arXiv subjects

Francois Barthelat

Publications and source records attributed to Francois Barthelat.

5 recordsLinked to original sources

arXiv2026

Nonlinear force response of modular lattice-based metamaterials

Lattice-based metamaterials provide lightweight platforms where local instabilities can govern the global mechanical response, enabling applications in energy routing, vibration isolation, and impact mitigation. Although much progress has been made in controlling deformation and buckling sequences through geometric design, the behavior of coupled nonlinear units over a large range of strain rates and their history-dependent response is less explored. Here, we investigate lattice-based mechanical metamaterials whose nonlinear buckling behavior can be harnessed through modular architectures. By combining modular units in series, we show that their interaction gives rise to emergent force responses, including transient weakening and enhanced force attenuation, that are absent in the individual modules. Furthermore, selected designs exhibit training behavior under cyclic loading, transitioning between distinct buckling states and revealing a history-dependent mechanical response. Our results demonstrate that modular, instability-driven metamaterials can be programmed and tuned not only through geometry but also through loading history, opening new avenues for designing a nonlinear stress-response in mechanical systems.

cond-mat.soft↗

arXiv2026

Stress Asymmetry in Hard Magnetic Soft Materials

Hard magnetic soft materials -- soft polymers embedded with hard magnetic particles -- are modeled using continuum magnetomechanical formulations in which the deformation and the magnetization field are the primary kinematic variables. A recent question in such formulations is whether the Cauchy stress is symmetric, which is directly related to frame invariance and angular momentum balance. This note discusses energetically equivalent formulations, related by a change of variables between referential and current descriptions of the magnetization, and shows that they generally yield different Cauchy stresses, including a change in their symmetry. Specifically, the formulation based on a referential magnetization produces a symmetric Cauchy stress, while that based on a current magnetization generally yields an asymmetric Cauchy stress. We highlight that when the internal variable (magnetization field) is at the energy-minimizing equilibrium configuration, the divergences of these stresses are the same, and both stresses are symmetric.

cond-mat.mtrl-sci↗

arXiv2025

Combined effects of particle geometry and applied vibrations on the mechanics and strength of entangled materials

Entangled materials offer attractive structural features including tensile strength and large deformations, combined with infinite assembly and disassembly capabilities. How the geometry of individual particles governs entanglement, and in turn translates into macroscopic structural properties, provides a rich landscape in terms of mechanics and offers intriguing possibilities in terms of structural design. Despite this potential, there are major knowledge gaps on the entanglement mechanisms and how they can generate strength. In particular, vibrations are known to have strong effects on entanglement and disentanglement but the exact mechanisms underlying these observations are unknown. In this report we present tensile tests and discrete element method (DEM) simulations on bundles of entangled staple-like particles that capture the combined effects of particle geometry and vibrations on local entanglement, tensile force chains and strength. We show that standard steel staples with $θ= 90^\circ$ crown-leg angle initially entangle better than $θ= 20^\circ$ modified staples because of their more "open" geometry. However, as vibrations are applied entanglement increase faster in $θ= 20^\circ$ bundles, so that they develop strong and stable tensile force chains, producing bundles which are almost ten times stronger than $θ= 90^\circ$ bundles. Both tensile strength and entanglement density increase with vibrations and also with deformations, up to a steady state value. At that point the rate of entanglement equals the rate of disentanglement, and each of these rates remains relatively high. Finally, we show that vibration can be used as a manipulation strategy to either entangle or disentangle staple-like entangled granular materials, with confinement playing a significant role in determining whether vibration promotes entanglement or disentanglement.

cond-mat.soft↗

arXiv2024

Facile "Pick-up" experiments and Monte Carlo simulations for the entanglement of tunable staple-like particles

Entangled matter provides intriguing perspectives in terms of deformation mechanisms, mechanical properties, assembly and disassembly. However, collective entanglement mechanisms are complex, occur over multiple length scales, and they are not fully understood to this day. In this report, we propose a simple pick-up test to measure the entanglement in staple-like particles with various leg lengths, crown-leg angles, and backbone thickness. We also present a new "throw-bounce-tangle" model based on a 3D geometrical entanglement criterion between two staples, and a Monte Carlo approach to predict the probabilities of entanglement in a bundle of staples. This relatively simple model is computationally efficient and it predicts an average density of entanglement which is consistent with the entanglement strength measured experimentally. Entanglement is very sensitive to the thickness of the backbone of the staples, even in regimes where that thickness is a small fraction (<0.04) of the other dimensions. We demonstrate an interesting use for this model to optimize staple-like particles for maximum entanglement. New designs of tunable "entangled granular metamaterials" can produce attractive combinations of strength, extensibility, and toughness that may soon outperform lightweight engineering materials such as solid foams and lattices.

cond-mat.soft↗

arXiv2024

Tunable entanglement and strength in "granular metamaterials" based on staple-like particles: Experiments and discrete element models

Entangled matter displays unusual and attractive properties and mechanisms: tensile strength, capabilities for assembly and disassembly, damage tolerance. While some of the attributes and mechanisms share some traits with traditional granular materials, fewer studies have focused on entanglement and strength and there are large gaps in our understanding of the mechanics of these materials. In this report we focus on the tensile properties and mechanics of bundles made of staple-like particles, and particularly on the effect of adjusting the angle between the legs and the crown in individual staples. Our experiments, combined with discrete element models, show competing mechanisms between entanglement strength and geometric engagement between particles, giving rise to an optimum crown-leg angle that maximizes strength. We also show that tensile forces are transmitted by a small fraction of the staples, which is organized in only 1-3 force chains. The formation and breakage of these chains is highly dynamic: as force chains break, they are replaced by fresh ones which were previously mechanically invisible. Entangled matter as "granular metamaterials" offer interesting perspectives in terms of materials design, and a vast design space for individual particles. Since their properties can be tuned with the shape of the staple, we interpret these entangled materials are "granular metamaterials" with unusual combination of properties: simultaneous strength and toughness, controlled assembly and disassembly, re-conformability, recyclability.

cond-mat.soft↗