Dilatational Strain Research Articles

Spatial Persistence of High Strain Events During Brittle Failure

AbstractThe onset of brittle failure in rocks includes dilatancy and strain localization. To better understand this nucleation process, we analyze the evolution of the local three‐dimensional strain tensor using X‐ray tomograms acquired during triaxial compression experiments on granite and sandstone. The onset of the localization of the compaction, dilation, and shear strain occurs when ∼65% of the rock volume experiences dilation. Tracking the locations of the high strains throughout loading suggests that the deformation that occurs early in loading influences the location of the system‐sized fracture network that produces macroscopic failure. This influence is larger in the sandstone experiments than the granite experiments, likely due to the microstructure of the sandstone. These results have important implications for detecting precursors to catastrophic failure.

Beyond 2D echocardiography: A novel multiparametric assessment of right ventricular dysfunction in transcatheter tricuspid valve repair

Abstract Background Patients with severe tricuspid regurgitation (TR) are heterogenous and complex in terms of etiology, comorbidities and state of disease. Right ventricular (RV) function measured by RV to pulmonary artery coupling (RVPAc) is prognostic in transcatheter tricuspid valve repair (T-TEER). However, traditional 2D echocardiographic measures have critical limitations and RVPAc fails to respect the degree of volume overload/dilation of the RV, which is a key clinical tracer for right ventricular dysfunction (RVD). Purpose We aimed to refine RVPAc by incorporating RV dilation, assessed by 3D echocardiography, to improve the assessment of RV dysfunction for an enhanced outcomeprediction in T-TEER patients. Methods We analyzed 262 patients undergoing T-TEER with complete 3D echocardiography. Results Despite similar RV function across groups, RV dilation (HR 1.85; 1.10, 3.12; p=0.020) and impaired RV free wall longitudinal strain (RVFWLS, HR 1.73, 1.02, 2.92, p=0.042) predicted increased 1-year mortality. A novel RVPAc parameter [RVFWLS/(3D-RVEDV*sPAPinvasive)] was developed, associating RVPA-Uncoupling with a tripled risk of death (HR 3.19, 1.7-6.0, p<0.001). NYHA Class IV and the new RVPAc were independent mortality predictors after T-TEER, with the modified RVPAc showing superior predictive value over traditional RVPAc (c-index 0.68 vs. 0.57, p=0.027). Conclusion The novel RVPAc parameter, integrating RV dilation and function, is a powerful predictor of survival post-T-TEER, underscoring the importance of timely intervention in severe TR and RVD. 3D echocardiography plays a critical role in assessing RV dimension and function, with implications for the management and prognosis of TR patients.Central Figure

Excavation-induced cracking of clastic rock: A true triaxial instantaneous unloading study with varied levels of initial damage

The cracking and squeezing problem in deep engineering significantly constrains project construction. To reveal the cracking mechanism of rock under instantaneous unloading, a self-designed rigid true triaxial experimental apparatus, equipped with groundbreaking electromagnetic unloading and high-speed camera functions, was utilized to conduct instantaneous unloading tests on clastic rock with varied levels of initial damage. The results indicate that samples undergo severe and irreversible lateral dilation during instantaneous unloading, with dilational strain rapidly increasing at higher initial damage levels. Instantaneous unloading induces the generation of numerous tensile microcracks, which propagate and coalesce rapidly. The crack propagation speed, as well as the length and width of the cracks at failure, increase with the rise of the initial damage level. The samples eventually exhibit two distinct macroscopic fracture zones: a tensile fracture zone and a tensile-shear mixed fracture zone. Analysis of acoustic emission hits and energy indicates that higher initial damage levels correspond to greater unloading damage, with a higher overall proportion of tensile cracks throughout the experiment. Under the induction of blasting excavation, radial stress is rapidly unloaded, and dense tensile cracks emerge in the immediate surrounding rock, leading to cracking and squeezing towards the free face. Importantly, higher initial damage levels intensify the squeezing effect. The self-developed equipment serves as a crucial technical tool for researching excavation unloading, and the insights derived from this study provide valuable guidance for understanding cracking mechanisms and informing the construction of deep engineering projects.

