Zdzisław Nowak, Ph.D., Dr. Habil., Eng.

Department of Theory of Continuous Media and Nanostructures (ZTOCiN)
Division of Polymer Physics (PFP)
position: assistant professor
telephone: (+48) 22 826 12 81 ext.: 454
room: 238
e-mail: znowak

Doctoral thesis
1988Zagadnienie lokalizacji deformacji lepkoplastycznych w tarczy kołowej wszechstronnie rozciąganej 
supervisor -- Prof. Piotr Perzyna, Ph.D., Dr. Habil., Eng., IPPT PAN
435 
Habilitation thesis
2007-10-25Metoda identyfikacji w mechanice materiałów ciągliwych z uszkodzeniami930
 
Supervision of doctoral theses
1.2015-03-26Nowak Marcin  Analiza deformacji i zniszczenia struktur komórkowych w zastosowaniu do symulacji procesu infiltracji pianki korundowej ciekłym metalem709
 

Recent publications
1.Zajączkowska U., Kucharski S., Nowak Z., Grabowska K., Morphometric and mechanical characteristics of Equisetum hyemale stem enhance its vibration, PLANTA, ISSN: 0032-0935, DOI: DOI 10.1007/s00425-017-2648-1, Vol.245, No.4, pp.835-848, 2017
Zajączkowska U., Kucharski S., Nowak Z., Grabowska K., Morphometric and mechanical characteristics of Equisetum hyemale stem enhance its vibration, PLANTA, ISSN: 0032-0935, DOI: DOI 10.1007/s00425-017-2648-1, Vol.245, No.4, pp.835-848, 2017

Abstract:
The order of the internodes, and their geometry and mechanical characteristics influence the capability of theEquisetumstem to vibrate, potentially stimulating spore liberation at the optimum stress setting along the stem.
Equisetum hyemale L. plants represent a special example of cellular solid construction with mechanical stability achieved by a high second moment of area and relatively high resistance against local buckling. We proposed the hypothesis that the order of E. hyemale L. stem internodes, their geometry and mechanical characteristics influence the capability of the stem to vibrate, stimulating spore liberation at the minimum stress setting value along the stem. An analysis of apex vibration was done based on videos presenting the behavior of an Equisetum clump filmed in a wind tunnel and also as a result of excitation by bending the stem by 20°. We compared these data with the vibrations of stems of the same size but deprived of the three topmost internodes. Also, we created a finite element model (FEM), upon which we have based the ‘natural’ stem vibration as a copy of the real object, ‘random’ with reshuffled internodes and ‘uniform’, created as one tube with the characters averaged from all internodes. The natural internode arrangement influences the frequency and amplitude of the apex vibration, maintaining an equal stress distribution in the stem, which may influence the capability for efficient spore spreading.

Keywords:
Mechanical properties, Plant biomechanics, Segmented structure, Stem vibration, Stress distribution, Wind

2.Nowak Z., Nowak M., Pęcherski R., Potoczek M., Śliwa R.E., Numerical Simulations of Mechanical Properties of Alumina Foams Based on Computed Tomography, JOURNAL OF MECHANICS OF MATERIALS AND STRUCTURES, ISSN: 1559-3959, DOI: 10.2140/jomms.2017.12.107, Vol.12, No.1, pp.107-121, 2017
Nowak Z., Nowak M., Pęcherski R., Potoczek M., Śliwa R.E., Numerical Simulations of Mechanical Properties of Alumina Foams Based on Computed Tomography, JOURNAL OF MECHANICS OF MATERIALS AND STRUCTURES, ISSN: 1559-3959, DOI: 10.2140/jomms.2017.12.107, Vol.12, No.1, pp.107-121, 2017

Abstract:
The aim of this paper is to apply the results of microtomography of alumina foam to create a numerical model and perform numerical simulations of compression tests. The geometric characteristics of real foam samples are estimated from tomographic and scanning electron microscopy images. The performance of the reconstructed models is compared to experimental values of elastic moduli. A preliminary analysis of failure strength simulations under compression of alumina foam is also provided.

Keywords:
Alumina open-cell foam, computed tomography microstructure, Young’s modulus, compressive strength of alumina foams

3.Poniżnik Z., Nowak Z., Basista M., Numerical modeling of deformation and fracture of reinforcing fibers in ceramic–metal composites, INTERNATIONAL JOURNAL OF DAMAGE MECHANICS, ISSN: 1056-7895, DOI: 10.1177/1056789515611945, Vol.26, No.5, pp.711-734, 2017
Poniżnik Z., Nowak Z., Basista M., Numerical modeling of deformation and fracture of reinforcing fibers in ceramic–metal composites, INTERNATIONAL JOURNAL OF DAMAGE MECHANICS, ISSN: 1056-7895, DOI: 10.1177/1056789515611945, Vol.26, No.5, pp.711-734, 2017

Abstract:
This paper is concerned with numerical modeling of deformation and fracture of a metal ligament bridging the crack faces in ceramic–metal composites, as a prerequisite for the determination of the J integral for composites with interpenetrating microstructure. A finite element model is proposed of an elasto-plastic crack-reinforcing fiber undergoing large plastic deformations and progressive debonding from the elastic matrix through a cohesive matrix–fiber interface. The σ-u relationships are derived first in the case of pullout of an elasto-plastic fiber embedded in an elastic matrix and then in uniaxial tension of the elasto-plastic fiber bridging the crack faces in elastic matrix. The obtained numerical results are discussed and compared with the theoretical predictions reported by other authors.

Keywords:
Ceramic–metal composites, fracture modeling, crack bridging, fiber pullout, cohesive interface, fiber debonding, finite element simulations

4.Basista M., Węglewski W., Bochenek K., Poniżnik Z., Nowak Z., Micro-CT Finite Element Analysis of Thermal Residual Stresses and Fracture in Metal-Ceramic Composites, Advanced Engineering Materials, ISSN: 1438-1656, DOI: 10.1002/adem.201600725, pp.1-9, 2016
Basista M., Węglewski W., Bochenek K., Poniżnik Z., Nowak Z., Micro-CT Finite Element Analysis of Thermal Residual Stresses and Fracture in Metal-Ceramic Composites, Advanced Engineering Materials, ISSN: 1438-1656, DOI: 10.1002/adem.201600725, pp.1-9, 2016

Abstract:
This paper presents a simple way of using X-ray micro-computed tomography (micro-CT) in numerical modeling of material properties of metal-ceramic composites. It shows step by step the proposed methodology with details of the finite element mesh creation, so that it can easily be reproduced by interested researchers. Two case studies are considered to show the proposed approach at work: i) determination of processing-induced residual stresses in hot pressed Cr/Al2O3 and NiAl/Al2O3 particulate composites and ii) determination of J-integral for an interpenetrating phase composite made of porous alumina preform infiltrated with molten copper. The method is straightforward and effective but has its limitations that are pointed out.

5.Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Mechanical properties of the ceramic open-cell foams of variable cell sizes, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2015-0333, Vol.60, No.3, pp.1957-1963, 2015
Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Mechanical properties of the ceramic open-cell foams of variable cell sizes, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2015-0333, Vol.60, No.3, pp.1957-1963, 2015

Abstract:
The mechanical properties and numerical model of ceramic alumina open-cell foam, which is produced by the chemical method of gelcasting with different cell sizes (porosities) are presented. Geometric characteristics of real foam samples were estimated from tomographic and scanning electron microscopy images. Using this information, numerical foam model was proposed. A good agreement between the numerical model and the results elaborated from microtomography was obtained. To simulate the deformation processes the finite element program ABAQUS was used. The main goal of this computation was to obtain macroscopic force as a function of applied vertical displacement in compression test.

