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تسجيل مستخدم جديدStress anisotropy in shear-jammed packings of frictionless disks
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We perform computational studies of repulsive, frictionless disks to investigate the development of stress anisotropy in mechanically stable (MS) packings. We focus on two protocols for generating MS packings: 1) isotropic compression and 2) applied simple or pure shear strain $gamma$ at fixed packing fraction $phi$. MS packings of frictionless disks occur as geometric families (i.e. parabolic segments with positive curvature) in the $phi$-$gamma$ plane. MS packings from protocol 1 populate parabolic segments with both signs of the slope, $dphi/dgamma >0$ and $dphi/dgamma <0$. In contrast, MS packings from protocol 2 populate segments with $dphi/dgamma <0$ only. For both simple and pure shear, we derive a relationship between the stress anisotropy and dilatancy $dphi/dgamma$ obeyed by MS packings along geometrical families. We show that for MS packings prepared using isotropic compression, the stress anisotropy distribution is Gaussian centered at zero with a standard deviation that decreases with increasing system size. For shear jammed MS packings, the stress anisotropy distribution is a convolution of Weibull distributions that depend on strain, which has a nonzero average and standard deviation in the large-system limit. We also develop a framework to calculate the stress anisotropy distribution for packings generated via protocol 2 in terms of the stress anisotropy distribution for packings generated via protocol 1. These results emphasize that for repulsive frictionless disks, different packing-generation protocols give rise to different MS packing probabilities, which lead to differences in macroscopic properties of MS packings.
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