Magnitude Of Strain Rate Research Articles

The Upper Crustal Deformation Field of Greece Inferred From GPS Data and Its Correlation With Earthquake Occurrence

AbstractWe present a new geodetic strain rate and rotation rate model for Greece that has been derived using a highly dense GPS velocity field. The spatial distribution and the resolved rates of the various velocity gradient tensor quantities provided updated constraints on the present‐day upper crustal deformation in the region and revealed new details not reported previously. The spatial distribution of the second invariant demonstrated that the overall magnitude of strain rates is highest across two well‐defined provinces. The first follows the North Anatolian Fault and its two branches within the north Aegean, crosses central Greece and through the Gulf of Corinth it terminates in western Greece, while the second encompasses the extensional province of western Turkey and the eastern Aegean Sea islands. Our estimates revealed that shearing affects some of the fault‐bounded grabens of central Greece that lie to the SW of the North Aegean Basin implying considerable oblique extension. We identified a narrow region of counterclockwise rotation whose location and kinematics have been induced by the net effect across the intersection of the clockwise rotating domains of western and central Greece. The Aegean microplate and the Anatolian plate are separated by a wide transition zone which accommodates the curved stretching of the entire plate system. In both edges of the Hellenic forearc the dominant mode of crustal strain is E‐W extension. We found that earthquakes of M ≥ 5.6 are spatially well‐correlated with high‐strain areas, indicating that strain rate mapping could be used to inform future probabilistic seismic hazard analyses.

Micromechanical response of an electrodeposited NiP metallic glass by pillar compression under extreme conditions

In this work, the mechanical properties of pulse electrodeposited amorphous nickel phosphorous (NiP), with ∼16 wt% P, was investigated for an improved understanding of the deformation behavior of metallic glasses at extreme conditions, particularly at the microscale. Upon decreasing the temperature to sub-ambient, both the yield strength and the shear band density increase. While the change of yield strength with temperature can be well explained by a cooperative shear model, the increase in the number of shear bands can be related to an increase in potential sites for activation of shear transformation zones due to the enhanced structural heterogeneity at lower temperatures. This, however, hinders the percolation of deformation units and leads to a decrease in the shear band propagation speed, from ∼50 nm/s at 295 K to ∼20 nm/s at 195 K. By testing micropillars across seven orders of magnitude in strain rate, a two-stage strain rate sensitivity is observed, from nearly negligible at the quasi-static range (m1 = 0.001 ± 0.002 for 10−3 s−1 to 10−1 s−1) to highly positive at dynamic high strain rate range (m2 = 0.02 ± 0.004 for 1 s−1 to 1000 s−1). This transition implies a change in the yield-controlling process, from the diffusion-assisted relaxation at quasi-static conditions to the rate of energy barrier crossing of shear transformation zones at high strain rates. These findings highlight several distinctive features of microscale metallic glasses, including the reduced shear band velocity at sub-ambient temperature and the two-stage strain rate sensitivity.

Prediction of fractures by using the stress field in medium to deep shale gas reservoirs: A case study of Late Ordovician–early Silurian shale gas reservoirs in the Nanchuan region, South China

Containing representative shale gas reservoirs, the Wufeng–Longmaxi Formations in the Nanchuan region in South China have been modified by three compressional tectonic movements (in the Late Jurassic to Early Cretaceous, Late Cretaceous, and Cenozoic to present). These movements formed deeply buried reservoirs with complex in situ stresses and rapid directional changes, influencing the state of shale gas reservoirs fractures. Numerical modeling applied to model the stress field in the three periods showed that the maximum compressive horizontal principal stress (σHmax), strain rate, and fault slip rate regimes transformed from a thrust and strike-slip regime to a thrust and strike-slip regime to a thrust regime. The σHmax direction changed from NW–SE and WNW–ESE to WNW–ESE and nearly E–W and then to multiple directions. The magnitude of strain rate changed from -16 ∼ -15 to -17.7 ∼ -15.6 to -18.8 ∼ -15.8. The fault slip rate changed from 0 to 0.029 mm/a to 0–0.0026 mm/a to 0–0.0012 mm/a. These data strongly agree with data from drilled wells and outcrops and show that the present-day stress field is the superposed effect of multistage movements. Semiquantitative research was conducted on shale gas fracture openness and fracture development. Fracture openness is favorable when the angle between the σHmax direction and nearby faults is ≤45° and the distance from the fault is >2 km, and fracture development is favorable when the magnitude of the strain rate is <-17.6 and the fault slip rate is <0.00036 mm/a. Accordingly, we predicted fractured shale gas reservoirs.

