Papers by Keyword: Homogenization

Abstract: This research studied the effect of tin (Sn) on the surface dullness of ENAC44300 aluminum alloy commercial grade for die casting applications.Tin impurities in the alloy composition led to surface dullness which degraded the quality of the alloy. This investigation found that bulk structure as well as microstructure were affected by the presence of high Sn content. Porosity increased in the amount and size and microstructural change was evident when the alloy containing high Sn (0.67%) was homoginized at 550°C.

Abstract: Due to its ecological interest and large availability, a renewed attention is paid to earth as building material. Indeed, raw earth consumes CO₂ only during its processing and transportation, and it provides a natural hygrothermal comfort. However, its mechanical properties are highly linked to its composition, which causes an important variability of performances. That is why any soil has to be characterized before being used as a building material. The aim of this study is to propose a model able to predict the hydromechanical behavior of a reconstituted soil according to its composition. As earth is a heterogeneous material, the model is based on homogenization procedures. The sand is considered as spherical inclusions inside a clay matrix. The particularity of the model stands to consider both positive and negative effects of volume variation and mechanical properties of clay under hydric variations. The model parameters are determined according to an original experimental campaign, which is conducted on various mixes of a single type of clay (kaolinite) and of sand, and water. The experimental study provides some mechanical properties of the mixes versus water content and sand content to test the ability of the homogenization model to assess the main properties of this material.

Abstract: The commercial Al–Zn–Mg–Cu-based alloys (7xxx series) are widely used in metalworking, automotive and aircraft industries as well as in aeronautical applications. The positive effect of the Sc,Zr-addition on mechanical properties of laboratory Al-based alloys is generally known. The microstructure, mechanical and thermal properties of the conventionally cast, heat-treated and cold-rolled Al–Zn–Mg–Cu (–Sc–Zr) alloys during isochronal annealing and natural ageing were studied. Microstructure observation by scanning electron microscopy and transmission electron microscopy proved the Zn,Mg,Cu-containing eutectic phase at grain boundaries. The distinct changes in microhardness curves as well as in a heat flow of the alloys studied are mainly caused by dissolution of the clusters/Guinier-Preston (GP) zones and precipitation of particles from the Al–Zn–Mg–Cu system. An easier diffusion of Zn, Mg and Cu atoms along dislocations in the cold-rolled alloys is responsible for the precipitation of the Zn,Mg,Cu-containing particles at lower temperatures compared to the cast alloys. Microhardness values of the heat-treated alloys increase immediately from the beginning of natural ageing due to the formation of the clusters/GP zones. Addition of Sc and Zr elements results in a higher hardness above ~ 270 °C due to a strengthening by coherent secondary Al₃(Sc,Zr) particles with a good thermal stability. Sc,Zr-addition has probably no influence on the evolution of the solute clusters/GP zones.

Abstract: This paper focuses on the characterization of the mechanical behaviour of concrete incorporating different percentages of brick waste aggregates (BWA). Compressive strength, splitting tensile strength and elastic modulus of this material were measured based on standard laboratory tests and its microstructure was characterized based on scanning electron microscope (SEM) observations. A decrease in these properties was observed with the increase of BWA substitution ratio. However, this decrease remains moderate up to a substitution percentage of 30% (about 12% for compressive strength and elastic modulus and 8% for splitting-tensile strength). In addition, an increase in the concrete porosity was observed with the increase of BWA substitution ratio, which can explain the decrease observed in the measured mechanical characteristics. SEM views on concrete incorporating 100% of BWA showed that the interfacial transition zone (ITZ) and the cement paste present a higher porosity when compared to those of the reference concrete made with natural aggregates.Finally, a micromechanical analytical homogenization model predicting the elastic modulus of brick waste concrete (BWC) according to its composition is proposed where BWC is modelled as a three-phase composite. A good agreement was found between analytical predictions and experimental results proving that BWC mechanical characteristics are mainly governed by BWA mechanical properties and their volume fraction within concrete.

Abstract: Sinter hardening is a powder metallurgy processing route that combines the sintering and the heat treating processes in one step by gas quenching the components immediately after they have left the high temperature zone of the furnace. It is both economically attractive and ecologically beneficial since it renders deoiling processes unnecessary. The slower cooling rates associated with gas compared to oil quenching however requires special alloy concepts different to those known from wrought steels. In the present study it is shown that by admixing atomized masteralloy powders consisting of suitable combinations of Mn, Cr, Si, Fe and C to base iron or pre-alloyed steel powders, sinter hardening PM steel grades can be produced that transform to martensitic microstructure at cooling rates of 2-3 K/s as typical for industrial sinter hardening. This is confirmed by CCT diagrams and hardness measurements. However, metallographic investigations are also necessary because in sintered steels, the cores of the largest base powder particles are alloyed very slowly during sintering and therefore tend to result in soft spots in the sinter hardened microstructure which are mostly not discernible in the CCT diagrams. Here, even slight pre-alloying of the base powder with Mo and/or Cr is helpful, both increasing the hardenability of the steels compared to base plain iron and avoiding soft spots in the microstructure.

