Fractal Dimension of Grain Boundary during Heating. Comparison between Images Analyses and Monte Carlo Simulation

There are few articles that mention fractal dimension in grain growth mechanism. Some authors build a simplified analytic model showing that initial fractal dimension of grain boundary has an influence on interface modification velocity. Nevertheless they postulate the relation L = c s(1−Δ) where L is the grain length, c is a constant, s is grain size and Δ the fractal dimension. The aims of this paper is to experimentally analyze by image analysis the fractal dimension of A5 aluminum sheet grain boundaries during heating and to simulate their evolution by a Monte Carlo method to validate experimental data.. It is shown by Monte-Carlo simulation and confirmed experimentally that the grain growth process decreases the fractal dimension of grain border. It can be concluded that it is very hazardous to build a model of grain growth without including the effect of grain’s morphology. The macroscopic fractal morphology of the grain structure could then be used to validate microscopic relation between Monte Carlo Steps time and real time

Simulation of the thermal profile of a mushy metallic sample during tensile tests

Strain measurement is a major challenge in tensile tests performed in a mushy state. While non-contact technique devices like the laser speckle extensometer remain the most reliable facility for this type of measurement, these devices are often not readily available. So the strain measurement is usually performed by determining the length of the ‘‘hot zone’’ of the sample. This is possible with the help of the thermal profile associated with the sample under heating. The purpose of our work is to develop a numerical model to predict the thermal profile of a A356 aluminum alloy sample at high temperature, taking into account the device geometry and characteristics. We simulate the joule heating effect using the FE software Abaqus. Our model takes into account the grips of a Gleeble machine, the thermal contact conductance and electrical contact resistance at the grip-sample interfaces, as well as the convection heat transfer on the free surfaces of the system. These thermo-physical properties have been determined by fitting the experimental thermal profile obtained at 545°C. The model was then used to simulate the temperature profile on the sample at higher temperatures (when the sample is in the mushy state). The thermal profile predicted by our model is in excellent agreement with the profile obtained experimentally

Fractal Dimension of Grain Boundary during Heating. Comparison between Images Analyses and Monte Carlo Simulation

There are few articles that mention fractal dimension in grain growth mechanism. Some authors build a simplified analytic model showing that initial fractal dimension of grain boundary has an influence on interface modification velocity. Nevertheless they postulate the relation L = c s(1−Δ) where L is the grain length, c is a constant, s is grain size and Δ the fractal dimension. The aims of this paper is to experimentally analyze by image analysis the fractal dimension of A5 aluminum sheet grain boundaries during heating and to simulate their evolution by a Monte Carlo method to validate experimental data.. It is shown by Monte-Carlo simulation and confirmed experimentally that the grain growth process decreases the fractal dimension of grain border. It can be concluded that it is very hazardous to build a model of grain growth without including the effect of grain’s morphology. The macroscopic fractal morphology of the grain structure could then be used to validate microscopic relation between Monte Carlo Steps time and real time

Multiscale modelling of morphological evolution of rough surface duringsuperficial, volume and evaporation-condensation diffusions

Fractal functions are used to model a metallic interface. An analytical model described by three partial differential equations is built to model time evolution of the surface during heating including three different mechanisms of diffusion: superficial diffusion (SD), volume diffusion (VD) and diffusion by evaporation-condensation (DEC). Initial topographies are modeled by Stochastic Weierstraβ functions because of their ability to reproduce experimental roughness profiles. Applied to an aluminum alloy at 550°C, a high number of roughness parameters and their variance are calculated. A classification method shows that the best geometrical approach that discriminates heat effect is the fractal dimension. The most popular parameter, Ra, badly discriminates processes (classification number = 58). The four order spectral moments of the roughness profile are correlated with the evolution of profile. It is shown theoretically that the superficial diffusion depends directly to the fourth spectral moment of the roughness profile

Numerical Prediction of Stresses at High Temperature of 3rd Generation Advanced High Strength Steels During Resistance Spot Welding - Liquid Metal Embrittlement Risk Assessment. Methodology to Create and Validate a Reliable and Robust Numerical Material Card

The prediction of stress level during Resistance Spot Welding at high temperature is very useful to reduce and/or avoid Liquid Metal Embrittlement phenomenon. However, the experimental estimation of stress level into metal sheets during a Resistance Spot Welding process is impractical. Therefore, a numerical methodology to predict mechanical stresses, using more accessible experiments, is proposed in this work