The (In)sensitivity of Granular Creep to Materials and Boundaries

AbstractSoils around the planet creep, despite wide variations in particle properties and environments. This sub‐yield “flow” of soil interacts with a variety of boundaries, in terms of geometry and friction. Here we explore the veracity of recent observations of undisturbed, gravity‐driven creep, by testing a suite of materials and boundary configurations in an experimental hillslope. Using an optical interferometry technique, we demonstrate that creep is a generic relaxation process whose qualitative dynamics are insensitive to grain properties. Velocity profiles are exponential, albeit with a defect near the no‐slip boundary. Quantitative patterns such as spatial variability and magnitude of strain rates, however, are exquisitely sensitive to the details of the experiment. The emerging picture is that creep is accomplished by localized plastic failure, which induces an elastic redistribution. Similar patterns have been observed in model glasses and on earthquake faults, indicating that sub‐yield relaxation in disordered materials may share common physics.

Novel nanoindentation strain rate sweep method for continuously investigating the strain rate sensitivity of materials at the nanoscale

We introduce a new nanoindentation method to continuously measure the hardness while sweeping through orders of magnitudes of strain rates within a single experiment. While nanoindentation already allows the determination of the strain rate sensitivity of materials by means of strain rate jump tests, these are typically limited to few discrete strain rates. With the new method, the strain rate sensitivity can be measured continuously as a function of the strain rate. Applications to fused silica, Zn-22 %Al superplastic alloy, single crystalline aluminum, various nanocrystalline metals and a palladium-based metallic glass are shown. Besides some discrepancy with the reference measurements, the new method seems only affected by the presence of a strong nanoindentation size effect. Provided this indentation size effect is not excessively large and can be corrected for accurately, the method proves robust, with no suggestion that the direction of the strain rate sweep affects the evaluation of the strain rate sensitivity.

High strain rate effects in masonry structures under waterborne debris impacts

Masonry buildings are vulnerable to extreme hydrodynamic events such as floods or tsunamis. Post-disaster surveys have shown that waterborne debris impacts can significantly damage masonry walls during these events. To simulate these actions, the current design or research practice is to compute the force–time diagram of the impact and then use it for dynamic analyses. Standing on the current knowledge, debris impacts are highly impulsive, but it is not clear if such loads are fast enough to activate the high strain rate effects in masonry, i.e. the strain rate dependency of material properties. The present study aims to answer this question, for the first time, following nonlinear Finite Element (FE) simulations. Simulations are conducted on a masonry wall, following a micro-modelling strategy, subjected to water flow and waterborne debris impact under different scenarios. It is found that the strain rates exceed the critical threshold after which strain rate effects are considerable. Such a finding, initially obtained using the minimum design demand for log-type debris imposed by ASCE/SEI 7-22, is further extended to a range of impact force–time diagrams different in impact duration and peak force (corresponding to different debris properties or flow velocity). It is also shown that the impact location (i.e. midspan or close to the boundary) affects the strain rate magnitude because of the changes in the impact stiffness and the activated failure mechanisms. Furthermore, it is found that the dynamic tensile post-elastic behaviour of the materials is the most influencing parameter in the structural response. These results open a new area in the field of assessment and design of masonry structures to waterborne debris and guide the development of future experiments, numerical simulations or design relations.

Influence of Solid Solutions on the Al2024 High-Temperature Deformation Behavior.

The mechanical properties of 2024 aluminum alloy were studied after two different tempers. The T351 temper (solution heat treatment, stress relief, and natural aging) leads to high hardness and toughness. A thermal treatment consisting of heat-treating at 280 °C for 48 h and slow cooling in a furnace, named TT temper, was performed to increase the precipitate size and their separation while minimizing the amount of solutes in solid solution, which produced the minimum hardness for an overaged Al2024 alloy and a lower tensile flow stress than for the T351 temper. The flow stress strongly decreases and the elongation to failure strongly increases for both materials above 300 °C. Differences in strain rate at a given stress in the power law regime at all temperatures for both tempers and compared with pure aluminum are attributed to the influence of solutes in solid solutions, affecting both the glide and climb of dislocations. However, the stacking fault energy, SFE, alone does not account for the hot deformation behavior. Thus, it is the synergistic effect of various solutes that affects the entire deformation process, causing a decrease of three or four orders of magnitude in strain rate for a given stress with respect to the pure aluminum matrix values.

