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Affiliation to IPPT PAN

1.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

2.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.

3.Marszałek A., Burczyński T., Ordered fuzzy random variable: definition and the concept of normality, INFORMATION SCIENCES, ISSN: 0020-0255, DOI: 10.1016/j.ins.2020.08.120, pp.1-12, 2020
Marszałek A., Burczyński T., Ordered fuzzy random variable: definition and the concept of normality, INFORMATION SCIENCES, ISSN: 0020-0255, DOI: 10.1016/j.ins.2020.08.120, pp.1-12, 2020

Abstract:
The concept of fuzzy random variable combines two sources of uncertainty: randomness and fuzziness, whereas the model of ordered fuzzy numbers provides a representation of inaccurate quantitative data, and is an alternative to the standard fuzzy numbers model proposed by Zadeh. This paper develops the model of ordered fuzzy numbers by defining the concept of fuzzy random variables for these numbers, called further ordered fuzzy random variables. Thanks to the well-defined arithmetic of ordered fuzzy numbers (existence of neutral and opposite elements) and the introduced ordered fuzzy random variables; it becomes possible to construct fully fuzzy stochastic time series models such as e.g., the autoregressive model or the GARCH model in the form of classical equations, which can be estimated using the least-squares or the maximum likelihood method. Furthermore, the concept of normality of ordered fuzzy random variables and the method to generate pseudo-random ordered fuzzy variables with normal distribution are introduced.

Keywords:
ordered fuzzy numbers, fuzzy random variables, ordered fuzzy random variables, normal ordered fuzzy random variable

4.Maździarz M., Mościcki T., New zirconium diboride polymorphs—first-principles calculations, Materials, ISSN: 1996-1944, DOI: 10.3390/ma13133022, Vol.13, No.13, pp.3022-1-13, 2020
Maździarz M., Mościcki T., New zirconium diboride polymorphs—first-principles calculations, Materials, ISSN: 1996-1944, DOI: 10.3390/ma13133022, Vol.13, No.13, pp.3022-1-13, 2020

Abstract:
Two new hypothetical zirconium diboride (ZrB 2) polymorphs: (hP6-P6 3 /mmc-space group, no. 194) and (oP6-Pmmn-space group, no. 59), were thoroughly studied under the first-principles density functional theory calculations from the structural, mechanical and thermodynamic properties point of view. The proposed phases are thermodynamically stable (negative formation enthalpy). Studies of mechanical properties indicate that new polymorphs are less hard than the known phase (hP3-P6/mmm-space group, no. 191) and are not brittle. Analysis of phonon band structure and density of states (DOS) also show that the phonon modes have positive frequencies everywhere and the new ZrB 2 phases are not only mechanically but also dynamically stable. The estimated acoustic Debye temperature, ΘD, for the two new proposed ZrB 2 phases is about 760 K. The thermodynamic properties such as internal energy, free energy, entropy and constant-volume specific heat are also presented.

Keywords:
zirconium diboride, ab initio calculations, mechanical properties, elastic properties, phonons

5.Nosewicz S., Rojek J., Chmielewski M., Discrete element framework for determination of sintering and postsintering residual stresses of particle reinforced composites, Materials, ISSN: 1996-1944, DOI: 10.3390/ma13184015, Vol.13, No.18, pp.4015-1- 20, 2020
Nosewicz S., Rojek J., Chmielewski M., Discrete element framework for determination of sintering and postsintering residual stresses of particle reinforced composites, Materials, ISSN: 1996-1944, DOI: 10.3390/ma13184015, Vol.13, No.18, pp.4015-1- 20, 2020

Abstract:
In this paper, the discrete element method framework is employed to determine and analyze the stresses induced during and after the powder metallurgy process of particle-reinforced composite. Applied mechanical loading and the differences in the thermal expansion coefficients of metal/intermetallic matrix and ceramic reinforcing particles during cooling produce the complex state of stresses in and between the particles, leading to the occurrence of material defects, such as cracks, and in consequence the composite degradation. Therefore, the viscoelastic model of pressure-assisted sintering of a two-phase powder mixture is applied in order to study the stress field of particle assembly of intermetallic-ceramic composite NiAl/Al2O3. The stress evaluation is performed at two levels: macroscopic and microscopic. Macroscopic averaged stress is determined using the homogenization method using the representative volume element. Microscopic stresses are calculated both in the body of particles and in the contact interface (necks) between particles. Obtained results are in line with the cooling mechanism of the two-phase materials.

