Critical State Research Articles

Particle crushing and critical state of volcanic pumice – 2018 Hokkaido Eastern Iburi Earthquake

Volcanic pumice, with special characteristics such as crushable particles and high water retention, is distributed throughout Japan and serves as the source layer for slope hazards characterised by post-failure gentle slope flows and long-distance flows. The aim of this study is to determine the relationship between the crushing characteristics and the mechanical properties of porous pumice, which often contributes to such disasters. As the porous pumice material, Ta-d pumice, which caused numerous slope disasters during the 2018 Hokkaido Eastern Iburi Earthquake in Japan, was collected and subjected to a series of triaxial compression tests. The grain size distribution of the pumice before all the tests was adjusted to be uniform, and the amount of crushing was quantified by measuring the grain size distribution after the tests. The results suggest that the critical state and isotropic consolidation of porous pumice can be systematically expressed in a three-dimensional space with the axes of the void ratio, mean effective stress, and degree of particle crushing. Furthermore, a gentle slope disaster with an inclination of less than 21°, that had occurred at the site from which the Ta-d pumice was collected, was discussed in terms of its flow potential, showing that the flow distance can be adequately explained.

Installation of open-ended piles: A numerical investigation into the effects on the state of silica sand

Up to this day, there are great uncertainties in the design procedures of monopiles, especially concerning the soil state condition and penetration response during their installation. A numerical model, based on the Coupled Eulerian method and using the hypoplastic law with intergranular strain, is proposed and validated in this paper, after which a series of open-ended pile installation tests have been carried out numerically, to investigate the influence of the jacked installation on the initial conditions for three types of silica sand. A range of soil densities and pile diameters is considered in this analysis. A full investigation of the installation forces, stress level, changes in volume-stress level and voids ratio is conducted. The numerical solution provided a correlation between the penetration resistance and the granulometric properties of the studied sands. Subsequently, the radial stresses in the surrounding soil mass are correlated with the type of sand and its relative density. The stress-volume state of a set of points in the soil domain during installation is presented and discussed from the critical state framework, revealing the contribution of the in-situ state in the pile installation. Finally, the lateral earth pressure resulting after installation is presented.

Neutral plane of single pile in clay subjected to surcharge loading using the “critical state soil mechanics” (CSSM)

ABSTRACT Piles are designed to support direct loads, however, floating piles in clay are often subjected to indirect loading (surcharge). In this case, the pile’s shaft will be subjected to negative skin friction on part or on its full length, depending on the value of the surcharge, soil condition and pile’s length. The total negative skin friction acting on the pile’s shaft is known as the drag-load, which will reduce the pile capacity and perhaps pull the pile out of its cap, leading to catastrophic failure of the structure. A numerical model was developed using the finite element technique to simulate the case of a single pile floating in clay subjected to surcharge. The model utilizes the concept of the Critical State Soil Mechanics (CSSM) and the constitutive law of the Modified Cam Clay (MCC). The MCC is capable of incorporating the effect of soil deformation and the stress history into the stresses acting on the pile’s shaft. It is widely used in modelling geomechanics problems. The objective of this study is to determine the location of the neutral plane on the pile’s shaft for a given surcharge, soil condition and pile’s length. Thus, the positive and negative skin frictions acting on the pile’s shaft can be determined and accordingly the pile capacity. After validating the numerical models with the data available in the literature, the model was used to generate a wide range of data, which commonly used in practice, to examine the effect of the parameters which govern the location of the neutral plane for these piles. Design charts and design example are presented.

A shear‐transformation‐zone model for time‐dependent behaviours of clay

AbstractA shear‐transformation‐zone (STZ) model is proposed for time‐dependent behaviours of clay, in which the viscoplastic deformation is described by the evolution of a temperature‐like state variable. The model is featured by rate‐dependent dilatancy and a unique critical state stress ratio. In its present form, it has nine parameters, most of which can be handily calibrated, and can predict the rate‐dependent undrained shear strength, primary, and secondary creep, as well as stress relaxation for normally consolidated clay under complex stress paths using a single set of parameters. The capabilities of the model have been verified by available experimental results on five different clays.

