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1. Scaling of relaxation and excess entropy in plastically deformed amorphous solids

   https://doi.org/10.1073/pnas.2000698117  

   Galloway, K. Lawrence; Ma, Xiaoguang; Keim, Nathan C.; Jerolmack, Douglas J.; Yodh, Arjun G.; Arratia, Paulo E. (June 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   When stressed sufficiently, solid materials yield and deform plastically via reorganization of microscopic constituents. Indeed, it is possible to alter the microstructure of materials by judicious application of stress, an empirical process utilized in practice to enhance the mechanical properties of metals. Understanding the interdependence of plastic flow and microscopic structure in these nonequilibrium states, however, remains a major challenge. Here, we experimentally investigate this relationship, between the relaxation dynamics and microscopic structure of disordered colloidal solids during plastic deformation. We apply oscillatory shear to solid colloidal monolayers and study their particle trajectories as a function of shear rate in the plastic regime. Under these circumstances, the strain rate, the relaxation rate associated with plastic flow, and the sample microscopic structure oscillate together, but with different phases. Interestingly, the experiments reveal that the relaxation rate associated with plastic flow at time t is correlated with the strain rate and sample microscopic structure measured at earlier and later times, respectively. The relaxation rate, in this nonstationary condition, exhibits power-law, shear-thinning behavior and scales exponentially with sample excess entropy. Thus, measurement of sample static structure (excess entropy) provides insight about both strain rate and constituent rearrangement dynamics in the sample at earlier times. 

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2. Brittle and ductile yielding in soft materials

   https://doi.org/10.1073/pnas.2401409121  

   Kamani, Krutarth M; Rogers, Simon A (May 2024, Proceedings of the National Academy of Sciences)

   Many soft materials yield under mechanical loading, but how this transition from solid-like behavior to liquid-like behavior occurs can vary significantly. Understanding the physics of yielding is of great interest for the behavior of biological, environmental, and industrial materials, including those used as inks in additive manufacturing and muds and soils. For some materials, the yielding transition is gradual, while others yield abruptly. We refer to these behaviors as being ductile and brittle. The key rheological signatures of brittle yielding include a stress overshoot in steady-shear-startup tests and a steep increase in the loss modulus during oscillatory amplitude sweeps. In this work, we show how this spectrum of yielding behaviors may be accounted for in a continuum model for yield stress materials by introducing a parameter we call the brittility factor. Physically, an increased brittility decreases the contribution of recoverable deformation to plastic deformation, which impacts the rate at which yielding occurs. The model predictions are successfully compared to results of different rheological protocols from a number of real yield stress fluids with different microstructures, indicating the general applicability of the phenomenon of brittility. Our study shows that the brittility of soft materials plays a critical role in determining the rate of the yielding transition and provides a simple tool for understanding its effects under various loading conditions. 

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3. Influence of Environmental Surroundings on the Mechanical Properties of Ultrathin Polymer Membranes

   https://doi.org/10.1002/pol.20250562  

   Bay, R Kōnane (September 2025, Journal of Polymer Science)

   ABSTRACT Polymer thin films are critical for many applications, including water filtration and gas separation membranes. In these applications, polymer films can experience elevated temperatures, elevated pressures/pressure gradients, and varying liquid/gas environments. However, the majority of work on the mechanical properties of ultrathin polymer films has focused on the impact of thickness at ambient conditions. In contrast, less work has focused on the effect of non‐ambient environmental conditions. This perspective reviews the bulk and thin film literature on how environmental conditions can influence the solid mechanics of glassy polymers, highlighting the unresolved questions that remain. We focus on two dense polymer thin film membrane applications: water desalination and CO₂capture. These applications will benefit from investigating the influence of environmental operating conditions on their mechanical properties. To accomplish these studies, tensile testers for ultrathin films will need to be modified to measure the impact of temperature (heating stage), liquid interactions (liquid support layer), and gas interactions (instrument enclosure). Measuring the influence of hydraulic pressure on the thin film mechanical properties will require a creative approach in the future. Modifying these instruments will yield future studies on the impact of the surrounding environment on the solid mechanics of ultrathin polymer films. 

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4. Constitutive Behavior of Olivine Gouge Across the Brittle‐Ductile Transition

   https://doi.org/10.1029/2023GL105916  

   Barbot, Sylvain; Zhang, Lei (December 2023, Geophysical Research Letters)

   Abstract The bottom of the lithosphere is characterized by a thermally controlled transition from brittle to ductile deformation. While the mechanical behavior of rocks firmly within the brittle and ductile regimes is relatively well understood, how the transition operates remains elusive. Here, we study the mechanical properties of pure olivine gouge from 100 to 500°C under 100 MPa pore‐fluid pressure in a triaxial deformation apparatus as a proxy for the mechanical properties of the upper mantle across the brittle‐ductile transition. We describe the mechanical data with a rate‐, state‐, and temperature‐dependent constitutive law with multiple thermally activated deformation mechanisms. The stress power exponents decrease from 70 ± 10 in the brittle regime to 17 ± 3 and 4 ± 2 in the semi‐brittle and ductile regimes, respectively. The mechanical model consistently explains the mechanical behavior of olivine gouge across the brittle‐ductile transition, capturing the gradual evolution from cataclasis to crystal plasticity. 

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5. The Brittle–Ductile Transition and the Formation of Compaction Bands in the Savonnières Limestone: Impact of the Stress and Pore Fluid

   https://doi.org/10.1007/s00603-022-02963-z  

   Sari, Mustafa; Sarout, Joel; Poulet, Thomas; Dautriat, Jeremie; Veveakis, Manolis (January 2022, Rock Mechanics and Rock Engineering)

   Abstract Carbonate sediments play a prominent role on the global geological stage as they store more than $$60\%$$ 60 % of world’s oil and $$40\%$$ 40 % of world’s gas reserves. Prediction of the deformation and failure of porous carbonates is, therefore, essential to minimise reservoir compaction, fault reactivation, or wellbore instability. This relies on our understanding of the mechanisms underlying the observed inelastic response to fluid injection or deviatoric stress perturbations. Understanding the impact of deformation/failure on the hydraulic properties of the rock is also essential as injection/production rates will be affected. In this work, we present new experimental results from triaxial deformation experiments carried out to elucidate the behaviour of a porous limestone reservoir analogue (Savonnières limestone). Drained triaxial and isotropic compression tests were conducted at five different confining pressures in dry and water-saturated conditions. Stress–strain data and X-ray tomography images of the rock indicate two distinct types of deformation and failure regimes: at low confinement (10 MPa) brittle failure in the form of dilatant shear banding was dominant; whereas at higher confinement compaction bands orthogonal to the maximum principal stress formed. In addition to the pore pressure effect, the presence of water in the pore space significantly weakened the rock, thereby shrinking the yield envelope compared to the dry conditions, and shifted the brittle–ductile transition to lower effective confining pressures (from 35 MPa to 29 MPa). Finally, permeability measurements during deformation show a reduction of an order of magnitude in the ductile regime due to the formation of the compaction bands. These results highlight the importance of considering the role of the saturating fluid in the brittle–ductile response of porous rocks and elucidate some of the microstructural processes taking place during this transition. 

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