Micro-macro methods: states and transitions from particles to continuum

  • Luding, Stefan (University of Twente)
  • Vescovi, Dalila (Politecnico di Milano)
  • Magnanimo, Vanessa ()

Please login to view abstract download link

An overview/review and special items about the subject of the mini-symposium is given in this talk. In order to understand the fundamental micro-mechanics one can use particle simulation methods [2,4], where often the fluid between the particles is important too, but neglected here. Large-scale applications (due to their enormous particle numbers) have to be addressed by coarse-grained models or by continuum theory. To bridge the gap between the scales, so-called micro-macro transition methods are necessary, which translate particle positions, velocities and forces into density-, stress-, and strain-fields. These macroscopic quantities must be compatible with the conservation equations for mass and momentum of continuum theory. Furthermore, some additional non-classical fields might be needed to describe the micro- structure or the statistical fluctuations, e.g., the fabric or the kinetic energy, before one can reach the ultimate goal of understanding and solving application problems. From a theoretical point of view, our understanding of the rheology of granular matter has greatly improved in the recent years; a remaining key question is how to extend the solid-mechanics and flow rheology to deal with different mechanical responses that naturally occur in many granular processes. Due to their discontinuous and inhomogeneous nature, granular systems can behave like solids, if a network of contacts develops within the medium, or like fluids whenever the grains are largely spaced and free to move in any direction, interacting only through inertial collisions. The diverse transitions from fluid to solid, and back from solid to fluid, as well as the transient evolutions between those states are still not fully understood. We present a universal, nonlinear, visco-elasto-plastic material model for the mechanics related to the failure of solids (solid-fluid-transitions) and to the stagnation or jamming (fluid-solid transitions) that includes also the history of material structure and the dynamics as state variables [3], as based on DEM particle simulations [2,3,4].