A General Approach for Kinetic Modeling of Solid-Gas Reactions at Reactor Scale: Application to Kaolinite Dehydroxylation

Understanding the industrial reactors behavior is a difficult task in the case of solid state reactions such as solid-gas reactions. Indeed the solid phase is a granular medium through which circulate gaseous reactants and products. The properties of such a medium are modified in space and time due to reactions occurring at a microscopic scale. The thermodynamic conditions are driven not only by the operating conditions but also by the heat and mass transfers in the reactor. We propose to numerically resolve the thermohydraulic equations combined with kinetic laws which describe the heterogeneous reactions. The major advantage of this approach is due to the large variety of kinetic models of grains transformation (~40) compared to the usual approach, especially in the case of surface nucleation and growth processes which need to quantitatively describe the grain conversion kinetics at a microscopic scale due to nucleation frequency and growth rate laws obtained in separate isothermal and isobaric experiments. The heat and mass transfers terms entering in the balance equations at a macroscopic scale depend on the kinetics evaluated at the microscopic scale. These equations give the temperature and partial pressure in the reactor, which in turn influence the microscopic kinetic behavior

Simulation of the thermal profile of a mushy metallic sample during tensile tests

Strain measurement is a major challenge in tensile tests performed in a mushy state. While non-contact technique devices like the laser speckle extensometer remain the most reliable facility for this type of measurement, these devices are often not readily available. So the strain measurement is usually performed by determining the length of the ‘‘hot zone’’ of the sample. This is possible with the help of the thermal profile associated with the sample under heating. The purpose of our work is to develop a numerical model to predict the thermal profile of a A356 aluminum alloy sample at high temperature, taking into account the device geometry and characteristics. We simulate the joule heating effect using the FE software Abaqus. Our model takes into account the grips of a Gleeble machine, the thermal contact conductance and electrical contact resistance at the grip-sample interfaces, as well as the convection heat transfer on the free surfaces of the system. These thermo-physical properties have been determined by fitting the experimental thermal profile obtained at 545°C. The model was then used to simulate the temperature profile on the sample at higher temperatures (when the sample is in the mushy state). The thermal profile predicted by our model is in excellent agreement with the profile obtained experimentally

Comportement thermomécanique de l’alliage 600 en flexion 4 points

Ce travail s’intéresse à l’endommagement de l’alliage base nickel 600 connu sous le nom commercial d’inconel 600 utilisé particulièrement au niveau des circuits primaires des réacteurs nucléaires à eau pressurisée. Ainsi, des essais de flexion 4 points sont effectués à l’aide d’un montage spécifique sous vide secondaire, dans un domaine de température répondant aux conditions réelles de fonctionnement des générateurs de vapeur s’étalant de 350 à 550°C. Le suivi de ces essais en conditions in situ par émission acoustique a permis de vérifier l’absence d’endommagement des échantillons utilisés. Les courbes des contraintes en fonction de la flèche obtenues à partir des données expérimentales qui sont la force et le déplacement conduisent à la détermination du module de Young et de la limite d’élasticité du matériau. D’autres essais, sous air et sous vapeur d’eau sont envisagés, afin de pouvoir remonter jusqu’au comportement viscoplastique de l’inconel 600 dans la gamme de température visée, par méthode inverse.Mots Clés: inconel 600; corrosion sous contrainte; oxydation; émission acoustique; flexion 4 points. This work concerns the damage of a nickel-based alloy known under the commercial name Inconel 600, usually used on the level of the primary circuits of the pressurized water nuclear reactors. The 4 points bending tests are carried out under secondary vacuum. In order to answer the real conditions of the operations, the temperature range which explored is chosen between 350°C to 550°C. The use of acoustic emission shows that there is no damage of the sample itself during such mechanical tests. From the curves of stress-strain and deflection, obtained from experimental tests; mechanical characteristics of material such as the Young modulus and the yield strength are determinate. Other tests under air and water vapour are considered in order to be able to obtain the viscoplastic behaviour of material in the range of temperature concerned by inverse method.Keywords: inconel 600; stress corrosion cracking; oxidation; acoustic emission; 4 points bending.