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1. Investigation of Murine Vaginal Creep Response to Altered Mechanical Loads

   https://doi.org/10.1115/1.4052365  

   Clark-Patterson, Gabrielle L.; McGuire, Jeffrey A.; Desrosiers, Laurephile; Knoepp, Leise R.; De Vita, Raffaella; Miller, Kristin S. (December 2021, Journal of Biomechanical Engineering)

   Abstract The vagina is a viscoelastic fibromuscular organ that provides support to the pelvic organs. The viscoelastic properties of the vagina are understudied but may be critical for pelvic stability. Most studies evaluate vaginal viscoelasticity under a single uniaxial load; however, the vagina is subjected to dynamic multiaxial loading in the body. It is unknown how varied multiaxial loading conditions affect vaginal viscoelastic behavior and which microstructural processes dictate the viscoelastic response. Therefore, the objective was to develop methods using extension-inflation protocols to quantify vaginal viscoelastic creep under various circumferential and axial loads. Then, the protocol was applied to quantify vaginal creep and collagen microstructure in the fibulin-5 wildtype and haploinsufficient vaginas. To evaluate pressure-dependent creep, the fibulin-5 wildtype and haploinsufficient vaginas (n = 7/genotype) were subjected to various constant pressures at the physiologic length for 100 s. For axial length-dependent creep, the vaginas (n = 7/genotype) were extended to various fixed axial lengths then subjected to the mean in vivo pressure for 100 s. Second-harmonic generation imaging was performed to quantify collagen fiber organization and undulation (n = 3/genotype). Increased pressure significantly increased creep strain in the wildtype, but not the haploinsufficient vagina. The axial length did not significantly affect the creep rate or strain in both genotypes. Collagen undulation varied through the depth of the subepithelium but not between genotypes. These findings suggest that the creep response to loading may vary with biological processes and pathologies, therefore, evaluating vaginal creep under various circumferential loads may be important to understand vaginal function. 

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2. Creep of CarbFix Basalt: Influence of Rock-fluid Interaction

   https://doi.org/10.5194/se-2021-114  

   Xing, T. (September 2021, Solid earth discussions)

   Geological carbon sequestration provides permanent CO2 storage to mitigate the current high concentration of CO2 in the atmosphere. CO2 mineralization in basalts has been proven to be one of the most secure storage options. For successful implementation and future improvements of this technology, the time-dependent deformation behavior of reservoir rocks in presence of reactive fluids needs to be studied in detail. We conducted load stepping creep experiments on basalts from the CarbFix site (Iceland) under several pore fluid conditions (dry, H2O-saturated and H2O+CO2-saturated) at temperature, T≈80 °C and effective pressure, Peff = 50 MPa, during which we collected mechanical, acoustic and pore fluid chemistry data. We observed transient creep at stresses as low as 11% of the ultimate failure strength, well below the stress level at the onset of bulk dilatancy. Acoustic emissions (AEs) correlated strongly with strain accumulation, indicating that the creep deformation was a brittle process in agreement with microstructural observations. The rate and magnitude of AEs were higher in fluid-saturated experiments than in dry conditions. We infer that the predominant mechanism governing creep deformation is time- and stress-dependent sub-critical dilatant cracking. Our results suggest that the presence of aqueous fluids exerts first order control on creep deformation of basaltic rocks, while the composition of the fluids plays only a secondary role under the studied conditions. 

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3. Fracture Characteristics of Shale: Unraveling CO2-Driven Mechanical Metamorphosis at Microscale

   https://doi.org/10.56952/ARMA-2024-0162  

   Mahgoub, S A; Abedi, S (June 2024, ARMA)

