Partner: Prof. Tomasz Sadowski, Ph.D., Dr. Habil., Eng.

Lublin University of Technology (PL)

Doctoral thesis
1985Zginanie płyt uszkadzających się anizotropowo 
supervisor -- Prof. Jan A. König, Ph.D., IPPT PAN
420 
Habilitation thesis
2002Opis rozwoju uszkodzeń i stany graniczne materiałów ceramicznych 
Recent publications
1.Postek E., Sadowski T., Impact model of WC/Co composite, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2019.01.084, No.213, pp.231-242, 2019
Abstract:

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

Keywords:

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

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
2.Postek E., Sadowski T., Temperature Effects during Impact Testing of a Two-Phase Metal-Ceramic Composite Material, Materials, ISSN: 1996-1944, DOI: 10.3390/ma12101629, Vol.12, No.1629, pp.1-13, 2019
Abstract:

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

Keywords:

metal-ceramic composite, impact, coupled problem, thermomechanics

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
3.Postek E., Sadowski T., Distributed microcracking process of WC/Co cermet under dynamic impulse compressive loading, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2018.04.014, Vol.194, pp.494-508, 2018
Abstract:

Cermet Materials (CM), for example, WC/Co, have very good mechanical, thermal and wear properties. They are used for manufacturing of cutting tools. However, their behavior under dynamic loads is still not properly understood.
Experiments, e.g. Siegl and Fischmester (1988) and Ravichandran (1994), indicate that the fracture energy of
WC/Co is expended through ductile failure of the Co: (1) close to the binder/tungsten carbide interface (Liu et al., 2017) [64] or by (2) dimple rupture across the interphase (Sigl and Exner, 1987) [22]. Stress concentrations around grain boundaries lead to initiation of microcracks which are dispersed by dynamic loading.
The main goal of the paper is to investigate the previously formulated models of the two-phase composite (Sadowski et al., 2005, 2006, 2007; Dębski and Sadowski, 2014, 2017) [47–51] in the case of dynamic compressive
pulses that are common in the case of cutting tools. We have taken into account complex spatial distribution of cermet phases, grain/binder interfaces modeled by interface elements, possibility of cracks appearance within binders using interface elements as well, and rotation of brittle grains.
The obtained results show that microcracking process and stress distributions are different for quasi-static and dynamic loadings. Early development of microcracks distribution revealed by damage parameter was observed.

Keywords:

Cermet, Dynamic compressive impulse, Interface elements, Distributed microcracking process

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
4.Postek E., Sadowski T., Dynamic pulse sensitivity of WC/Co composite, COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2017.10.092, No.203, pp.498-512, 2018
Abstract:

Cutting tools are manufactured among others from cermet (e.g. WC/Co) having excellent mechanical properties. Geometry of the internal microstructure is complex and mechanical response due to quasi-static or dynamic loading is difficult to be described. Particularly, the dynamic loading is not investigated enough precise up till now.
Experimental evidences, e.g. Siegl and Fischmester (1988), Ravichandran (1994), indicate that the fracture energy of WC/Co is expended through ductile failure of the Co: (1) near the binder/tungsten carbide interface or by (2) dimple rupture across the interphase. Concentrations of stresses around grain boundaries lead to initiation of microcrack system, which is dispersed for dynamic loading.
The aim of the paper is to extend the previously formulated models (Sadowski et al., 2005, 2006, 2007, Dębski and Sadowski, 2014, 2017) of the polycrystalline composite towards more advanced finite element formulation, applicable for description of the cermet behavior under dynamic pulses. The model takes into account: (1) spatial distribution of the cermet constituents, (2) system of grain boundaries/binder interfaces modeled by interface elements, (3) rotation of brittle grains.
The obtained results show that stress distributions and gradual microcracking processes are quite different for quasi-static and dynamic loadings. It was revealed by damage parameter indicating concentration of microcracks.

