Transient Deformation Research Articles

Modeling and characterization of dynamic recrystallization under variable deformation states

Flexible rolling with variable deformation states has brought new challenges to dynamic recrystallization (DRX) theory based on conventional constant deformation state. Modeling and characterization of DRX are investigated, inspired by the successful application of constitutive models and EBSD technique in the field of characterizing the recrystallization of metallic materials, combined with the characteristics of flow stress. Two constitutive models for constant and transient deformation states were considered. The dynamic recovery effect was integrated into the model for predicting the flow stress and DRX volume fraction. A hot processing map was established to predict the instability region. Various DRX synergistic regulation mechanisms and crystallographic orientation distribution under a transient deformation state were explored. The results suggest that DRX is the main softening characteristic under various deformation states. The predicted flow stress of the constant and transient models are in good agreement with the experimental values. The regulation mechanism of DRX transforms from continuous DRX to discontinuous DRX when the strain rate dynamic decreases. DRX grains display a random orientation distribution, and the crystallographic orientation is toward the 〈111〉 fiber parallel to the normal direction of the compression axis when the DRX volume fraction is high. These findings provide insight into the DRX constitutive description and microstructure evolution under variable deformation states.

Spatiotemporal Evolution of the Seismicity in the Alto Tiberina Fault System Revealed by a High‐Resolution Template Matching Catalog

AbstractThe Alto Tiberina Fault system, located in the Northern Apennines (Italy), consists of a low angle normal fault (LANF) which radiates micro‐seismicity that can be explained by continuous creep. On top of the LANF, a network of syn‐ and antithetic high angle faults frequently hosts seismic swarms, one of which has been associated with a transient aseismic deformation signal. To study in detail the seismicity and its relationships with aseismic deformation processes occurring in this fault system, we apply template matching on seismic data recorded at an array of borehole stations, to derive a high‐resolution earthquake catalog. Thanks to the additionally detected events, we are able to reveal time periods of increased spatial‐ and temporal clustering during an aseismic deformation event. This reflects the complex evolution of aseismic slip together with the complexity of the shallow fault system. Along the LANF, we observe a bimodal type of seismicity, with diffuse seismicity active continuously, and short‐lived bursts of seismicity that could indicate rapid fluid releases. We additionally identify repeating earthquakes. These events not necessarily match a simple creep model and therefore open the possibility for new models to explain the seismicity along the LANF.

Present-day fault kinematic around the eastern Himalayan Syntaxis and probable viscoelastic relaxation perturbation following the 1950 Mw 8.7 Assam earthquake

Strike-slip and tensile/dip-slip rates around the EHS region from the elastic block model. • An elastic block model was constructed to analyze the fault slip rates and regional kinematic around the Eastern Himalayan Syntaxis (EHS). • The postseismic viscoelastic relaxation effects caused by the 1950 Assam Mw 8.7 earthquake is still significant even after 65 years. • The interseismic slip rate across the eastern Himalaya derived from pure elastic solution may be overestimated if ignoring the viscoelastic relaxation effects. The Eastern Himalayan Syntaxis (EHS) played important role in accommodating the intracontinental deformation and material flow in southeastern Tibet. Quantifying the regional kinematics around the EHS is critical for understanding the deformation mechanism of the Tibetan Plateau. In this study, we compiled all available GPS measurements and constructed an elastic block model to analyze the fault kinematics around the EHS. The results suggest that the deformation characteristics around the EHS can be well explained by a linear spherical block model that considers the intra-block homogeneous strain. The fault slip rates from the block model agree well with the late Quaternary slip rates, suggesting that the GPS-derived slip rates can generally represent the long-term slip rates. However, some relatively large residuals, especially in the frontal EHS region, are still detectable, suggesting that various other factors, such as the postseismic viscoelastic relaxation, may also influence the deformation. We simulated the postseismic viscoelastic relaxation deformation caused by the 1950 Mw 8.7 Assam earthquake endured as the largest intracontinental earthquake ever recorded. The results indicate significant postseismic viscoelastic deformation due to the Assam earthquake even after 65 years. The interseismic convergence rates across the Mishmi thrust and the Arunachal Himalaya derived from pure elastic solution may be overestimated if ignoring the viscoelastic relaxation effects. The spatial variations of convergence rates across the central and eastern Himalayas could be partly related to the transient deformation following great Himalayan earthquakes.

