Browsing by Author "Parashkevova, Ludmila"
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Item Mechanical Properties Assessments for Materials of High Porosity and Light Alloys with Predominant Embedded Phases(Springer Science and Business Media Deutschland GmbH, 2021) Parashkevova, Ludmila; Drenchev, Ludmil; Egizabal, Pedro; Georgiev, Ivan; Kostadinov, Hristo; Lilkova, Elena; Tecnalia Research & InnovationIn the present contribution, upgrading the findings of previous works, [11], new models are proposed for evaluation of effective mechanical properties of light alloys regarded as multiphase composites. This study concerns three - phase composites with high volume fraction of non-matrix phases. The elastic properties assessments of such materials are calculated by analytical approach based on the variant of Differential Effective Medium (DEM) method. Here in the methodology from [10, 11] is further developed for two cases: composite type A and composite type B. The composite A consists of matrix and two inclusion phases. The matrix material is much softer than the inclusions material of the first kind and at it is much harder than the inclusions of second kind. The composite B is a closed cell porous material. It is assumed that the high porosity is induced by spherical pores of two sets very different by size: Di≫ di. At high volume fraction of pore space the average diameter of small pores is comparable to the inter-pores distance (cell’s wall). For assessment of the elastic moduli of both composites A an B a two-step homogenization procedures are applied. New yield conditions for the composites A and B are derived to define the initial plastic state of composites. Hill’s strain energy equivalent condition and leading role of matrix are taken into account describing the transition point from elastic to plastic state.Item Modelling of Light Mg and Al Based Alloys as “in situ” Composites(SPRINGER INT PUBLISHING AG, GEWERBESTRASSE 11, CHAM, CH-6330, SWITZERLAND, 2017-10-26) Parashkevova, Ludmila; Egizabal, Pedro; Todorov, Michail; Georgiev, Ivan; Georgiev, Krassimir; Georgiev, Ivan; Tecnalia Research & InnovationThe present paper is aimed to further elucidate the microstructure properties relationship of light alloys containing additional hard particles. The materials studded are magnesium alloys from the system AZ (Mg–Al–Mn–Zn) and mechanically alloyed aluminum reinforced with carbide and oxide particles. Strengthening and hardening phenomena in Metal Matrix Multiphase heterogeneous Materials (MMMM) are considered in this study from the view point of mechanics of nano- and micro-composites. A semi-analytical approach is adopted taking into account the manufacturing processing and microstructure features. Multilevel homogenization procedure is performed, accounting for size effects. In the model applied the metal matrix is considered as an elastic–plastic micropolar media and the hard phases (precipitations Mg17Al12, TiC, Al4C3, Al2O3) are treated as conventional elastic Cauchy materials. Experimentally observed dependence of the characteristic matrix length on the volume fraction of the hardening phases is modeled and numerically simulated in the case of ball-milled Al alloyed with Al4C3 and Al2O3. For AZ alloys the impact of intermetallic phase Mg17Al12 is discussed in the frame of presented composite model and the strengthening effect of the addition of small amount of TiC is estimated.