Keywords:
sintering, discrete element method, residual stress, particle-reinforced composites

6.Akhter M.J., Kuś W., Mrozek A., Burczyński T., Mechanical properties of monolayer MoS2 with randomly distributed defects, Materials, ISSN: 1996-1944, DOI: 10.3390/ma13061307, Vol.13, No.6, pp.1307-1-14, 2020
Akhter M.J., Kuś W., Mrozek A., Burczyński T., Mechanical properties of monolayer MoS2 with randomly distributed defects, Materials, ISSN: 1996-1944, DOI: 10.3390/ma13061307, Vol.13, No.6, pp.1307-1-14, 2020

Abstract:
The variation of elastic constants stiffness coefficients with respect to different percentage ratios of defects in monolayer molybdenum disulfide (MLMoS2) is reported for a particular set of atomistic nanostructural characteristics. The common method suggested is to use conventional defects such as single vacancy or di vacancy, and the recent studies use stone-walled multiple defects for highlighting the differences in the mechanical and electronic properties of 2D materials. Modeling the size influence of monolayer MoS2 by generating defects which are randomly distributed for a different percentage from 0% to 25% is considered in the paper. In this work, the geometry of the monolayer MoS2 defects modeled as randomized over the domain are taken into account. For simulation, the molecular static method is adopted and study the effect of elastic stiffness parameters of the 2D MoS2 material. Our findings reveals that the expansion of defects concentration leads to a decrease in the elastic properties, the sheer decrease in the elastic properties is found at 25%. We also study the diffusion of Molybdenum (Mo) in Sulphur (S) layers of atoms within MoS2 with Mo antisite defects. The elastic constants dwindle in the case of antisite defects too, but when compared to pure defects, the reduction was to a smaller extent in monolayer MoS2. Nevertheless, the Mo diffusion in sulfur gets to be more and more isotropic with the increase in the defect concentrations and elastic stiffness decreases with antisite defects concentration up to 25%. The distribution of antisite defects plays a vital role in modulating Mo diffusion in sulfur. These results will be helpful and give insights in the design of 2D materials.

Keywords:
mono-layer MoS2, mechanical properties, molecular statics/dynamics, defects, random distributed defects

7.Postek E., Sadowski T., Thermomechanical effects during impact testing of WC/Co composite material, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2020.112054, Vol.241, pp.112054-1-25, 2020
Postek E., Sadowski T., Thermomechanical effects during impact testing of WC/Co composite material, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2020.112054, Vol.241, pp.112054-1-25, 2020

Abstract:
WC/Co metal-matrix ceramic composites (MMCs) are used for manufacturing cutting and drilling tools, surgical tools, mill inserts, jet engines, and other high-responsibility structures. The combination of a phase of hard wolfram carbide (WC) grains with a metallic ductile interface of cobalt (Co) yields a complex microstructure with significantly different mechanical properties of the phases. The aim of this study is to investigate the thermomechanical behavior of the MMC polycrystalline material with ductile binders under impact conditions. An adiabatic and coupled thermomechanical analysis of the WC/Co composite under impact loading is performed using FEM. The heat conduction is considered in the analysis in order to capture heat transfer in the polycrystalline structure, i.e. between the grains and the grain boundaries (GBs). The Johnson-Cook yield function is used in the constitutive model of the ductile Co interface, while the WC phase is linear elastic. The motivation comes from the observation that the heat conductivity effect is often omitted, even in recent papers **[75]. Significant differences between temperatures and plastic strains in the adiabatic and coupled solutions are observed, which leads to the main conclusion that the adiabatic solution should not be used for assessing the impact response of the composite material.