Keywords:
mechanical properties of foams, alumina open-cell foam, Young modulus, strength of alumina foams

6.Nowak Z., Perzyna P., The Identfication Procedure for The Constitutive Model of Elasto-Viscoplasticity Describing the Behaviour of Nanocrystalline Titanium, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.62, No.3, pp.221-240, 2014
Nowak Z., Perzyna P., The Identfication Procedure for The Constitutive Model of Elasto-Viscoplasticity Describing the Behaviour of Nanocrystalline Titanium, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.62, No.3, pp.221-240, 2014

Abstract:
The main objective of the present paper is the description of the behaviour of the ultrafine- grained (UFG) titanium by the constitutive model of elasto-viscoplasticity with the development of the identification procedure. We intend to utilize the constitutive model of the thermodynamical theory of elasto-viscoplasticity for description of nanocrystalline metals presented by Perzyna [21]. The identification procedure is based on experimental observation data obtained by JIA et al. [11] for ultrafine-grained titanium and by Wang et al. [25] for nanostructured titanium. Hexagonal close-packed (hcp) ultrafine-grained titanium processed by sever plastic deformation (SPD) has gained wide interest due to its excellent mechanical properties and potential applications as biomedical implants

Keywords:
elasto-viscoplasticity, nanocrystalline titanium, uniaxial compression

7.Nowak M., Nowak Z., Pęcherski R.B., Potoczek M., Śliwa R.E., On the reconstruction method of ceramic foam structures and the methodology of Young modulus determination, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.2478/amm-2013-0154, Vol.58, No.4, pp.1219-1222, 2013
Nowak M., Nowak Z., Pęcherski R.B., Potoczek M., Śliwa R.E., On the reconstruction method of ceramic foam structures and the methodology of Young modulus determination, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.2478/amm-2013-0154, Vol.58, No.4, pp.1219-1222, 2013

Abstract:
In the present paper a finite element model was used to investigate the mechanical properties such as Young’s modulus of open-cell ceramic foam. Finite element discretization was derived from real foam specimen by computer tomography images. The generated 3D geometry of the ceramic foam was used to simulate deformation process under compression. The own numerical procedure was developed to control finite element mesh density by changing the element size. Several numerical simulations of compression test have been carried out using commercial finite element code ABAQUS. The size of the ceramic specimen and the density of finite element mesh were examined. The influence of type and size of finite element on the value of Young’s modulus was studied, as well. The obtained numerical results have been compared with the results of experimental investigations carried out by Ortega [11]. It is shown that numerical results are in close agreement with experiment. It appears also that the dependency of Young’s modulus of ceramic foam on density of finite element mesh cannot be ignored.

Keywords:
foams, 3D image analysis, cellular ceramics, FE modeling, porous alumina, mechanical properties

8.Frąś T., Nowak Z., Perzyna P., Pęcherski R.B., Identification of the model describing viscoplastic behaviour of high strength metals, INVERSE PROBLEMS IN SCIENCE AND ENGINEERING, ISSN: 1741-5977, DOI: 10.1080/17415977.2010.531474, Vol.19, No.1, pp.17-30, 2011
Frąś T., Nowak Z., Perzyna P., Pęcherski R.B., Identification of the model describing viscoplastic behaviour of high strength metals, INVERSE PROBLEMS IN SCIENCE AND ENGINEERING, ISSN: 1741-5977, DOI: 10.1080/17415977.2010.531474, Vol.19, No.1, pp.17-30, 2011

Abstract:
Ultrafine grained (UFG) and nanocrystalline metals (nc-metals) are studied. Experimental investigations of the behaviour of such materials under quasistatic as well as dynamic loading conditions related with microscopic observations show that in many cases the dominant mechanism of plastic strain is a multiscale development of shear deformation modes. The comprehensive discussion of these phenomena in UFG and nc-metals is given in M.A. Meyers, A. Mishra and D.J. Benson [Mechanical properties of nanocrystalline materials, Progr. Mater. Sci. 51 (2006), pp. 427–556], where it has been shown that the deformation mode of nanocrystalline materials changes as the grain size decreases into the ultrafine region. For smaller grain sizes (d < 300 nm) shear band development occurs immediately after the onset of plastic flow. Significant strain-rate dependence of the flow stress, particularly at high strain rates, was also emphasized. Our objective is to identify the parameters of Perzyna constitutive model, a new description of viscoplastic deformation, which accounts for the observed shear banding. The viscoplasticity model proposed earlier by Perzyna [Fundamental problems in viscoplasticity, Adv. Mech. 9 (1966), pp. 243–377] was extended in order to describe the shear banding contribution in Z. Nowak, P. Perzyna, R.B. Pecherski [Description of viscoplastic fow accounting for shear banding, Arch. Metall. Mater. 52 (2007), pp. 217–222]. The shear banding contribution function, which was introduced formerly by Pe¸cherski [Modelling of large plastic deformation produced by micro-shear banding, Arch. Mech. 44 (1992), pp. 563–584] and applied in continuum plasticity accounting for shear banding in R.B. Pecherski [Macroscopic measure of the rate of deformation produced by micro-shear banding, Arch. Mech. 49 (1997), pp. 385–401] plays pivotal role in the viscoplasticity model. The derived constitutive equations were identified and verified with the application of experimental data provided in the article by D. Jia, K.T. Ramesh and E. Ma [Effects of nanocrystalline and ultrafne grain sizes on constitutive behavior and shear bands in iron, Acta Mat. 51 (2003), pp. 3495–3509], where quasistatic and dynamic compression tests with UFG and nanocrystalline iron specimens of a wide range of mean grain size were reported. Numerical simulation of the compression of the prismatic specimen was made by the ABAQUS FEM program with UMAT subroutine. Comparison with experimental results proved the validity of the
identified parameters and the possibilities of the application of the proposed description for other high strength metals.

Keywords:
Ultra fine grained metals, nanocrystalline metals, viscoplastic deformation, shear banding, shear banding contribution function, numerical simulation of compression test, identification of the model parameters

9.Potoczek M., Śliwa R.E., Pęcherski R.B., Nowak Z., Nowak M., Modelowanie struktury geometrycznej i wytrzymałości na ściskanie pianek ceramicznych przeznaczonych do infiltracji ciekłymi metalami, RUDY I METALE NIEŻELAZNE, ISSN: 0035-9696, Vol.R56, No.11, pp.594-598, 2011
Potoczek M., Śliwa R.E., Pęcherski R.B., Nowak Z., Nowak M., Modelowanie struktury geometrycznej i wytrzymałości na ściskanie pianek ceramicznych przeznaczonych do infiltracji ciekłymi metalami, RUDY I METALE NIEŻELAZNE, ISSN: 0035-9696, Vol.R56, No.11, pp.594-598, 2011

Abstract:
Kompozyty metalowo-ceramiczne o strukturze infiltrowanej charakteryzują się unikatową przestrzenną strukturą wzajemnie przenikających się szkieletów fazy metalicznej i fazy ceramicznej. Najczęstszym sposobem wytwarzania tego typu kompozytów jest infiltracja roztopionego metalu do porowatej kształtki ceramicznej. W niniejszej pracy zastosowano piankowe kształtki korundowe (alfa-Al2O3), wytworzone nową metodą otrzymywania ceramiki porowatej, którą jest żelowanie spienionej zawiesiny (ang. gelcasting of foams). W projektowaniu właściwości mechanicznych pianek ceramicznych przeznaczonych do infiltracji roztopionym metalem, a także w badaniach właściwości mechanicznych kompozytów w postaci pianki ceramicznej infiltrowanej metalem powstaje potrzeba odtworzenia struktury ceramicznej szkieletu kompozytu.