Large‐Scale Extensional Strain in Southern Tibet From Sentinel‐1 InSAR and GNSS Data

AbstractIn this study, we utilize C‐band Sentinel‐1 radar images from 2015 to 2022, combined with interseismic horizontal GNSS velocities, to construct large‐scale, high‐resolution, 3‐D velocity and strain rate maps over a vast region of southern Tibet. We show the distribution of prevailing dilatational strain accumulation along the seven major rift zones. Using 2‐D elastic dislocations invoking a two‐fault model in a Bayesian framework, we quantified the decadal extension rates across the seven rift zones, and we suggest a total extension rate of 18.4 ± 1.7 mm/yr, consistent with geological and geodetic estimates. The resulting strain rate maps, combined with the earthquake catalog, help us identify areas with high earthquake potential. Our study enhances our understanding of the present‐day tectonics and kinematics in southern Tibet and provides important constraints for seismic hazard assessment in this region.

Coseismic surface ruptures of 20 strike-slip earthquakes measured from geodetic imaging data

Observations of coseismic surface ruptures are widely used for examining faulting mechanics and kinematics, and in fault displacement hazard analysis. Here, first, we provide new remote sensing observations of 20 historic surface rupturing continental strike-slip earthquakes (6.1 ≤ Mw≤ 7.9). To measure the near-field surface deformation pattern, we have processed a range of raw radar and optical images from satellite and aerial platforms with pixel tracking techniques, and in two cases using standard interferometric synthetic aperture radar (InSAR). We provide a range of observations, including surface displacement maps that constrain at least the horizontal component of surface motion (2D), and for three events the full 3D components. Second, we provide strain invariants for each event, which includes the finite dilatational strain, strain magnitudes, the vorticity, and maximum shear strain. Third, we provide a total of 134 surface fault rupture traces that are mapped manually from the displacement maps. Finally, we provide 2648 measurements of coseismic horizontal fault-parallel surface fault slip that are measured objectively using swath profiles with a function fitting method that we have developed.

First-principles calculations to investigate effects of strains on structural, electronic, thermodynamic, optical and thermoelectric properties of NaAs3P5 alloy

Herein, the structural, optical, electronic and thermoelectric properties of the NaAs3P5 were investigated by Ab-initio calculations. The electronic results of NaAs3P5 showed that this compound has a metallic characteristic. The optical response of this compound has been studied using optical parameters such as complex dielectric function, refractive index, optical conductivity, electron energy loss, and absorption coefficient. This compound is an n-type material, as determined by thermoelectric experiments because it has a negative Seebeck coefficient when the strain is at 20 %. The highest value of the figure of merit (ZT) is about 0.021. Besides, the obtained value of PF is 7595.5 W−1.K−2.s−1 for 20 % of the strain. As the ZT trend grows, the alloy is being promoted as a potential contender for thermoelectric power production. Applying dilatation strain can improve the mechanical and thermodynamic stability of NaAs3P5 because many solid-state physical characteristics, such as heat capacity, thermal expansion coefficient, and entropy, are related to the Debye temperature.

Computational exploration of strain‐induced in the physical characteristics of inverse‐spinel Li2RuSn4 via density functional theory

AbstractIn this research, the physical properties of the inverse‐spinel Li2RuSn4 compound have been investigated using ab‐initio computational methods within the Wien2k package. The LSDA+mBJ approach was employed to determine the exchange‐correlation potential. The compound was found to exhibit metallic and nonmagnetic behavior in terms of electronic properties. The optical characteristics have been analyzed along xx, yy, and zz directions, revealing an increase in absorption coefficient with rising photon energies, culminating in a prominent peak in the UV domain. The higher intensity in xx and yy directions signify stronger absorption along these axes. The thermodynamic properties of Li2RuSn4, including volume, Debye temperature, Grüneisen parameter, volumetric thermal expansion coefficient, and lattice thermal conductivity were examined. The Debye temperature was found to rise proportionally with tensile strain and decrease with temperature, suggesting that dilatation strain can enhance the mechanical and thermal stability of the compound. The thermoelectric analysis revealed n‐type behavior, with negative Seebeck coefficient values. This research offers valuable insights into the properties of Li2RuSn4, contributing to the understanding of its potential applications.