On asymmetric vortex pair interactions in shear

This study examines the two-dimensional interaction of two unequal co-rotating viscous vortices in uniform background shear. Numerical simulations are performed for vortex pairs having various circulation ratios $\varLambda _0 = \varGamma _{1,0}/\varGamma _{2,0} = (\omega _{1,0}/\omega _{2,0})(a^2_{1,0}/a^2_{2,0}) \leqslant 1$ , corresponding to different initial characteristic radii $a_{i,0}$ and peak vorticities $\omega _{i,0}$ of each vortex $i=1,2$ , in shears of various strengths $\zeta _0 = \omega _S/\omega _{2,0}$ , where $\omega _S$ is the constant vorticity of the shear. Two primary flow regimes are observed: separations ( $\zeta _0 &lt; \zeta _{sep} &lt; 0$ ), in which the vortices move apart continuously, and henditions ( $\zeta _0 &gt; \zeta _{sep}$ ), in which the interaction results in a single vortex (where $\zeta _{sep}$ is the adverse shear strength beyond which separation occurs). Vortex motion and values of $\zeta _{sep}(\varLambda _0)$ are well-predicted by a point-vortex model for unequal vortices. In vortex-dominated henditions, shear varies the peak–peak distance $b$ , and vortex deformation. The main convective interaction begins when core detrainment of one vortex is established, and proceeds similarly to the no-shear ( $\zeta _0 = 0$ ) case: merger occurs if the second vortex also detrains, engendering mutual entrainment; otherwise straining out occurs. Detrainment requires persistence of straining of both sufficient magnitude, as indicated by relative straining above a consistent critical value, $(S/\omega )_i &gt; (S/\omega )_{cr}$ , where $S$ is the strain rate magnitude at the vorticity peak, and conducive direction. Hendition outcomes are assessed in terms of an enhancement factor $\varepsilon \equiv \varGamma _{end}/\varGamma _{2,start}$ . Although $\varepsilon$ generally varies with $\zeta _0$ , $(a^2_{1,0} /a^2_{2,0} )$ and $(\omega _{1,0}/\omega _{2,0})$ in a complicated manner, this variation is well-characterized by the pair's starting enstrophy ratio, $Z_2/Z_1$ . Within a transition region between merger and straining out (approximately $1.65 &lt; Z_2/Z_1 &lt; 1.9$ ), shear of either sense may increase $\varepsilon$ .

Review of Nonlocal-in-Time Damping Models in the Dynamics of Structures

In the present paper, the nonlocal-in-time damping models, called “damping-with-memory” models, are reviewed. Since such models do not involve the distribution along the longitudinal coordinate, they are easily adjustable for the FEM (Finite Element Model) algorithm, which is a big advantage due to the fact that FEM is the most-used method in engineering calculations. Within damping-with-memory models, the internal damping of a structure at the current time, is assumed to be dependent not only on the instant strain-rate magnitude or displacement-velocity magnitude but also on the strain-rate or velocity values along the previous time history. The greater the gap between the two time points, the lower the influence that one of them has on the other. To implement a composite beam vibration simulation involving damping with memory, the equation of motion of a structure written in the matrix form could be solved using the central difference method. The models constructed could be calibrated based on 3D numerical simulation data with the least squares method. It has been shown that the results obtained using the implementation of a calibrated damping-with-memory model within the 1D finite-element beam algorithm are in good correlation with those given by the 3D-FEM numerical simulation data.

Integration of Distributed Dense Polish GNSS Data for Monitoring the Low Deformation Rates of Earth’s Crust

This research concerns the possibility of monitoring low deformation rates in tectonically stable regions using GPS/GNSS observations. The study was conducted in an area of Poland located in Central and Eastern Europe, where horizontal stress resulting from plate boundary forces in the N–S or NNE–SSW direction has been observed. This stress can translate into deformation of the Earth’s surface. The problem, however, is that it corresponds to strain rate magnitudes of much lower than 10 × 10−9 per year. This is not much higher than the figure determined using current GNSS observation capabilities. In this study, long-term observations from several GNSS networks were used. The result was a very dense but irregular velocity field. By carefully analyzing and filtering the data, it was possible to eliminate the impact of various errors, creating a more consistent velocity field. This article presents a final GNSS strain rate model for Poland and determines the impacts of the analysis methods on its variation. Regardless of the filtering method adopted, dominant compression rates in the N-S direction are evident. Moreover, this result is consistent despite the use of varying velocity. This shows that even in tectonically stable regions, strain rates can be monitored at 10−9 per year (below 3 × 10−9/year).