Keywords:
Kompozyty metalowo-ceramiczne, pianki ceramiczne, modelowanie, symulacje MES

10.Nowacki W.K., Nowak Z., Perzyna P., Pęcherski R.B., Effect of strain rate on ductile fracture. A new methodology, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.48, No.4, pp.1003-1026, 2010
Nowacki W.K., Nowak Z., Perzyna P., Pęcherski R.B., Effect of strain rate on ductile fracture. A new methodology, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.48, No.4, pp.1003-1026, 2010

Abstract:
The aim of our study is to discuss a new methodology to account for the effect of strain rate on ductile fracture phenomena. Theory of inelastic materials accounting for the effects of microshear bands and microdamage is presented. The influence of microshear bands is explained by means of a function describing the instantaneous contribution of shear banding in the total rate of plastic deformation. The experimental investigations of the effect of strain rate on ductile fracture with use of the results of a dynamic double shear test of DH-36 steel with thermographic observations are reported. The registration of temperature evolution during the deformation process can provide additional data for the identification of the shear banding contribution function and the onset of ductile fracture.

Keywords:
Effect of strain rate, ductile fracture, dynamic double shear test, DH-36 steel, thermographic observation

11.Nowak Z., Constitutive modelling and parameter identification for rubber-like materials, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.LVI, No.2, pp.117-157, 2008
Nowak Z., Constitutive modelling and parameter identification for rubber-like materials, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.LVI, No.2, pp.117-157, 2008

Abstract:
The aim of the paper is to determine the phenomenological model to characterize the stress-strain relation and to simulate the behaviour of solid polyurethane (PUR) rubbers used in civil engineering, as well as to present the process of identification of model parameters for such materials. For the material studied the strain energy density function was established and a general constitutive relationship for the second-order tensor of Piola–Kirchhoff stress for elasticity is determined. Constitutive relationships for engineering stress in terms of the principal stretches are also specified. The paper presents the method of identification of parameters for constitutive models of hyperelasticity and hypoelasticity for the accessible experimental data. The applied identification procedure is based on the feature of two-phase structure of polyurethane material and is supported by the experimental data from uniaxial quasi-static tension and compression tests. In the analysis, the material behaviour was considered both for the case of incompressible deformation and also for the case of slightly compressible, nonlinearly elastic materials that are homogeneous and isotropic. The change of volume was admitted too, in range of large deformations in a tension and compression test. The attempt of description of stress-softening phenomenon was undertaken in rubber-like materials, for a given level of strain, under unloading (the Mullins effect) caused by the damage of microstructure of this material. Different descriptions of the stress-softening phenomenon were already proposed in the literature but they fail to give fully satisfactory conformity of experimental data with theoretical predictions. The phenomenological model by Elias–Zúñiga and Beatty, A new phenomenological model for stress-softening in elastomers, ZAMP, 53, 794–814, 2002, for such materials was modified by different softening functions and a simplified version of this model was identified, based on the experimental data. In the proposed model, the damage of microstructure was described by a new exponential function, which depends on the current magnitude of intensity of strain and its earlier maximum value during the process of material loading. In this paper, a suitable analysis of existent models and their verification based on experimental data for polyurethane rubber is presented for uniaxial experiments. It is shown that the magnitude of stress-softening varies with strain and this phenomenon increases with the magnitude of the pre-strain and the type of loading: monotonic tension, compression or cyclic loading. The obtained results are presented graphically for uniaxial tension and compression.

Keywords:
Rubber-like material, hyperelastic constitutive model, damage of polyurethane rubber

12.Nowak Z., Perzyna P., Pęcherski R.B., Description of viscoplastic flow accounting for shear banding, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, Vol.52, No.2, pp.217-222, 2007
Nowak Z., Perzyna P., Pęcherski R.B., Description of viscoplastic flow accounting for shear banding, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, Vol.52, No.2, pp.217-222, 2007

Abstract:
The subject of the study is concerned with ultra fine grained (ufg) and nanocrystalline metals (nc-metals). Experimental investigations of the behaviour of such materials under quasistatic as well as dynamic loading conditions related with microscopic observations show that in many cases the dominant mechanism of plastic strain is multiscale development of shear deformation modes – called shear banding. The comprehensive discussion of these phenomena in ufg and nc-metals is given in [1], [2] and [3], where it has been shown that the deformation mode of nanocrystalline materials changes as the grain size decreases into the ultrafine region. For smaller grain sizes (d < 300 nm) shear band development occurs immediately after the onset of plastic flow. Significant strain-rate dependence of the flow stress, particularly at high strain rates was also emphasized. Our objective is to propose a new description of viscoplastic deformation, which accounts for the observed shear banding. Viscoplasticity model proposed earlier by P e r z y n a [4], [5] was extended in order to describe the shear banding contribution. The shear banding contribution function, which was introduced formerly by P ę c h e r s k i [6], [7] and applied in continuum plasticity accounting for shear banding in [8] and [9] as well as in [10] and [11] plays pivotal role in the viscoplasticity model. The derived constitutive equations were identified and verified with application of experimental data provided in paper [2], where quasistatic and dynamic compression tests of ufg and nanocrystalline iron specimens of a wide range of mean grain size were reported. The possibilities of the application of the proposed description for other ufg and nc-metals are discussed.

Keywords:
Viscoplastic flow, shear banding, micro-shear bands, nanocrystalline metals, nc-metals, ultra fine grain (ufg) metals

13.Nowak Z., Stachurski A., Robust identification of an augmented Gurson model for elasto-plastic porous media, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.58, pp.125-154, 2006
Nowak Z., Stachurski A., Robust identification of an augmented Gurson model for elasto-plastic porous media, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.58, pp.125-154, 2006

Abstract:
In the paper we investigate the robust identification approach to identify the material parameters in the augmented Gurson model for the elasto-plastic porous media. We consider the robust loss function given by Huber [9], Beaton and Tuckey [38] and the loss function based on the l1–norm. The resulting minimization problem is solved by means of our own implementation of the Boender et al. global minimization method. Our aim is to compare the results with our earlier standard least squares estimates. In the paper, the effects of nucleation and growth of voids in the plastic porous media are investigated. Three different forms of the model are considered: the augmented Gurson model (total porosity model) with variable nucleation and growth material function, the same model with constant growth material function and the separated porosity model. The identification of the material functions parameters is based on Fischer’s experimental data set for axisymmetric tension of steel specimens.