Dynamic modes of a capsule under oscillating shear flow with finite inertia

Inertia may significantly influence the transient deformation process and the steady-state structure of a deformable capsule. The behavior of a two-dimensional deformable capsule in shear flow at finite Reynolds numbers (Re) is studied numerically. By simulating numerous cases with different Re and frequencies (f), we observed persistent oscillation, asymmetric oscillation, deflected oscillation, and stable modes. The phase diagram in the Re–f plane is presented. At low frequencies, a capsule shows a phase-lag phenomenon between the deformation and the applied shear. At moderate frequencies, the anomaly of decreasing maximum deformation with increasing Re is observed. The anomaly is attributed to the mode shift. In addition, a scaling law of the maximum deformation of the capsule as a function of Re and f is proposed. This study may shed some light on the identification and screening of cells in vitro as well as the transport and breakup of cells in vivo.

Ballistic loading and survivability of optical fiber sensing layers for soft body armor evaluation

The authors previously demonstrated the use of FBG sensors in Kevlar mats behind body armor to measure the transient back face deformation (BFD) during ballistic testing. This paper presents a novel sensor system based on a Fiber Bragg Grating embedded in silicone mats to improve the survivability of the body armor in-situ strain sensing layers. Due to the large amount of deformation, a relative slip between the optical fibers and the supporting structure is needed to maintain the performance of the sensors and determine the relationship between the measured strain and deformation shape. Two silicone materials were tested, Smooth-Sil 950 and Sorta-Clear 40, in both 1 mm and 2 mm thicknesses to evaluate their survivability and impact on BFD. To enhance slipping between the fibers and surrounding silicone a thin layer of petroleum jelly was placed on the fibers prior to being cast in the silicone mats. The 1 mm Sorta-Clear 40 mats performed best in silicone survivability, FBG survivability and minimal impact on the BFD. The new system improves on key deficiencies that were found from inserting the fibers directly into the Kevlar with minimal to no impact on the back face deformation.

Development of LSN-based pipe repair rate models utilising data from the 2011 Christchurch earthquakes

The Canterbury Earthquake Sequence (CES) adversely impacted built, economic and social environments. This included widespread physical damage to the water supply pipe network in Christchurch, resulting in long service disruptions. The transient and permanent ground deformations generated by the earthquakes in the CES caused a range of pipe damage, particularly in the MW 6.2 22 February 2011 and the relatively less damaging MW 6.0 13 June 2011 event. Damage to the pipes in both events was largely attributed to liquefaction and lateral spreading effects. Pipes made of ductile material (e.g. PVC, HDPE) sustained lesser damage (and therefore lower repair rates) compared to the pipes made of non-ductile material (e.g. AC, CI). In all cases, the repair rates (number of repairs per kilometre) typically increased with increasing liquefaction severity. Utilising the pipe repair dataset and Liquefaction Severity Number (LSN) maps generated from extensive geotechnical investigation following the CES events, new repair rate prediction models for water pipes subjected to liquefaction effects have been derived and are presented in this paper. Repair data from both earthquakes has been analysed independently and in combination, providing two sets of repair rate functions and different levels of uncertainty. Repair rate functions were first derived from pipes grouped by combination of diameter (i.e. ϕ < 75 mm or ϕ ≥ 75 mm) and material type (i.e. ductile or non-ductile). The models were then refined by adding correction factors for those material types and diameters with sufficient sample length. Correction factors were derived for AC, CI, PVC pipes of diameter ≥75 mm and for MDPE and HDPE80 pipes of diameter <75 mm. Galvanised Iron (GI) pipes performed poorly during the earthquakes, resulting in very high repair rates compared to the other non-ductile pipes of diameter <75 mm damaged in the network; this warranted a separate repair rate model to be developed for this pipe type. The proposed models can be used in risk assessment of water pipe networks; i.e. to estimate the number of pipe repairs from potential liquefaction damage from future earthquakes.

