A Coupled Diffusion-Mechanical Lattice Model for the Degradation of Graphite Active Particles of Li-Ion Battery Anodes

The performance,durability of lithium-ion batteries (LIBs) are constrained by the degradation mechanisms that take place during charge,discharge cycles. Degradation of active particles (APs) of LIBs is a complex problem involving several physical phenomena (e.g.,diffusion,mechanical deformation,heat transfer,to cite a few). During lithium insertion,extraction cycles,volume changes in the AP result in high mechanical stresses and,consequently,mechanical damage that promotes capacity fade. In this work,we present a microscale 3D finite element model that takes into account the coupled effects between lithium diffusion,mechanical stress within the AP. Using the surface of an ellipsoid as the base for the geometrical construction,we are able to generate different shapes of APs,with both concave,convex surfaces. Porosity,other types of defects that may be present inside the AP are explicitly modeled,different volume fractions,shapes,orientations are also accounted for. In our approach,the material is discretized into a lattice of one-dimensional elements: we consider beam elements for the mechanical problem,while in the diffusive approach,the material is treated as an assembly of 'nanopipes' through which the flow of Li-ions takes place. The same lattice network is used for both simulations. We follow a classical lattice model approach to characterize the fracture behavior of a single AP of a LIB anode when subjected to charge/discharge cycles. The material of the APs analyzed in this work is graphite,which presents a brittle,disordered material structure,making it suitable for lattice modeling. The mechanical problem is solved,obtaining the crack patterns associated with specific charge,discharge strategies,potential initial defects. The simulation results correctly reproduce the experimental observations on mechanical stresses,the evolution of damage. This lattice model framework analyzing the degradation in the APs of LIBs (durability) can be used to provide more information regarding the microstructural evolution,morphological changes,mechanical degradation in APs,identify improvement strategies

Computational Multiscale Solvers for Continuum Approaches

Computational multiscale analyses are currently ubiquitous in science and technology. Different problems of interest-e.g., mechanical, fluid, thermal, or electromagnetic-involving a domain with two or more clearly distinguished spatial or temporal scales, are candidates to be solved by using this technique. Moreover, the predictable capability and potential of multiscale analysis may result in an interesting tool for the development of new concept materials, with desired macroscopic or apparent properties through the design of their microstructure, which is now even more possible with the combination of nanotechnology and additive manufacturing. Indeed, the information in terms of field variables at a finer scale is available by solving its associated localization problem. In this work, a review on the algorithmic treatment of multiscale analyses of several problems with a technological interest is presented. The paper collects both classical and modern techniques of multiscale simulation such as those based on the proper generalized decomposition (PGD) approach. Moreover, an overview of available software for the implementation of such numerical schemes is also carried out. The availability and usefulness of this technique in the design of complex microstructural systems are highlighted along the text. In this review, the fine, and hence the coarse scale, are associated with continuum variables so atomistic approaches and coarse-graining transfer techniques are out of the scope of this paper.Abengoa Researc

A Finite Element‑Based Methodology for the Thermo‑mechanical Analysis of Early Age Behavior in Concrete Structures

This paper presents a general procedure based on fracture mechanics models in order to analyze the level of cracking and structural safety in reinforced concrete elements at early ages, depending on the stripping time. Our procedure involves the development of a thermo-mechanical numerical model based on the finite element method that accounts for the change in the mechanical properties of concrete with time. Moreover, fracture mechanisms are analyzed by means of a material damage model, which is characterized via specific experimental results obtained for standard specimens and notched beams under three-point bending testing. The loading conditions are both thermal and mechanical, and are obtained from the hydration process for a given concrete dosage. The presented methodology allows for the determination of the optimal stripping time, whereas it helps assessing the analysis of the cracking and the stress states of the elements under consideration. A practical application, namely the analysis of a retaining wall, is used to validate our methodology, showing its suitability in engineering practice.Ministerio de Economía y Competitividad BIA2016-75431-

Mesoscale Characterization of Fracture Properties of Steel Fiber-Reinforced Concrete Using a Lattice–Particle Model

This work presents a lattice–particle model for the analysis of steel fiber-reinforced concrete (SFRC). In this approach, fibers are explicitly modeled and connected to the concrete matrix lattice via interface elements. The interface behavior was calibrated by means of pullout tests and a range for the bond properties is proposed. The model was validated with analytical and experimental results under uniaxial tension and compression, demonstrating the ability of the model to correctly describe the effect of fiber volume fraction and distribution on fracture properties of SFRC. The lattice–particle model was integrated into a hierarchical homogenization-based scheme in which macroscopic material parameters are obtained from mesoscale simulations. Moreover, a representative volume element (RVE) analysis was carried out and the results shows that such an RVE does exist in the post-peak regime and until localization takes place. Finally, the multiscale upscaling strategy was successfully validated with three-point bending tests.Ministerio de Economía y Competitividad BIA2013-48352-