Keywords:
Gurson model, elasto-plastic porous media, robust identification, Huber loss function, Beaton and Tuckey loss function, l1–norm loss function

14.Pieczyska E.A., Pęcherski R.B., Gadaj S.P., Nowacki W.K., Nowak Z., Matyjewski M., Experimental and theoretical investigations of glass fibre reinforced composite subjected to uniaxial compression for a wide spectrum of strain rates, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.58, pp.273-291, 2006
Pieczyska E.A., Pęcherski R.B., Gadaj S.P., Nowacki W.K., Nowak Z., Matyjewski M., Experimental and theoretical investigations of glass fibre reinforced composite subjected to uniaxial compression for a wide spectrum of strain rates, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.58, pp.273-291, 2006

Abstract:
Results of static and dynamic compression tests for two types of glass fibrereinforced polypropylene composites are presented. Stress-strain curves showing the influence of the strain rate on the composite mechanical properties have been obtained.
A three-dimensional description of the material behavior during the deformation has been developed. The material constitutive parameters have been calculated.
Specification of the parameters and description of the methods used for their identification have been worked out. The results are discussed in terms of the deformation processes and the material non-homogeneity.

Keywords:
static and dynamic compression tests, glass fibrereinforced polypropylene composites, Stress-strain curves, constitutive model, three-dimensional description

15.Pęcherski R.B., Nalepka K.T., Nowak Z., Próba modelowania mechanicznych własności nanometali, INŻYNIERIA MATERIAŁOWA, ISSN: 0208-6247, Vol.4, pp.170-174, 2005
Pęcherski R.B., Nalepka K.T., Nowak Z., Próba modelowania mechanicznych własności nanometali, INŻYNIERIA MATERIAŁOWA, ISSN: 0208-6247, Vol.4, pp.170-174, 2005

Abstract:
W pracy przedyskutowano aktualne problemy modelowania własności mechanicznych metali o strukturze nanometrycznej. Omówiono możliwości opisu deformacji sprężysto-plastycznej i lepkoplastycznej materiałów o bimodalnym rozkładzie ziarn. Przedstawiono wyniki badań sprężystych własności nanoziarn oraz identyfikacji ich spręzystych stanów granicznych z zastosowaniem kwantowo-mechanicznych obliczeń z pierwszych zasad (ab initio) na przykładzie idealnego kryształu miedzi. Wskazano na możliwości dalszych badań zmierzających do opracowania przesłanek potrzebnych do projektowania nanomateriałów.

Keywords:
nanometale, obliczenia ab initio, kryształ miedzi, modelowanie własnosci mechanicznych, sprężyste stany graniczne

16.Nowak Z., Stachurski A., Global Optimization Approach to Material Functions Identification in Plastic Flow of Voided Media, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.47, pp.1-36, 1989
17.Perzyna P., Nowak Z., Równanie ewolucji pustek w obszarze szyjki, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.24, pp.1-23, 1985
18.Nowak Z., Obliczenia oporu profilów lotniczych, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.35, pp.1-38, 1974

List of recent monographs
1.
99
Nowak Z., Metoda identyfikacji w mechanice materiałów ciągliwych z uszkodzeniami, Rozprawa habilitacyjna, IPPT Reports on Fundamental Technological Research, 5, pp.1-213, 2006
List of chapters in recent monographs
1.
64
Perzyna P., Nowak Z., Mathematical methods in continuum mechanics, rozdział: The identification procedure for the constitutive model of elasto-viscoplasticity describing the behaviour of nanocrystalline iron during quasistatic and dynamic loading processes, Technical University of Łódź, K. Wilmański, B. Michalak, J. Jędrysiak (Eds.), pp.63-88, 2011
2.
211
Pęcherski R.B., Nowacki W.K., Nowak Z., Perzyna P., Workshop in Memory of Prof. J.R. Klepaczko: Dynamic Behaviour of Materials, rozdział: Effect of strain rate on ductile fracture. A new methodology, LPMM, Metz, Rusinek A., Chevrier P. (Eds.), pp.65-73, 2009

Conference papers
1.Pęcherski R.B., Kowalczyk-Gajewska K., Nowak Z., Opis udziału pasm ścinania w płynięciu plastycznym polikrystalicznych metali z uwzględnieniem wpływu zmiany drogi odkształcenia, Niejednorodności odkształcenia w procesach przeróbki plastycznej i rekrystalizacji, Seminarium poświęcone 70. rocznicy urodzin Profesora Z. Jasieńskiego, 2005-01-21/01-21, Kraków (PL), pp.191-202, 2005

Conference abstracts
1.Kowalewski Z.L., Nowak Z., Pęcherski R.B., Investigations of Tantalum at Direct Impact Compression Tests on Miniaturized Specimens, PLASTICITY 2017, INTERNATIONAL CONFERENCE ON PLASTICITY, DAMAGE, AND FRACTURE 2017, 2017-01-03/01-09, Puerto Vallarta (MX), pp.100-102, 2017
Kowalewski Z.L., Nowak Z., Pęcherski R.B., Investigations of Tantalum at Direct Impact Compression Tests on Miniaturized Specimens, PLASTICITY 2017, INTERNATIONAL CONFERENCE ON PLASTICITY, DAMAGE, AND FRACTURE 2017, 2017-01-03/01-09, Puerto Vallarta (MX), pp.100-102, 2017

Abstract:
In the paper the results of experimental and numerical investigations concerning an influence of strain rate on mechanical properties of pure tantalum are presented. Experiments were carried out using Direct Impact Compression Test (DICT) technique (Malinowski et al. [2007]). The Perzyna elasto-viscoplasticity theory (Perzyna [1966]) was applied to predict the dynamic compression yield strength of the tested material at strain rates from 1.0 x10-3 s−1 to 0.5 x106 s−1.

2.Nowak Z., Kowalewski Z.L., Pęcherski R.B., A numerical solution of longitudinal wave propagation in a miniaturized specimens of tantalum at direct impact compression test, DYMAT, 10th Workshop, 2016-08-24/08-26, Poznań (PL), pp.69-71, 2016
Nowak Z., Kowalewski Z.L., Pęcherski R.B., A numerical solution of longitudinal wave propagation in a miniaturized specimens of tantalum at direct impact compression test, DYMAT, 10th Workshop, 2016-08-24/08-26, Poznań (PL), pp.69-71, 2016

Abstract:
The results of experimental and numerical investigations concerning an influence of strain rate on mechanical properties of pure tantalum are presented. Experiments were carried out using Direct Impact Compression Test (DICT) technique. The miniaturization concept of the experimental setup for the dimensions of specimen (diameter dS = 1.5 mm and thickness lS = 0.50 mm), Hopkinson transmitter bar diameter (dH = 3.0 mm) and the striker (diameter dI = 11.5 mm and the length lI =12 mm), together with application of a novel optical arrangement for measurement of striker velocity, enabled compression tests to be executed at strain rates from 1.0 x103 s−1 to 0.5 x106 s−1. The Perzyna elasto-viscoplasticity theory is applied to predict the dynamic compression yield strength of the tested material at different strain rates. In the course of specimens deformation by means of the DICT technique, it was observed that the peak force obtained from the strain gauge mounted on the transmitter Hopkinson bar was lower than the peak force obtained within the framework of the uniaxial stress wave analysis. An explanation of this discrepancy is provided due to the analysis of the localization of deformation in the tested specimens considered as three-dimensional body subjected to high strain rate loading and the resulting stress wave attenuation as it propagates within the specimen.

