About

Francois Barthelat is a professor in the Paul M. Rady Mechanical Engineering department at the University of Colorado Boulder. His research focuses on materials, bioinspiration, and micro-architecture, where he combines theoretical mechanics, numerical modeling, optimization, experimental mechanics, 3D printing, and biology to explore new material designs. His work aims to create materials that combine properties traditionally difficult to achieve simultaneously, such as stiff and impact-resistant materials that are also flexible or capable of morphing under different loading conditions. His research involves drawing inspiration from natural materials like bone, seashells, teeth, skin, and fish scales, and utilizing material architecture—integrating hard and soft materials, weak interfaces, and geometries—to control deformation and fracture mechanisms. Current projects include morphing materials inspired by fish fins, engineered granular materials, entangled matter, and innovative architectures for impact mitigation. His societal impact efforts focus on developing lighter, stronger, recyclable, and damage-healing materials that can lead to significant savings in transportation and have applications in robotics and biomedical devices.

Research topics

• Materials science
• Computer Science
• Composite material
• Biology
• Nanotechnology

Selected publications

• Stress Asymmetry in Hard Magnetic Soft Materials

  arXiv (Cornell University) · 2026-03-31

  preprintOpen access

  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.

  PublisherDOI

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

  Journal of Applied Physics · 2026-04-10

  preprintOpen accessSenior author

  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. However, there are major knowledge gaps on the entanglement mechanisms and how they can generate strength. In this report, we present tensile tests and discrete element method 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. Standard steel staples with θ = 90° crown-leg angle initially entangle better than θ = 20° modified staples because of their more “open” geometry. However, as vibrations are applied, entanglement increases faster in θ = 20° bundles so that they develop strong and stable tensile force chains, producing bundles which are almost ten times stronger than θ = 90° bundles. Both tensile strength and entanglement density increase with vibrations and with deformations, up to a steady state value where the rate of entanglement balances the rate of disentanglement. Finally, we show that vibration and mechanical confinement can be used as a strategy to manipulate entanglement and disentanglement for disassembly and recycling. This work provides a fundamental understanding of how particle geometry and vibrations govern the properties of entangled materials, which can lead to better design guidelines for lightweight, reversible materials and structures and aggregate architectures.

  PublisherDOI

• Stress Asymmetry in Hard Magnetic Soft Materials

  Journal of Applied Mechanics · 2026-03-30

  articleOpen access

  Abstract 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.

  PublisherOA PDFDOI

• Penetration and macroscale “hardness” of fully dense FCC granular crystals: experiments and models

  npj Metamaterials · 2026-03-13

  articleOpen accessSenior authorCorresponding

  The sharp penetration of granular materials is relevant to a variety of applications, including the locomotion of animals and robots on sandy grounds, defensive structures or civil constructions. In traditional granular materials, the grains “flow” around the advancing penetrator like a viscous liquid, which involves frictional dissipation but produces limited resistance to penetration. In this report, we explore the mechanical performance and mechanics of fully dense FCC granular crystals subjected to sharp penetration. These “granular metamaterials”, at the boundary between traditional granular materials and architected materials, are about 1000 times more resistant to penetration than traditional granular materials made of randomly distributed spheres. Using experiments and discrete element models, we show that despite the high mechanical confinement of the crystals, frictional sliding along specific slip planes is a prominent deformation mechanism up to the failure of the uppermost layer of grains. In addition, as the indenter is “wedged” between the grains, large compressive forces develop in the transverse directions, which eventually lead to the sudden buckling of the uppermost layer of grains, and to “explosive” failures involving the ejection of grains. As penetration proceeds, this loading-buckling cycle repeats, as layers are defeated in sequence. We finally show that once the surface layers of the crystal are destroyed by the penetrator, the crystal can be “healed” with vibrations and then punctured again with no loss of mechanical performance. These granular “metamaterials” can serve as a platform to develop additional strengthening strategies inspired by metallurgy, and they can find applications for rapid and versatile construction of static structures or as lightweight protective materials in a multitude of applications (e.g., buildings, body armor and vehicles).

  PublisherOA PDFDOI

• Comparing inelastic deformations and strength in dense FCC and HCP granular crystals: Experiments and models

  Journal of the Mechanics and Physics of Solids · 2025-07-28 · 1 citations

  articleSenior authorCorresponding
  PublisherDOI

• Strength, Stability and Interlocking Efficacy in Topologically Interlocked Materials Based on Tetrahedra and Octahedra

  SSRN Electronic Journal · 2025-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Tuning geometry in staple-like entangled particles: “pick-up” experiments and Monte Carlo simulations

  Granular Matter · 2025-05-19 · 6 citations

  articleOpen accessSenior author

  Abstract 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 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 finally 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.

  PublisherOA PDFDOI

• Tunable entanglement and strength with engineered staple-like particles: Experiments and discrete element models

  Journal of the Mechanics and Physics of Solids · 2025-03-31 · 5 citations

  articleSenior authorCorresponding
  PublisherDOI

• Strength, stability, and interlocking efficacy in topologically interlocked materials based on tetrahedra and octahedra

  International Journal of Solids and Structures · 2025-07-17 · 2 citations

  articleSenior author
  PublisherDOI

• Stiff morphing composite beams inspired from fish fins

  Interface Focus · 2024-06-01 · 2 citations

  articleOpen accessSenior authorCorresponding

  Morphing materials are typically either very compliant to achieve large shape changes or very stiff but with small shape changes that require large actuation forces. Interestingly, fish fins overcome these limitations: fish fins do not contain muscles, yet they can change the shape of their fins with high precision and speed while producing large hydrodynamic forces without collapsing. Here, we present a 'stiff' morphing beam inspired from the individual rays in natural fish fins. These synthetic rays are made of acrylic (PMMA) outer beams ('hemitrichs') connected with rubber ligaments which are 3-4 orders of magnitude more compliant. Combinations of experiments and models of these synthetic rays show strong nonlinear geometrical effects: the ligaments are 'mechanically invisible' at small deformations, but they delay buckling and improve the stability of the ray at large deformations. We use the models and experiments to explore designs with variable ligament densities, and we generate design guidelines for optimum morphing shape (captured using the first moment of curvature), that capture the trade-offs between morphing compliance (ease of morphing the structure) and flexural stiffness. The design guidelines proposed here can help the development of stiff morphing bioinspired structures for a variety of applications in aerospace, biomedicine or robotics.

  PublisherOA PDFDOI

Recent grants

• Mechanics of Crystallization, Deformation and Phase Transformation in Granular Materials with Engineered Grain Geometries

  NSF · $392k · 2021–2025

Frequent coauthors

• J. William Pro

  McGill University

  26 shared

• Mohammad Mirkhalaf

  Queensland University of Technology

  25 shared

• Ahmad Khayer Dastjerdi

  McGill University

  21 shared

• Reza Rabiei

  McGill University

  18 shared

• Florent Hannard

  UCLouvain

  17 shared

• Deju Zhu

  15 shared

• Horacio D. Espinosa

  Northwestern University

  14 shared

• Markus J. Buehler

  11 shared

Labs

• Barthelat LabPI

  Laboratory for Advanced Materials & Bioinspiration

Awards & honors

• Chwang-Seto Faculty Scholar, McGill University (2018)
• Visiting Professor, Institut d’Alembert, Jussieu, France (Ju…
• Department of National Defence /NSERC Discovery Grant Supple…
• Acta Biomaterialia Outstanding Reviewer (2015)
• Discovery Accelerator Supplement (2012-2015)