relative density) have been compared. It has been shown that although both models represent properly macroscopic behaviour of the material at the sintering process, the Hertz model produces the results closer to the real experimental ones during the initial compaction stage. Evaluation of macroscopic quantities enables implementation of the discrete element model in the framework of the multiscale modelling framework which is currently developed for sintering processes.

Keywords:
Powder metallurgy, Sintering, Initial compaction, Elasticity, Discrete element method

6.Maździarz M., Mrozek A., Kuś W., Burczyński T., First-principles study of new X-graphene and Y-graphene polymorphs generated by the two stage strategy, MATERIALS CHEMISTRY AND PHYSICS, ISSN: 0254-0584, DOI: 10.1016/j.matchemphys.2017.08.066, Vol.202, pp.7-14, 2017
Maździarz M., Mrozek A., Kuś W., Burczyński T., First-principles study of new X-graphene and Y-graphene polymorphs generated by the two stage strategy, MATERIALS CHEMISTRY AND PHYSICS, ISSN: 0254-0584, DOI: 10.1016/j.matchemphys.2017.08.066, Vol.202, pp.7-14, 2017

Abstract:
Two potentially new, 2D-graphene-like materials have been generated by the two stage searching strategy combining molecular and ab initio approach. The two candidates obtained from the evolutionary based algorithm and molecular calculations were then in depth analysed using first-principles Density Functional Theory from the mechanical, structural, phonon and electronic properties point of view. Both proposed polymorphs of graphene (oP8-P2mm) are mechanically and dynamically stable and can be metallic-like.

Keywords:
Carbon; Graphene; Ab initio calculations; Mechanical properties; Elastic properties

7.Chmielewski M., Pietrzak K., Strojny-Nędza A., Jarząbek D., Nosewicz S., Investigations of interface properties in copper-silicon carbide composites, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0200, Vol.62, No.2B, pp.1315-1318, 2017
Chmielewski M., Pietrzak K., Strojny-Nędza A., Jarząbek D., Nosewicz S., Investigations of interface properties in copper-silicon carbide composites, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0200, Vol.62, No.2B, pp.1315-1318, 2017

Abstract:
This paper analyses the technological aspects of the interface formation in the copper-silicon carbide composite and its effect on the material’s microstructure and properties. Cu-SiC composites with two different volume content of ceramic reinforcement were fabricated by hot pressing (HP) and spark plasma sintering (SPS) technique. In order to protect SiC surface from its decomposition, the powder was coated with a thin tungsten layer using plasma vapour deposition (PVD) method. Microstructural analyses provided by scanning electron microscopy revealed the significant differences at metal-ceramic interface. Adhesion force and fracture strength of the interface between SiC particles and copper matrix were measured. Thermal conductivity of composites was determined using laser flash method. The obtained results are discussed with reference to changes in the area of metal-ceramic boundary.

Keywords:
copper matrix composites, silicon carbide, interface, thermal conductivity, adhesion

8.Rojek J., Nosewicz S., Chmielewski M., MICRO-MACRO RELATIONSHIPS FROM DISCRETE ELEMENT SIMULATIONS OF SINTERING, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, DOI: 10.1615/IntJMultCompEng.2017020322, Vol.15, No.4, pp.323-342, 2017
Rojek J., Nosewicz S., Chmielewski M., MICRO-MACRO RELATIONSHIPS FROM DISCRETE ELEMENT SIMULATIONS OF SINTERING, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, DOI: 10.1615/IntJMultCompEng.2017020322, Vol.15, No.4, pp.323-342, 2017

Abstract:
A two-scale modeling framework for sintering processes has been presented. Formulation of the micromechanical model of sintering developed in the discrete element method and basic relationships in the macroscopic model of sintering have been briefly reviewed. The methodology to determine macroscopic quantities–stress, strains, and constitutive viscous properties-from the discrete element simulations has been presented. This methodology has been applied to modeling of NiAl sintering. First, the discrete element model (DEM) has been calibrated by fitting the numerical densification curve to the experimental data. The DEM model with calibrated parameters has been used in simulations specially conceived to give macroscopic viscous moduli of the sintered material. Using the averaging procedures macroscopic stresses and strains have been calculated. Strain rates have been obtained differentiating the strain curves with respect to time. Finally, the viscous constitutive properties of the sintered material have been determined. The dependence of the shear and volumetric viscous moduli on the relative density (or equivalently) on the porosity has been obtained. It has been found that the numerical simulations predict a similar dependence as that assumed in the phenomenological macroscopic models. Thus, the validity of the micro-macro relationships obtained from the discrete element simulations of powder sintering has been confirmed. The proposed methodology allows us to use the discrete element model in the framework of multiscale modeling of sintering.

