Influence of Normal Stress, Shear Velocity and Materials on Steady-State Shear Resistance and Viscosity of Rapid Dry Granular Flows
Hu, W., Y. Li, H. Gou, X. Jia, L. Zhou, and C. Chang
Journal of Geophysical Research Solid Earth 130, no. 6 (2025)
Résumé: Understanding the rheological behavior of rapid granular flows is crucial for understanding various geological processes, such as fast fault slip and rapid motion of landslides. In this study, we conducted rotary shear experiments on different granular materials, spanning a range of shear velocities from slow to rapid and under varying normal stresses, to investigate the evolution of mechanical behavior under different flow conditions. The experimental results showed that steady-state shear resistance varied with normal stress and material composition at shear velocities below 1 m/s. A consistent velocity-dependent trend was observed. The steady-state shear resistance of the sample experienced a transition from velocity-strengthening behavior at low shear velocities (below 0.1 m/s) to velocity-weakening behavior at higher shear velocities (above 0.1 m/s). Interestingly, at shear velocities exceeding 1 m/s, the steady-state shear resistance became independent of normal stress and material composition, converging to a similar steady-state value for both crushable and uncrushable materials. Although normal stress and mineral composition had a limited influence on steady-state shear resistance at high shear rates, they significantly affected the weakening rate (the transition from peak strength to steady-state shear resistance), which was strongly correlated with the material's crushing ability, as characterized by the Weibull modulus. These findings provide insights into the mechanisms governing the hypermobility of mega-landslides and the rapid dynamics of geological flows.
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Nonmonotonic Radiative Heat Transfer in the Transition from Far Field to Near Field
Guillemot, V., R. Messina, V. Krachmalnicoff, R. Carminati, P. Ben-Abdallah, W. Poirier, and Y. De Wilde
Physical Review Letters 134, no. 19 (2025)
Résumé: We present high precision measurements of the radiative heat transfer of a glass microsphere immersed in a thermal bath in vacuum facing three different planar substrates (SiO2, SiC, and Au), which exhibit very different optical behaviors in the infrared region. Using a thermoresistive probe on a cantilever, we show the nonmonotonic behavior of the radiative flux between the microsphere and its environment when the microsphere is brought closer to the substrate in the far-field to near-field transition regime. We demonstrate that this unexpected behavior is related to the singularities of dressed emission mechanisms in this three-body system sphere-substrate bath with respect to the separation distance.
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Sensitivity of Lamb waves in viscoelastic polymer plates to surface contamination
Spytek, J., D. A. Kiefer, R. K. Ing, C. Prada, J. Grando, and J. De Rosny
Ultrasonics 149, 107571 (2025)
Résumé: Detecting surface contamination on thin thermoformed polymer plates is a critical issue for various industrial applications. Lamb waves offer a promising solution, though their effectiveness is challenged by the strong attenuation and anisotropy of the polymer plates. This issue is addressed in the context of a calcium carbonate (CaCO3) layer deposited on a polypropylene (PP) plate. First, the viscoelastic properties of the PP material are determined using a genetic algorithm inversion of data measured with a scanning laser vibrometer. Second, using a bi-layer plate model, the elastic properties and thickness of the CaCO3 layer are estimated. Based on the model, the sensitivity analysis is performed, demonstrating considerable effectiveness of the A1 Lamb mode in detecting thin layers of CaCO3 compared to Lamb modes A0 and S0. Finally, a direct application of this work is illustrated through in-situ monitoring of CaCO3 contaminants using a straightforward inter-transducer measurement.
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Modeling conductive thermal transport in three-dimensional fibrous media with fiber-to-fiber contacts
Gaunand, C., Y. De Wilde, A. François, V. Grigorova-Moutiers, and K. Joulain
Physical Review Applied 23, no. 3 (2025)
Résumé: Understanding heat transfers in fibrous materials, particularly conduction, is a major challenge due to their heterogeneous and multiscale nature, and the unknown contribution of fiber-to-fiber contacts. In most previous modeling studies, the existence of thermal contact resistance is not considered, and the computational complexity limits the size of simulated samples, which often leads to imprecise or inaccurate predictions. The same problem arises when considering electrical conduction through fibrous materials. In this work, we describe a computationally efficient simulation approach based on a multinodal representation to analyze the steady-state heat conduction through the solid structure in numerically generated three-dimensional fibrous networks, including contact resistance. We show that the solid conductivity in these networks is governed by a master curve that depends on a single parameter: a characteristic ratio representing the interplay between the intrinsic fiber conductivity and contact resistance as well as the influence of other geometric parameters, which numerically validates previous theoretical studies. However, we observe a deviation to this established theory for poorly connected networks. We derive an expression for a correction factor, considering the influence of correlations between fiber temperatures, and we then find good agreement with our simulation data. Our results demonstrate that the solid conductivity can be fully predicted based on geometric quantities, regardless of the extent of network connectivity, thus generalizing previous studies on this topic. This work, contributing to improve our understanding of conductive heat transport in fibrous media, may prove useful in the development of accurate predictive models and optimization strategies for fibrous insulation materials.
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