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We performed finite element simulations of spherical indentation of Li-ion pouch cells. Our model fully resolves different layers in the cell. The results of the layer resolved models were compared to the models available in the literature that treat the cell as an equivalent homogenized continuum material. Simulations were carried out for different sizes of the spherical indenter. We show that calibration of a failure criterion for the cell in the homogenized model depends on the indenter size, whereas in the layer-resoled model, such dependency is greatly diminished. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0151613jes] All rights reserved.Manuscript submitted March 7, 2016; revised manuscript received August 29, 2016. Published September 12, 2016 With increased use of batteries for automotive applications it is important to understand the mechanical behavior of such batteries under impact loading, which can cause severe damage to the battery system. One of the biggest challenges to developing accurate numerical models for battery deformation is the treatment of the cell mechanical response. A lithium-ion pouch cell consists of large number of stacked positive and negative electrodes that are kept apart by a porous polymeric separator to prevent an internal short circuit of the cell. Active electrodes are coated on copper (anode) or aluminum (cathode) thin metal foils, and the entire cell structure is encased in a metalized polymer pouch. The cell structure consisting of electrodes and separator, but without the protective enclosure, is termed as a jellyroll. Modeling the mechanical behavior of this structure during indentation is the subject of this paper.Most of the work on mechanical abuse of Li-ion batteries is based on homogenizing the cell structure with effective properties following a suitable constitutive model. Electrodes are compressible porous bonded aggregates and their behavior is found to be similar to compressible foams.3,4,5 When homogenized material is used to model the cell, the failure criterion is determined by prescribing a threshold value of internal variables in the constitutive model to match the experimental result. This calibration depends on physical and mechanical attributes of the cell (experiments have to be repeated for each new cell), the size of the indenter, and on the model discretization. In this work we have carried out mechanical simulations of Li-ion pouch cell with resolved internal layer structure of the cell, and compared the approach to the homogenization method. Dependence of onset of failure in the homogenized model on the punch diameter is discussed. In, 1,2 the authors have used representative-sandwich formulation to model the pouch cell. In this modeling approach there is an explicit re...

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The solidification microstructure in IN718 during additive manufacturing was modeled using phase field simulations. The novelty of the research includes the use of a surrogate Ni-Fe-Nb alloy that has the same equilibrium solidification range as IN718 as the model system for phase field simulations, the integration of the model alloy thermodynamics with the phase field simulations, and the use of high-performance computing tools to perform the simulations with a high enough spatial resolution for realistically capturing the dendrite morphology and the level of microsegregation seen under additive manufacturing conditions. Heat transfer and fluid flow models were used to compute the steady state temperature gradient and an average value of the solid-liquid (s-l) interface velocity that were used as input for the phase field simulations. The simulations show that the solidification morphology is sensitive to the spacing between the columnar structures. Spacing narrower than a critical value results in continued growth of a columnar microstructure, while above a critical value the columnar structure evolves into a columnar dendritic structure through the formation of secondary arms. These results are discussed in terms of the existing columnar to dendritic transition (CDT) theories. The measured interdendritic Nb concentration, the primary and secondary arm spacing is in reasonable agreement with experimental measurements performed on the nickel-base superalloy IN718. and solidification of a powder bed using moving heat sources based on electron beam or laser. Part of the previously solidified layer is re-melted during a subsequent pass. The solidification microstructure that develops during the process is influenced both by the thermal history as well as the underlying structure in the previously solidified layer. The characteristics of the solidification microstructure including primary and secondary dendrite arms spacing, solute distribution within the dendrites and the dendrite orientations have a direct bearing on the mechanical properties of the as-processed component. Also, during post-processing heat treatment, evolution of the microstructure depends on the primary solidification structure due to potential solid-state transformations. Therefore, it is important to quantitatively predict the solidification microstructure in a given alloy, under a given set of processing parameters. An excellent review of the processing-structure relationships during AM of structural alloys is available in a recent publication [1].A key feature of the powder bed fusion processes is the extremely high cooling rate experienced by the melt pool. Typical cooling rates are of the order of 10 6 K/s. Under extreme conditions, the velocity of the solid-liquid (s-l) interface can approach several meters per second, especially along the heat source travel direction. This could cause significant deviation from thermodynamic equilibrium at the moving s-l interface. Non-equilibrium solute-partitioning could lead to a reduction in the solute...