Elementary processes in dilatational plasticity of glasses

Materials typically fail under complex stress states, essentially involving dilatational (volumetric) components that eventually lead to material decohesion/separation. It is therefore important to understand dilatational irreversible deformation—i.e., dilatational plasticity—en route to failure. In the context of glasses, much focus has been given to shear (volume-preserving) plasticity, both in terms of the stress states considered and the corresponding material response. Here, using a recently developed methodology and extensive computer simulations, we shed basic light on the elementary processes mediating dilatational plasticity in glasses. We show that plastic instabilities, corresponding to singularities of the glass Hessian, generically feature both dilatational and shear irreversible strain components. The relative magnitude and statistics of the strain components depend both on the symmetry of the driving stress (e.g., shear versus hydrostatic tension) and on the cohesive (attractive) part of the interatomic interaction. We further show that the tensorial shear component of the plastic strain is generally nonplanar and also extract the characteristic volume of plastic instabilities. Elucidating the fundamental properties of the elementary micromechanical building blocks of plasticity in glasses sets the stage for addressing larger-scale, collective phenomena in dilatational plasticity such as topological changes in the form of cavitation and ductile-to-brittle transitions. As a first step in this direction, we show that the elastic moduli markedly soften during dilatational plastic deformation approaching cavitation. Published by the American Physical Society 2024

Strain accumulation in the Mentawai Forearc Sliver, Indonesia, inferred from continuous GNSS-derived strain rate

The Mentawai Forearc Sliver (MFS) is characterized by oblique deformation formed as slip partitioned between normal and parallel trench plate convergence. The surge of great earthquakes from 2004 to 2012 along the adjacent Sunda trench left a large unbroken segment known as the Mentawai Seismic Gap. Here, we adopted continuous Global Navigation Satellite System (GNSS) observation data to identify the present regional crustal deformation using geodetic strain rates. The principal strain rate, dilatation rate, and maximum shear strain rate are about 0.13 microstrain/yr, 0.2 microstrain/yr, and 0.1 microstrain/yr, respectively, with the range of its uncertainties between 0.01 and 0.04 microstrain/yr. The dilatation and maximum shear strain rates reveal the spatial coverage of strike-slip duplex and backthrust tectonics along the Mentawai Forearc Sliver.

Determining Stress Orientation in Rock Valley, Nevada, Using Ambient Seismic Noise

AbstractThe stress field and the mechanical properties of rocks are important to consider for nuclear explosion monitoring due to their effect on seismic wave radiation from earthquakes and explosions. At the Rock Valley Direct Comparison site, the regional orientation of the maximum horizontal compressive stress (SHmax) is well constrained, but it is unknown whether there are local heterogeneities. Here, I show that stress-induced anisotropy in nonlinear elasticity can be used to estimate the orientation of SHmax. Rocks have compliant internal contacts, such as fractures and mineral grain boundaries, that respond to applied strains more strongly than individual mineral crystals. This strain response is asymmetric between compressive and dilatational strains and is affected by anisotropy in the ambient stress field. Traditional seismic velocity measurements are of strain-averaged velocity, which is less sensitive than nonlinear elasticity to the behavior of compliant internal contacts and therefore the stress field and fracture behavior. My results show that the orientation of SHmax measured using ambient seismic noise aligns with regional estimates, with some heterogeneity that can also be explained by the limitations of the seismic array. I demonstrate the potential of a passive technique for monitoring the stress field in places that currently lack local measurements.