A Computational Framework for Time‐Dependent Deformation in Viscoelastic Magmatic Systems

AbstractTime‐dependent ground deformation is a key observable in active magmatic systems, but is challenging to characterize. Here we present a numerical framework for modeling transient deformation and stress around a subsurface, spheroidal pressurized magma reservoir within a viscoelastic half‐space with variable material coefficients, utilizing a high‐order finite‐element method and explicit time‐stepping. We derive numerically stable time steps and verify convergence, then explore the frequency dependence of surface displacement associated with cyclic pressure applied to a spherical reservoir beneath a stress‐free surface. We consider a Maxwell rheology and a steady geothermal gradient, which gives rise to spatially variable viscoelastic material properties. The temporal response of the system is quantified with a transfer function that connects peak surface deformation to reservoir pressurization in the frequency domain. The amplitude and phase of this transfer function characterize the viscoelastic response of the system, and imply a framework for characterizing general deformation time series through superposition. Transfer function components vary with the frequency of pressure forcing and are modulated strongly by the background temperature field. The dominantly viscous region around the reservoir is also frequency dependent, through a local Deborah number that measures pressurization period against a spatially varying Maxwell relaxation time. This near‐reservoir region defines a spatially complex viscous/elastic transition whose volume depends on the frequency of forcing. Our computational and transfer function analysis framework represents a general approach for studying transient viscoelastic crustal responses to magmatic forcing through spectral decomposition of deformation time series, such as long‐duration geodetic observations.

Creep properties of siltstone-like materials with different unloading confining pressures under seepage

Deep enclosing rocks exhibit non-homogeneous characteristics of dense joints and fissure development. Soft rocks subjected to multiple factors, such as high stress and hydrostatic pressure, are prone to damage and significant deformation, which can lead to instability of the surrounding rocks, failure of the supporting structure, and other accidents. In this study, we investigated the creep behaviour of deep soft rocks and siltstone-like materials subjected to different unloading confining pressures coupled with a high stress field and seepage. Subsequently, the laws and behaviours of parameters, such as the transient strain, creep deformation, and creep rate were derived and analysed under various conditions. The results indicate that the radial creep curve exhibits a variation pattern similar to that of the axial creep. However, the extent of radial creep exceeds that of axial creep in soft siltstone-like rocks under unloading confining pressure conditions. We derived expressions for the constitutive relation of siltstone-like specimens under various unloading confining pressure conditions in the presence of seepage using an improved viscoelasticmodel that considered the coupling effect of fissure and seepage flow. The correlation coefficients of the calculated model values with the experimental values, as obtained by the non-linear least-squares fitting, were all above 0.9178, indicating that the proposed model can accurately characterise the creep process in fissured siltstone.

Transient nuclear deformation primes epigenetic state and promotes cell reprogramming.

Cell reprogramming has wide applications in tissue regeneration, disease modelling and personalized medicine. In addition to biochemical cues, mechanical forces also contribute to the modulation of the epigenetic state and a variety of cell functions through distinct mechanisms that are not fully understood. Here we show that millisecond deformation of the cell nucleus caused by confinement into microfluidic channels results in wrinkling and transient disassembly of the nuclear lamina, local detachment of lamina-associated domains in chromatin and a decrease of histone methylation (histone H3 lysine 9 trimethylation) and DNA methylation. These global changes in chromatin at the early stage of cell reprogramming boost the conversion of fibroblasts into neurons and can be partially reproduced by inhibition of histone H3 lysine 9 and DNA methylation. This mechanopriming approach also triggers macrophage reprogramming into neurons and fibroblast conversion into induced pluripotent stem cells, being thus a promising mechanically based epigenetic state modulation method for cell engineering.

