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This paper develops a multi-scale mechanical-electrochemical model which enables fully coupled mechanics and electrochemistry at both particle and electrode levels. At the particle level, solid diffusion is modeled using a generalized chemical potential to capture the effects of mechanical stress and phase transformation. At the electrode level, the stress arising from particle interaction is incorporated in a continuum model. This particle interaction stress is in addition to the traditional concept of intercalation stress inside isolated particles. The particle and continuum electrode levels are linked by the particle interaction stress as loads on the particle surface, and by consideration of stress on the electrochemical reaction rate on the particle surface. The effect of mechanical stress on electrochemical reaction results in a stress-dependent over-potential between particle and electrolyte. Stress gradient in an electrode leads to inhomogeneous intercalation/deintercalation currents for particles depending on their interaction stress with neighbors, resulting in stress gradient induced inhomogeneous state of charge. Conversely, non-uniform intercalation/deintercalation currents in an electrode lead to stress between particles. With this model we have an important finding: an electrochemically inactive region in an electrode causes stress built-up. This model provides a powerful tool to address various problems such as fracture in-between particles. [ABSTRACT FROM AUTHOR]

The mechanics of crushing and breaking of particles is one of the most intractable problems in materials science. The stressed states of processed materials are significantly inhomogeneous, and thus the deformation and disintegration mechanisms vary greatly. Two techniques have been developed for realizing these processes as a quasi-homogeneous transition. The device and method developed by Enikolopian transform a solid polymer spontaneously into powder. The same loading system is now used for obtaining fine-grained metals, similarly as when using the ECAP device developed by Valiev. Both techniques are now used for obtaining nanostructured materials. The common feature of both types of methods is the formation of new physical surfaces. These are particle-free oversurfaces or grain boundaries. The method requires a supply of energy in the form of mechanical work, and this is mostly done by simultaneous action of pressure and shear stress. The formation of free oversurfaces in stressed solid bodies is the subject of fracture mechanics. The Griffith equation is employed to describe the problem. [ABSTRACT FROM AUTHOR]

Abstract: A numerical model was developed that combines complex porous coating microstructures with continuum mechanics simulations. Platy (hexagonal plates) and blocky (frusta) particles were packed computationally. Polymer nano-bridges were then placed between the packed particles to establish network continuity. Slices from the 3-dimensional packings were extracted and a finite element method implemented to determine the mechanical properties. As a function of shape, high aspect ratio plates might be expected to resist load more effectively than 1:1 aspect ratio frusta. However, when the polymer fractions are high and there is low binder spread across the particle surfaces, the frustum packings exhibit higher tensile modulus values than the platy packings. These packed frusta have more stable solid state networks than higher aspect ratio platy packings and consequently resist load more effectively. [Copyright &y& Elsevier]