Keywords:

Metal-ceramic composite, Interface elements, Crack propagation, Dynamic loading,

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
5.Postek E., Sadowski T., Qualitative comparison of dynamic compressive pressure load and impact of WC/Co composite, International Journal of Refractory Metals and Hard Materials, ISSN: 0263-4368, DOI: 10.1016/j.ijrmhm.2018.07.009, Vol.77, pp.68-81, 2018
Abstract:

Degradation of Cermet Materials (CM) under impact and pulse pressure is not thoroughly investigated. In this
study, we qualitatively compare the behaviour of WC/Co samples under these types of loading.
The new models of impact and dynamic compressive load of a WC/Co plate were investigated. We developed two models of the composite plate, namely, a continuous model and a model with crack appearance possibility in the interfaces/binders.
We noted a qualitative difference of the shapes of the deformed structure due to different models and kind of loading. The differences also concern the Mises stress, equivalent plastic strains and damage parameter.
The proposed models are suitable for both impact and pressure load. The possibility of cracks appearance should not be neglected. In case of the model with discontinuities, for both kinds of loads, the grains rotation and sliding is more distinct than in case of the continuous model.

Keywords:

Cermet, Impact, Pressure load, Interface elements, Distributed microcracking process, Numerical models

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
6.Postek E., Sadowski T., Cracks in Interfaces and Around Their Junctions in WC/Co Composite, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.64, No.4, pp.589-596, 2016
Abstract:

WC/Co ceramic metal-matrix composites are characterized by very high mechanical properties that allow for application of the composites mostly in production of different types of cutting tools. By combining in a composite structure a phase of brittle hard wolfram carbide (WC) grains with a metallic interface of cobalt (Co) that exhibits plastic properties, a geometrically complex microstructure with significantly different mechanical properties of the combined phases is created, see Fig. 1a. The presence of the elastic-plastic interface material, i.e. Co binder, in the composite structure is the reason for initiation of technological defects – mainly material porosity. During material loading pores start to coalesce and finally one can observe creation of microcracks system distributed along interfaces. The aim of the paper is to show the previously formulated model [1, 2] of the polycrystalline composite to be extended towards cracks development around the junctions of the interfaces. The obtained numerical results indicate that in the junctions high stress concentrations were observed, which leads to crack initiation and its further unstable propagation, and finally the composite failure. Results indicate that the first crack appears close to the junction and that the load carrying capacity of the sample is overestimated if a crack model in the interfaces is not assumed.

Keywords:

metal-ceramic composite, interface elements, crack propagation at composite junctions

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
7.Postek E.W., Sadowski T., Assessing the influence of porosity in the deformation of metal-ceramic composites, COMPOSITE INTERFACES, ISSN: 0927-6440, DOI: 10.1163/092764410X554049, Vol.18, No.1, pp.57-76, 2011
Abstract:

The aim of the paper is to develop the previously formulated model [19, 20] of the polycrystalline composite to include porosity growth at metallic interfaces of metal-ceramic composites (MCCs). Examples of this kind of MCCs are: (1) a two-phase material composed of brittle grains WC joined by the plastic binder Co, which can contain a small degree of porosity introduced during the cooling process [31], (2) TiC-Mo2C hard phase grains surrounded by tough binder phase Ni [12]. This work focuses on the description of the deformation of the MCC material including the modelling of a real material internal structure taking into account porosity growth during the loading. Experimental observations of the WC/Co composite [10] indicate that the majority of the fracture energy of MCC is expended through ductile failure of the plastic binder Co (dimple rupture across the binder or in the binder near the binder/carbide interface). This process is preceded by porosity growth at metallic interfaces and finally leads to inter-granular cracks propagation.