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

8.Błachowski B., Świercz A., Ostrowski M., Tauzowski P., Olaszek P., Jankowski Ł., Convex relaxation for efficient sensor layout optimization in large‐scale structures subjected to moving loads, Computer-Aided Civil and Infrastructure Engineering, ISSN: 1093-9687, DOI: 10.1111/mice.12553, Vol.35, No.10, pp.1085-1100, 2020
Błachowski B., Świercz A., Ostrowski M., Tauzowski P., Olaszek P., Jankowski Ł., Convex relaxation for efficient sensor layout optimization in large‐scale structures subjected to moving loads, Computer-Aided Civil and Infrastructure Engineering, ISSN: 1093-9687, DOI: 10.1111/mice.12553, Vol.35, No.10, pp.1085-1100, 2020

Abstract:
This paper proposes a computationally effective framework for load‐dependent optimal sensor placement in large‐scale civil engineering structures subjected to moving loads. Two common problems are addressed: selection of modes to be monitored and computational effectiveness. Typical sensor placement methods assume that the set of modes to be monitored is known. In practice, determination of such modes of interest is not straightforward. A practical approach is proposed that facilitates the selection of modes in a quasi‐automatic way based on the structural response at the candidate sensor locations to typical operational loads. The criterion used to assess sensor placement is based on Kammer's Effective Independence (EFI). However, in contrast to typical implementations of EFI, which treat the problem as a computationally demanding discrete problem and use greedy optimization, an approach based on convex relaxation is proposed. A notion of sensor density is applied, which converts the original combinatorial problem into a computationally tractable continuous optimization problem. The proposed framework is tested in application to a real tied‐arch railway bridge located in central Poland.

Keywords:
optimal sensor placement, effective independence method, Fisher information matrix

9.Byra M., Jarosik P., Szubert A., Galperine M., Ojeda-Fournier H., Olson L., O'Boyle M., Comstock Ch., Andre M., Breast mass segmentation in ultrasound with selective kernel U-Net convolutional neural network, Biomedical Signal Processing and Control, ISSN: 1746-8094, DOI: 10.1016/j.bspc.2020.102027, Vol.61, pp.102027-1-10, 2020
Byra M., Jarosik P., Szubert A., Galperine M., Ojeda-Fournier H., Olson L., O'Boyle M., Comstock Ch., Andre M., Breast mass segmentation in ultrasound with selective kernel U-Net convolutional neural network, Biomedical Signal Processing and Control, ISSN: 1746-8094, DOI: 10.1016/j.bspc.2020.102027, Vol.61, pp.102027-1-10, 2020

Abstract:
In this work, we propose a deep learning method for breast mass segmentation in ultrasound (US). Variations in breast mass size and image characteristics make the automatic segmentation difficult. To addressthis issue, we developed a selective kernel (SK) U-Net convolutional neural network. The aim of the SKswas to adjust network's receptive fields via an attention mechanism, and fuse feature maps extractedwith dilated and conventional convolutions. The proposed method was developed and evaluated usingUS images collected from 882 breast masses. Moreover, we used three datasets of US images collectedat different medical centers for testing (893 US images). On our test set of 150 US images, the SK-U-Netachieved mean Dice score of 0.826, and outperformed regular U-Net, Dice score of 0.778. When evaluatedon three separate datasets, the proposed method yielded mean Dice scores ranging from 0.646 to 0.780. Additional fine-tuning of our better-performing model with data collected at different centers improvedmean Dice scores by ~6%. SK-U-Net utilized both dilated and regular convolutions to process US images. We found strong correlation, Spearman's rank coefficient of 0.7, between the utilization of dilated convo-lutions and breast mass size in the case of network's expansion path. Our study shows the usefulness ofdeep learning methods for breast mass segmentation. SK-U-Net implementation and pre-trained weightscan be found at github.com/mbyr/bus_seg.

Keywords:
attention mechanism, breast mass segmentation, convolutional neural networks, deep learning, receptive field, ultrasound imaging

10.Colabella L., Cisilino A., Fachinotti V., Capiel C., Kowalczyk P., Multiscale design of artificial bones with biomimetic elastic microstructures, Journal of the Mechanical Behavior of Biomedical Materials, ISSN: 1751-6161, DOI: 10.1016/j.jmbbm.2020.103748, Vol.108, pp.103748-1-9, 2020
Colabella L., Cisilino A., Fachinotti V., Capiel C., Kowalczyk P., Multiscale design of artificial bones with biomimetic elastic microstructures, Journal of the Mechanical Behavior of Biomedical Materials, ISSN: 1751-6161, DOI: 10.1016/j.jmbbm.2020.103748, Vol.108, pp.103748-1-9, 2020