   ABSTRACT:This study investigates the distinction between unreacted shale samples and those exposed to CO2-rich brine under elevated temperature (100°C) and pressure (1800 psi) conditions over 28 days. Samples underwent scratch testing under constant loading to ensure independent penetration depth, circumventing variability associated with load-dependent outcomes prevalent in progressive loading methodologies. Vertical hardness profiles revealed significant variations between reacted and unreacted regions, influenced by differential dissolution and precipitation characteristics, while horizontal hardness provided limited insights, particularly in the reacted region where higher tangential forces and deeper scratches indicated greater material compressibility. Distinct scratch path variations were observed, with fractures absent in the ductile reacted region at lower testing forces. The shale samples were sourced from the Eagle Ford Formation, providing insights into the mechanical response of carbonate-rich shale rocks in extreme environments. This research enhances understanding of shale's mechanical properties and material responses under diverse operational conditions, elucidating interactions with influential environmental factors, particularly in CO2-exposed scenarios. Conducted at a microscale level, this study offers detailed insights into material behavior, crucial for predicting long-term stability of geostructures exposed to reactive brine and potential CO2 leakage in subsurface reservoirs. 1. INTRODUCTIONThe investigation into chemical interactions between carbonate rocks and acidic brine is cruical for understanding complex mechanical and microstructural transformations essential for applications like geostructure stability, CO2 storage, and energy exploitation. Under elevated pressure and temperature conditions, the equilibrium between injected fluids and rocks undergoes alterations, leading to geochemical responses, especially with the presence of CO2 as a supercritical phase or in aqueous form (Prakash et al. 2023a; Prakash et al. 2022). In this context, investigating fracture properties becomes essential, aiming to comprehend the development and propagation of fractures within reacted formations to evaluate structural integrity and potential pathways for fluid migration.Prior geochemical investigations have explored the localized repercussions of CO2 attacks on rock permeability, shedding light on alterations attributed to carbonate precipitation sealing fractures and pores or the dissolution of diverse minerals (Burnside et al. 2013; Minardi et al. 2021). Shale rocks exposed to acidic brine predominantly undergo carbonate reactions, particularly carbonates dissolution and precipitation (Prakash et al., 2022; Prakash et al. 2023b). Experimental studies on fracture mechanics and mechanical properties have utilized conventional methods such as single edge notched bend, chevron notched beam, three-point bending, and semi-circular bending tests, acknowledging their inherent limitations (Smith & Chowdary, 1975; Bazant and Kazemi, 1990; Helmer et al. 2014; Dubey et al., 2020). 

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4. Episodic Slow Slip Hosted by Talc‐Bearing Metasomatic Rocks: High Strain Rates and Stress Amplification in a Chemically Reacting Shear Zone

   https://doi.org/10.1029/2022GL101083  

   Hoover, W. F.; Condit, C. B.; Lindquist, P. C.; Moser, A. C.; Guevara, V. E. (November 2022, Geophysical Research Letters)

   Abstract Episodic tremor and slow slip (ETS) downdip of the subduction seismogenic zone are poorly understood slip behaviors of the seismic cycle. Talc, a common metasomatic mineral at the subduction interface, is suggested to host slow slip but this hypothesis has not been tested in the rock record. We investigate actinolite microstructures from talc‐bearing and talc‐free rocks exhumed from the depths of modern ETS (Pimu'nga/Santa Catalina Island, California). Actinolite deformed by dissolution‐reprecipitation creep in the talc‐free rock and dislocation creep ± cataclasis in the talc‐bearing rock. This contrast results from stress amplification in the talc‐bearing rock produced by high strain rates in surrounding weak talc. We hypothesize that higher strain rates in the talc‐bearing sample represent episodic slow slip, while lower strain rates in the talc‐free sample represent intervening aseismic creep. This work highlights the need to consider fluid‐mediated chemical change in studies of subduction zone deformation and seismicity. 

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5. Reassessing cold sintering in the framework of pressure solution theory

   https://doi.org/10.1016/j.jeurceramsoc.2022.09.053  

   Ndayishimiye, Arnaud (January 2023, Journal of the European Ceramic Society)

   Cold sintering densification and coarsening mechanisms are considered from the perspective of the nonequilibrium chemo-mechanical process known in Earth Sciences as pressure solution creep (or dissolutionprecipitation creep). This is an important mechanism of densification and deformation in many geological rock formations in the Earth’s upper crust, and although very slow in nature, it is of direct relevance to the cold sintering process. In cold sintering, we select particulate materials and identify experimental processing parameters to significantly accelerate the kinetics of dissolution-precipitation phenomena, with appropriate consideration of chemistry, applied stress, particle size and temperatures. In the theory of pressure solution, pressure-driven densification is considered to involve the consecutive stages of dissolution at grain contact points, then diffusive transport along the grain boundaries towards open pore surfaces, and then precipitation, all driven by chemical potential gradients. In this study, it is shown that cold sintering of BaTiO3, ZnO and KH2PO4 (KDP) ceramic materials proceeds by the same type of serial process, with the pressure solution creep rate being controlled by the slowest kinetic step. This is demonstrated by the values of activation energy (Ea) for densification, which are in good agreement with the existing literature on dissolution, precipitation, or coarsening. The influence of pressure on the morphology of ZnO grains also supports the pressure solution mechanism. Other characteristics that can be understood qualitatively in terms of pressure solution are observed in the in systems such as BaTiO3 and KDP. We further consider activation energies for grain growth with respect to the precipitation process, as well as evidence for coalescence and Ostwald ripening during cold sintering. For completeness we also consider materials that show significant plastic deformation under compression. Our findings point the way for new advances in densification, microstructural control, and reductions in cold sintering pressure, via the use of appropriate transient solvents in metals and hybrid organic-inorganic systems, such as the Methylammonium lead bromide (MAPBr) perovskite. 

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