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In this review paper, a critical assessment of the main degradation processes in three key components of solid oxide fuel cells and electrolysers (negative and positive electrodes and the interconnect) is undertaken, attempting prioritization of respective degradation effects and recommendation of the best approaches in their experimental ascertainment and numerical modeling. Besides different approaches to quantifying the degradation rate of an operating solid oxide cell (SOC), the latest advancements in microstructural representation (3D imaging and reconstruction) of SOC electrodes are reviewed, applied to the quantification of triple‐phase boundary (TPB) lengths and morphology evolution over time. The intrinsic degradation processes in the negative (fuel) electrode and the positive (oxygen) electrode are discussed, covering first the composition and governing mechanisms of the respective electrodes, followed by a comprehensive evaluation of the most important factors of degradation during operation. By this systematic identification of dominant degradation processes, measurement techniques, and modeling approaches, the foundations are laid for the definition of meaningful accelerated stress testing of SOC cells and stacks, which will help the technology achieve the constantly more demanding durability targets in market applications. [ABSTRACT FROM AUTHOR]

A multi-scale model for the analysis of granular systems is proposed, which combines the principles of a coupled FEM-DEM approach with a novel servo-control methodology for the implementation of appropriate micro-scale boundary conditions. A mesh convergence study is performed, whereby the results of a quasi-static biaxial compression test are compared with those obtained by direct numerical simulations. The comparison demonstrates the capability of the multi-scale method to realistically capture the macro-scale response, even for macroscopic domains characterized by a relatively coarse mesh; this makes it possible to accurately analyse large-scale granular systems in a computationally efficient manner. The multi-scale framework is applied to study in a systematic manner the role of individual micro-structural characteristics on the effective macro-scale response. The effect of particle contact friction, particle rotation, and initial fabric anisotropy on the overall response is considered, as measured in terms of the evolution of the effective stress, the volumetric deformation, the average coordination number and the induced anisotropy. The trends observed are in accordance with notions from physics, and observations from experiments and other DEM simulations presented in the literature. Hence, it is concluded that the present framework provides an adequate tool for exploring the effect of micro-structural characteristics on the macroscopic response of large-scale granular structures. [ABSTRACT FROM AUTHOR]

In the paper numerical simulation of the foamed metal structures using numerical homogenization algorithm is prescribed. The first, numerical model of heterogeneous porous simplified structures of typical foamed metal, based on the FEM was built and material parameters (coefficients of elasticity matrix of the considered structure) were determined with use of numerical homogenization algorithm. In the work the different RVE models of structure were created and their properties were compared at different relative density, different numbers and the size and structure of the arrangement of voids. Finally, obtained results were used in modeling of typical elements made from foam metals structures - sandwich structures and hollow profiles filling with metal foam. Three point bending test was performed for sandwich structures. Simulation were done for different dimensions of cladding and core. Additionally, the torsion test was performed for profiles filling with metal foam. Typical behavior for torsion was observed. [ABSTRACT FROM AUTHOR]

Nuclear graphite has a complex microstructure and displays quasi-brittle fracture characteristics. Multi-scale experimental characterisation (micrometre-scale to centimetre-scale) and numerical modelling were performed for (i) PG25 filter graphite with pores only (52 vol.%); and (ii) Gilsocarbon nuclear graphite with pores and aggregates. Modelling results show that the average mechanical properties and the scatter of the data both decrease monotonically with increase in specimen size. Strain fields and crack patterns were modelled and fit with experimental observations. The benefits of the model as a valuable tool in studying the influence of microstructural parameters on the fracture of nuclear graphites are discussed. [ABSTRACT FROM AUTHOR]

• A multi-scale modelling approach has been presented to investigate the underpinning mechanisms of microstructure-sensitive damage of single crystal Sn-3Ag-0.5Cu solder joints of a ball grid array board assembly subject to thermal cycling. • Systematic studies of β-Sn crystal orientation and its role in thermal fatigue damage development within solder joints have been shown and compared to experimental observations and analysis. • It provides evidence-based optimization for solder microstructural design under in-service thermomechanical fatigue. This paper presents a multi-scale modelling approach to investigate the underpinning mechanisms of microstructure-sensitive damage of single crystal Sn-3Ag-0.5Cu (wt%, SAC305) solder joints of a Ball Grid Array (BGA) board assembly subject to thermal cycling. The multi-scale scheme couples board-scale modelling at the continuum macro-scale and individual solder modelling at the crystal micro-scale. Systematic studies of tin crystal orientation and its role in fatigue damage have been compared to experimental observations. Crystallographic orientation is examined with respect to damage development, providing evidence-based optimal solder microstructural design for in-service thermomechanical fatigue. [Display omitted] [ABSTRACT FROM AUTHOR]

