Papers by Keyword: Homogenization

Abstract: Use of fluidized bed combustion fly ash as an admixture for manufacture of cement based composite materials is not quite common now, however, there are real ways of utilizing its potential. The most important negative feature of this fly ash is its variable chemical composition, which supports formation of new forms growing within the structure with negative impact of durability of the composite material. The morphology of this type of fly ash is also not very favorable as it has negative influence on consistency. Fluidized bed combustion fly ash considerably deteriorates consistency of cement mixture, which results in higher water-cement ratio and consequently worsening of physico-mechanical and durability parameters of the whole composite. Therefore the question arises how to eliminate this negative influence on consistency without the necessity of increasing water cement ratio.

Abstract: The aim of this study is to investigate the effect of mortar/unit thickness ratio and unit configuration on the masonry wall behaviour and on masonry structure modelling. Firstly, five wall models with different mortar/unit thickness ratios and with different sizes of units are micro-modelled by using SAP2000 software. The results of these walls are used to obtain the material properties of anisotropic macro-models in vertical and horizontal directions. Secondly, a sample unreinforced masonry structure is simulated by the same software using anisotropic material properties. Earthquake loading is applied following the Turkish seismic code. Responses of these five structure models are compared with each other and also with their isotropic modelled counterparts. It is observed that isotropic modelling overestimates the rigidity of the structure around 3-5% for low mortar/unit thickness ratios, but underestimates the rigidity around 5-7% for high mortar/unit thickness ratios

Abstract: The microstructure evolution during homogenization of 2A66 Al-Cu-Li alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC). The results showed that the dendritic segregation can be found in the ingot of experimental alloy. Numerous eutectic phases can be observed in the grain boundary, and the distribution of the main elements along the interdendritic region varied asymmetrically. It was found that the main secondary phase was Al₂Cu. Differential scanning calorimeter (DSC) results showed that the over-burnt temperature of 2A66 Al-Cu-Li alloy was 515°C. With the increase of homogenization temperature in the area of 480°C~510°C, the boundaries of experimental alloy became sharp and the most of secondary phase dissolved into the matrix. The experimental alloy heat treated at 520°C was over-burnt. The Al₃Zr precipitated and α (Al) super-lattice was observed by TEM in the experimental alloy after homogenization.

Abstract: Electromagnetic stirring (EMS) process, as an advanced melt treatment technology, is increasingly applied in metallurgy industry. Direct chill (DC) casting process by annular electromagnetic stirring (A-EMS) was applied in this study to investigate the solidification behavior of a modified 7N01 alloy, and the effects of DC casting process without EMS, and A-EMS casting process on microstructure, composition segregation and mechanical properties of continuously cast billets were compared. The research results showed that the billets with higher performance, lower macro-segregation, more uniformly fine solidification structure were obtained in case of A-EMS.

Abstract: The design of novel mechanical microstructures having auxetic behaviour is proposed in this paper using techniques of topology optimization for compliant mechanisms. The resulting microstructure can be modified in order to cover additional needs, not included in the topology optimization formulation. Classical structural optimization, contact mechanics, homogenization and nonlinear finite element analysis are used for this step. Thus, the modified microstructure or composite is studied with numerical homogenization in order to verify that it still has the wished auxetic behaviour. Finally, nonlinear finite element analysis shows how the auxetic behaviour is influenced by unilateral contact between the constituent materials, large displacements and elastoplasticity.

Abstract: Measurements of basic materials properties of building materials with pozzolanic waste admixture originated from grinding of thermally insulating bricks were performed by means of pycnometry method. Besides, the thermal conductivity dependence on the moisture content measurements were carried out by using a non-stationary pulse method. Obtained data were subsequently analyzed by simple Wiener’s bounds and sophisticated homogenization formula taking into account the shape of ellipsoidal pore inclusions. Validity of applied homogenization models were assessed by comparison of the measured and the calculated data. On the basis of experimental data and homogenization analysis, the shape effect on the thermal conductivity is discussed.

Abstract: This work is devoted to the study of thermal and mechanical properties (stiffness and thermal conductivity tensors) of multiphase composite materials (mortar with PCMs). A micro-macro modeling is presented in order to predict these properties by using some classical homogenization schemes. The effective thermo-mechanical behavior is then analyzed by considering various PCM particle forms, concentrations, and orientations.

Abstract: The coupling between mechanical and chemical behaviors is investigated. The Generalized Eigenstrain Method is used and enables to take easily into account several couplings, such as damage and corrosion. Modeling is then performed and compared for different configurations. Chemical reactions and diffusion effects are thus described in order to improve accuracy of such a micromechanical time-dependent model. Application is then performed on a steel reinforced concrete material. Moreover, a particular and original coupling has been introduced, which is justified by thermodynamics arguments.

Abstract: The effects of the homogenization conditions on the microstructure of Al-Zn-Mg-Cu-Zr-0.5Er alloy were investigated by differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). The results showed that a lot of coarse phases existed in as-cast Al-Zn-Mg-Cu-Zr-0.5Er alloy. The dissolvable phases at grain boundary consisted of Mg₃₂ (Al, Zn)₄₉. The residual phases dissolved into the matrix gradually during homogenization with increasing temperature and prolonging holding time. When the temperature increased to 465°C, and time prolongs to 24h, the main phase disappeared except the Fe and Er enriched phase, as a result of its high melting temperature. Taking into account the precipitation of Al₃Er, we used a two-step homogenization .Hence, the optimum parameters of homogenization were 400 °C for 4 h and 465 °C for 24 h, which are good for the presence of coherent, elastically hard and nanosized Al₃(Er, Zr) particles and the dissolvable coarse phases .

Abstract: The rare earth element Ce was added in Mg-2.0Zn-1.0Mn magnesium alloys. And the homogenizing treatment and the extrusion deformation tests for the alloy were carried out. The effects of the Ce addition and homogenization on the microstructure and mechanical properties of Mg-2.0Zn-1.0Mn magnesium alloys were studied in the present investigation. The results showed that the addition of Ce can effectively refine the grain size of ZM21 alloy, improve the mechanical properties of magnesium alloy ZM21 and reduce the latent heat and solidification temperature range of the alloy. Homogenizing annealing treatment slightly affected the microstructure and mechanical properties of ZM21 alloy extrusion products but significantly affected the ZM21+Ce magnesium alloy. The fracture analysis indicated that the fracture of the two alloys was mixed fracture, while the fracture of magnesium alloy ZM21+Ce showed more ductile fracture feature.