Backstresses in geologic materials quantified by nanoindentation load-drop experiments

ABSTRACT Transient creep of geologic materials is inferred to control many large-scale phenomena such as post-seismic deformation and post-glacial isostatic readjustment. Viscoelastic simulations can reproduce transient creep measured at Earth’s surface via GPS, but these approaches are entirely phenomenological, lacking a microphysical basis. This empirical nature limits our ability to extrapolate to future events and longer time scales. Recent experimental work has identified the importance of strain hardening and backstresses among dislocations in the transient deformation of geologic materials at both high and low temperatures, but very few experimental measurements of such backstresses exist. Here, we develop a nanoindentation load-drop method that can measure the magnitude of backstresses in a material. Using this method and a self-similar Berkovich tip, we measure backstresses in single crystals of olivine, quartz, and plagioclase feldspar at a range of indentation depths from 100–1750 nm, corresponding to geometrically necessary dislocation (GND) densities of order 1014–1015 m−2. Our results reveal a power-law relationship between backstress and GND density with an exponent ranging from 0.44–0.55 for each material, in close agreement with the theoretical prediction (0.5) from Taylor hardening. This work supports the assertion that backstresses and their evolution must be considered in future models of both transient and steady-state deformation in the Earth.

741 Structural adaptations of epidermal stem cells to mechanical stress

The skin has a pronounced ability to adapt to physical changes in the environment by exhibiting plasticity at the cellular level. Transient mechanical deformations applied to the skin are accommodated without permanent changes to tissue structure. However, sustained physical stress induces long-lasting alterations in the skin, which are mediated by shifts in keratinocyte activity. To elucidate the cellular mechanism of epidermal stem cell plasticity, we implemented 2-photon intravital imaging to capture the response of keratinocytes in live mouse skin, to varying degrees of mechanical force.

Identifying Geographical Patterns of Transient Deformation in the Geological Sea Level Record

AbstractIn this study, we examine the effect of transient mantle creep on the prediction of glacial isostatic adjustment (GIA) signals. Specifically, we compare predictions of relative sea level (RSL) change from GIA from a set of Earth models in which transient creep parameters are varied in a simple Burgers model to a reference case with a Maxwell viscoelastic rheology. The model predictions are evaluated in two ways: first, relative to each other to quantify the effect of parameter variation, and second, for their ability to reproduce well‐constrained sea level records from selected locations. Both the resolution and geographic location of the RSL observations determine whether the data can distinguish between model cases. Model predictions are most sensitive to the inclusion of transient mantle deformation in regions that are near‐field and peripheral relative to former ice sheets. This sensitivity appears particularly true along the North American west coast in the region of the former Cordilleran Ice Sheet, which experienced rapid sea‐level fall following deglaciation between 14 and 12 kyr BP. Relative to the Maxwell case, Burgers models better reproduce this rapid phase of regional postglacial sea‐level fall. As well, computed goodness‐of‐fit values in this region show a clear preference for models where transient deformation is present in the whole or lower mantle, and for models where the rigidity of the Kelvin element is weakened relative to the rigidity of the Maxwell element. In contrast, model predictions of relative sea‐level change in the far‐field show weak sensitivity to the inclusion of transient deformation.

Analysis of the Thermal Effects on the Behaviour of Steel Connection Beam Section

Steel connection is utilized to link the beam and column. It moves the plastic hinge structure away at a predetermined distance from the face of the column. To lower the cross-sectional area of the beam flanges, several shape cuts (uniform, radius, taper, and straight cut) are available, and a piece of the beam flanges at the column face is purposefully intended to yield and plastic hinge. The use of a lowered beam section connection reduces stress absorption since the criteria for a strong column–weak beam are met. The ANSYS 14.5 software was used to model four types of reduced beam sections by decreasing the beam flange. In various patterns, fatigue behaviour was studied. The objective of this project is to evaluate the deformations, stresses and transient temperatures deformations, and stresses of the reduced beam section at static structural analysis. In comparison to other connections, steel connection reduced beam section ductile and dissipated energy more. A nonlinear finite element software was used, along with a static study of exhaustion responsiveness transient temperatures. The analysis is carried out to identify the thermal effects on the behaviour of material properties in the elastic and plastic regions. The members with cuts have performed superior in comparison with members without cuts.

