Stress Memory Effects Research Articles

Strain-driven Kovacs-like memory effect in glasses

Studying complex relaxation behaviors is of critical importance for understanding the nature of glasses. Here we report a Kovacs-like memory effect in glasses, manifested by non-monotonic stress relaxation during two-step high-to-low strains stimulations. During the stress relaxation process, if the strain jumps from a higher state to a lower state, the stress does not continue to decrease, but increases first and then decreases. The memory effect becomes stronger when the atomic motions become highly collective with a large activation energy, e.g. the strain in the first stage is larger, the temperature is higher, and the stimulation is longer. The physical origin of the stress memory effect is studied based on the relaxation kinetics and the in-situ synchrotron X-ray experiments. The stress memory effect is probably a universal phenomenon in different types of glasses.

3-D velocity distribution of amphibolites collected from various crustal depths

The elastic properties of nineteen samples of crystalline rocks – amphibolites from different areas/boreholes were studied in order to elucidate possible depth effect on the elastic properties of these mineralogically relatively homogenous rocks. The samples were taken from three different crustal levels – shallow (tens of meters) Stařechov (Czech Republic), medium (first thousands of meters) KTB (Germany), and extreme crustal depths (up to 12 km) KSDB3 (Russia). The elastic properties were first determined experimentally using a high-pressure apparatus allowing for multidirectional (3D) ultrasonic sounding at various levels of confining pressure. The effect of main rock fabric components was evaluated using the method of inverse calculation from experimental data. The observed increase of elastic wave velocity and elastic constants with depth could be explained by the stress memory effect.

Intergenerational and Transgenerational Effects of Drought Stress on Winter Wheat (Triticum aestivum L.).

The environments where the progenitors are grown have the potential to affect the expression of traits in their offspring. Currently, there are various hypotheses regarding the evolutionary and ecological importance of stress memory effects. There is uncertainty regarding its occurrence, persistence, predictability, and adaptive value. In this study, fifteen winter wheat cultivars were grown under drought and well-watered (control) treatments for two seasons to produce seeds with all possible combinations of drought exposure histories. A comprehensive analysis to estimate transgenerational (grandparental effects), intergenerational (parental effects), and their combined memory effects on offspring traits under both control and drought moisture treatments was performed. There were significant memory effects in most of the evaluated traits ranging from +787% to -39.0% changes in both seed quality and plant traits. The expression of stress memory was highly dependent on generation and number of exposures, trait and season. Under drought treatment, the combination of grandparental and parental stress memories was additive in all traits, but their strength were variable when considered separately. Stress memory enhanced the performance of offspring under similar stressful conditions: increased plant height, above-ground biomass, number of grains per plant, grain weight per plant and water potential. This study offers valuable new insights into the occurrence of drought stress memory, the complexities of the effects, possible physiological and metabolic alterations explaining the detected differences, and impacts towards a clearer understanding of their generation and context-dependency. This article is protected by copyright. All rights reserved.

Effects of drought stress memory on the accumulation of stress-protective compounds in naturally grown pine and spruce

Forest trees are subjected to multiple stressors during their long lifetime and therefore require effective and finely regulated stress-protective systems. Stressors can induce protective systems either directly or with the involvement of stress memory mechanisms. Stress memory has only begun to be uncovered in model plants and is unexplored in coniferous species. Therefore, we studied the possible role of stress memory in the regulation of the accumulation of stress-protective compounds (heat shock proteins, dehydrins, proline) in the needles of naturally grown Scots pine and Norway spruce trees subjected to the subsequent action of long-term (multiyear) and short-term (seasonal) water shortages. Although the water deficit was relatively mild, it significantly influenced the pattern of expression of stress memory-related heat shock factor (HSF) and SWI/SNF genes, indicating the formation of stress memory in both species. In spruce, dehydrin accumulation was increased by water shortage in a manner compatible with Type II stress memory. The accumulation of HSP40 in spruce needles was positively influenced by long-term water shortage, but this increase was unlikely to be of biological importance due to the concomitant decrease in HSP70, HSP90 and HSP101 accumulation. Finally, proline accumulation was negatively influenced by short-term water deficit in spruce. In pine, no one protective compound accumulated in response to water stress. Taken together, the results indicate that the accumulation of stress-protective compounds was generally independent of stress memory effects both in pine and in spruce.