Abstract: This work deals with the basic research and development of new technologies of cement-based invert grouting, in the recipe of which the appropriately selected secondary raw materials will be used as much as possible. This new grout will be part of a new comprehensive system for the remediation of chemically exposed building structures, such as sewers, silage pits and wastewater treatment plants. The aim of this work is to monitor the influence of the method and the degree of homogenization of the developed recipes on selected physical-mechanical properties of the injection material. For the needs of this work, several basic recipes were proposed, as well as the methodology of production of test specimens, their storage and testing. At the same time, three homogenization methods were chosen, differing in the manner and degree of implementation. The basic characteristics of grouting materials, which were monitored in this work, include the viscosity and processability of fresh material. Due to the requirement for increased resistance of the new material, the compressive strength and absorbency of the hardened test specimens 40 × 40 × 160 mm were monitored depending on the maturation time. The research results so far show that thorough homogenization has a fundamental effect on achieving the required physical-mechanical properties. The final methodology of homogenization of dry components will be used in the pre-preparation of all materials of the new chemically resistant remediation system, including the sprayed mixture.

Abstract: The microstructure evolution of Al-Zn-Mg-Cu alloy with erbium was studied by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) during homogenization process. The results showed that there were serious component segregation in the as-cast structure of the alloy, mainly composed of T(AlZnMgCu) , S(Al₂CuMg) and a small amount of Al₈Cu₄Er and Al₇Cu₂Fe. The overheating temperature of the alloy was 482.5 °C. After homogenized at 470 °C for 24 h, the dissolution of T(AlZnMgCu) phase and S(Al₂CuMg) phase reached to a balance, but the residual Al₈Cu₄Er phase could not be dissolved completely. Compared with single-stage homogenization, Al₃(Er,Zr) dispersion phase with smaller grain size and more uniform distribution can be obtained after two stage homogenization process of 400 °C for 8 h followed by 470 °C for 24 h. By comparing the residue of non-equilibrium eutectic phase, two-stage homogenization is the best.

Abstract: The microstructure and segregation of 7N01 aluminum alloy microalloyed with Er and Zr before and after homogenization process at 470 °C for 24 h have been investigated using transmission electron microscope (TEM), and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS) and transmission electron detecter (STEM). SEM images and EDS line scan results showed that there were dendritic segregation of Mg and Zn and micron-sized primary phases along dendrites in the as-cast alloy. The primary phases were mainly Al₂Mg₃Zn₃ containing Al, Zn, Mg and Mn. And a small amount of primary phases were the particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr. After homogenization at 470°C for 24 h, dendritic segregation of Mg and Zn was eliminated, Al₂Mg₃Zn₃ and the particles containing Al, Zn, Mg and Mn were basically dissolved. The particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr remained. Meanwhile, TEM and STEM images showed that a large number of secondary phases appeared after the homogenization, which were mainly distributed in the inter-dendrite area. EDS results showed that the block-shaped and rod-shaped phases with the width of 10-70 nm and length of 100-500 nm were the particles containing Al, Cr and Mn or Al, Mg, Cr and Mn, and the ellipsoid secondary phase with the size of 50-100 nm was MgZn₂.

Abstract: The work is devoted to the construction of analytical solutions for the stress-strain state of a cylindrical hollow elastic rod with a layered structure along the radius. Earlier, the problem of finding the stress-strain state of a rod of composite material fixed at one end with the applied forces and moments of forces at the other end was considered. An approximate representation of the solutions was given, which included auxiliary problems on one fragment of the cylinder, consisting of periodically repeating similar fragments. Such auxiliary problems in the general case do not have an analytical solution. In this paper it is shown that in the presence of radial symmetry of the rod section, it is possible to construct a stress-strain state in an analytical form. In addition, tensile and bending stiffness can be presented in an analytical form. The latter circumstance allows us to set a problem of optimizing the stiffness characteristics of a rod with its fixed weight. Optimization is carried out by varying the thickness of the layers of the same materials.

Abstract: The paper presents a mathematical model of a finite element for modeling imperfect interface conditions for two contacting surfaces. The element is used in the numerical implementation of the Asymptotic Averaging Method (AAM) for the determination of effective elastic properties of composite materials under investigation. Numerical experiments are carried out to calculate the elastic properties taking into account the adhesion layer using a displacements field jump condition at the phase boundary. Results are compared with adhesion modeling using an additional bulk phase.