Localized strain characterization of cardiomyopathy in Duchenne muscular dystrophy using novel 4D kinematic analysis of cine cardiovascular magnetic resonance

BackgroundCardiomyopathy (CMP) is the most common cause of mortality in Duchenne muscular dystrophy (DMD), though the age of onset and clinical progression vary. We applied a novel 4D (3D + time) strain analysis method using cine cardiovascular magnetic resonance (CMR) imaging data to determine if localized strain metrics derived from 4D image analysis would be sensitive and specific for characterizing DMD CMP. MethodsWe analyzed short-axis cine CMR image stacks from 43 DMD patients (median age: 12.23 yrs [10.6–16.5]; [interquartile range]) and 25 male healthy controls (median age: 16.2 yrs [13.3–20.7]). A subset of 25 male DMD patients age-matched to the controls (median age: 15.7 yrs [14.0-17.8]) was used for comparative metrics. CMR images were compiled into 4D sequences for feature-tracking strain analysis using custom-built software. Unpaired t-test and receiver operator characteristic area under the curve (AUC) analysis were used to determine statistical significance. Spearman's rho was used to determine correlation. ResultsDMD patients had a range of CMP severity: 15 (35% of total) had left ventricular ejection fraction (LVEF) > 55% with no findings of myocardial late gadolinium enhancement (LGE), 15 (35%) had findings of LGE with LVEF > 55% and 13 (30%) had LGE with LVEF < 55%. The magnitude of the peak basal circumferential strain, basal radial strain, and basal surface area strain were all significantly decreased in DMD patients relative to healthy controls (p < 0.001) with AUC values of 0.80, 0.89, and 0.84 respectively for peak strain and 0.96, 0.91, and 0.98 respectively for systolic strain rate. Peak basal radial strain, basal radial systolic strain rate, and basal circumferential systolic strain rate magnitude values were also significantly decreased in mild CMP (No LGE, LVEF > 55%) compared to a healthy control group (p< 0.001 for all). Surface area strain significantly correlated with LVEF and extracellular volume (ECV) respectively in the basal (rho = − 0.45, 0.40), mid (rho = − 0.46, 0.46), and apical (rho = − 0.42, 0.47) regions. ConclusionStrain analysis of 3D cine CMR images in DMD CMP patients generates localized kinematic parameters that strongly differentiate disease from control and correlate with LVEF and ECV.

Nonlinear Relaxation Time in Glassy Poly(methyl methacrylate) Subjected to Tensile Creep Stresses

Nonlinear viscoelastic behavior of glassy poly(methyl methacrylate) (PMMA) subjected to high tensile creep stresses was studied. Right after the loading of creep stress, a rapid decrease of strain rate as a function of strain was observed, indicating behavior of linear viscoelastic solid. Then after showing a sharp minimum, the strain rate gradually increased due to nonlinear flow and reached to almost constant maximum values at steady flow state, and then slightly decreased. Strain range in which the nonlinear flow was observed did not strongly depend on the magnitude of creep stress and temperature, although magnitude of strain rate was obviously affected by these conditions. Nonlinear single relaxation time τ for the glass in the nonlinear flow range of strain was evaluated by means of a simple mechanical model. The nonlinear relaxation time τ decreased with increasing time t to a steady value appeared in the steady flow state. A quantity τ/t was found to be an almost unique decreasing function of strain independently of differences in magnitude of creep stress and temperature. This characteristic dependence of relaxation time τ on strain was considered as a result of a constant decreasing slope of τ-t relation, which slightly depends on the magnitude of stress, during transient flow state under constant high stresses.

The effects of ultrasonic vibration on Portevin–Le Chatelier (PLC) effect and stress-strain behavior in aluminum alloy 2024

The effect of ultrasonic vibration on the stress-strain behavior and the Portevin–Le Chatelier (PLC) effect in aluminum alloy 2024 O temper and T4 were investigated based on ultrasonically assisted micro-tensile tests. Flow stress in both heat treatments was found to be decreasing when ultrasonic vibration is applied. A higher percentage of stress reduction and the residual softening effect was observed in O temper. High-speed digital image correlation reveals the enhanced PLC bands in both heat treatments. While no PLC band was observed in T4 originally, clear PLC bands appear with applied ultrasound. Spatio-temporal analysis revealed that in both O temper and T4 conditions, the critical strain of the PLC effect decreases under ultrasonic vibration. In addition, a higher strain rate magnitude was observed in conditions with ultrasonic vibration.

