arXiv subjects

Juan C. Petit

Publications and source records attributed to Juan C. Petit.

7 recordsLinked to original sources

arXiv2026

Percolation of a rod-like particle in a static bed of spheres: trapping and passing

We numerically investigate percolation of independent frictionless glued-sphere rod-like particles under gravity through a disordered static bed of larger spheres. We identify two distinct regimes: a \emph{trapping} regime, where rods stop after percolating a limited distance in the bed and a \emph{passing} regime, where rods percolate continuously with constant mean velocity. The transition between these regimes is governed by the length of the rod and the geometrical trapping threshold for spherical particles based on the rod diameter and the minimum pore throat diameter defined by three touching large spheres. The percolation velocity for all rod geometries, including the single sphere limit, collapses onto a single curve when scaled with the gravitational acceleration and the bed sphere diameter. The results also demonstrate that short rods percolate nearly twice as fast as long rods due to the geometric constraints associated with the disordered pore structure of the static bed. Consequently, long rods are more susceptible to trapping via specific contact configurations with the bed spheres, which differ from those for short rods. These results reveal how shape anisotropy introduces dynamical constraints and thresholds in granular percolation, with implications for predicting segregation in mixtures of non-spherical particles.

cond-mat.soft↗

arXiv2025

Vibrational similarities in jamming-unjamming of polycrystalline and disordered granular packings

We investigate the vibrational properties of polycrystalline monodisperse and disordered bidisperse granular packings during jamming and unjamming using discrete element method simulations. Both systems deviate from Debye scaling at low frequencies $(ω)$, but only bidisperse packings exhibit a low-$ω$ plateau. The low $ω$ exponent ($α$) in bidisperse packings evolves smoothly from zero (plateau) to near one (Debye scaling) with increasing packing fraction, whereas in polycrystalline packings, it changes discontinuously near jamming/unjamming, due to the nature of the contact network rearrangements. Despite structural modifications during the compression-decompression cycle, the exponent remains unchanged at the same distance from jamming density, regardless of the history. Nonaffine displacements and contact orientational order further confirm that structural features that impact low-$ω$ vibrational states and, hence, mechanical properties are largely restored upon decompression, reinforcing vibrational similarities between jamming and unjamming states.

cond-mat.soft↗

arXiv2025

Additional jamming transition in 2D bidisperse granular packings

We present a jamming diagram for 2D bidisperse granular systems, capturing two distinct jamming transitions. The first occurs as large particles form a jammed structure, while the second, emerging at a critical small-particle concentration, $X_{\mathrm{S}}^{*} \approx 0.21$, and size ratio, $δ^{*} \approx 0.25$, involves small particles jamming into the voids of the existing large-particle structure upon further compression. Below this threshold, small particles fill voids within the large-particle network, increasing packing density. Beyond this point, excess small particles disrupt efficient packing, resulting in looser structures. \jp{These results, consistent with previous 3D studies, demonstrate that the second transition occurs at a well-defined point in the $(X_{\mathrm{S}}, δ)$ plane, independent of dimensionality, likely driven by the geometric saturation of available space around particles, void closure, and structural arrangement.

cond-mat.soft↗

arXiv2023

Structural transitions in jammed asymmetric bidisperse granular packings

We study the local structural changes along the jamming transitions in asymmetric bidisperse granu\-lar packings. The local structure of the packing is assessed by the contact orientational order, $\tilde{Q}_{\ell}$, that quantifies the contribution of each contact configuration (Large-Large, Small-Small, Large-Small, Small-Large) in the jammed structure. The partial values of $\tilde{Q}_{\ell}$ are calculated with respect to known ordered lattices that are fixed by the size ratio, $δ$, of the particles. We find that the packing undergoes a structural transition at $ϕ_J$, manifested by a sudden jump in the partial $\tilde{Q}_{\ell}$. Each contact configuration contributes to the jammed structure in a different way, changing with $δ$ and concentration of small particles, $X_{\mathrm{S}}$. The results show not only that the packing undergoes a structural change upon jamming, but also that bidisperse packings exhibit local HCP and FCC structures also found in monodisperse packings. This suggests that the jammed structure of bidisperse systems is inherently endowed with local structural order. These results are relevant in understanding how the arrangement of particles determines the strength of bidisperse granular packings.

cond-mat.soft↗

arXiv2022

Bulk Modulus along Jamming Transition Lines of Bidisperse Granular Packings

We present 3D DEM simulations of bidisperse granular packings to investigate their jamming densities, $ϕ_J$, and dimensionless bulk moduli, $K$, as a function of the size ratio, $δ$, and the concentration of small particles, $X_{\mathrm S}$. We determine the partial and total bulk moduli for each packing and report the jamming transition diagram, i.e., the density or volume fraction marking both the first and second transitions of the system. At a large enough size difference, e.g., $δ\le 0.22$, $X^{*}_{\mathrm S}$ divides the diagram with most small particles either non-jammed or jammed jointly with large ones. We find that the bulk modulus $K$ jumps at $X^{*}_{\mathrm S}(δ= 0.15) \approx 0.21$, at the maximum jamming density, where both particle species mix most efficiently, while for $X_{\mathrm S} < X^{*}_{\mathrm S}$ $K$ is decoupled in two scenarios as a result of the first and second jamming transition. Along the second transition, $K$ rises relative to the values found at the first transition, however, is still small compared to $K$ at $X^{*}_{\mathrm S}$. While the first transition is sharp, the second is smooth, carried by small-large interactions, while the small-small contacts display a transition. This demonstrates that for low enough $δ$ and $X_{\mathrm S}$, the jamming of small particles indeed impacts the internal resistance of the system. Our new results will allow tuning the bulk modulus $K$ or other properties, such as the wave speed, by choosing specific sizes and concentrations based on a better understanding of whether small particles contribute to the jammed structure or not, and how the micromechanical structure behaves at either transition.

cond-mat.soft↗

arXiv2020

Additional transition line in jammed asymmetric bidisperse granular packings

We present numerical evidence for an additional discontinuous transition inside the jammed regime for an asymmetric bidisperse granular packing upon compression. This additional transition line separates jammed states with networks of predominantly large particles from jammed networks formed by both large and small particles, and the transition is indicated by a discontinuity in the number of particles contributing to the jammed network. The additional transition line emerges from the curves of jamming transitions and terminates in an end-point where the discontinuity vanishes. The additional line is starting at a size ratio around $δ= 0.22$ and grows longer for smaller $δ$. For $δ\to 0$, the additional transition line approaches a limit that can be derived analytically. The observed jamming scenarios are reminiscent of glass-glass transitions found in colloidal glasses.

cond-mat.soft↗

arXiv2018

Reduction of the bulk modulus with polydispersity in non-cohesive granular solids

We study the effect of grain polydispersity on the bulk modulus in non-cohesive two dimensional granular solids. Molecular dynamics simulations in two dimensions are used to describe polydisperse samples that reach a stationary limit after a number of hysteresis cycles. For stationary samples, we obtain that the packing with the highest polydispersity has the lowest bulk modulus. We compute the correlation between normal and tangential forces with grain size using the concept of {\it branch vector/contact length}. Classifying the contact lengths and forces by their size compared to the average length and average force respectively, we find that strong normal and tangential forces are carried by large contact lengths, generally composed of at least one large grain. This behavior is more dominant as polydispersity increases, making force networks more anisotropic and removing the support, from small grains, in the loading direction thus reducing the bulk modulus of the granular pack. Our results for two dimensions describe qualitatively the results of three dimensional experiments.

cond-mat.soft↗