Monitoring Velocity Change Over 20 Years at Parkfield

AbstractWe monitored the time history of the velocity change (dv/v) from 2002 to 2022 to investigate temporal changes in the physical state near the Parkfield Region of the San Andreas Fault throughout the interseismic period. Following the coseismic decrease in dv/v caused by the 2003 San Simeon (SS) and the 2004 Parkfield earthquakes, the dv/v heals logarithmically and shows a net long‐term increase in which the current dv/v level is equivalent to, or exceeding, the value before the 2003 SS earthquake. We investigated this long‐term trend by fitting the model accounting for the environmental and coseismic effects to the channel‐weighted dv/v time series. We confirmed with the metrics of Akaike information criterion and Bayesian information criterion that the additional term of either a linear trend term, or a residual healing term for the case where the healing had not been completed before the SS earthquake occurred, robustly improved the fit to the data. We eventually evaluated the sensitivity of the dv/v time history to the GNSS‐derived strain field around the fault. The cumulative dilatational strain spatially averaged around the seismic stations shows a slight extension, which is opposite to what would be expected for an increase in dv/v. However, the cumulative rotated axial strain shows compression in a range near the maximum contractional horizontal strain (azimuth of N35°W to N45°E), suggesting that the closing of pre‐existing microcracks aligned perpendicular to the axial contractional strains would be a candidate to cause the long‐term increase observed in the multiple station pairs.

Numerical study of effective parameters on true triaxial test results in rigid type apparatus

Operational parameters in true triaxial loading devices (TTA), such as the loading rod dimensions, friction between the loading platens and sample faces, loading gap, and one-side loading may affect the test results. Knowledge of the effect of each parameter is very important to correctly interpret rock behavior and to optimize these devices. Employing the Flac3D finite difference software, a rigid type true triaxial systemdesigned and builtat Amirkabir University of Iran (AUT-TTA) was simulated andinvestigated in this study. The results indicate that increasing the ratio of the rod cross-section to the loading platen area leads to an increase in the sample confinement, so, more uniform stress distribution occurs in the rock sample. The loading gap reduces strength of the rock specimen and leads to concentration of tensile stresses at the sample edges. The end effect leads to an increase in the stress level and a pseudo-hardening behavior in the samples. Also, the end effect is intensified under one-side loading condition compared to two-side loading. Comparison between results of AUT-TTA numerical simulation and analytical analysis (ideal conditions without considering operational parameters) indicates that the slope of the stress–strain diagram has low sensitivity to operational parameters. The most important operational factor affecting the stress level and dilatation stress is the end effect and other operational parameters have little effect. All parameters lead to an increase in the dilation strain. The clear edge and one-sided loading under low intermediate principal stresses and the end effect under high intermediate principal stresses have the greatest effect on the dilation strain.

The effect of dilatational and distortional strain energy density on crack initiation

AbstractTo investigate the distinct influences of dilatational strain energy density (Dil‐SED) and distortional strain energy density (Dis‐SED) on crack initiation, quasi‐static loading tests were performed on centrally cracked polymethyl methacrylate samples, employing digital image correlation equipment. Our findings unveiled that the Dil‐SED promotes crack initiation, while the Dis‐SED inhibits it. Additionally, it was found that the direction obtained by the ratio of these two strain energy densities was closer to the crack initiation direction than the direction associated with the maximum Dil‐SED and minimum Dis‐SED values. Furthermore, experimental and finite element method (FEM) results indicated that the distribution of these two strain energy densities remains relatively insensitive to the core region's radius . By understanding Dil‐SED and Dis‐SED magnitudes and their impacts on crack initiation, material failure can be predicted and prevented.

Linking local microstructure to fracture location in a two-dimensional amorphous solid under isotropic strain.

Brittle fracturing of materials is common in natural and industrial processes over a variety of length scales. Knowledge of individual particle dynamics is vital to obtain deeper insight into the atomistic processes governing crack propagation in such materials, yet it is challenging to obtain these details in experiments. We propose an experimental approach where isotropic dilational strain is applied to a densely packed monolayer of attractive colloidal microspheres, resulting in fracture. Using brightfield microscopy and particle tracking, we examine the microstructural evolution of the monolayer during fracturing. Furthermore, we propose and test a parameter termed Weakness that estimates the likelihood for particles to be on a crack line, based on a quantified representation of the microstructure in combination with a machine learning algorithm. Regions that are more prone to fracture exhibit an increased Weakness value, however the exact location of a crack depends on the nucleation site, which cannot be predicted a priori. An analysis of the microstructural features that most contribute to increased Weakness values suggests that local density is more important than orientational order. Our methodology and results provide a basis for further research on microscopic processes during the fracturing process.