The understanding and the prediction of the failure behaviour of materials with pronounced microstructural effects is of crucial importance. This paper presents a novel computational methodology for the handling of fracture on the basis of the microscale behaviour. The basic principles presented here allow the incorporation of an adaptive discretization scheme of the structure as a function of the evolution of strain localization in the underlying microstructure. The proposed quasi-discrete methodology bridges two scales: the scale of the material microstructure, modelled with a continuum type description; and the structural scale, where a discrete description of the material is adopted. The damaging material at the structural scale is divided into unit volumes, called cells, which are represented as a discrete network of points. The scale transition is inspired by computational homogenization techniques; however it does not rely on classical averaging theorems. The structural discrete equilibrium problem is formulated in terms of the underlying fine scale computations. Particular boundary conditions are developed on the scale of the material microstructure to address damage localization problems. The performance of this quasi-discrete method with the enhanced boundary conditions is assessed using different computational test cases. The predictions of the quasi-discrete scheme agree well with reference solutions obtained through direct numerical simulations, both in terms of crack patterns and load versus displacement responses. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a closed form expression for the sensitivity of the macroscopic heat conductivity tensor for two-dimensional problems to topological microstructural changes of the underlying material. The sensitivity formula is remarkably simple. It is derived by applying the concept of topological derivative within a variational multi-scale framework for steady-state heat conduction where the macroscopic temperature gradient and heat flux are defined as volume averages of their microscopic counterparts over a representative volume element (RVE) of material. The classical Fourier law is assumed to hold at the scale referred to as microscopic (the RVE). The derived sensitivity – a symmetric second order tensor field over the RVE domain – measures how the estimated macroscopic conductivity tensor changes when a small circular inclusion is introduced at the micro-scale. The proposed formula finds potential application in the design and optimisation of heat conducting materials. [Copyright &y& Elsevier]

• A transient, non-isothermal and multi-scale model of PEM-based dehumidification was developed. • Local heat and mass transfer of anode-side catalyst layer with reconstructed microstructures were modelled by the lattice Boltzmann method. • The interaction between anode CL and other layers, and its effect on air conditions was investigated. • Though uniform distribution can be achieved rapidly in CL(<100s), it takes much longer for air outlet to reach transient equilibrium (1000s for moisture content and 7000s for temperature). • Calculated effective mass diffusivity and heat conductivity of CL are 7.71×10-6 m2/s and 0.063 W/m•K. • The randomly arranged particles makes the CL the hottest and driest part of PEM element. As an independent and ultra-compact method, PEM-based dehumidifiers are promising, while accurate modelling of anode-side transport is still challenging. The theoretical model developed in this study is transient, two-dimensional and non-isothermal based on the lattice Boltzmann method, emphasizing the anode-side catalyst layer (CL) with reconstructed microstructures. Then the pore-scale CL modelling was coupled with the macro-scale simulation of air channel and diffusion layer (DL), and experimentally validated by a 3.5 cm2 dehumidifier. Results showed that the CL microstructure significantly affects the air outlet parameters of PEM dehumidifiers, especially in the beginning state. Although the uniform distribution of vapor concentration can be achieved immediately in CL, the time required for the air outlet to reach transient equilibrium is much longer, which is around 1000s for the moisture content and 7000s for the temperature. The moisture transfer resistance at the beginning state mainly exists in CL, then it moves to both CL and DL (close to the interface) when it reaches equilibrium. Due to the continuous heat generation, the temperature flux in CL dominates in the anode side, and increases by 5-6 times during dehumidification. The calculated values of effective mass diffusivity and thermal conductivity of CL are 7.71×10−6 m2/s and 0.063 W/m•K. The randomly arranged catalyst particles makes CL the hottest (2~3°C higher) and driest (half the DL concentration) part of PEM element, which severely limits the whole performance. This modelling reveals the interaction between anode-side CL with microstructures and the performance, considering the transient heat and mass transfer. [ABSTRACT FROM AUTHOR]