Keywords:
direct impact test, numerical simulations, tantalum

3.Poniżnik Z., Nowak Z., Basista M., Numerical modeling of fracture toughness of metal-ceramic interpenetrating phase composites with account of material microstructure, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), No.P198, pp.1-2, 2016
Poniżnik Z., Nowak Z., Basista M., Numerical modeling of fracture toughness of metal-ceramic interpenetrating phase composites with account of material microstructure, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), No.P198, pp.1-2, 2016

Abstract:
The motivation for research on interpenetrating phase composites and possible applications of these novel materials were given in [1]. A rationale behind designing an IPC is to achieve a highly durable material that would combine the most desirable properties of the constituent phases: the high hardness and wear resistance of ceramic and improved fracture toughness and thermal conductivity due to the metal content. The interpenetrating metal-ceramic composites may have remarkable applicability in different sectors of industry, e.g. automotive and aerospace. They should, thus, be carefully investigated in terms of processing routes, material properties and modeling of material response to service conditions.
A 3D FEM model in ABAQUS of the fracture parameters and crack growth in bi-continuous metal-ceramic composites with interpenetrating microstructure (IPC) is proposed. The crack is modeled using the extended finite element method (XFEM) [4]. The J-integral and fracture toughness KIc are determined for a real IPC microstructure obtained from micro-CT images. The fracture parameters (i.e. fracture toughness KIc, J integral, crack opening displacement) are key mechanical characteristics of IPC composites because of the brittleness of the ceramic phase. The main effects occurring in metal-ceramic IPC during fracture are described (cf. [2], [3]).

Keywords:
Ceramic-metal composites, interpenetrating microstructure, fracture toughness, crack growth, numerical modeling, XFEM

4.Poniżnik Z., Nowak Z., Basista M., Numerical modeling of crack growth in interpenetrating metal-ceramic composites, ICDM2, 2nd International Conference on Damage Mechanics, 2015-07-08/07-11, Troyes (FR), pp.41, 2015
Poniżnik Z., Nowak Z., Basista M., Numerical modeling of crack growth in interpenetrating metal-ceramic composites, ICDM2, 2nd International Conference on Damage Mechanics, 2015-07-08/07-11, Troyes (FR), pp.41, 2015

Abstract:
A 3D FEM model for crack growth in bi‐continuous metal‐ceramic composites with interpenetrating microstructure (IPC) is proposed. The results for the load‐displacements relationship in a plastically deformable reinforcing fibre computed by means of different material models will be shown. The J‐integral and fracture toughness will be determined for a simplified IPC microstructure with reinforcing ligaments modeled as axisymmetric fibres, and for real IPC microstructure obtained from micro‐CT images

Keywords:
interpenetrating phase composites, bi‐continuous composites, metal‐ceramic composites, crack bridging, crack growth, fracture toughness, finite element method

5.Nowak M., Pęcherski R.B., Nowak Z., Frąś L.J., Numeryczna rekonstrukcja struktury pianek otwartokomórkowych z wykorzystaniem tomografii komuterowej, OMIS'2015, XI Konferencja Odkształcalność Metali i Stopów, 2015-11-17/11-20, Łańcut (PL), pp.61-62, 2015
Nowak M., Pęcherski R.B., Nowak Z., Frąś L.J., Numeryczna rekonstrukcja struktury pianek otwartokomórkowych z wykorzystaniem tomografii komuterowej, OMIS'2015, XI Konferencja Odkształcalność Metali i Stopów, 2015-11-17/11-20, Łańcut (PL), pp.61-62, 2015

Abstract:
Przedmiotem badań niniejszej pracy jest numeryczna rekonstrukcja struktur rzeczywistych pianek otwartokomórkowych w celu wygenerowania reprezentatywnego elementu objetości. Analizowane są dwa rodzaje pianek (ceramiczna i polimerowa), których porowatość wynosi odpowiednio 90% i 94%. Oba rodzaje pianek zostały przebadane z użyciem mikrotomografu komputerowego. Uzyskane dane zostały zaimportowane do programu ScanIP, przy pomocy którego przeprowadzono cyfrową obróbkę uzyskanych obrazów oraz wydzielono fazę reprezentującą szkielet pianki.

Keywords:
numeryczna rekonstrukcja, struktury otwartokomórkowe, pianki metaliczne, mikrotomografia komputerowa

6.Nowak Z., Nowak M., Pęcherski R.B., Numeryczna analiza dynamicznych procesów ściskania metalicznych pianek otwartokomórkowych, OMIS'2015, XI Konferencja Odkształcalność Metali i Stopów, 2015-11-17/11-20, Łańcut (PL), pp.59-60, 2015
Nowak Z., Nowak M., Pęcherski R.B., Numeryczna analiza dynamicznych procesów ściskania metalicznych pianek otwartokomórkowych, OMIS'2015, XI Konferencja Odkształcalność Metali i Stopów, 2015-11-17/11-20, Łańcut (PL), pp.59-60, 2015

Abstract:
W pracy dokonano analizy wielkości sił zgniatania, energii dyssypacji oraz sposobów deformowania się dwóch typów metalicznych pianek otwartokomórkowych sciskanych dynamicznie z różnymi prędkościami. Zbadano pianki o strukturze wypukłej oraz o komórkach wklęsłych, które charakteryzują się ujemnym wspołczynnikiem Poissona.

Keywords:
dynamiczna analiza, procesy zgniatania, pianki metaliczne, struktury otwarokomórkowe

7.Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Numerical simulations of mechanical properties of alumina foams based on computer tomography, PCM-CMM 2015, 3rd Polish Congress of Mechanics and 21st Computer Methods in Mechanics, 2015-09-08/09-11, Gdańsk (PL), pp.853-854, 2015
Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Numerical simulations of mechanical properties of alumina foams based on computer tomography, PCM-CMM 2015, 3rd Polish Congress of Mechanics and 21st Computer Methods in Mechanics, 2015-09-08/09-11, Gdańsk (PL), pp.853-854, 2015

Abstract:
The aim of the paper is to apply the results of microtomography of alumina foam to create the numerical model and perform the numerical simulations of compression tests. The geometric characteristics of real foam samples are estimated from tomographic and scanning electron microscopy images. The performance of the reconstructed models is compared to experimental values of elastic moduli.

Keywords:
Alumina open-cell foam, the computed tomography microstructure, Young modulus, the compressive strength of alumina foams

8.Pęcherski R.B., Nowak M., Nowak Z., Numerical simulation of dynamic processes in metal foams. I. virtual metallic foam, PETER 2015, Annual International Workshop on Dynamic Behaviour of Structures and Materials, Interaction and Friction Across the Strain Rates, 2015-08-26/08-28, London (GB), Vol.1, pp.19-20, 2015
Pęcherski R.B., Nowak M., Nowak Z., Numerical simulation of dynamic processes in metal foams. I. virtual metallic foam, PETER 2015, Annual International Workshop on Dynamic Behaviour of Structures and Materials, Interaction and Friction Across the Strain Rates, 2015-08-26/08-28, London (GB), Vol.1, pp.19-20, 2015

Abstract:
The design of new multifunctional foams requires the solution of the following questions: in what way to fabricate metallic foams of assumed skeleton structure, how to produce tomograms, i.e. 3D virtual foam reconstructions of real foam structure [1], how to elaborate methods of numerical simulations of assumed processes in auxetic foams with use of the tomograms. Depending on manufacturing method the cells obtain convex or concave shape. The materials with convex cell structure reveal positive value of Poisson’s ratio, that is if a sample is stretching, then its cross-section is getting thinner. The complex structure of the foam related with reentrant cells produces the opposite effect during stretching of a sample, i.e. its cross-section is increasing. Then the negative Poisson’s ratio is observed and such foams become auxetic. The aim of the study is to study the third question. The motivation is given in [2], where it has been stressed that numerical simulations predicting a new material’s behaviour reduce laboratory costs and accelerates the trial and error procedure.