Cu@Co with Dilatation Strain for High-Performance Electrocatalytic Reduction of Low-Concentration Nitric Oxide.

Electrocatalytic reduction of nitric oxide (NO) to ammonia (NH3 ) is a clean and sustainable strategy to simultaneously remove NO and synthesize NH3 . However, the conversion of low concentration NO to NH3 is still a huge challenge. In this work, the dilatation strain between Cu and Co interface over Cu@Co catalyst is built up and investigated for electroreduction of low concentration NO (volume ratio of 1%) to NH3 . The catalyst shows a high NH3 yield of 627.20µg h-1 cm-2 and a Faradaic efficiency of 76.54%. Through the combination of spherical aberration-corrected transmission electron microscopy and geometric phase analyses, it shows that Co atoms occupy Cu lattice sites to form dilatation strain in the xy direction within Co region. Further density functional theory calculations and NO temperature-programmed desorption (NO-TPD) results show that the surface dilatation strain on Cu@Co is helpful to enhance the NO adsorption and reduce energy barrier of the rate-determining step (*NO to *NOH), thereby accelerating the catalytic reaction. To simultaneously realize NO exhaust gas removal, NH3 green synthesis, and electricity output, a Zn-NO battery with Cu@Co cathode is assembled with a power density of 3.08mW cm-2 and an NH3 yield of 273.37µg h-1 cm-2 .

Co- and Pre-Seismic Crustal Deformations Related to Large Earthquakes Between Years of 2009 and 2023 Using Continuous CORS-TR GNSS Observations in the Anatolian Diagonal (Turkey)

Synoptic animations of internal displacements and deformations of the earth's crust were obtained based on the results of continuous GNSS observations in Eastern Anatolia from 2009 to 2023. The spatiotemporal patterns of the seismic deformation process in connection with the tectonics of the region have been identified. It is shown that dilatation and total shear strains evolve in concert with the migration of the strongest earthquakes Elazig, Elazig-Malatya and devastate Karamanmaraş series. Two years before the occurrence of the devastating earthquakes of 2023, a deficit of internal displacements of GNSS stations developed in the area of their epicenters. The conducted research suggests that the strongest events of 2009-2023 are connected by a unitary seismic deformation process. The most important action in this case is the SW movement of the Anatolian block as monolithic element. In the development of movements and deformations, a flow of increasing stresses is observed in the direction from Karliova Triple Junction to the SW to the area of the strongest seismic events on 02.2023. It originates east of the Karliova Triple Junction where the Arabian Plate encounters an obstacle. The role of mantle flows in the seismic process is assessed

Time-Scaling Creep in Salt Rocks for Underground Storage

Salt is an elastoviscoplastic material that exhibits time-dependent deformation (creep). Experimental measurements of salt creep behavior help predict underground gas repositories’ long-term geomechanical behavior. Previous time-scaling creep experiments have focused on the axial strain of unconsolidated sands. i.e., time-scaling creep effects under zero lateral strain conditions without describing the creep behavior of the radial strain. In addition, the time-scaling creep of the radial and axial strain has not been investigated in salts. A comparative testing procedure and analysis method was conducted on Spindletop salt plugs using triaxial tests for multistage triaxial tests (MST) and different holding time durations and stress regimes, resulting in time-dependent strain responses (creep tests). The MST showed evolving deformational mechanisms under the mapped yield surface based on the irrecoverable to recoverable strain ratio beginning with crack closure or conformance, plasticity, and ending at early crystal surface failure. Unlike unconsolidated sands, salts showed both time and strain amplitude scaling. The axial and radial strain data show scaling behavior under low and high levels of deviatoric stress separated by a transitional period. The salt showed only an axial creep response at low deviatoric stress distally from the yield surface (one-dimesional (1D) response or zero lateral strain), which indicates negative dilatant deformation or uniaxial compaction. In contrast, the salts showed equal strain amplitude scaling factors both axially and radially at high deviatoric stress proximal to the yield surface (two-dimensional (2D) response or unconstrained boundary condition), which suggests positive dilatant deformation. Microstructural images showed accumulated creep damage under high deviatoric stress associated with parallel planes of dislocation-intergranular slip, microcracking, and compaction-induced dilational strains. The period of scaling is interpreted as regions where a single mechanism is dominating. Strain amplitude scaling for both low and high deviatoric creep stress tests provides inputs for a constitutive model of creep response in understanding the magnitude of mechanical damage associated with time-independent stress-strain curves in salts for the structural integrity of salt caverns during cyclic fluid injection and depletion.

