We study the influence of relative humidity (RH) on the nonlinear elastic response of granular media. Previous work has shown that the nonlinear elastic response of consolidated granular media like rocks likely arises from two distinct mechanisms; however, we do not have a clear understanding of their physical origins at the microscopic scale. Here, we conduct dynamic acousto-elastic testing (DAET) on samples of glass beads under dry (∼10%), ambient (∼60%), and humid (∼100%) conditions at room temperature and a constant static stress of 4 MPa. DAET allows us to retrieve the full nonlinear elastic response, including transient softening and hysteretic effects. We find that the elastic nonlinearity of humid samples is an order of magnitude larger than dry samples. Moreover, we find that all extracted nonlinear parameters increase with RH. This overall increase in nonlinearity is consistent with findings from previous studies and with the hypothesis that water adsorption on the grains makes the contact junctions weaker and prone to greater disturbances when subjected to dynamic stressing. Our results also suggest that, if indeed both mechanisms coexist, they are affected in a similar fashion in these glass bead samples and cannot be distinguished by varying RH.
This study focuses on unraveling the microphysical origins of the nonlinear elastic effects, which are pervasive in the Earth's crust. Here, we examine the influence of grain shape on the elastic nonlinearity of granular assemblies. We find that the elastic nonlinearity of angular sand particles is of the same order of magnitude as that previously measured in spherical glass beads. However, while the elastic nonlinearity of glass beads increases by an order of magnitude with RH that of sand particles is rather RH independent. We attribute this difference to the angularity of sand particles: absorbed water on the spherical grains weakens the junctions making them more nonlinear, while no such effect occurs in sand due to grain interlocking. Additionally, for one of the nonlinear parameters that likely arises from shearing/partial slip of the grain junctions, we observe a sharp amplitude threshold in sand which is not observed in glass beads.
This study focuses on unraveling the microphysical origins of the nonlinear elastic effects, which are pervasive in the Earth’s crust. Here, we examine the influence of grain shape on the elastic nonlinearity of granular assemblies. We find that the elastic nonlinearity of angular sand particles is of the same order of magnitude as that previously measured in spherical glass beads. However, while the elastic nonlinearity of glass beads increases by an order of magnitude with RH, that of sand particles is rather RH independent. We attribute this difference to the angularity of sand particles: absorbed water on the spherical grains weakens the junctions making them more nonlinear, while no such effect occurs in sand due to grain interlocking. Additionally, for one of the nonlinear parameters that likely arises from shearing/partial slip of the grain junctions, we observe a sharp amplitude threshold in sand which is not observed in glass beads.
This study focuses on unraveling the microphysical origins of the nonlinear elastic effects, which are pervasive in the Earth’s crust. Here, we examine the influence of grain shape and relative humidity (RH) on the elastic nonlinearity of granular assemblies made of spherical glass beads and angular sand particles. We find that their elastic nonlinearity is of the same order of magnitude. However, while the elastic nonlinearity of glass beads increases with RH, that of sand particles is rather RH independent. We attribute this difference to the angularity of sand particles; absorbed water on the spherical grains weakens the junctions making them more nonlinear, while no such effect occurs in sand due to grain interlocking. Additionally, for one of the nonlinear parameters that likely arises from shearing/partial slip of the grain junctions, we observe a sharp amplitude threshold in sand which is not observed in glass beads.
Compared to standard nonlinear ultrasonic techniques based on harmonic generation or resonance tests that provide an average nonlinearity level, Dynamic Acousto-Elastic Testing (DAET) is a pump-probe approach that allows one to track the nonlinear elastic response at each phase of the dynamic cycle, and to quantify additional features such as transient softening/weakening and hysteresis. These so-called nonlinear signatures can help us unravel the origins of the nonlinear response at the micro/mesoscopic scale. In this talk, we first review some of the DAET results obtained by our group and others in a wide range of materials from cracked metals to rocks and unconsolidated granular media. Next, we present some of our most recent results where we investigate the effect of relative humidity (RH) on the nonlinear elastic response of granular media. We use DAET on samples of glass beads under dry (∼10%), ambient (∼60%) and humid (∼100%) conditions. We find that all extracted nonlinear parameters in humid samples increases by an order of magnitude compared to those in dry samples. This is consistent with the idea that water adsorption on the grains makes the contact junctions weaker. This has great relevance when trying to quantify the nonlinearity of porous materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.