Abstract:
Cancellous bone is a highly porous, heterogeneous, and anisotropic material which can be found at the epiphyses of long bones and in the vertebral bodies. The hierarchical architecture makes cancellous bone a prime example of a lightweight natural material that combines strength with toughness. Better understanding the mechanics of cancellous bone is of interest for the diagnosis of bone diseases, the evaluation of the risk of fracture, and for the design of artificial bones and bone scaffolds for tissue engineering. A multiscale optimization method to maximize the stiffness of artificial bones using biomimetic cellular microstructures described by a finite set of geometrical micro-parameters is presented here. The most outstanding characteristics of its implementation are the use of: an interior point optimization algorithm, a precalculated response surface methodology for the evaluation of the elastic tensor of the microstructure as an analytical function of the micro-parameters, and the adjoint method for the computation of the sensitivity of the macroscopic mechanical response to the variation of the micro-parameters. The performance and effectiveness of the tool are evaluated by solving a problem that consists in finding the optimal distribution of the microstructures for a proximal end of a femur subjected to physiological loads. Two strategies for the specification of the solid volume fraction constraints are assessed. The results are compared with data of a computed tomography study of an actual human bone. The model successfully predicts the main features of the spatial arrangement of the trabecular and cortical microstructures of the natural bone.

Keywords:
multiscale optimization, cancellous bone, bone scaffolds, parameterized microstructures

11.Meissner M., Wiśniewski K., Investigation of damping effects on low-frequency steady-state acoustical behaviour of coupled spaces, Royal Society Open Science, ISSN: 2054-5703, DOI: 10.1098/rsos.200514, Vol.7, No.8, pp.200514-1-14, 2020
Meissner M., Wiśniewski K., Investigation of damping effects on low-frequency steady-state acoustical behaviour of coupled spaces, Royal Society Open Science, ISSN: 2054-5703, DOI: 10.1098/rsos.200514, Vol.7, No.8, pp.200514-1-14, 2020

Abstract:
In the low-frequency range, the acoustical behaviour of enclosed spaces is strongly influenced by excited acoustic modes resulting in a spatial irregularity of a steady-state sound field. In the paper, this problem has been examined theoretically and numerically for a system of coupled spaces with complex-valued conditions on boundary surfaces. Using a modal expansion method, an analytic formula for the Green's function was derived allowing to predict the interior sound field for a pure-tone excitation. To quantify the spatial irregularity of steady-state sound field, the parameter referred to as the mean spatial deviation was introduced. A numerical simulation was carried out for the system consisting of two coupled rectangular subspaces. Eigenfunctions and eigenfrequencies for this system were determined using the high-accuracy eigenvalue solver. As was evidenced by computational data, for small sound damping on absorptive walls the mean spatial deviation peaks at frequencies corresponding to eigenfrequencies of strongly localized modes. However, if the sound damping is much higher, the main cause of spatial irregularity of the interior sound field is the appearance of sharp valleys in a spatial distribution of a sound pressure level.

Keywords:
interior acoustics, coupled spaces, steady-state sound field, modal expansion method, sound damping, Green's function

12.Błachowski B., Tauzowski P., Lógó J., Yield limited optimal topology design of elastoplastic structures, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-019-02447-9, pp.1-24, 2020
Błachowski B., Tauzowski P., Lógó J., Yield limited optimal topology design of elastoplastic structures, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-019-02447-9, pp.1-24, 2020

Abstract:
This study is devoted to a novel method for topology optimization of elastoplastic structures subjected to stress constraints. It should be noted that in spite of the classical solutions of the different type of elastoplastic topology problems are more than 70 years old, the integration of the Prandtl-Reuss constitutive equations into the topology optimization process is not very often investigated in the last three decades. In the presented methodology where the classical variational principles of plasticity and the functor-oriented programming technique are applied in topology design, the aim is to find a minimum weight structure which is able to carry a given load, fulfills the allowable stress limit, and is made of a linearly elastic, perfectly plastic material. The optimal structure is found in an iterative way using only a stress intensity distribution and a return mapping algorithm. The method determines representative stresses at every Gaussian point, averages them inside every finite element using the von Mises yield criterion, and removes material proportionally to the stress intensities in individual finite elements. The procedure is repeated until the limit load capacity is exceeded under a given loading. The effectiveness of the methodology is illustrated with three numerical examples. Additionally, different topologies are presented for a purely elastic and an elastoplastic material, respectively. It is also demonstrated that the proposed method is able to find the optimal elastoplastic topology for a problem with a computational mesh of the order of tens of thousands of finite elements.