This paper presents micromechanical modelling of the MCC response in the case of uniaxial tension of 3-D Representative Volume Element (RVE) with the application of the Finite Element Analysis (FEA). The MCC material includes: elastic grains and inter-granular metallic layers containing technological pores that create its real complex internal structure. The quasi-static deformation process of the material comprises elastic deformation of brittle grains, elasto-plastic deformation of inter-granular layers (of different thickness: 2-4 mu m) and additional deformation due to micro-porosity development in the layers. A micro-sample analysis leads to the conclusion that a small amount of technological porosity changes the qualitative behaviour of the MCC including deformation, rotation of grains, roughness, and level of plastic strains. (C) Koninklijke Brill NV, Leiden, 2011

Keywords:

Interface porosity, Gurson-Tvergaard model, polycrystalline ceramic composites, INTER-GRANULAR LAYERS, POLYCRYSTALLINE CERAMICS, FRACTURE, GROWTH, PREDICTION, STRENGTH, BEHAVIOR, TENSION, CERMETS, MODEL

Affiliations:
Postek E.W.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
8.Sadowski T., Postek E., Denis Ch., Stress distribution due to discontinuities in polycrystalline ceramics containing metallic inter-granular layers, COMPUTATIONAL MATERIALS SCIENCE, ISSN: 0927-0256, Vol.39, pp.230-236, 2007
9.Sadowski T., Hardy S.J., Postek E., A new model for the time-dependent behaviour of polycrystalline ceramic materials with metallic inter-granular layers under tension, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, Vol.424, pp.230-238, 2006
10.Sadowski T., Hardy S.J., Postek E.W., Prediction of the mechanical response of polycrystalline ceramics containing metallic intergranular layers under uniaxial tension, COMPUTATIONAL MATERIALS SCIENCE, ISSN: 0927-0256, Vol.34, pp.46-63, 2005
11.Sadowski T., Propozycja prostego modelu konstytutywnego dla polikrystalicznej ceramiki osłabionej układem pęknięć międzyziarnowych, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.36, pp.1-25, 1989

List of chapters in recent monographs
1.
526
Sadowski T., Samborski S., Mróz Z., IUTAM Symposium on Analytical and Computational Fracture Mechanics of Non-Homogeneous Materials, rozdział: Gradual Degradation of Initially Porous Polycrystalline Ceramics Subjected to Quasi-Static Tension, Springer, Dordrecht, series Solid Mechanics and its Applications, 97, pp.401-405, 2002

Conference papers
1.Postek E., Sadowski T., Impact Modelling of Cermet Composites, AMS 2018, 7th International Conference on Advanced Materials and Structures - AMS 2018, 2018-03-28/03-31, Timisoara (RO), DOI: 10.1088/1757-899X/416/1/012088, Vol.416, pp.1-8, 2018
Abstract:

Abstract. The WC/Co is one of broad class of cermet materials (CM) that are applied in
fabrication of machining tools. It means that they are subjected to different kind of dynamic
loadings. They have very good mechanical properties. However, the degradation of the CM
material under dynamic load has not been enough thoroughly investigated. Experimental
results yield that the dissipation of the fracture energy in WC/Co samples is due to Co ductile
failure at the WC and Co interface [1] and/or dimple rupture mechanism [2]. Stress
concentrations about stress raisers such as grain bounds cause microcracking that is further
propagated by dynamic loading. However, there are no such predictions for impact conditions.
The main goals of the presentation are to explore the formerly created models of the two-phase
composite [3, 4] towards impact conditions impacts and give qualitative predictions of the
crack and plastic strains initiation for such cases. It has been found that microcracks
development process and stress fields depend on impact velocity and the existence of
discontinuities: (1) inside the Co binder and (2) the interface between the binder and the grains.
Estimation of the microcracks distribution by means of damage parameter is given.

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
2.Postek E., Sadowski T., Description of the Behaviour of Cellular Composite with Weak Filling Material, IUTAM Symposium on Mechanical Properties of Cellular Materials, 2007-09-17/09-20, Cachan (FR), pp.181-188, 2009
3.Sadowski T., Postek E., An influence of the elastic properties of composite components on the mechanical response of polycrystalline structures at yield level, IUTAM Symposium on Scaling in Solid Mechanics, 2007-06-25/06-29, Cardiff (GB), DOI: 10.1007/978-1-4020-9033-2_19, pp.199-208, 2009
Abstract:

The aim of this paper is to present a constitutive model in the case of an uniaxial tension of the polycrystalline materials including the inter-granular metallic layers, creating its internal structure. The paper is focused on the discussion of the elastic properties of a composite components influence on the overall material response. The effective continuum model was applied to get the constitutive relations. Representative Volume Element (RVE) was analysed taking into consideration an initial internal structure of the material obtained from SME photographs. Owing to a high complexity of the internal structure of the composite material, FEA technique was used to get macroscopic stress-strain correlations. They include gradual changes of the internal structure of the material due to porosity and cracks development under tension.