Integrated computational materials engineering in solar plants: the virtual materials design project

The final publication is available at Springer via http://dx.doi.org/10.1007/s11837-018-2970-5The high temperatures required for efficient operation of solar thermal power plants constitutes one of the major challenges of this technology. Gaining insight into materials behavior at very high temperatures is critical to improve their techno-economic feasibility. Standard material characterization approaches become inefficient, as extensive testing campaigns are required. We propose a multiscale–multiphysical approach that accounts for materials composition to (1) predict the behavior of both Inconel 625 and new solar salts, and (2) assess the thermomechanical performance of key components. We carried out a complete thermoelastic multiscale analysis that spans six time and length scales in a single simulation platform, combining discrete and continuum tools (from quantum to continuum mechanics). These applications show the substantial economic benefits that may be achieved by an ICME approach in the energy sector, reducing the cost of prototypes while decreasing development times and maintenance costs due to a better understanding of materials behavior.Peer ReviewedPostprint (author's final draft

Multiscale Analysis of the Influence of Steel Fiber Reinforcement on the Shear Strength of Post-Tensioned Dry Joints

In this work we follow a multiscale methodology to characterize the structural performance of post-tensioned steel fiber-reinforced concrete dry joints. At the material level, we use an experimentally validated lattice-particle model whose input parameters are the properties of the di erent phases themselves (i.e., mortar, aggregates, fibers) and mixing information. This model is used to obtain the mechanical properties used in the structural-level simulations of the joints in terms of constitutive laws. The structural analyses are performed using the concrete damage plasticity model, which allows us to quantify the e ect of fiber addition on the shear strength of the dry joints and their ductility. Our simulations agree well with other macroscopic models in the case of plain concrete and show, once again, that the American Association of State Highway Transportation O cials (AASHTO) code overestimates the nominal shear capacity of multiple-keyed joints. Regarding the fiber addition, we observe that it promotes an important increase in the shear capacity, but the prestress level is still more relevant in this sense. Based on our simulations, we propose an updated shear capacity estimate accounting for the fiber volume fraction. Finally, a clear increase in the ductility of the joint is observed when the fiber volume content is increased.Ministerio de Economía y Competitividad BIA2016-75431-

Multiscale thermo-mechanical analysis of multi-layered coatings in solar thermal applications

Solar selective coatings can be multi-layered materials that optimize the solar absorption while reducing thermal radiation losses, granting the material long-term stability. These layers are deposited on structural materials (e.g., stainless steel, Inconel) in order to enhance the optical and thermal properties of the heat transfer system. However, interesting questions regarding their mechanical stability arise when operating at high temperatures. In this work, a full thermo-mechanical multiscale methodology is presented, covering the nano-, micro-, and macroscopic scales. In such methodology, fundamental material properties are determined by means of molecular dynamics simulations that are consequently implemented at the microstructural level by means of finite element analyses. On the other hand, the macroscale problem is solved while taking into account the effect of the microstructure via thermo-mechanical homogenization on a representative volume element (RVE). The methodology presented herein has been successfully implemented in a reference problem in concentrating solar power plants, namely the characterization of a carbon-based nanocomposite and the obtained results are in agreement with the expected theoretical values, demonstrating that it is now possible to apply successfully the concepts behind Integrated Computational Materials Engineering to design new coatings for complex realistic thermo-mechanical applications.Peer ReviewedPostprint (author's final draft

Lattice-Particle Microstructural Model for Ion Diffusion in Graphite Electrode Batteries

In this work, we propose a lattice-particle approach to study ionic diffusion across graphite electrodes. In our approach, we generate virtual representative volume elements (RVE) of the electrode material based on its composition, i.e., active particles, carbon additives, and binder. Porosity is also accounted for as an input parameter. To account for the evolution of the ionic concentration, Fickean diffusion is considered. This problem is solved within a network of one-dimensional elements, which is constructed upon the particles of the RVE, yielding a three-dimensional lattice. We use the centraldifference time-integration scheme to solve the transient problem within the framework of the finite element method for the spatial discretization. One of the main advantages of our approach is that we are able to reduce the number of degrees of freedom and thus the computational cost in comparison to the conventional continuum-based finite element simulations. For the transport simulations, we consider Li ions, although our approach can be also applied to other type of species, such as PF

Archivos y Bibliotecas

We analyze the situation in 2004 of the Regional System of Archives and Libraries (Murcia), to identify the main shortcomings. According to them, action proposals are made to guarantee the right of public access to information, culture and education in Murcia