Role of viscosity in the preferential concentration of heated, bidispersed particles

We study the effect of temperature-dependent viscosity on the preferential concentration of bidispersed, externally-heated solid particles in decaying isotropic turbulence via direct numerical simulations (DNS). More specifically, we investigate the role of liquid- and gas-like viscosity–which respectively decrease and increase with temperature–on the preferential concentration of small and large particles due to turbulence. The bidispersed particles enhance the overall distribution compared to monodispersed flows as the voids created by the particles of one size are occupied by the other particles. Particle clusters emerge irrespective of the Stokes number although the clustering characteristics differ based on the functional form of the temperature-dependent viscosity. When particles are externally heated in a variable viscosity flow, the Kolmogorov-based Stokes number, Stη, is not sufficient to predict preferential concentration. Increased clustering is observed, especially for small-sized particles, as the fluid is heated and turbulence decays. This increased clustering is explained through a viscous capturing mechanism in which the initial clustering, prior to the onset of heating, is responsible for the creation of local hot-spots in the flow as the particles are heated. In a gas, these higher temperature regions have higher viscosity which cause other particles to be captured due to the increased drag. The increased drag of the gas results in a lower fluid-particle drift velocity as compared to the liquid, despite the significantly lower turbulent kinetic energy of the flow. The relative distribution of the particles as a function of vorticity and strain rate magnitude reveals a bimodal distribution in which a higher proportion of the particles aggregate in mid- and high strain/vorticity regions as the turbulence decays.

CFD simulations of flow fields during ultrafiltration: Effects of hydrodynamic strain rates with and without a particle cake layer on the permeation of mobile genetic elements

Membrane ultrafiltration (UF) combined with inline dosing of powdered activated carbon (PAC) are popular hybrid processes for water reclamation. However, hydrodynamic forces can allow mobile genetic elements (MGEs) that are larger than the membrane pore size to penetrate through UF membranes. The flow fields in the feed channel of a dead-end UF membrane module were modelled using computational fluid dynamics (CFD) in order to analyze shear and elongational strain rates and associated potential hydrodynamic effects by a PAC particle layer on MGE retention. The most significant magnitudes of strain rates occurred within a distance of tens of nanometers from the membrane surface, meaning that this is where significant deformation of MGEs occurs. Since flow fields were not considerably altered at the membrane surface, the presence of the PAC particle layer was expected to have a negligible impact on the permeation of MGEs through UF membrane pores.

Evolution of deformation twinning mechanisms in magnesium from low to high strain rates

We present a systematic investigation of {101¯2} extension twinning mechanism in single crystal magnesium micropillars deformed over seven orders of magnitude of strain rate, from 10–4 to 500 s−1, revealing how the accommodation of newly formed twins evolves with and depends on the kinetic compatibility of interfacial processes when high deformation rates are imposed. By combination of post-mortem 3D Electron Backscattered Diffraction, Transmission Kikuchi Diffraction and Transmission Electron Microscopy techniques, this work unveils the progressive evolution of the accommodating twin mechanisms from low to high strain rate, correlating differences in mechanical behavior with differences in twin crystallography. Away from quasi–static conditions, simple considerations of twinning shear do not suffice to describe unconventional twin morphologies, requiring the competition between newly activated dislocations and lattice distortions for allowing the evolution of the twin boundary along non–invariant twin planes. Under shock compressions, the basal/prismatic transformation establishing a lattice misorientation of 90° entirely governs the parent → twin conversion. The results illustrated here confirm that some of the recent interpretations deduced by particular twin morphologies are not universally valid and that deformation twinning is not only stress- but also strongly time–controlled.