Keywords:

Polycrystalline ceramics, inter-granular layers, different elastic properties of components

Affiliations:
Sadowski T.-Lublin University of Technology (PL)
Postek E.-IPPT PAN
4.Postek E., Sadowski T., Denis C., Modelling of metallic inter-granular layers in polycrystalline ceramics, BMC 8, 8th International Symposium on Brittle Matrix Composites, 2005-10-23/10-25, Warszawa (PL), pp.495-506, 2006
5.Postek E., Sadowski T., Hardy S.J., Numerical modelling of mechanical response of a two-phase composite, IUTAM Symposium on Multiscale Modelling of Damage and Fracture Processes in Composite Materials, Lublin University of Technology, 2005-05-23/05-27, Kazimierz Dolny (PL), pp.193-200, 2006
6.Postek E.W., Hardy S.J., Sadowski T., Finite strain behaviour of a polycrystalline ceramic composite with intergranular layers, Plasticity 2006, 12th International Symposium on Plasticity and Its Current Applications, 2006-07-17/07-22, Halifax (CA), pp.205-207, 2006

Conference abstracts
1.Postek E., Sadowski T., Boniecki M., Impact of Al2O3/ZrO2 Composite, Qualitative Comparison of Compositions, RANM2019, Fourth International Conference on Recent Advances in Nonlinear Mechanics, 2019-05-07/05-10, Łódź (PL), pp.226-228, 2019
Abstract:

The ceramic composites Al2O3/ZrO2 are used for different kind of implants
since they are nontoxic and nonallergic [1]. The composites of different composition
of both compounds are obtained by sintering at the temperature 1600◦C. The amount
of zirconia in the composite is normally up to 30% volume. The investigation of such
properties like Youngs modulus, toughness and flexural strength is presented in [2]. The
properties of ZrO2 compound with stabilization of Y2O3 are described in [3].

Keywords:

Al2O3/Zr02, composite compositions, impact, peridynamics

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
Boniecki M.-Institute of Electronic Materials Technology (PL)
2.Postek E., Sadowski T., Temperature effect in 2 phase ceramic based composite during impact conditions, ICCS21, 21st International Conference on Composite Materials, 2018-09-04/09-07, Bologna (IT), DOI: 10.15651/978-88-938-5079-7, pp.100, 2018
Abstract:

Cermet Materials (CM) are often used for manufacturing of different cutting tools. They have very good mechanical, wear and thermal properties. In our opinion, the dynamic load is still not enough thoroughly analysed, and the impact load as well. The tools are subjected to different dynamic effects.We have taken into account complex spatial distribution of cermet phases, grain/binder interfaces modeled by interface elements, possibility of cracks appearance within binders using interface elements as well, and rotation of brittle grains.
The main goal of the presentation is to develop further previously formulated models of two-phase composite [1-4] to capture effects of temperature due to impact. The source of the thermal loading is the conversion of plastic work into heat [5, 6]. The increase of temperature takes place in the Co interfaces. We investigate adiabatic and fully coupled solutions.
We note differences in the behaviour of the samples when the thermal loading is not considered. We have found that the thermal softening effect in the interface material is important as well. We enhance the description of the damage mechanism in the presence of temperature increase.
Acknowledgements
This work was financially supported by Ministry of Science and Higher Education (Poland) within the statutory research (IPPT PAN) and National Science Centre (Poland) project No 2016/21/B/ST8/01027 (Lublin University of Technology). The calculations were done at the Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw, Poland. The licenses for the MSC Patran and Abaqus programs were provided by Academic Computer Centre in Gdańsk, Poland.

