Linking micro-structure to macro-behavior of granular matter: from flowing heterogeneously to morphing adaptively
Department of Mechanical Engineering & Materials Science Special Seminar
Liuchi Li, PhD
Lawrence Berkeley National Laboratory (LBNL)
"Linking micro-structure to macro-behavior of granular matter: from flowing heterogeneously to morphing adaptively"
Abstract: Understanding inter-particle contacts and forces (i.e., granular microstructures) remains a fundamental goal in predicting and/or controlling the collective behavior of granular media. In this talk, I will present my past and ongoing work relevant to this topic in two parts.
In the first part, I will summarize how granular microstructures correlate to two types of collective behavior of granular media: spatial phase transitions of heterogeneous granular flows [1] and bending modulus adaptations of shape-morphing granular fabrics [2]. Concerning granular flows, by using an experimentally validated Discrete Element Method (DEM) model, we propose a micro-scale parameter quantifying the level of structural anisotropy, that can for the first time elucidate spatial phase transitions in heterogeneous granular flows - from a gas-like layer to a fluid-like layer and finally to a solid-like layer - in dependent of imposed boundary conditions and loading rates. Further, in solid-like layers, this micro-structural quantity correlates to bulk effective friction, an integral macroscale quantity in constitutive modeling. Concerning granular fabrics, by using an experimentally validated DEM model, we discover a power-law correlation between bending modulus (a macroscale quantity) of granular fabrics and coordination number (a micro-scale quantity) regardless of confining pressure and constituent particle shape, in reminiscence of the canonical power law scaling for packing of frictionless sphere near jamming. The discovered power law scaling opens a venue of rational designing these shape-morphing granular fabrics for desired functionalities.
Having shown the fundamental significance of granular microstructure, in the second part, I will briefly discuss my very recent work studying granular microstructures of mechanically disordered (in contrast to the commonly studied geometrically disordered) granular media [3]. Specifically, through a self-implemented and verified Finite Element Method (FEM) algorithm incorporated with contact mechanics, we show quantitatively that a heterogeneous force distribution can also emerge from solely mechanically disordered granular media (e.g., mono-sized disks arranged over either a square or a hexagonal lattice). We anticipate in the future to establish a framework that can tactically combine geometric and mechanical disorder to realize active control of granular microstructure, thereby opening a venue of engineering novel granular media through inverse design.
[1] LC Li and JE Andrade. "Identifying spatial transitions in heterogeneous granular flow." Granular matter, 22(2):1-16, 2020.
[2] YF Wang*, LC Li*, D Hofmann, JE Andrade and D Chiara. "Structured fabrics with tunable mechanical properties." Nature, under minor revision.
[3] LC Li. "Emerging contact force heterogeneity in ordered soft granular media." To be submitted.
Bio: Dr. Liuchi Li is currently a postdoctoral research fellow at the Lawrence Berkeley National Laboratory (LBNL). He received his B.S. in Civil Engineering (with honor) from Tongji University in 2014 and his Ph.D. in Applied Mechanics with a minor in Applied and Computational Mathematics from the California Institute of Technology (Caltech) in 2020. His research interests lie in developing mechanistic and coherent multiscale understandings of how granular media collectively behave (e.g., solid-fluid phase transitions) and harnessing such understandings for engineering applications (e.g., designing adaptive structures).
Tuesday, March 23, 2021
3:00 pm
Host: Professor Madhu Venkadesan
Contact department for Zoom details.