A Fractional Order Creep Damage Model for Microbially Improved Expansive Soils

Microbial Induced Calcite Precipitation method was used to improve the expansive soils of Nanning, Guangxi. The nonlinear shear creep behavior of microbially improved expansive soil was studied by triaxial consolidation drainage shear test. The results show that when the expansive soil was applied a small partial stress, the creep curve of soil exhibits transient deformation and decay creep. When the partial stress reaches a certain value, there is decay creep, steady-state creep and accelerated creep successively showed on the creep curve. The stress-strain isochronous curves reflect there are obvious nonlinear characteristics in the creep process of improved expansive soils. The degree of this nonlinearity is related to the creep time and stress level. The longer the creep time as well as the higher the stress level, the higher the degree of nonlinearity. Based on the fractional calculus theory and statistical damage theory, the probability density function of Weibull distribution was introduced, and the damage degradation of soft component viscosity coefficient was considered. As a result, a fractional-order damage creep model which can describe the shear creep evolution of microbially improved expansive soils is established. Compared with the Kelvin creep model of integer order and the Burgers creep model of fractional order, the fractional order damage creep model has not only better comparative evaluation results but also more higher computational accuracy. It indicates that the fractional-order damage creep model can better describe the whole process of shear creep in microbially improved expansive soils. The above findings provide a theoretical basis for the study of deformation analysis of microbially improved expansive soils under long-term loading.

Autonomous push button–controlled rapid insulin release from a piezoelectrically activated subcutaneous cell implant

Traceless physical cues are desirable for remote control of the in situ production and real-time dosing of biopharmaceuticals in cell-based therapies. However, current optogenetic, magnetogenetic, or electrogenetic devices require sophisticated electronics, complex artificial intelligence–assisted software, and external energy supplies for power and control. Here, we describe a self-sufficient subcutaneous push button–controlled cellular implant powered simply by repeated gentle finger pressure exerted on the overlying skin. Pushing the button causes transient percutaneous deformation of the implant’s embedded piezoelectric membrane, which produces sufficient low-voltage energy inside a semi-permeable platinum-coated cell chamber to mediate rapid release of a biopharmaceutical from engineered electro-sensitive human cells. Release is fine-tuned by varying the frequency and duration of finger-pressing stimulation. As proof of concept, we show that finger-pressure activation of the subcutaneous implant can restore normoglycemia in a mouse model of type 1 diabetes. Self-sufficient push-button devices may provide a new level of convenience for patients to control their cell-based therapies.

The effects of couple stress lubricants and surface roughness on squeeze EHL motion between porous medium layer and elastic ball

This paper investigated the effects of porous media layer (PML) and couple stress (CS) lubricants at pure squeeze action in an isothermal elastohydrodynamic lubrication (EHL) point contact with surface roughness (SRN) under constant load condition. The modified transient stochastic Reynolds equation was derived in polar coordinates by means of the Christensen’s stochastic theory and the Stokes’s CS fluid theory. The Gauss-Seidel method (GSM) and the finite difference method (FDM) were both used to solve simultaneously modified transient stochastic Reynolds, force equilibrium, elasticity deformation, and rheology equations. The simulation results revealed that the greater permeability ( K) and porous layer thickness (Φ) are, the smaller central pressures ( Pc) are, and the smaller film thicknesses ( H) are. The times required for achieving maximum central pressures (Pcmax) decrease with increasing K and Φ. Due to squeeze and elastic deformation effects, the slope values of central velocity ( Vc) change from negative to positive. The magnitude of Vc and Vmin decreased with decreasing K and Φ. The Hcmin of circular type RN are greater than that of radial type RN. The Pcmax of radial type RN are slightly greater than that of circular type RN.

Calibrating Out-of-Equilibrium Electron–Phonon Couplings in Photoexcited MoS2

Nonequilibrium electron-phonon coupling (EPC) serves as a dominant interaction in a multitude of transient processes, including photoinduced phase transitions, coherent phonon generation, and possible light-induced superconductivity. Here we use monolayer MoS2 as a prototype to investigate the variation in electron-phonon couplings under laser excitation, on the basis of real-time time-dependent density functional theory simulations. Phonon softening, anisotropic modification of the deformation potential, and enhancement of EPC are observed, which are attributed to the reduced electronic screening and modulated potential energy surfaces by photoexcitation. Furthermore, by tracking the transient deformation potential and nonthermal electronic population, we can monitor the ultrafast time evolution of the energy exchange rate between electrons and phonons upon laser excitation. This work provides an effective strategy to investigate the nonequilibrium EPC and constructs a scaffold for understanding nonequilibrium states beyond the multitemperature models.