References:
[1] Sadowski T, Hardy S, Postek E. Prediction of the mechanical response of polycrystalline ceramics containing metallic intergranular layers under uniaxial tension. Comput Mat Sci 2005;34:46-63.
[2] Sadowski T, Hardy S, Postek E. A new model for the time-dependent of polycrystalline ceramic materials with metallic inter-granular layers under tension. Mat. Sci. Eng. A 2006;424:230-238.
[3] Sadowski T, Postek E, Denis C. Stress distribution due to discontinuities in polycrystalline ceramics containing metallic inter-granular layers. Comput Mat Sci 2007;39: 230-236.
[4] Postek E, Sadowski T. Dynamic pulse sensitivity of WC/Co composite, (accepted in Composite Structures).
[5] Wriggers P, Miehe C, Kleiber M, Simo JC. On the coupled thermomechanical treatment of necking problems via finite element methods. Int. J. Num. Meth. Eng. 1992; 33:869–883.
[6] Rojek J, Onate E, Postek E. Application of explicit FE codes to simulation of sheet and bulk metal forming processes. J. Mat. Proc. Tech. 1998; 80–81: 620–627.

Keywords:

cermet composites, coupled solutions, thermomechanics

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
3.Postek E., Sadowski T., Model uderzenia z dużą prędkością płytki wykonanej z kompozytu dwufazowego, początek procesu, PLASTMET, 11 KONFERENCJA ZINTEGROWANE STUDIA PODSTAW DEFORMACJI PLASTYCZNEJ METALI, 2018-11-27/11-30, Łańcut (PL), pp.122-123, 2018
Abstract:

Materiały metaloceramiczne są często stosowane w elementach, które mogą być poddane uderzeniom. Jednak większość prac dotyczących obciążeń dynamicznych dotyczy kompozytów warstwowych. Techniki oceny obciążeń uderzeniowych dla kompozytów dobrze przedstawione są w pracy [1]. Przykładem kompozytu dwufazowego jest WC/Co. Ten rodzaj kompozytu jest często modelowany jako posiadający sprężysto plastyczne wypełnienie oraz sprężyste ziarna. Powodem tego jest wysoka odporność na zniszczenie materiału WC. Przedstawiamy rozszerzenie wcześniej opracowanych modeli [2], w których zakładana była idealna sprężystość ziaren. W nowym modelu zakładamy możliwość zniszczenia ziaren. Badamy układ, w którym próbka uderza o sztywną ścianę z różnymi prędkościami.

Keywords:

Obciążenia uderzeniowe, węglik wolframu, kompozyt dwufazowy, metoda elementów skończonych

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
4.Postek E., Sadowski T., Temperature effects during impact of WC/Co composites, SolMech 2018, 41st SOLID MECHANICS CONFERENCE, 2018-08-27/08-31, Warszawa (PL), pp.1, 2018
Abstract:

Generally, the papers on dynamic loading of composites more focus on the layered composites, for example [1]. High attention is paid to blast load. However, in our opinion, the process of impact a gap for analysis of WC/Co composite during impact conditions. During impact of WC/Co composite objects and the other composites with metallic binder heat of plastic work is generated. If the process is fast enough the problem can be treated as adiabatic. However, more common situation is slower process when the heat is generated in metallic interfaces and the neighbouring grains are heated due to conduction. The process should be rather considered as coupled [2]. We developed our model of WC/Co composite towards impact load, [3].

Keywords:

thermomechanics, coupled problems, composites

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)
5.Postek E., Sadowski T., Impact modelling of cerment composite, The 7th International Conference on Advanced Materials and Structures, 2018-03-28/03-31, Timisoara (RO), pp.111, 2018
6.Postek E., Sadowski T., Impact Models of WC-Co Composite, CERMODEL 2017Modelling and Simulation Meet Innovation in Ceramics Technology, 2017-07-26/07-28, Trento (IT), pp.1, 2017
7.Postek E., Sadowski T., A Crack Model Around Junctions in WC/Co Composite, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), pp.1, 2016
Keywords:

Metal-Ceramic Composite, Interface Elements, Crack Propagation at Composite Junctions

Affiliations:
Postek E.-IPPT PAN
Sadowski T.-Lublin University of Technology (PL)