Keywords:
Metallic open-cell foam with the convex or concave cells, the foam of OFHC Cu skeleton, the foam structure with use of computer tomography images, numerical simulation of dynamic processes in metal foams

9.Nowak Z., Nowak M., Pęcherski R.B., Numerical simulation of the dynamic processes in metal foams. Part II. Compression tests of open cell copper foams, PETER 2015, Annual International Workshop on Dynamic Behaviour of Structures and Materials, Interaction and Friction Across the Strain Rates, 2015-08-26/08-28, London (GB), Vol.1, pp.21-22, 2015
Nowak Z., Nowak M., Pęcherski R.B., Numerical simulation of the dynamic processes in metal foams. Part II. Compression tests of open cell copper foams, PETER 2015, Annual International Workshop on Dynamic Behaviour of Structures and Materials, Interaction and Friction Across the Strain Rates, 2015-08-26/08-28, London (GB), Vol.1, pp.21-22, 2015

Abstract:
Metallic cellular materials have been widely acknowledged for their multifunctional applications related also with energy absorption capability in addition to their light weight. In recent years, the auxetic materials revealing negative Poisson’s ratio have attracted much attention. Up to date, the research of auxetics is mainly concentrating on the cell design and the static response, although the auxetic materials also demonstrate potential for energy absorption, fracture retardant, and high-velocity impacts resistance. In the paper, a comparative study is reported on the high-velocity impact responses of two type metallic cellular foams, that is, convex open cell foam and auxetic foam. The material of the skeleton of the virtual foam is assumed to be isotropic and elastic-plastic. For numerical simulations the constitutive relation is applied which defines the behaviour of oxygen-free high conductivity copper (OFHC) using the experimental data reported in Nemat-Nasser and Li (1998) and Rusinek at al. (2010). The impact limits and absorption energy of the two foams are obtained by means of explicit nonlinear finite element simulations using ABAQUS. It has been found that the auxetic foam is superior to the convex cell foam in impact resistance because of the material concentration at the impacted area due to the negative Poisson’s ratio effect.

Keywords:
Open-cell foams, the impact resistance of convex and auxetic copper (OFHC) foams

10.Nowak Z., Nowak M., Pęcherski R.B., Numerical simulation of metal forming processes with application of modified elastic-plastic model, 8th Workshop on Dynamic Behaviour of Materials and Its Applications in Industrial Processes, 2014-06-25/06-27, Warszawa (PL), pp.51-52, 2014
Nowak Z., Nowak M., Pęcherski R.B., Numerical simulation of metal forming processes with application of modified elastic-plastic model, 8th Workshop on Dynamic Behaviour of Materials and Its Applications in Industrial Processes, 2014-06-25/06-27, Warszawa (PL), pp.51-52, 2014

Abstract:
Finite element method is an efficient numerical tool to analyse problems of the sheet metal forming processes including cup drawing and stamping. Proper description of material properties is crucial for accurate analysis. In particular, the anisotropy and asymmetry of elastic range, related with strength differential effect (SDE), of considered materials play an important role in finite element simulation. The paper presents a new yield criterion for the transversal isotropy of metal sheets under plane stress conditions which is an extension of the isotropic yield function proposed by Burzyński (1928) (Studium nad hipotezami Burzyński’s doctoral dissertation ”Study on material effort hypotheses”, Engng. Trans., 2009, t. 57, nr 3–4, s. 185–215) . One additional coefficient has been introduced in order to allow a better representation of plastic behavior of metal sheets. The proposed yield condition includes the influence of first invariant of the stress tensor and also the strength differential effect. The system of equations describing the sheet metal forming process is solved by algorithm using the return mapping procedure. Plane stress constraint is incorporated into the Newton-Raphson iteration loop. The proposed algorithm is verified by performing a numerical test using shell elements in commercial FEM software ABAQUS/EXPLICIT with a developed VUMAT subroutine.

Keywords:
the strength differential effect, a new yield criterion for the transversal isotropy of metal sheets, numerical simulations of cup deep drawing process

11.Nowak M., Nowak Z., Pęcherski R.B., Energy-based multisurface limit criteria in application for modelling and simulation of metal forming processes, 8th Workshop on Dynamic Behaviour of Materials and Its Applications in Industrial Processes, 2014-06-25/06-27, Warszawa (PL), pp.53-54, 2014
Nowak M., Nowak Z., Pęcherski R.B., Energy-based multisurface limit criteria in application for modelling and simulation of metal forming processes, 8th Workshop on Dynamic Behaviour of Materials and Its Applications in Industrial Processes, 2014-06-25/06-27, Warszawa (PL), pp.53-54, 2014

Abstract:
Metallic materials are usually used in engineering applications in the as received state. In such a case, developing in in the course of manufacturing processes texture induces anisotropy of mechanical properties and produces often the so-called strength differential effect (SDE).The precise description of elastic properties and formulation of limit criterion requires application of the formalism used typically for anisotropic solids. It is a complex and difficult task related with
proper experimental characterisation of all material parameters. In some cases, however, a simple model of isotropic solid revealing possible strength differential effect and certain correction for the limit strength in shear can be proposed. It is in accord with the observation that developing texture influences mostly shear strength of metallic solids.

Keywords:
A simple model of isotropic solid, strength differential effect, the limit strength in shear

12.Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Własności mechaniczne pianek ceramicznych o komórkach otwartych i różnej porowatości, IX Seminarium Naukowe ZINTEGROWANE STUDIA PODSTAW DEFORMACJI PLASTYCZNEJ METALI PLASTMET, 2014-11-25/11-28, Łańcut (PL), pp.1-2, 2014
Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Własności mechaniczne pianek ceramicznych o komórkach otwartych i różnej porowatości, IX Seminarium Naukowe ZINTEGROWANE STUDIA PODSTAW DEFORMACJI PLASTYCZNEJ METALI PLASTMET, 2014-11-25/11-28, Łańcut (PL), pp.1-2, 2014

Abstract:
W pracy określono własności mechaniczne i przedstawiono model numeryczny ceramicznej pianki korundowej, otrzymanej metodą żelowania spienionej zawiesiny (gelcasting). Metoda ta pozwala wytwarzać pianki zawierające kmórki o różnej wielkości, a w konsekwencji otrzymywać pianki o różnej porowatości. Wielkości charakteryzujące geometrię rzeczywistych pianek ustalono z wykorzystaniem obrazów tomograficznych 3D oraz obrazów z mikroskopu skaningowego. Informacje te wykorzystano przy opracowaniu modelu numerycznego badanej pianki. Symulacje numeryczne procesów deformacji przeprowadzono z zastosowaniem programu elementow skończonych ABAQUS.

