A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity. This dislocation-based model predicts strengthening of materials when a gradient in stress acts over dislocation sourceobstacle configurations. The model has a physical length scale, the spacing of dislocation obstacles, and is validated by several levels of discrete-dislocation simulations. When incorporated into a continuum viscoplastic model, predictions for bending and torsion in polycrystalline metals show excellent agreement with experiments in the initial strengthening and subsequent hardening as a function of both sample-size dependence and grain size, when the operative obstacle spacing is proportional to the grain size.continuum modeling | size effects | strengthening mechanisms C onventional continuum plasticity models are inherently sizeindependent and so are unable to predict size effects now observed in many experiments, including micro-and nano-indentation hardness (1, 2), flow strength of nanocrystalline metals (3), micro-and nanopillars (4), nanoasperities (5), single and polycrystalline thin films (6), bending of thin beams (7,8), and torsion of metal wires (9, 10). However, the physical length scales that control the strengthening are not clearly established. One origin of size effects is attributable to geometrically necessary dislocations (GNDs), which must exist when there are plastic strain gradients in a material. This has led to the development of continuum strain gradient plasticity (ϵGP) models, which introduce a phenomenological dependence of strengthening and/or hardening on the plastic strain gradient and an associated phenomenological length scale that determines the magnitude of the effects (11-17). ϵGP models can adjust the length scale to fit experiments, but (i) predicting different experiments on the same material using the same length scale has proven to be difficult and (ii) different ϵGP models deduce different length scales and different trends in the flow stress (8,18). Moreover, recent experiments suggest an inverse correlation between strength and GND density (19), which is outside the scope of current thinking. Previously undescribed mechanistic insights are thus needed.Here, we propose a previously undescribed model, "stressgradient plasticity" (σGP), that arises naturally from the classic analysis of dislocation pileups in source-obstacle configurations. The average obstacle spacing immediately emerges as the material length scale controlling strengthening in the presence of a stress gradient. The model and analysis thus deviate from current thinking that attributes size effects solely to GNDs, focusing instead on the dislocation obstacles that actually control flow strength. The average spacing between dislocation obstacles has been proposed as a potential candidate for the length scale controlling size effects (12), and several studies have attempted to incorporate this length scale into phenomenological ϵGP models with reasona...

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Internal Li deposition in isolated pores inside the solid electrolyte (SE) is found to be one of the main reasons for dendrites growth (short) in solid-state batteries, due to the presence of electronic conductivity of the SE. In this work we show for the first time a clear picture of how this happens and what the controlling factors are. We also propose several solutions to reduce/eliminate the dendrites growth caused by internal deposition.