Abstract: Material property evolution during processing is governed by the evolution of the underlying microstructure. We present an efficient technique for tailoring texture development and thus, optimizing properties in forming processes involving polycrystalline materials. The deformation process simulator allows simulation of texture formation using a continuum representation of the orientation distribution function. An efficient multi-scale sensitivity analysis technique is then introduced that allows computation of the sensitivity of microstructure field variables such as slip resistances and texture with respect to perturbations in macro-scale forming parameters such as forging rates, die shapes and preform shapes. These sensitivities are used within a gradient-based optimization framework for computational design of material property distribution during metal forming processes. Effectiveness of the developed computational scheme is demonstrated through computationally intensive examples that address control of properties such as Young’s modulus, strength and magnetic hysteresis loss in finished products. [Copyright &y& Elsevier]

Abstract: Recent developments in multi-scale modelling, based on atomic scale calculations, are leading to a growing conviction that modelling will soon be used to design material components for nuclear reactors. In this article we discuss this assumption on the basis of the relationship between experimental studies and theoretical calculations of the microstructural evolution of materials under irradiation. In the first part of the paper, the available numerical models for long term microstructural evolutions are briefly reviewed. The experimental methods are presented in a second part. In the third part, several examples of fruitful relationships between modelling and experiments are discussed. To cite this article: A. Barbu, C. R. Physique 9 (2008). [Copyright &y& Elsevier]

Abstract: Numerical modelling on the micro- and meso-level of concrete is presented. The formation of the microstructure, including the matrix and the interfacial transition zones between aggregate particles is modelled explicitly on the micro-level. The outcome of these simulations are used in a meso-level model (lattice model) to study the formation of (micro-)cracking in concrete consisting of particles embedded in a matrix. The different matrix and interface properties as well as the level of restraining of deformations is included in these simulations. Three concrete mixes with different water–cement ratio are investigated. A lower w/c shows more autogenous shrinkage, higher eigenstresses and thus a higher tendency for cracking. From the simulations it is found that eigenstresses caused by autogenous shrinkage reduce the tensile strength of the concrete. However, it is also concluded that the local material properties are very important and influence the outcome of the simulations to a large extent. Furthermore, the influence of microcracking or weak zones on the ductility of multi-phase materials is investigated. It is found that the ratio between the strengths of the components in a material determines the width of the fracture process zone and also the ductility of the material. [Copyright &y& Elsevier]

Snow material is an example of a geomaterial whose micro-structure plays a significant role in its overall constitutive behaviour. A snow sample can be regarded at the microscopic level as a cohesive granular assembly; the behaviour of ice bonds at the interface of each pair of grains in contact, which has a substantial influence on the overall behaviour, can be expressed in a straightforward manner. This paper derives the constitutive behaviour of the snowpack on the macroscopic level from a microscopic-scale description, taking into account a statistical description of the fabrics. In this approach, the location of each particle does not play a role, but the probability of a grain bond existing in a given direction is investigated. Modelling the creation or the failure of contacts in given directions makes it possible to analyse how the probability density of having contacts in these directions evolves. As an example, the relevance of this constitutive approach is examined using the standard creeping and triaxial tests. [ABSTRACT FROM AUTHOR]

• Polycrystalline microstructure of hydrided Zr incorporating individual micro-hydride. • Multiscale: micrometric autocatalytic hydride stacks in hundreds of grains at the mm scale. • Fully analytical model able to generate the fuel cladding microstructure in seconds. • Benchmarked against experimental images for different notch geometries. A mechanistic understanding of hydrogen diffusion and hydride precipitation at the microscale underpins the prediction of delayed hydride cracking in zirconium alloy nuclear fuel cladding. We present a novel approach to modelling the microstructures created by hydride precipitation at loaded notches in polycrystalline Zr alloys. The model is multi-scale in that it includes the elastic dipole tensor of interstitial hydrogen in α -Zr, it treats the stress-driven diffusion of hydrogen at the meso-level (mm), it calculates the thermodynamically favourable spatial arrangement of microhydrides and their assembly into macrohydride colonies, in a textured polycrystalline sample, and it treats the full elastic field of the loaded notch and all the hydrides at a scale similar to the cladding thickness. A simplifying innovation is the representation of the elastic field of a microhydride by a dislocation dipole, where the Burgers vector is set to create the experimentally measured strain in the 〈 1 1 ¯ 0 0 〉 direction. The model provides a predictive framework for treating elastic anisotropy, a variety of potential nucleation sites, and different grain sizes. Simulated micrographs of hydride networks in polycrystalline samples with blunt and sharper loaded notches are compared with experimental micrographs obtained at the same scale. The simulations are extremely fast and calculations typically take around tens of seconds. This makes it possible to carry out detailed sensitivity studies with respect to several pertinent metallurgical variables, as well as conducting ensemble averaging of hydride microstructures. [ABSTRACT FROM AUTHOR]