Hot Deformation Behaviour and Constitutive Equation of Mg-9Gd-4Y-2Zn-0.5Zr Alloy

The thermal deformation behaviour of Mg-9Gd-4Y-2Zn-0.5Zr alloy at temperatures of 360–480 °C, strain rates of 0.001–1 s−1 and a maximum deformation degree of 60% was investigated in uniaxial hot compression experiments on a Gleeble 3800 thermomechanical simulator. A constitutive equation suitable for plastic deformation was constructed from the Arrhenius equation. The experimental results indicate that due to work hardening, the flow stress of the alloy rapidly reached peak stress with increased strain in the initial deformation stage and then began to decrease and stabilize, indicating that the deformation behaviour of the alloy conformed to steady-state rheological characteristics. The average deformation activation energy of this alloy was Q = 223.334 kJ·mol−1. Moreover, a processing map based on material dynamic modelling was established, and the law describing the influence of the machining parameters on deformation was obtained. The experimental results indicate that the effects of deformation temperature, strain rate and strain magnitude on the peak dissipation efficiency factor and instability range were highly significant. With the increase in the strain variable, the flow instability range increased gradually, but the coefficient of the peak power dissipation rate decreased gradually. The optimum deformation temperature and strain rate of this alloy during hot working were 400–480 °C and 0.001–0.01 s−1, respectively.

Defect reversibility regulates dynamic tensile strength in silicon carbide at high strain rates

To reveal the relationship between atomic-scale activity and bulk materials properties, we report all-atom molecular dynamics (MD) simulations of the deformation and dynamic failure of mono- and nanocrystalline silicon carbide (SiC) ceramics. We establish a direct link between the reversibility of defects and dynamic tensile strength of a nominally brittle ceramic over a wide range (six orders of magnitude) of strain rates, bridging the simulation regime to current experimental capabilities that enable the observation of lattice dynamics over extremely short timescales. Our results reveal that SiC exhibits a highly reversible deformation twinning mechanism in response to loading along the [001] crystal direction below a critical compression strain. The remarkable reversibility of the active defects allows the crystal to retain its high strength. Beyond a critical strain, the process becomes unstable, and self-activated twin boundary motion is triggered, yielding irreversibly intertwined defects, resulting in a significant reduction in strength.

A numerical evaluation of flows through an SMX-Plus mixer

A numerical investigation of the flow through an SMX+ mixer was undertaken in this study. Three elements were placed in series to assess various hydrodynamic parameters. Single-phase flows of different viscosities flowing at a hydraulic Reynolds number between 220 and 660 were considered to ensure turbulent conditions inside the mixer. The data was validated against pressure drop measurements collected under a wide range of hydrodynamic conditions.The results show that a three-dimensional velocity field dominate the flow within the mixer where the distribution of the strain rate and vorticity magnitudes undergo large fluctuations. The extensional efficiency was found to increase substantially in the first part of each mixer, indicating good dispersive behavior; however, its value decreased to values below 0.5 downstream of the last element. This was due to the presence of a significant rotational core as the fluid flowed farther from the last mixer. The core region of the flow spiraled on its axis as it moved downstream while the near-wall area whirled orthogonal to the flow direction. This also explained the persistence of a flatter velocity profile downstream of the mixing section. The energy dissipation rate and kinetic energy were also analyzed.

Shear Variation at the Ice‐Till Interface Changes the Spatial Distribution of Till Porosity and Meltwater Drainage

AbstractMany subglacial environments consist of a fine‐grained, deformable sediment bed, known as till, hosting an active hydrological system that routes meltwater. Observations show that the till undergoes substantial shear deformation as a result of the motion of the overlying ice. The deformation of the till, coupled with the dynamics of the hydrological system, is further affected by the substantial strain rate variability in subglacial conditions resulting from spatial heterogeneity at the bed. However, it is not clear if the relatively low magnitudes of strain rates affect the bed structure or its hydrology. We study how laterally varying shear along the ice‐bed interface alters sediment porosity and affects the flux of meltwater through the pore spaces. We use a discrete element model consisting of a collection of spherical, elasto‐frictional grains with water‐saturated pore spaces to simulate the deformation of the granular bed. Our results show that a deforming granular layer exhibits substantial spatial variability in porosity in the pseudo‐static shear regime, where shear strain rates are relatively low. In particular, laterally varying shear at the shearing interface creates a narrow zone of elevated porosity which has increased susceptibility to plastic failure. Despite the changes in porosity, our analysis suggests that the pore pressure equilibrates near‐instantaneously relative to the deformation at critical state, inhibiting potential strain rate dependence of the deformation caused by bed hardening or weakening resulting from pore pressure changes. We relate shear variation to porosity evolution and drainage element formation in actively deforming subglacial tills.