Defect and Diffusion Forum Vol. 354

Abstract: In this paper a universal heat equation for fully coupled thermal structural finite element analysis of deformable solids capable of predicting ductile-to-brittle failure mode transition at high strain rates is presented. In the problem mathematical formulation appropriate strain measures describing the onset and the growth of ductile and total damage and heat generation rate per unit volume to model dissipation-induced heating have been employed, which were extended with the heat equation. The model was implemented into a finite element code utilizing an improved weak form for updated Lagrangian formulation, an extended NoIHKH material model for cyclic plasticity of metals applicable in wide range of strain rates and the Jaumann rate in the form of the Green-Naghdi rate in the co-rotational Cauchy’s stress objective integration. The model verification showed excellent agreement with the modelled experiment at low strain rates. Plastic bending of a cantilever has been studied at higher strain rates. A few selected analysis results are presented and briefly discussed.

Abstract: Estimating the relative complex permeability of each component of samarium-substituted yttrium iron garnet nanoparticles in poly-vinylidene-fluride (Sm-YIG-PVDF) composite samples via a numerical optimization method is performed using a MATLAB program. The optimization is taken as the optimized parameters that yield a minimum sum for the absolute differences between the calculated impedance obtained by using the permeability calculated from Maxwell-Garnett (MG) formula and the measured equivalent one over the entire frequency range named the objective function (M). The guessed (estimated) ranges of the complex permeability are based on the measured values of each component of Sm-YIG-PVDF composite samples. The optimized (optimum) impedance values are in very good agreement with the measured ones for each composite and within the estimated ranges. More details on the optimization procedure and the permeability of different composition of the Sm-YIG-PVDF composite materials are illustrated.

Abstract: Mathematical description of alloys solidification on the macro scale can be formulated using the one domain method (fixed domain approach). The energy equation corresponding to this model contains the parameter called the substitute thermal capacity (STC). The analytical form of STC results from the assumption concerning the course of the function f_S = f_S (T) describing the changes of solid state volumetric fraction and the temperature at the point considered. Between border temperatures T_S , T_L the function f_S changes from 1 to 0. In this paper the volumetric fraction f_S (more precisely f_L = 1- f_S ) is found using the simple models of macrosegregation (the lever arm rule, the Scheil model). In this way one obtains the formulas determining the course of STC resulting from the certain physical considerations and this approach seems to be closer to the real course of thermal processes proceeding in domain of solidifying alloy.

Abstract: Humidity sensitive layers elaborated from pure HMDSO and TEOS by PECVD technique have been studied. Humidity sensing properties including impedance relative humidity (RH) and current RH characteristics were investigated. TEOS films show higher sensitivity and excellent linearity over the explored range of humidity (20–95% RH). However, HMDSO films exhibits a small response and recovery of about 8 and 34 s for humidification and desiccation, respectively, in addition to very low hysteresis (2%). Structural analyses of sensitive layers were characterized by Fourier transform infrared spectroscopy (FTIR).

Abstract: As the polypropylene resin of high consumption, has as a consequence, the same feature among the resins most discarded after use. This generates high amount of waste in landfills, causing environmental problems, because the polypropylene presents difficulty in the short term, degradation by micro-organisms in the trash. Thus, this resin recycling proposals are always welcome, raising the possibility of reuse, and reducing the concentration of the landfills, thereby helping to minimize the negative effects of its disposal on the environment. Some manufacturers of rubber products, using as raw materials EPDM, report that are discarded after processing the waste, largely in landfills. Thus, the proposed reuse of byproduct, also will not contribute to the degradation of the environment. The aim of this work was to produce compositions (mixtures) with different concentrations of polypropylene and EPDM recycled materials, and evaluate the effect of ultraviolet and gamma radiation, rheological properties, thermal, mechanical and morphological, of the composites. The compounds obtained showed that waste rubber modified thermoplastic properties of polypropylene when irradiated by both UV radiation, such as gamma radiation.Comparing the hardness and impact tests, it was observed that the values ​​decreased with respect to the material not irradiated (UV or gamma). This effect is due mainly to the presence of the EPDM rubber, because the PP when subjected to gamma radiation or UV at low doses has an increase in mechanical properties.

Abstract: The Kirkendall effect appears due to the unbalanced diffusion fluxes causing the vacancy flux. There are several numerical methods that allow to predict the position of Kirkendall plane after the diffusion couple annealing. In this work for the first time the entropy density distribution is used to estimate the trajectory of the Kirkendall plane. The entropy density distribution is calculated with use of the bi-velocity method, which combines: (1) the volume continuity, (2) the conservation of mass, (3) momentum and (4) entropy-density. The method is applied to simulate the diffusion in Ni-Pd diffusion couple.

Abstract: In the present paper, we have employed the application of artificial neural networks (ANN) to predict effective heat storage coefficient (HSC) of building materials. First we prepared a database to train and test the models developed here. Two types of architectures from different networks are developed, one with three inputs and the other with four inputs mixed architecture combining an ANN with a theoretical model developed by us previously. These ANN models are built, trained and tested by the feed forward back propagation algorithm, to obtain the effective properties of building materials from the properties of their constituents. Feed forward back propagation neural network structure has been developed, which includes an input layer, a hidden layer and an output layer. The number of neurons in the input layer is equal to the number of input parameters and the number of neurons in the output layer is equal to the output parameters. A good agreement has been found between the predicted values using ANN and the experimental results reported in the literature.

Abstract: The growth of phases by reactive diffusion in Mo-Si and W-Si systems are compared. The crystal structures of MSi₂ and M₅Si₃ phases (M = Mo, W) are similar in these two systems. However, the diffusion rates of the components change systematically with a change in the atomic number. Integrated diffusion coefficients in both phases increase with an increasing atomic number of refractory elements i.e. from Mo to W. On the other hand, the ratio of diffusivities of the components decreases. This indicates a relative increase in the diffusion rates of the metal components with increasing atomic number and a difference in defects concentrations in these two systems.

Abstract: Abstract. Metallic nuclear fuel plates are nowadays an alternative to the ceramic ones in the sense that the uranium density can be increased at lower enrichment. Higher thermal conductivity is also a key factor favouring such fuels for power reactors. Uranium reacts promptly with oxygen and nitrogen at high temperatures to catastrophic corrosion due to non-protective oxide layers, which imparts hot forming processes. The gamma phase body centred cubic structure can be retained at room temperature by annealing the U-7.5Nb-2.5Zr (wt.%) alloy followed by quenching, where the deformation can be extensive. The resulted highly deformed gamma supersaturated structure is subjected further to competitive recovery/recrystallization and phase precipitation phenomena whose are studied in the work. The U-7.5Nb-2.5Zr alloy was melted into plasma and induction furnaces and afterwards annealed to gamma phase. The normalized alloy was cold rolled and underwent isochronal and isothermal treatments. The microstructure evolution was monitored by optical microscopy, X-ray diffraction analysis and hardness measurements. The results show the precipitation events of α” and α+γ₃ phases are dominant over recovery in the range 200oC < T < 500oC. Above 500oC the recrystallization is the main process leading to softening and initial Vickers hardness recovery. One refined gamma phase grain structure was obtained (~8.0 μm) after annealing at 700oC for 2.5 hours.