Diffusion in Solids and Liquids II, DSL-2006 II

Paper Title Page

Authors: Veneta Grigorova, Dimitar Roussev, Stephane Jobic
Abstract: In the present paper we studied the thermodynamical behaviour under high pressure of two MTe2-type compounds (M = Pd, Pt) by applying the thermodynamical method, which we elaborated in previous studies [1,2]. The two discussed compounds are representatives of the CdI2 structure type, which is bi-dimensional and as such is atypical for the big family of lamellar MQ2- type dichalcogenides (Q=S, Se, Te). Specific of lamellar structure is the strong ionicity of the bonds. Its direct consequence is cleavage obtaining, lubrication properties, anisotropic physic properties. One of the most interesting points stands on the possibility for realising interactions between the layers of different types of ions. That could be done under high pressure by any of the following transformation processes: (i) a phase transition to the typical pyrite structure; (ii) a phase rearrangements changing the parameters of the crystal cell but keeping the 2D-type structure. The computation of the volumetric thermodynamical functions showed that both PdTe2 and PtTe2 do not undergo any classical phase transition [1]. But we observed a curious difference in their stability: PtTe2 loosed its stability quite fast and PdTe2 was quite stable. Aiming to clarify if the difference in the volumetric entropy generation was due to different phase rearrangements, we calculated the longitudinal thermodynamical functions. In such a way we detected that both PdTe2 and PtTe2 undergo a phase rearrangement. The change along one of the space axis in both compounds was compensated by the reverse change along the other space axis. Like this no changes at the volumetric level were observed. The longitudinal calculations gave an explanation for the differences in entropy generation at volumetric level: beyond the rearrangement point PdTe2 decreases its entropy generation, i.e. its new arrangement is somehow stable under increasing pressure. While, beyond its rearrangement point PtTe2 increases its entropy generation, i.e. even in the new arrangement it loses stability under increasing pressure. We conclude that both PdTe2 and PtTe2 do not undergo a classical phase transition at volumetric level. At longitudinal level both compounds undergo phase rearrangement. A difference between PdTe2 and PtTe2 is observed in their entropy generation beyond the rearrangement point.
Authors: N. Joulaee, Ahmed Makradi, Saïd Ahzi, Moe A. Khaleel
Abstract: The arrangement of ceramic layers in laminated structures is an interesting way to enhance the flaw tolerance of brittle ceramic materials. The interfaces are expected to deflect cracks, increasing the fracture energy of the laminate compared to a monolithic material and thus raising the toughness. The target of this study is to predict the volume fraction of pores, in porous layers, required to cause crack deflection. Formulation of the fracture toughness and fracture energy as function of the material porosity is presented for random and ordered pores distribution. The effect of crack tip-flaws interaction is considered to estimate the pores volume fraction needed for crack deflection. In this work, dense and porous layers of NiO-YSZ material similar to the one used in the fuel cells technology are considered. The fracture energy of a porous material with an ordered distribution of pores shows a possibility of crack deflection at a porosity of 22.5%. However for a system with randomly distributed pores this possibility can be seen at 36% of porosity.
Authors: Lin Dong, Ahmed Makradi, Saïd Ahzi, Yves Remond
Abstract: In the selective laser sintering (SLS) manufacturing technique a pre-heated layer of material powder undergoes a laser radiation in a selective way to produce three dimensional metallic or polymeric solid parts. Here, we consider sintering of polymer powder. The phase transformation in this process involves the material heat transfer which is strongly affected by the material sintering phenomena. A transient three dimensional finite element model is developed to simulate the phase transformation during the selective laser sintering process. This model takes into account the heat transfer in the material (powder and solid), the sintering and the transient nature of this process. The numerical simulation of the set of equations, describing the problem, is made possible by means of the commercial finite element software Abaqus. A bi-level structure integration procedure is chosen, in which the density is integrated at the outer level and the heat equation is integrated in the inner level. After successfully computing the integration of the density, a material Jacobian representing the thermal phenomena is computed and supplemented the Abaqus Code via an implicit user subroutine material. Results for temperature and density distribution, using a polycarbonate powder, are presented and discussed.
Authors: S. M'Guil, Saïd Ahzi, H. Youssef, J. Grácio, Moe A. Khaleel