Keywords:
pianki ceramiczne, metoda żelowania, porowatość, symulacje numeryczne procesów deformacji tomografia komputerowa, mikroskopia skaningowa

13.Nowak Z., Grosman F., Lumelskyy D., Nowak M., Pęcherski R.B., Rojek J., Tkocz M., Metal cup deep drawing processes – numerical simulation and experimental verification, SolMech 2014, 39th Solid Mechanics Conference, 2014-09-01/09-05, Zakopane (PL), pp.47-48, 2014
Nowak Z., Grosman F., Lumelskyy D., Nowak M., Pęcherski R.B., Rojek J., Tkocz M., Metal cup deep drawing processes – numerical simulation and experimental verification, SolMech 2014, 39th Solid Mechanics Conference, 2014-09-01/09-05, Zakopane (PL), pp.47-48, 2014

Abstract:
Finite element method is an efficient numerical tool to analyse problems of the sheet metal forming processes in particular cup drawing and stamping. Proper description of material properties is crucial for accurate analysis. In particular, the anisotropy and asymmetry of elastic range, which is related with strength differential effect (SDE), of considered materials play an important role in finite element simulation. For metal forming analysis with use of traditional models many experimental tests are usually needed to obtain the adequate description of anisotropic behaviour of metal sheets. Therefore, the search for new models, which are based on simplified description of the effects of anisotropy and SDE requiring less experimental tests seems to be justified.
The paper presents the application of a new yield criterion for the transversal isotropy of metal sheets under plane stress conditions. The proposed criterion is based on the study of yield criteria accounting for SDE and anisotropy nade by W. Burzyński [1]. The system of equations describing the sheet metal forming process is solved by the algorithm using the return mapping procedure. Plane stress constraint is incorporated into the Newton-Raphson iteration loop. The proposed algorithm is verified by performing the numerical calculations using shell elements of the commercial FEM sftware ABAQUS/EXPLICIT with own VUMAT subroutine.

Keywords:
metal sheet forming, metal cup deep drawing, FE numerical simulations, strength differential effect, anisotropy and asymmetry of elastic range, transversal isotropy

14.Nowak Z., Nowak M., Pęcherski R.B., A plane stress elastic-plastic analysis of sheet metal cup deep drawing processes, SSTA, 10th Jubilee Conference on Shell Structures - Theory and Applications, 2013-10-16/10-18, Gdańsk (PL), pp.129-132, 2013
Nowak Z., Nowak M., Pęcherski R.B., A plane stress elastic-plastic analysis of sheet metal cup deep drawing processes, SSTA, 10th Jubilee Conference on Shell Structures - Theory and Applications, 2013-10-16/10-18, Gdańsk (PL), pp.129-132, 2013

Abstract:
The paper presents a new yield criterion for the transversal isotropy of metal sheets under plane-stress conditions which is an extension of the isotropic yield function proposed by Burzynski (Burzynski W. 1928). Studium nad hipotezami Burzynski's doctoral dissertation

Keywords:
elastic-plastic analysis, transversal isotropy, metal sheets, deep drawing process, FE simulations, Burzyński yield condition, strength differential effect

15.Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Numerical characterization and estimation of elastic properties of ceramic foams, 7th International Workshop on Dynamic Behaviour of Materials and its Applications in Industrial Processes, 2013-05-08/05-10, Madryt (ES), pp.41-42, 2013
Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., Numerical characterization and estimation of elastic properties of ceramic foams, 7th International Workshop on Dynamic Behaviour of Materials and its Applications in Industrial Processes, 2013-05-08/05-10, Madryt (ES), pp.41-42, 2013

Abstract:
In this work a numerical model of real foam with different cell sizes is presented and its applications are discussed. Geometric characteristics of real foam samples were estimated from tomographic and scanning electron microscopy images. Using this information, numerical foam model was proposed. The examples of generated numerically structures are shown. A good agreement between numerical model and the results elaborated from microtomography was obtained.

Keywords:
Alumina open-cell foam, foam with different cell sizes, numerical foam model based on tomographic and scanning electron microscopy images

16.Nowak Z., Nowak M., Pęcherski R.B., Numerical analysis of the cup deep drawing process with use of new yield condition for plane stress states, CMM 2013, 20th International Conference on Computer Methods in Mechanics, 2013-08-27/08-31, Poznań (PL), No.MS07, pp.9-10, 2013
Nowak Z., Nowak M., Pęcherski R.B., Numerical analysis of the cup deep drawing process with use of new yield condition for plane stress states, CMM 2013, 20th International Conference on Computer Methods in Mechanics, 2013-08-27/08-31, Poznań (PL), No.MS07, pp.9-10, 2013

Abstract:
The elastoplastic constitutive equations for materials under plane stress condition with new yield criterion have been proposed. This yield condition accounts for the effect of strength differential effect. The system of equations of sheet metal forming process is solved by algorithm using the return mapping procedure. Plane stress constrain is incorporated into the Newton-Raphson iteration loop. The proposed algorithm is verified by performing numerical tests using shell elements in commercial FEM software ABAQUS/EXPLICIT with developed VUMAT subroutine. It is shown that the proposed approach provides the satisfactory prediction of material behaviour, at least in the cases when the anisotropy effects are not so advanced.

Keywords:
anisotropic behaviour of metal sheets, strength differential effect, explicit finite element analysis, plane stress

17.Perzyna P., Nowak Z., The description of the behaviour of the ultrafine-grained titanium by the constitutive model of elasto-viscoplasticity, CMM 2013, 20th International Conference on Computer Methods in Mechanics, 2013-08-27/08-31, Poznań (PL), No.TS03, pp.23-24, 2013
Perzyna P., Nowak Z., The description of the behaviour of the ultrafine-grained titanium by the constitutive model of elasto-viscoplasticity, CMM 2013, 20th International Conference on Computer Methods in Mechanics, 2013-08-27/08-31, Poznań (PL), No.TS03, pp.23-24, 2013

Abstract:
The main objective of the present paper is the description of the behaviour of the ultrafine-grained (UFG) titanium by the constitutive model of elasto-viscoplasticity with the development of the identification procedure. We intend to utilize the constitutive model of the thermodynamical theory of elasto-viscoplasticity for description of nanocrystalline metals presented by Perzyna (2010)[1]. The identification procedure is based on experimental observation data obtained by Jia et al. (2001)[4] for ultrafine-grained titanium and by Wang et al. (2007) [5] for nanostructured titanium. Hexagonal close-packed (hcp) ultrafine-grained titanium processed by sever plastic deformation (SPD) has gained wide interest due to its excellent mechanical properties and potential applications as biomedical implants.

Keywords:
Elasto-viscoplasticity, ultrafine-grained titanium, uniaxial compression

18.Poniżnik Z., Basista M., Nowak Z., Modeling of effective elastic constants and fracture toughness in metal-ceramic composites with interpenetrating microstructure, ICF13, 13th International Conference on Fracture, 2013-06-16/06-21, Beijing (CN), No.S12-009, pp.81, 2013
Poniżnik Z., Basista M., Nowak Z., Modeling of effective elastic constants and fracture toughness in metal-ceramic composites with interpenetrating microstructure, ICF13, 13th International Conference on Fracture, 2013-06-16/06-21, Beijing (CN), No.S12-009, pp.81, 2013

Abstract:
The paper is focused on modeling of the overall elastic properties and crack toughening mechanism by bridging in metal-ceramic interpenetrating phase composites (IPC). The Tuchinskii-Feng analytical model (Feng 2004) especially devised for IPC microstructures is further developed. Numerical FEM models of the effective elastic constants are implemented for the simplified 3-D cross microstructure and real microstructures based on micro-CT scans. The energy release rate increase due to crack bridging (Mataga 1989) is modeled numerically. The stress-displacement relationships in the reinforcing fibers undergoing large strains and delamination from the matrix materials are obtained and then applied as material models for the bridging reinforcements in compact-tension test specimen of the fracture toughness determination. The J integral for this specimen is calculated by FEM (Abaqus) with reinforcing ligaments modeled as truss and cohesive elements. The growth of a bridged crack is also modeled numerically.