Keywords:
discrete element method, sintering, simulation, micro-macro relationships, multiscale modeling

9.Maździarz M., Rojek J., Nosewicz S., ESTIMATION OF MICROMECHANICAL NiAl SINTERING MODEL PARAMETERS FROM THE MOLECULAR SIMULATIONS, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, DOI: 10.1615/IntJMultCompEng.2017020289 , Vol.15, No.4, pp.343-358, 2017
Maździarz M., Rojek J., Nosewicz S., ESTIMATION OF MICROMECHANICAL NiAl SINTERING MODEL PARAMETERS FROM THE MOLECULAR SIMULATIONS, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, DOI: 10.1615/IntJMultCompEng.2017020289 , Vol.15, No.4, pp.343-358, 2017

Abstract:
Molecular statics/dynamics estimation of constitutive parameters for a micromechanical NiAl sintering model is reported in this paper. The parameters include temperature-dependent diffusion coefficients, surface energy, and linear thermal expansion. These parameters define material behavior during sintering and are used in the sintering particle model implemented in the discrete element model. The investigated material, the NiAl intermetallic, belongs to novel materials characterized by advantageous mechanical properties. Various machine elements are manufactured from a pure NiAl powder or from powder mixtures containing the NiAl using the sintering technology. It is well known that sintering is governed by diffusion. Therefore diffusive properties are important parameters of the micromechanical model of sintering. Numerical estimation of the model parameters by simulations at the lower scale is a powerful tool alternative to experimental methods. Molecular statics and dynamics models for NiAl have been created using the embedded atom model potential. Numerical simulations have allowed us to estimate the volume, surface, and grain-boundary diffusivity for the B2-type NiAl in the 1573 to 1673 K temperature range. Dependence of the diffusion coefficients on temperature has been determined and validity of the Arrhenius-type temperature dependency has been assessed. The parameters evaluated numerically have been compared with available experimental data as well as with theoretical predictions obtained with other methods. Many of the results presented in this paper have a pioneer character and are not known in the literature.

Keywords:
NiAl, sintering, diffusivity, molecular dynamics, molecular statics, nanoparticles

10.Mrozek A., Kuś W., Burczyński T., METHOD FOR DETERMINING STRUCTURES OF NEW CARBON-BASED 2DMATERIALS WITH PREDEFINED MECHANICAL PROPERTIES, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, Vol.15, No.5, pp.379-394, 2017
Mrozek A., Kuś W., Burczyński T., METHOD FOR DETERMINING STRUCTURES OF NEW CARBON-BASED 2DMATERIALS WITH PREDEFINED MECHANICAL PROPERTIES, INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING, ISSN: 1543-1649, Vol.15, No.5, pp.379-394, 2017

Abstract:
The following article presents the description and application of an algorithm for optimal searching for the new stable atomic arrangements of two-dimensional graphenelike carbon lattices with predefined mechanical properties. The proposed method combines the evolutionary algorithm and the conjugate-gradient optimization. The main goal of the optimization is to find stable arrangements of carbon atoms placed in the unit cell with imposed periodic boundary conditions, which reveal desired mechanical properties. Examples of the newly obtained models of the flat, carbon materials are presented. Their mechanical properties are additionally validated during the simulation of the tensile tests using molecular dynamics.