Abstract: In this work, we propose a comparison between two different approaches for the simulation of the large deformation response and crystallographic texture evolution in polycrystals. The first approach is the well-know self-consistent scheme. For this, we used the Visco-Plastic- Self-Consistent (VPSC) approach. The second approach is based on a recently developed intermediate modeling. In a first part of this paper, we present the VPSC model. In a second part, we define the intermediate linear modeling which is based on a linear combination of Taylor and Sachs models using a weight parameter. For the comparison of these two approaches, we present different results in the case of uniaxial tests for an FCC polycrystal for different values of the weight parameter for the intermediate modeling and for different formulations of the macroscopic moduli in the self-consistent model.
Authors: Gennady Mishuris, Wiktoria Miszuris, Andreas Öchsner
Abstract: Imperfect transmission conditions modelling a thin intermediate layer between two bonded materials in a dissimilar strip are derived in this paper. The interphase material is assumed to be heat-resistant and situated in a thin rectangular domain between the main materials. Different types of the interphase are investigated: homogeneous and inhomogeneous; linear and nonlinear ones.
Authors: Gennady Mishuris, Wiktoria Miszuris, Andreas Öchsner
Abstract: Imperfect transmission conditions modelling a thin 2D intermediate layer between two bonded materials in a dissimilar strip have been derived and analytically analysed in another paper of this issue. In this paper, the validity of these transmission conditions for heat conduction problems has been investigated due to the finite element method (FEM) for various cases: namely, steady-state under uniform boundary conditions with constant or functional- dependent, i.e. temperature or spatial coordinate, conductivities of the interphase, non-uniform boundary conditions and finally for transient analysis. It is shown that the accuracy of the transmission conditions is excellent over the whole range of the interphase and that typical edge effects known from structural problems are not observable under the chosen problem parameters.
Authors: Pablo A. Muñoz-Rojas, M. Vaz
Abstract: The Modified Local Green’s Function Method (MLGFM) is an integral method which uses appropriately chosen Green’s function projections obtained numerically with the aid of auxiliary finite element problems. Its applicability includes those cases for which a fundamental solution does not exist or is very cumbersome. The MLGFM was studied intensely in the 90´s with promising results, especially for tractions and heat fluxes at the boundaries. The present contribution compares this method for heat flux evaluation in anisotropic media with finite volumes and finite elements. The latter approximates heat fluxes using a superconvergent patch recovery scheme, whereas the former computes flux quantities directly at nodes. The numerical example uses linear elements and includes non-homogeneous temperature and flux boundary conditions.
Authors: B. Neto, P.S. André
Abstract: The chromatic dispersion of optical fiber is a limiting factor in the increase of optical communications transmission bitrates. Chirped Fiber Bragg Gratings submitted to temperature gradients can provide tuneable dispersion compensation, being the tuneability achieved by an appropriate control of the applied temperature gradient. In this work we propose a numerical model that describes heat transfer mechanisms along the fiber grating and its surroundings to obtain a temperature distribution along the fiber grating longitudinal axis. This model, which enables the subsequent modeling of the grating dispersion, demonstrated that the temperature distribution in a steady state is linear. The subsequent modeling of the fiber grating chromatic dispersion agreed with experimental results.
Authors: Ekaterina Pesetskaya, Andreas Öchsner, Sergei Rogosin
Abstract: The effective conductivity of 2D doubly periodic porous materials with temperature dependent material properties is investigated. An arbitrary number of disjoint parallel cylindri- cal pores in a representative cell is considered. A multiply connected unbounded domain in the complex plane can serve as a geometrical description of such kind of materials. The problem of determination of the effective conductivity can be reduced to a boundary value problem for the Laplace equation on the multiply connected domain. This problem is analytically solved by the method of functional equations. An explicit formula for the effective conductivity is found. It contains the basic models’ parameters and elliptic Eisenstein functions.
Authors: Ekaterina Pesetskaya, Thomas Fiedler, Andreas Öchsner
Abstract: The effective conductivity of 2D porous materials with temperature dependent matrix properties is investigated by two different approaches: namely, a numerical and an analytical method. A model with disjoint parallel cylindrical pores in a representative cell is considered. The numerical method is represented by the finite element method. In the scope of the analytical method, the nonlinear boundary value problem which describes conducting properties of the materials is solved by the methods of complex analysis, and the effective conductivity is represented in an explicit form via the solution of this problem. The values of the effective conductivity obtained by two these methods are compared.

Showing 11 to 20 of 39 Paper Titles