Size dependence of the yield threshold in dense granular materials

Abstract eng:
Yield of granular materials is typically modeled by local, pressure-dependent criteria, such as the Drucker-Prager condition, in which yield at a point is assessed based only on the stress. However, nonlocal effects lead to phenomena that cannot be captured with local yield conditions. For example, flows of thin layers of grains down an inclined surface exhibit a size effect whereby thinner layers require more tilt to begin flowing, and hence, sufficiently thin layers will not flow, even when the stress in the layer exceeds the yield condition. Recently, a new continuum model – the nonlocal granular fluidity (NGF) model – was successfully used to predict steady granular flow fields in a variety of flow configurations. In this work, we show that the NGF model is also capable of quantitatively describing the size-dependent strengthening of thin granular bodies – both in flow down an incline and in linear shear with gravity.

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