|Title||Microscopic Origins of Shear Jamming for 2D Frictional Grains|
|Author(s)||Wang, Dong; Ren, Jie; Dijksman, Joshua A.; Zheng, Hu; Behringer, Robert P.|
|Source||Physical Review Letters 120 (2018)20. - ISSN 0031-9007|
Physical Chemistry and Soft Matter
|Publication type||Refereed Article in a scientific journal|
Shear jamming (SJ) occurs for frictional granular materials with packing fractions φ in φS<φ<φJ0, when the material is subject to shear strain γ starting from a force-free state. Here, φJμ is the isotropic jamming point for particles with a friction coefficient μ. SJ states have mechanically stable anisotropic force networks, e.g., force chains. Here, we investigate the origins of SJ by considering small-scale structures - trimers and branches - whose response to shear leads to SJ. Trimers are any three grains where the two outer grains contact a center one. Branches occur where three or more quasilinear force chain segments intersect. Certain trimers respond to shear by compressing and bending; bending is a nonlinear symmetry-breaking process that can push particles in the dilation direction faster than the affine dilation. We identify these structures in physical experiments on systems of two-dimensional frictional discs, and verify their role in SJ. Trimer bending and branch creation both increase Z above Ziso≃3 needed for jamming 2D frictional grains, and grow the strong force network, leading to SJ.