Delineating the effects of ignition propensity and Markstein number on deflagration-to-detonation transition

Although the process through which a deflagration transitions to a detonation (DDT) has been studied for over a century, it is not well-understood how the propensity for DDT varies among different combustible mixtures. We investigate the effect of two fundamental mixture properties, ignition delay (τign) and Markstein number (Ma), on this stochastic process. Experiments were conducted in a smooth cylindrical tube, and the critical state (characterized by the velocity of the reacting front) at which a detonation formed from an accelerating deflagration was measured. The novelty of the study lies in the selection of mixture compositions that enabled changing only one relevant combustion property at a time and hence isolating the sensitivity to that property. Experiments with mixtures with similar deflagrative properties but different τign revealed that the critical state is not measurably sensitive to ignition propensity. Mixtures studied with different thermo-diffusive properties revealed that Ma has a strong effect on the critical state. Specifically, thermo-diffusively-unstable mixtures (with low Ma) underwent DDT at significantly lower velocities. Furthermore, experiments were performed with and without a spiral to isolate the effect of flame wrinkling and turbulence. The spiral-affected flames underwent DDT at lower velocities, similar to thermo-diffusively-unstable mixtures. This observed effect of thermo-diffusive nature of the mixture and turbulence on DDT propensity is not predicted by existing models.

MODELING MOBILE SHALES UNDER CONTRACTION: CRITICAL ANALYSES OF NEW ANALOG SIMULATIONS OF SHALE TECTONICS AND COMPARISON WITH SALT-BEARING SYSTEMS

Weak substrates, such as salt and mobile shales, exert a strong control on deformation styles in all structural settings, especially those undergoing contraction. Despite both materials being very weak, they are mechanically very different. Salt is weak and will flow in a ductile fashion under most geologic conditions, whereas shales only become mobile after reaching critical state. Many sandbox-style physical or analog modeling studies have typically utilized a salt analog, viscous silicone polymer, as a proxy for mobile shales. However, to more accurately model mobile shale behavior the model material needs to exhibit a yield strength. One such material is Carbopol which is made up of micro-gel grains that are elasto-plastic, separated by a viscous interstitial ?uid. The abundance of the grains depends on the concentration of the mixture. Our results show that Carbopol does behave much differently than the traditional salt analog during contraction. PDMS typically undergoes bulk deformation and inflation under contraction, whereas Carbopol forms discrete, intense shear zones, and contains zones of little to no strain where its yield strength has not been exceeded. Below the shale analog, brittle layers typically form imbricate thrust stacks, jacking up the overburden, with shear zones propagating out from thrust tips along and through the shale proxy. Strain analyses reveal complex switching of activity within the Carbopol and overlying sediments. Models reveal that even a very thin layer of Carbopol can act as a highly-efficient detachment, and form more geologically realistic shortening structures, especially where these detachments are vertically stacked and horizontally offset. We believe that Carbopol is a powerful mobile-shale analog and opens new modeling directions because, as far as we are aware, this material has never been incorporated into a traditional sandbox model. Future work will seek to incorporate this material into more complex and three-dimensional sandbox-style models.

Superconductivity in atomically thin films: Two-dimensional critical state model

The comprehensive understanding of superconductivity is a multiscale task that involves several levels, starting from the electronic scale determining the microscopic mechanism, going to the phenomenological scale describing vortices and the continuum-elastic scale describing vortex matter, to the macroscopic scale relevant in technological applications. The prime example for such a macro-phenomenological description is the Bean model that is hugely successful in describing the magnetic and transport properties of bulk superconducting devices. Motivated by the development of novel devices based on superconductivity in atomically thin films, such as twisted-layer graphene, here, we present a simple macro-phenomenological description of the critical state in such two-dimensional (2D) thin films. While transverse screening and demagnetization can be neglected in these systems, thereby simplifying the task in comparison with usual film- and platelet-shaped samples, surface and bulk pinning are important elements to be included. We use our 2D critical state model to describe the transport and magnetic properties of 2D thin-film devices, including the phenomenon of nonreciprocal transport in devices with asymmetric boundaries and the superconducting diode effect. Published by the American Physical Society 2024