An evolutionary model and classification scheme for nephrite jade based on veining, fabric development, and the role of dissolution–precipitation

Although nephrite jade has been collected and treasured since the Stone Age, we lack a clear understanding of how it forms during deformation and metasomatism in shear zones. Using microstructural analysis of samples from Taiwan, California, and New Zealand, we propose a conceptual model for the evolution of nephrite jade that distinguishes four nephrite types based on mode of formation and textural characteristics: (1) primary (type 1a) or folded (type 1b) vein nephrite, (2) crenulated nephrite (type 2), (3) foliated semi-nephrite (type 3), and (4) nodular or domainal nephrite (type 4). We interpret the texture of our analysed samples to represent snapshots of a progressive textural evolution similar to that experienced by other deformed and fine-grained metamorphic rocks that develop under fluid-present, greenschist-facies conditions. Our observations suggest that types 2 and 3 nephrite can evolve from vein nephrite (type 1) by the development of crenulated and foliated metamorphic fabrics, during which the most important deformation process is dissolution–precipitation. However, development of metamorphic fabrics can be interrupted by transient brittle deformation, leading to the formation of type 4 nephrite that is characterised by nodular or angular clasts of nephrite in a nephritic matrix.

Transient hydrology-induced elastic deformation and land subsidence in Australia constrained by contemporary geodetic measurements

Earth's lithospheric deformation in response to geophysical and climatic processes manifests as a wide range of spatio-temporal elastic/viscoelastic deformation, including seismic and tectonic motion, mantle flow, and climate-induced hydrologic-cyrospheric-atmospheric mass transports. We use increasingly accurate contemporary geodetic measurements, including those from GPS, Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) missions, to quantify the competing processes of the hydrological cycle and geodynamics within the Australian continental lithosphere over the last two decades, 2002 to 2020. Observed precipitation and temperature anomalies reveal that anthropogenic climate change may have exerted significant impact on the terrestrial water storage (TWS) evolution in Australia, as evidenced by anomalous fluctuation during the 2010-2012 El Niño Southern Oscillation (ENSO) events. In particular, enhanced TWS inferred from the geodetic observations is shown to be highly correlated with increased precipitation during the 2010-2012 La Niña event. The GPS observed vertical land motion cannot be completely explained by the elastic deformation induced by surface water storage variations across Australia, nor by the Glacial Isostatic Adjustment (GIA) geophysical process. We suggest that the geodetic-observed land subsidence of Australia at high spatial scales could be related to anthropogenic aquifer groundwater depletion, while the long wavelength signals may be associated with reference frame error and then tectonic deformation.

Three-dimensional fluid-structural interaction and thermal analysis of a large diameter horizontal cryogenic transfer line

This paper focuses on the thermal stress analysis and the thermal bowing phenomenon in a large 12-inch diameter cryogenic transfer line during chill-down with liquid oxygen. To investigate the chill-down characteristics and corresponding thermal stress generation, a threedimensional fluid-structural numerical model has been adopted in this work. The numerical simulation is performed on a 2 m long transfer line having an internal diameter of 30.48 cm (12 inch). Three dimensional modelling has been performed to numerate the channel wall temperature distribution along with the flow, at the top and the bottom portions. Based on the temperature data from CFD calculations, transient structural analysis and deformation of the transfer line are studied using a finite element model. Results show that the bowing in the transfer line occurs when there is a strong circumferential variation in temperature. Furthermore, this study provides a numerical simulation that predicts the chill-down time and the time when a stratified flow occurs in the line. This numerical method has been found to be a useful tool for the evaluation, design, and development of a large diameter cryogenic transfer line for transportation of large quantity of cryogenic fluid.