Estimation of stresses in a massive granite using laser ultra-sonic testing and stress memory effect

This paper addresses in-situ stress-estimation methods based on the Kaiser effect. The physical and mechanical properties of granite, diorite, and granodiorite samples selected at different depth intervals of the core obtained from a wellbore were examined. The ultimate uniaxial compressive strength, modulus of elasticity, and Poisson’s ratio of the rock samples were determined using presses and strain gauges. Also, local longitudinal and shear wave velocities were measured using a high-accuracy laser-ultrasonic system with a view to assessing the structure of the samples. Based on the resulting elastic wave velocity maps, samples with no obvious discontinuities were chosen. These undisturbed samples were subjected to uniaxial compression and their acoustic emission was simultaneously measured. In-situ stresses were estimated from the results of the interpretation of acoustic emission measurements. The experimental in-situ stresses were compared with the results of a numerical simulation. The ratio of the estimated in-situ stresses to the calculated ones is within the range from 0.81 to 1.11. This means that the laser ultrasonic and acoustic emission methods make it possible to effectively estimate in-situ stresses in a rock mass and assess the degree of rock mass damage.

Micro-mechanism of brittle creep in saturated sandstone and its mechanical behavior after creep damage

Understanding the micro-mechanism of brittle creep in saturated rocks and studying their mechanical behaviors after creep damage are of great significance to the design of rock engineering and the prediction of the long-term evolution of the Earth's crust. In this study, we first performed a series of uniaxial creep tests with different creep stage cut-offs on saturated intact sandstones. The brittle creep mechanism of the specimens was explored microscopically by analyzing P-wave velocity, acoustic emission (AE), and nuclear magnetic resonance (NMR) measurements. Then, specimens with different degrees of creep damage were subjected to a secondary short-term loading test or creep test, and their short- and long-term mechanical behaviors, together with AE monitoring, were systematically investigated. The experimental results show that (1) the anisotropy of the specimens increases significantly during creep, with the axial and lateral P-wave velocities exhibiting a difference of 30% at the onset of tertiary creep. (2) The tensile cracks dominate the transient creep stage and the early part of the steady creep stage, while the shear cracks dominate thereafter. (3) The porosities of the specimens increase with the loading stages, and the porosity increments corresponding to small pores are greater than those corresponding to large pores, for all creep stages. (4) Specimens with different degrees of creep damage show greater deformability, and their short-term and creep mechanical parameters, except for uniaxial strength, change dramatically. (5) The AE characteristics of creep-damaged specimens differ significantly from those of intact specimens, and the Kaiser stress memory effect was observed during reloading, with the memory stress being the previous creep stress.

The Stress‐Memory Effect of Fracture Stiffness During Cyclic Loading in Low‐Permeability Sandstone

AbstractThe hydraulic performance and mechanical stability of open fractures are crucial for several subsurface applications including fractured geothermal reservoirs or nuclear waste repositories. Their hydraulic and mechanical properties (fluid flow and fracture stiffness) are both strongly dependent on the fracture geometry. Any change in effective stress impacts aperture and thus the ability of fractures to promote flow. Here, we carried out flow experiments with shear displaced tensile fractures in pre‐loaded, low‐permeability sandstones with two different cyclic loading scenarios with up to 60 MPa hydrostatic confining pressure. During “constant cyclic loading” (CCL) experiments, the fracture was repeatedly loaded to the same peak stress (up to 60 MPa). During “progressive cyclic loading” (PCL) experiments, the confining pressure was progressively increased in each cycle (up to 15, 30, 45, and 60 MPa). The matrix and fracture deformation was monitored using axial and circumferential LVDT extensometers to obtain the fracture stiffness. The fracture geometry before and after the experiment was compared by calculating the aperture distribution from 3D surface scans. Initial loading with confining pressure of the fracture leads to a linear fracture specific stiffness evolution. For any subsequent stress cycles fracture stiffness shifts to a nonlinear behavior. The transition is shown to be related to a stress memory effect, similar to the “Kaiser Effect” for acoustic emissions. Progressive loading of fractures possibly leads to less permeability reduction compared to continuous cyclic loading.