Keywords:
topology optimization, elastoplastic structures, minimum-weight design, stress constraints

13.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

14.Jarosik P., Klimonda Z., Lewandowski M., Byra M., Breast lesion classification based on ultrasonic radio-frequency signals using convolutional neural networks, Biocybernetics and Biomedical Engineering, ISSN: 0208-5216, DOI: 10.1016/j.bbe.2020.04.002, Vol.40, No.3, pp.977-986, 2020
Jarosik P., Klimonda Z., Lewandowski M., Byra M., Breast lesion classification based on ultrasonic radio-frequency signals using convolutional neural networks, Biocybernetics and Biomedical Engineering, ISSN: 0208-5216, DOI: 10.1016/j.bbe.2020.04.002, Vol.40, No.3, pp.977-986, 2020

Abstract:
We propose a novel approach to breast mass classification based on deep learning models that utilize raw radio-frequency (RF) ultrasound (US) signals. US images, typically displayed by US scanners and used to develop computer-aided diagnosis systems, are reconstructed using raw RF data. However, information related to physical properties of tissues present in RF signals is partially lost due to the irreversible compression necessary to make raw data readable to the human eye. To utilize the information present in raw US data, we develop deep learning models that can automatically process small 2D patches of RF signals and their amplitude samples. We compare our approach with classification method based on the Nakagami parameter, a widely used quantitative US technique utilizing RF data amplitude samples. Our better performing deep learning model, trained using RF signals and their envelope samples, achieved good classification performance, with the area under the receiver attaining operating characteristic curve (AUC) and balanced accuracy of 0.772 and 0.710, respectively. The proposed method significantly outperformed the Nakagami parameter-based classifier, which achieved AUC and accuracy of 0.64 and 0.611, respectively. The developed deep learning models were used to generate parametric maps illustrating the level of mass malignancy. Our study presents the feasibility of using RF data for the development of deep learning breast mass classification models.

Keywords:
breast lesion classification, convolutional neural networks, deep learning, radio-frequency signals, ultrasound imaging

15.Postek E., Sadowski T., High-velocity impact of 2-phase WC-Co composite plate - beginning of the process, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.24425/amm.2020.131726, Vol.65, No.1, pp.265-274, 2020
Postek E., Sadowski T., High-velocity impact of 2-phase WC-Co composite plate - beginning of the process, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.24425/amm.2020.131726, Vol.65, No.1, pp.265-274, 2020

Abstract:
2-phase composites are often used for high demanding parts that can undergo impact loads. However, most of the papers on dynamic loading concerns layered composites. In our opinion, the impact loads are not considered thoroughly enough. Good examples of 2-phase composites are: (1) a WC/Co cermet or (2) a monolithic ceramic Al2O3/ZrO2. The WC/Co cermet is often modelled as having ductile elasto-plastic Co matrix and ideally elastic WC grains. It is because of very high crushing resistivity of the WC. In this paper, we present an extension to earlier elaborated models ([44]) with the assumption of ideal elasticity of the grains. The new and general numerical model for high-velocity impact of the 2-phase composites is proposed. The idea of this novelty relies on the introduction of crushability of grains in the composite and thermo-mechanical coupling. The model allows for description of the dynamic response both composite polycrystals made of: (1) 2 different purely elastic phases (e.g. Al2O3/ZrO2) or (2) one elastic phase and the second one plastic (e.g. cermet WC/Co), or (3) 2 elasto-plastic phases with different material properties and damage processes. In particular, the analysis was limited to the to the cases (2) and (3), i.e. we investigated the WC/Co polycrystal that impacted a rigid wall with the initial velocity equal to 50 m/s.

Keywords:
2-phase composites, cermet, Johnson-Cook plasticity, impact, numerical modelling