Effect of cobalt addition on the magneto-crystalline anisotropy parameter of sintered NiZn ferrites evaluated from magnetization curves

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Modeling of demagnetization processes in permanent magnets measured in closed-circuit geometry

International audienceThe hysteresis loops of nucleation-type magnets made of exchange-decoupled grains (i.e. sintered Nd-Fe-B magnets) reflect the discrete character of magnetization switching in such materials. Due to this discrete character, the experimental determination of coercivity depends on the measurement protocol. Finite element modelling allows to investigate how the pattern of reversed grains develops during sample demagnetization performed under closed-circuit conditions, provided that the basic features of the hysteresigraph are known. Numerical modelling provides a quantitative understanding of the collective effects which are very pronounced in the closed-circuit configuration and shows how they affect both the slope of the demagnetizing curve and the sample coercivity. With a grain coercive field standard deviation adjusted to 0.1 T, it is numerically found that the difference in coercivity between closed-and open-circuit configurations is 40 kA/m, in good agreement with previous experimental data

Measurement of the fracture energy at the interface between porous cathode layer and electrolyte in planar Solid Oxide Fuel Cells

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Compaction of aggregated ceramic powders: From contact laws to fracture and yield surfaces

Compaction ; ceramic powder ; aggregates ; discrete element simulation ; densification behavior ; cold compaction ; metal-powder ; localized ; densification ; induced anisotropy ; element method ; simulation ; compression ; formulation ; transitionInternational audienceThis work describes a methodology based on Discrete Element Method (DEM) simulations to generate yield and fracture surfaces for aggregated ceramic powders. The DEM simulations, which consider the length scale of porous aggregates. are used as numerical triaxial experiments to obtain the behavior of a small volume element of powder under a given load. The experimental identification procedure, which relies on the Design Of Experiment method, is designed to limit the number of experiments and simulations needed to obtain the model material parameters. These material parameters, which model the interactions between aggregates in the DEM simulations are identified using two simple experiments on a Uranium diOxide powder: closed-die compaction and diametrical compression test. The yield and fracture surfaces obtained from the DEM simulations provide valuable information on the behavior of the powder for stress states that are difficult or impossible to attain in complex triaxial tests