Keywords:
Effective elastic constants, Fracture toughness, Crack toughening, Crack bridging, Metal-ceramic composites, FEM

19.Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., The Compressive Strength of Ceramic Open-Cell Foams with the Variability of Cell Sizes, ICMM3, 3rd International Conference on Material Modelling incorporating 13th European Mechanics of Materials Conference, 2013-09-08/09-11, Warszawa (PL), pp.315-316, 2013
Nowak Z., Nowak M., Pęcherski R.B., Potoczek M., Śliwa R.E., The Compressive Strength of Ceramic Open-Cell Foams with the Variability of Cell Sizes, ICMM3, 3rd International Conference on Material Modelling incorporating 13th European Mechanics of Materials Conference, 2013-09-08/09-11, Warszawa (PL), pp.315-316, 2013

Abstract:
New aeronautic materials are obtained by liquid metal infiltration into a ceramic foam, called a preform. Ceramic preforms are produced by a new method of manufacturing of porous ceramics foams known as gelcasting. Porous ceramics fabricated by this method is characterized by a continuous network of spherical cells interconnected by circular windows. The open porosity due to the presence of windows creates good hydro-dynamical properties for liquid metals infiltration. For better understanding mechanical properties of such composites a numerical model of ceramic foam is needed, see e. g. ref. [1-4]. Geometry of ceramic foams can be generated in two steps. First, the coordinates of the center point of the spherical bubbles and its diameter are produced by PYTHON scripts. The diameters of spherical bubbles were estimated from microtomography and scanning electron microscopy images. On the other hand, the coordinates of the center points are determined in such a way that the bubbles have to intersect with each other. Finally, the intersecting bubbles are subtracted from the bulk block of any shape. Using this information, numerical foam model was proposed and good agreement between numerical model and real foam structure from microtomography was obtained. In this work we present a numerical model of real foam of alumina with different cell sizes and discuss its mechanical properties using several examples. The numerical simulations of uniaxial compression test have been performed. As a result the compressive strength of the investigated foams with porosities changing from 60 to 95 % were determined.

Keywords:
Porous ceramics foams produced by gelcasting, open-cell ceramic foam, the numerical simulations of uniaxial compression test, the compressive strength of alumina foams with porosities changing from 60 to 95 %

20.Nowak M., Nowak Z., Pęcherski R.B., Potoczek M., Śliwa R.E., Ocena mechanicznych właściwości ceramicznej pianki poddanej procesowi infiltracji, OMIS 2013, X Jubileuszowa Konferencja ODKSZTAŁCALNOŚĆ METALI I STOPÓW, 2013-11-26/11-29, Łańcut (PL), pp.1-2, 2013
Nowak M., Nowak Z., Pęcherski R.B., Potoczek M., Śliwa R.E., Ocena mechanicznych właściwości ceramicznej pianki poddanej procesowi infiltracji, OMIS 2013, X Jubileuszowa Konferencja ODKSZTAŁCALNOŚĆ METALI I STOPÓW, 2013-11-26/11-29, Łańcut (PL), pp.1-2, 2013

Abstract:
Celem pracy jest ocena granicznych ciśnień oraz temperatury procesu, dla których proces infiltracji zachodzi bez uszkodzenia pianki w skali makroskopowej. W pracy przedstawiono numeryczny model procesu wypełniania ceramicznej preformy o otwartej strukturze porów. W procesie wypełniania preformy ciekłym metalem lokalny wzrost naprężeń i kruchość materiału powodują pękanie części elementów pianki. Opracowano model numeryczny tego procesu, który zaimplementowano w programie ABAQUS. Dla określenia stanu naprężenia w piance użyto sprzężonej metody CEL (ang. the coupled Eulerian-Lagrangian method) w programie Abaqus/Explicit.

Keywords:
Proces infiltracji ceramicznych pianek ciekłym metalem, ocena granicznych ciśnień oraz temperatury procesu

21.Frąś T., Luckner J., Nowak M., Nowak Z., Pęcherski R., Analiza procesu formowania blach z uwzględnieniem różnicy wytrzymałości przy ściskaniu i rozciąganiu, PLASMET/2012, VIII Seminarium Naukowe Zintegrowane Studia Podstaw Deformacji Plastycznej Metali, 2012-11-20/11-23, Łańcut (PL), pp.1-3, 2012
22.Frąś T., Luckner J., Nowak M., Nowak Z., Pęcherski R., Rusinek A., Stręk A., Zastosowanie kryteriów granicznych Burzyńskiego I. Metale i kompozyty metaliczno-ceramiczne II. Pianki metaliczne, PLASMET/2012, VIII Seminarium Naukowe Zintegrowane Studia Podstaw Deformacji Plastycznej Metali, 2012-11-20/11-23, Łańcut (PL), pp.1-4, 2012
23.Nowak M., Nowak Z., Pęcherski R., Potoczek M., Śliwa R.E., Opracowanie metody rekonstrukcji struktury geometrycznej i sposobu wyznaczania modułu Younga pianek ceramicznych, PLASMET/2012, VIII Seminarium Naukowe Zintegrowane Studia Podstaw Deformacji Plastycznej Metali, 2012-11-20/11-23, Łańcut (PL), pp.1-3, 2012
24.Kowalewski Z.L., Nowak Z., Moćko W., Direct impact compression test of tantalum – experimental investigation and model identification, SolMech 2012, 38th Solid Mechanics Conference, 2012-08-27/08-31, Warszawa (PL), pp.128-129, 2012
25.Nowak Z., Frąś T., Nowak M., Pęcherski R.B., Analysis of the forming Processes Accounting for Asymmetry of Elastic Range, SolMech 2012, 38th Solid Mechanics Conference, 2012-08-27/08-31, Warszawa (PL), pp.92-93, 2012
26.Nowak M., Nowak Z., Pęcherski R., Potoczek M., Śliwa R.E., On the Geometry and Compressive Strength of Ceramic Foams, SolMech 2012, 38th Solid Mechanics Conference, 2012-08-27/08-31, Warszawa (PL), pp.174-175, 2012
27.Nowak Z., Perzyna P., The Identification Procedure for the Constitutive Model of Elasto-Viscoplasticity Describing the Behaviour of Nanocrystalline Titanium, SolMech 2012, 38th Solid Mechanics Conference, 2012-08-27/08-31, Warszawa (PL), pp.94-95, 2012
28.Nowak M., Luckner J., Nowak Z., Pęcherski R., Numerical simulation of the forming processes accounting for asymmetry of elastic range and initial anisotropy, CMM 2011, 19th International Conference on Computer Methods in Mechanics, 2011-05-09/05-12, Warszawa (PL), pp.383-1-2, 2011
29.Nowak Z., Perzyna P., The identification procedure for the constitutive model of elasto–viscoplasticity with microdamage and dynamic grain growth mechanisms describing the behaviour of nanocrystalline iron, CMM 2011, 19th International Conference on Computer Methods in Mechanics, 2011-05-09/05-12, Warszawa (PL), pp.385-1-2, 2011