A new instrument for interfacial dilational rheology.

We present a new design for an interfacial dilational rheometer that can generate oscillatory dilational strain on a planar air-liquid interface. The strain is generated by a pneumatic mechanism involving a deformable film, which forms a circular barrier that can contract or expand under different pressures. The interfacial stress is measured using a Wilhelmy rod. We carefully examine and demonstrate the effects of potential sources of measurement error, including inertia, drag, buoyancy, flow from the bulk phase, and surface waves. The design avoids mixed deformations present in other instruments and is currently capable of accurate measurements at frequencies up to ∼0.1Hz and dilational strains below 0.001, with potential for higher frequencies after further theoretical development. We demonstrate the integration of the interfacial dilational rheometer with a Langmuir trough by measuring the compression isotherm of an insoluble surfactant, stearic acid. Furthermore, we verify the capability of the interfacial dilational rheometer to perform frequency and amplitude sweeps and present the storage and loss moduli for a water-soluble surfactant, sodium dodecylbenzenesulfonate, at different concentrations.

A unified viscoelastic model of progressive damage and failure for solid propellants

A general viscoelastic model incorporating the progressive damage evolution and failure criterion is developed for solid propellants across a wide range of temperatures (223 K to 333 K) and strain rates (2.38 × 10−4 /s to 4.76×10−2/s). (i) The progressive damage evolution, characterized by continuous void cavitation and growth, is linked to a macroscopic damage variable derived from a simple damage potential threshold, making it possible to determine the microstructural damage from experimental data. (ii) The failure criterion introduces two microstructural ingredients: the strain energy density, which accounts for both the glassy and rubbery failure of the polymer matrix, capturing brittle and ductile fracture modes at low and high temperatures respectively; and the void volume limit accounts for interface debonding, a process of particle detachment from the matrix. The implementation of the model effectively predicts the damage response and failure strains under uniaxial tension, cyclic and complex loading as well as superimposed pressure. Results reveal strong temperature/strain-rate dependency in the tensile strength, volume dilatation, and failure strains. Given that the model unifies progressive damage with ultimate failure and requires only a few model parameters, it assists in establishing a fracture criterion for the nonlinear fracture behavior of viscoelastic materials.

Spatiotemporal Characteristics of Horizontal Crustal Deformation in the Sichuan–Yunnan Region Using GPS Data

Based on various velocity fields from Global Positioning System (GPS) data over nearly 20 years in the Sichuan–Yunnan region, this paper calculated the strain rate field and its spatiotemporal characteristics by using an improved least squares collocation method. We evaluated the calculated strain field by extensively discussing the impact of non-tectonic factors on the calculation. Subsequently, we described the present-day strain rate features and their spatiotemporal variations. The results indicate the necessity of considering the influence of non-tectonic factors when calculating the strain rate field by using GPS velocity data. Widespread strain accumulation is observed in the Sichuan–Yunnan region, and significant second strain rate invariant with an average value of 33.1 nanostrain/yr primarily occurs along the eastern boundary faults of the Sichuan–Yunnan rhomboid block, specifically the Xianshuihe–Anninghe–Zemuhe–Xiaojiang fault systems. These fault systems also demarcate the zones with negative and positive dilation strain. According to the spatiotemporal variations of strain rate fields, the northern and southern segments of the Xianshuihe Fault, the Anninghe Fault and its eastern adjacent faults, and the Xiaojiang Fault are undergoing intensifying strain. Consequently, these zones should be paid more attention due to their relatively higher seismic risk in the Sichuan–Yunnan region.