PERCUTANEOUS EDGE–TO–EDGE REPAIR OF MITRAL REGURGITATION IN CARDIAC AMYLOIDOSIS: DO IT BUT NOT TOO MUCH

Abstract We report the case of a 68 year old man with history of wild type TTR cardiac amyloidosis, treated with tafamidis since 1 year, symptomatic for advanced cardiac failure, already in optimal medical treatment, CRT–D, oral anticoagulation for permanent atrial fibrillation. The patient was hospitalised in our intensive care unit for refractory NYHA IV cardiac failure, anuria, very low ejection fraction combined with severe mitral regurgitation. He was treated with inotropes and diuretics then levosimendan however he remained in very critical state and we discussed the opportunity to reduce the mitral regurgitation by percutaneous edge to edge repair. In this setting of restrictive physiology literature is not unanimous and preload reduction secondary to mitral regurgitation treatment may sometimes be deleterious. We decided to offer our patient edge to edge repair by targeting a moderate reduction of mitral regurgitation and also considering some challenges linked to this pathology as atrial septal involvement with ovalis fossa relevant thickness. The procedure was successful with a reduction of mitral regurgitation grade from severe to mild–to moderate and this allowed the patient to re equilibrate his hemodynamic balance and he was able to be dismissed with a short term follow up program.

The Collapse Mechanism of Slope Rill Sidewall under Composite Erosion of Freeze-Thaw Cycles and Water

The composite erosion of freeze-thaw and water flow on slope rills is characterized by periodicity and spatial superposition. When revealing the collapse mechanism of slope rill sidewalls under the composite erosion of freeze-thaw and water flow, it is necessary to fully consider the effect of water migration and its impact on the stability of the rill sidewall. In this paper, we placed the self-developed collapse test system in an environmental chamber to carry out model tests on rill sidewall collapse on slopes under the composite erosion of freeze-thaw and water flow. We utilized three-dimensional reconstruction technology and the fixed grid coordinate method to reproduce the collapse process of the rill sidewall and precisely locate the top crack. We obtained the relationship between the water content of the specimen and mechanical indexes through the straight shear test. The main conclusions are as follows: The soil structure of the rill sidewall is significantly affected by the freeze-thaw cycle, which benefits capillary action in the soil. One freeze-thaw cycle has the most serious effect on the soil structure of the rill sidewall, and the change in the moisture field is more intense after the soil temperature drops below zero. The friction angle of the soil increases with the number of freeze-thaw cycles and tends to stabilize gradually. The effect of the freeze-thaw cycle on the rate of change of the water content of the soil at each position of the wall can be accurately described by a logarithmic function. The expression of the two-factor interaction effect on the rate of change of water content of soil at each position of the rill sidewall can be accurately fitted. We propose a calculation system for locating cracks at the top of the rill sidewall and determining the critical state of instability and collapse of the rill sidewall during the process of freeze-thaw and water flow composite erosion. The results of this research can help improve the accuracy of combined freeze-thaw and water flow erosion test equipment and the development of a prediction model for the collapse of the rill sidewall under compound erosion. This is of great significance for soil and water conservation and sustainability.

Heterogeneity, Bayesian thinking, and phenotyping in critical care: A primer.

