Emerging contact force heterogeneity in ordered soft granular media
Under external perturbations, inter-particle forces in disordered granular media are well known to form a heterogeneous distribution with filamentary patterns. Better understanding these forces and the distribution is important for predicting the collective behavior of granular media, the media second only to water as the most manipulated material in global industry. However, studies in this regard so far have been largely confined to granular media exhibiting only geometric heterogeneity, leaving the dimension of mechanical heterogeneity a rather uncharted area. Here, through a FEM contact mechanics model, we show that a heterogeneous inter-particle force distribution can also emerge from the dimension of mechanical heterogeneity alone. Specifically, we numerically study inter-particle forces in packing of mechanically heterogeneous disks arranged over either a square or a hexagonal lattice and under quasi-static isotropic compression. Our results show that, at the system scale, a hexagonal packing exhibit a more heterogeneous inter-particle force distribution than a square packing does; At the particle scale, for both packing lattices, preliminary analysis shows the consistent coexistence of outliers (i.e., softer disks sustaining larger forces while stiffer disks sustaining smaller forces) in comparison to their homogeneous counterparts, which implies the existence of nonlocal effect. Further analysis on the portion of outliers and on spatial contact force correlations suggest that the hexagonal packing shows more pronounced nonlocal effect over the square packing under small mechanical heterogeneity. However, such trend is reversed when assemblies becomes more mechanically heterogeneous. Lastly, we confirm that, in the absence of particle reorganization events, contact friction merely plays the role of packing stabilization while its variation has little effect on inter-particle forces and their distribution.
Additional Information© 2021 Elsevier. Received 31 May 2021, Revised 29 July 2021, Accepted 3 September 2021, Available online 11 September 2021. The authors would like to thank Dr. Ruobing Bai of Northeastern University and Dr. Siavash Monfared of Caltech for valuable comments on this paper. Part of the FEM contact mechanics implementation benefits from the computational mechanics course (AE/ME 108a) L.L. took in the fall of 2014 as a graduate student at Caltech. L.L. thanks the partial financial support provided by the Laboratory Directed Research and Development (LDRD) funding and the US Department of Energy (DOE), the Office of Nuclear Energy, Spent Fuel and Waste Disposition Campaign , under Contract No. DE-AC02-05CH11231 with Berkeley Lab. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Published - 1-s2.0-S0167663621002799-main.pdf
Accepted Version - 2108.00512.pdf
Supplemental Material - 1-s2.0-S0167663621002799-mmc1.pdf