Keywords:
2D atomic structures, graphenelike materials, hybrid algorithm, evolutionary algorithm, mechanical properties

11.Chmielewski M., Pietrzak K., Strojny-Nędza A., Kaszyca K., Zybala R., Bazarnik P., Lewandowska M., Nosewicz S., Microstructure and thermal properties of Cu-SiC composite materials depending on the sintering technique, SCIENCE OF SINTERING, ISSN: 0350-820X, DOI: 10.2298/SOS1701011C, Vol.49, pp.11-22, 2017
Chmielewski M., Pietrzak K., Strojny-Nędza A., Kaszyca K., Zybala R., Bazarnik P., Lewandowska M., Nosewicz S., Microstructure and thermal properties of Cu-SiC composite materials depending on the sintering technique, SCIENCE OF SINTERING, ISSN: 0350-820X, DOI: 10.2298/SOS1701011C, Vol.49, pp.11-22, 2017

Abstract:
The presented paper investigates the relationship between the microstructure and thermal properties of copper–silicon carbide composites obtained through hot pressing (HP) and spark plasma sintering (SPS) techniques. The microstructural analysis showed a better densification in the case of composites sintered in the SPS process. TEM investigations revealed the presence of silicon in the area of metallic matrix in the region close to metal ceramic boundary. It is the product of silicon dissolving process in copper occurring at an elevated temperature. The Cu-SiC interface is significantly defected in composites obtained through the hot pressing method, which has a major influence on the thermal conductivity of materials.

Keywords:
Metal matrix composites; Silicon carbide; Interface; Spark plasma sintering; Thermal conductivity.

12.Colabella L., Ibarra Pino A.A., Ballarre J., Kowalczyk P., Cisilino A.P., Calculation of cancellous bone elastic properties with the polarization-based FFT iterative scheme, International Journal for Numerical Methods in Biomedical Engineering, ISSN: 2040-7939, DOI: 10.1002/cnm.2879, Vol.33, No.11, pp.e2879-1-16, 2017
Colabella L., Ibarra Pino A.A., Ballarre J., Kowalczyk P., Cisilino A.P., Calculation of cancellous bone elastic properties with the polarization-based FFT iterative scheme, International Journal for Numerical Methods in Biomedical Engineering, ISSN: 2040-7939, DOI: 10.1002/cnm.2879, Vol.33, No.11, pp.e2879-1-16, 2017

Abstract:
The Fast Fourier Transform–based method, originally introduced by Moulinec and Suquet in 1994 has gained popularity for computing homogenized properties of composites. In this work, the method is used for the computational homogenization of the elastic properties of cancellous bone. To the authors' knowledge, this is the first study where the Fast Fourier Transform scheme is applied to bone mechanics. The performance of the method is analyzed for artificial and natural bone samples of 2 species: bovine femoral heads and implanted femurs of Hokkaido rats. Model geometries are constructed using data from X‐ray tomographies, and the bone tissue elastic properties are measured using microindentation and nanoindentation tests. Computed results are in excellent agreement with those available in the literature. The study shows the suitability of the method to accurately estimate the fully anisotropic elastic response of cancellous bone. Guidelines are provided for the construction of the models and the setting of the algorithm.

Keywords:
accelerated FFT method, cancellous bone, homogenized elastic properties

13.Błachowski B.D., Tauzowski P., Lógó J., Modal Approximation Based Optimal Design of Dynamically Loaded Plastic Structures, Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11016, pp.1-6, 2017
Błachowski B.D., Tauzowski P., Lógó J., Modal Approximation Based Optimal Design of Dynamically Loaded Plastic Structures, Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11016, pp.1-6, 2017

Abstract:
The purpose of this study is to present an optimal design procedure for elasto-plastic structures subjected to impact loading. The proposed method is based on mode approximation of the displacement field and assumption of constant acceleration of impacted structure during whole time of deformation process until the plastic displacement limit is reached. Derivation of the method begins with the application of the principle of conservation of linear momentum, followed by determination of inertial forces. The final stage of the method utilizes an optimization technique in order to find a minimum weight structure. Eventually, effectiveness and usefulness of the proposed method is demonstrated on the example of a planar truss structure subjected to dynamic loading caused by a mass impacting the structure with a given initial velocity.

Keywords:
structural dynamics, optimal design, elasto-plastic structures, short-time dynamic loading

14.Tauzowski P., Lógó J., Pintér E., Parametric Study on the Element Size Effect for Optimal Topologies, Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.0000, pp.1-10, 2017