In an effort to expedite the publication of articles, AJHP is posting manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time. To familiarize clinicians with the emerging concepts in critical care research of Bayesian thinking and personalized medicine through phenotyping and explain their clinical relevance by highlighting how they address the issues of frequent negative trials and heterogeneity of treatment effect. The past decades have seen many negative (effect-neutral) critical care trials of promising interventions, culminating in calls to improve the field's research through adopting Bayesian thinking and increasing personalization of critical care medicine through phenotyping. Bayesian analyses add interpretive power for clinicians as they summarize treatment effects based on probabilities of benefit or harm, contrasting with conventional frequentist statistics that either affirm or reject a null hypothesis. Critical care trials are beginning to include prospective Bayesian analyses, and many trials have undergone reanalysis with Bayesian methods. Phenotyping seeks to identify treatable traits to target interventions to patients expected to derive benefit. Phenotyping and subphenotyping have gained prominence in the most syndromic and heterogenous critical care disease states, acute respiratory distress syndrome and sepsis. Grouping of patients has been informative across a spectrum of clinically observable physiological parameters, biomarkers, and genomic data. Bayesian thinking and phenotyping are emerging as elements of adaptive clinical trials and predictive enrichment, paving the way for a new era of high-quality evidence. These concepts share a common goal, sifting through the noise of heterogeneity in critical care to increase the value of existing and future research. The future of critical care medicine will inevitably involve modification of statistical methods through Bayesian analyses and targeted therapeutics via phenotyping. Clinicians must be familiar with these systems that support recommendations to improve decision-making in the gray areas of critical care practice.

Undrained cavity expansion-contraction analysis in CASM and its application for pressuremeter tests

Many geotechnical scenarios involve cavity unloading from a loaded state, particularly in pressuremeter tests, and the unloading data of pressuremeter tests has exceptional attraction as it is less disturbed by the insertion process. However, the analyses for continuous cavity loading and unloading (i.e., cavity initially experiences expansion and then contracts) in critical state soils are rarely studied. To this end, a novel semi-analytical solution based on the unified state parameter model for clay and sand (CASM) is proposed for the whole expansion-contraction of spherical and cylindrical cavities under undrained condition. The problem assumes that the cavity is unloaded after a monotonic loading stage, leading to plastic regions during both loading and unloading periods. The cavity response for the whole expansion-contraction process is investigated, with the total pressure and stress paths at the cavity wall presented and validated against numerical simulation. The developed solution is successfully implemented to interpret both loading and unloading data of pressuremeter tests. The undrained shear strength, in-situ effective horizontal stress and initial overconsolidation ratio are back analyzed by using a curve fitting method based on the proposed solution.

Correlation of fabric parameters and characteristic features of granular material behaviour in DEM in constitutive modelling

AbstractThe anisotropic microstructure of granular materials has a profound effect on their macroscopic behaviour and can be characterised using a fabric tensor. To include of fabric in the critical state theory (CST), anisotropic critical state theory (ACST) was proposed by modifying the state parameter $$(\psi )$$ ( ψ ) of CST to a fabric-dependent dilatancy state parameter $$(\upzeta )$$ ( ζ ) . Noteworthy that $$\uppsi$$ ψ showed a very strong correlation with characteristic features (e.g. instability, phase transformation and characteristic state) of macroscopic behaviour and, as a result, it has been adopted in many constitutive models. While $$\upzeta$$ ζ aided the inclusion of fabric in ACST models, the correlation between $$\upzeta$$ ζ and characteristic features has not been evaluated in detail yet, although a large number of works are found on micromechanics and fabric only. In this study, a large number of discrete element method simulations for drained and undrained triaxial were conducted to evaluate the correlation between $$\upzeta$$ ζ and characteristic features. To this purpose, the correlation between stress ratio and both classic and dilatancy state parameter ($$\psi$$ ψ and $$\upzeta$$ ζ ) were studied in important characteristic features (e.g. instability, phase transformation and characteristic state). It was found that this correlation was improved using $$\upzeta$$ ζ which might be due to the inclusion of fabric in our model. This observation is new and significant for inclusion of fabric evolution in constitutive modelling.

Exploring the micro-to-macro response of granular soils with real particle shapes by way of μCT-aided DEM analyses

This contribution provides high-fidelity images of real granular materials with the aid of X-ray micro-computed tomography (μCT), and employs a multi-sphere representation to reconstruct non-spherical particles. Through discrete-element method (DEM) simulations of granular samples composed of these non-spherical clumps, the effect of particle shape on the macroscopic mechanical response and microscopic soil fabric evolution is examined for soil assemblies under triaxial compression. Simulation results indicate that materials with more irregular particles tend to show higher shear resistance in both peak and critical states, while exhibiting higher void ratio under isotropic loading conditions and in the critical state. The proposed critical state parameters for describing the sensitivity of the mean coordination number to confining pressures are larger as particles become more irregular. At a microscopic level of observation, directional and scalar parameters of particle contacts are sensitive to predefined particle shapes. More irregular materials appear to exhibit higher fabric anisotropy with respect to particle orientation in the critical state, while the branch vector is affected by both contact modes and particle shape. The critical stress ratio from the simulation results is validated by comparing with experimental results, and further found to be linearly linked to the shape-weighted fabric anisotropy indices.

Deflagration characteristics of N2 diluted propanal/air mixtures at elevated pressures

Hydrocarbon fuels, in addition to being direct sources of energy, also serve as crucial raw materials for numerous industrial processes. In this study, the oxidation of propanal to propionic acid under elevated pressures has garnered our attention due to the substantial heat release during the mixing of propanal and oxidants, posing considerable hazards to production. Fortunately, the introduction of N2 effectively mitigates these risks by reducing the laminar burning speed (SL) and peak deflagration pressure (Pm), and even preventing the ignition of mixtures. On this basis, the deflagration characteristics of propanal/N2/air mixtures were investigated in a 20 L spherical vessel at 348 K under various equivalent ratios (φ, 0.5 - 2.0), dilution rates (D, 0 - 0.5) and initial pressures (P0, 0.1 - 1.0 MPa). The combustion characteristics of propanal/N2/air were also analyzed through the 1-D laminar flame speed model, and the sensitivity analysis was performed to elucidate the effect of φ, D and P0 on the combustion of propanal. Results reveal that the addition of N2 stabilizes the flame propagation, and the Pm of propanal/N2/air mixtures decreases with the increasing D, with a sudden drop observed at a certain D level. However, the reduction of SL does not undergo an abrupt decrease across the entire dilution rate range. Furthermore, Pm exhibits a linear relationship with P0 at lower D, but this linear trend disappears once D approaches the critical suppression concentration. Interestingly, the critical suppression concentration of N2 increases with P0 at fuel-rich conditions, yet remains unaffected by P0 at fuel-lean conditions. Near the critical suppression concentration, a limiting burning speed (Slim) emerges, below which the flame is incapable of spontaneous propagation. Notably, Slim is not a fixed value, but varies according to the composition and initial state of the mixture. For a given gas component, an increase in P0 leads to a decline in Slim, while for gases with varying components, Slim is observed to be lower under fuel-rich conditions compared to fuel-lean scenarios. Also, both the addition of N2 and the augmentation of P0 significantly reduce the SL. When SL is comparable to the gas rise speed due to natural convection, the flame propagation becomes vulnerable to buoyancy instability. Meanwhile, the flame propagation may also be influenced by thermal diffusion instability and hydrodynamic instability. Under the combined effect of these instabilities, the flame is prone to be unstable. More importantly, when the flame contacting the upper wall of the is in a critical state where it can or cannot propagate downward, the irregularity of the disturbed flame may introduces uncertainty into the subsequent propagation, resulting in markedly different Pm even among mixtures with identical compositions.

Exploring Tailings Dam Stability Considering Uncertainties in the Critical State Parameters of the NorSand Model

Exploring Tailings Dam Stability Considering Uncertainties in the Critical State Parameters of the NorSand Model

Thermal Characteristics of Oil Film in Critical Lubrication State of Heavy Hydrostatic Bearing

Background: Lubrication failure has always been a concern in the research of heavy hydrostatic bearings. A preliminary study found that under a certain working condition, the heavy hydrostatic bearing will appear in the condition of zero local flow of oil film, which is called a critical lubrication state. It produces a significant thermal accumulation effect and affects the lubrication performance of the bearing. Objective: This paper takes Q1-205 double rectangular cavity hydrostatic thrust bearing as the research object and adopts the research method combining theoretical analysis, simulation, and experimental test to analyze the temperature rise and characteristics of the bearing when it is in critical lubrication state under different working conditions. Methods: The finite volume method is used to simulate the critical lubrication state under the condition of common load and rotating speed, and the corresponding operating parameters of the critical lubrication of heavy static support are obtained. Results: It is found that when the oil film is in the critical lubrication state, the low temperature zone is concentrated at the bearing position of the oil film, while the high temperature zone is concentrated at the counter-current side sealing edge Conclusion: The oil film's local temperature rise is intensified, and the heat accumulation phenomenon is serious because the heat cannot be taken away in time.

The strength prediction model of unidirectional fiber reinforced composites based on the renormalization group method

When unidirectional fiber reinforced composites are subjected to longitudinal tensile loading and reach a critical failure state, they experience a sudden transition from local damage to catastrophic failure, commonly termed as an avalanche event. This paper integrates the self-organized criticality theory (SOC) concepts into the prediction of longitudinal tensile strength of composites and establishes a strength prediction model of composites based on the renormalization group method (RGM). The predictions of the RGM model are successfully validated against experimental results in the literatures, and it demonstrates relatively acceptable predictive accuracy compared to classical strength criteria. Compared to other state-of-the-art prediction models considering stochastic fiber strength distribution, the RGM model effectively provides strength statistics for fiber bundles of any size and describes the occurrence of composites avalanche failure induced by local stress concentration. This present model can be very conveniently implemented as a User Material Subroutine (UMAT) for finite simulations, facilitating practical prediction of the strength of composites structures.

Avalanche statistics of fluctuation-induced fluxes from the SLPM and the W7-AS stellarator

Measurements of fluctuating floating potentials and ion saturation currents at different radial locations in the Santander Linear Plasma Machine (Castellanos et al 2005 Plasma Phys. Control. Fusion 47 2067) and at the edge of the W7-AS stellarator by means of radially movable Langmuir probes allow to infer the corresponding fluctuation-induced radial flux temporal series. Avalanche-like transport events are identified in the time series and statistically characterized in terms of avalanche size/duration/quiet-time distributions and size-duration scaling relations. Transport is diffusive in the inner and intermediate radial region of the SLPM r<rtr≈2.6 cm, undergoing a transition at rtr , becoming non-diffusive in the outermost region of the device, r>rtr . The results obtained at the edge of the W7-AS stellarator are similar to those found in SLPM for r>rtr , i.e. consistent with what would be expected for scale-free, self-similar plasma transport dynamics near a critical state.

Mechanical Characterization Potentials of Aluminide Diffusion Coatings on Molybdenum Substrates

A mechanical test strategy is designed to determine the resistance of protective intermetallic aluminum layers on molybdenum substrates. Performing mechanical experiments, such as compression, four‐point bending and indentation tests, the specific failure behavior and a potential impact of observed phase transformations within the interface zone on the structural integrity and adhesion strength are examined. Herein, the applied test structure aims at the description of damage characteristics and critical deformation states regarding the type of loading. In this respect, it focuses on delamination behavior under compressive load and crack channeling due to bending stress. The analysis of the mechanical experiments is supported by various measurement techniques, including 3D camera equipment (GOM) and an acoustic emission (AE) analysis system. In particular, the application of the AE technique in this work provides a helpful contribution to the detection of delamination failure and the development of multiple crack channeling. Considering the successfully applied experimental approaches, it is assumed that more complex coating‐base material combinations can be characterized this way with respect to preceding annealing effects and the thereby influenced load capacity of thin films under different loading types.

Entanglement negativity between separated regions in quantum critical systems

We study the entanglement between disjoint subregions in quantum critical systems through the lens of the logarithmic negativity. We work with systems in arbitrary dimensions, including conformal field theories and their corresponding lattice Hamiltonians, as well as resonating valence-bond states. At small separations, the logarithmic negativity is big and displays universal behavior, but we show nonperturbatively that it decays faster than any power at large separations. This can already be seen in the minimal setting of single-spin subregions. The corresponding absence of distillable entanglement at large separations generalizes the one-dimensional result, and indicates that quantum critical ground states do not possess long-range bipartite entanglement, at least for bosons. For systems with fermions, a more suitable definition of the logarithmic negativity exists that takes into account fermion parity, and we show that it decays algebraically. Along the way we obtain general results for the moments of the partially transposed density matrix. Published by the American Physical Society 2024