Stress Anisotropy Severely Affects Zinc Phosphate Network Formation

Using density-functional theory based simulations, we study how initially disconnected zinc phosphate molecules respond to different externally imposed deformations. Hybridization changes are observed in all cases, in which the coordination of zinc atoms changes irreversibly from tetrahedral to seesaw and square pyramidal, whereby the system stiffens substantially. The point at which stiff networks are formed does not only depend on the hydrostatic pressure. Stress anisotropy generally reduces the required hydrostatic network formation pressure. Moreover, networks obtained under isotropic deformations turn out stiffer, elastically more isotropic, and lower in energy after decompression than those produced under anisotropic stresses. We also find that the observed stress-memory effects are encoded to a significant degree in the arrangement of atoms in the second neighbor shell of the zinc atoms. These findings refine previously formulated conjectures of pressure-assisted cross-linking in zinc phosphate-based anti-wear films.Graphical

Stress Memory in Acoustic Emission of Rock Salt Samples in Cyclic Loading under Variable Temperature Effects

The behavior of acoustic emission in uniaxial cyclic loading of rock salt samples from the Kaliningrad deposit is determined. The samples were tested under varied temperatures and ratios of maximal stresses in sequential loading cycles. The experimental curves of acoustic emission activity and maximal stress and temperature of the previous cycle are obtained. Stress memory in acoustic emission manifests itself equally stably under constant higher and lower temperatures. Memory of the maximal stress of the previous cycle persists under higher temperature in the next cycle and vanishes under lower temperature in the next cycle. In case of the same maximal stresses and constant or higher temperatures in the successive cycles, the stress memory effect is vague: the stress estimated on this base is lower than the maximal stress of the previous cycle.

Seismicity induced during the development of the Rittershoffen geothermal field, France

The development of the Rittershoffen deep geothermal field (Alsace, Upper Rhine Graben) between 2012 and 2014 induced unfelt seismicity with a local magnitude of less than 1.6. This seismicity occurred during two types of operations: (1) mud losses in the Muschelkalk formation during the drilling of both wells of the doublet and (2) thermal and hydraulic stimulations of the GRT-1 well. Seismicity was also observed 4 days after the main hydraulic stimulation, although no specific operation was performed. During chemical stimulation, however, no induced seismicity was detected. In the context of all field development operations and their injection parameters (flow rates, overpressures, volumes), we detail the occurrence or lack of seismicity, its magnitude distribution and its spatial distribution. The observations suggest the presence of the rock stress memory effect (Kaiser effect) of the geothermal reservoir as well as uncritically stressed zones connected to the GRT-1 well and/or rock cohesion. A reduction of the seismic rate concurrent with an increase of injectivity was noticed as well as the reactivation of a couple of faults, including the Rittershoffen fault, which was targeted by the wells. These results are derived from the homogeneous and consistent catalogue of more than 1300 local earthquakes that is provided. This reference catalogue is based on a standard detection method, whose output was manually verified and improved. The given absolute locations have been computed in a calibrated, geologically realistic 3D velocity model. Our work builds on previous analyses addressing the seismicity induced by the GRT-1 hydraulic stimulation and places the results into a historical context, thus considering the full dynamics of the observed phenomena. This paper also complements existing descriptions of the hydrothermal characteristics of the deep reservoir by providing insights separate from the wells.

Physically Consistent Modeling of Dike‐Induced Deformation and Seismicity: Application to the 2014 Bárðarbunga Dike, Iceland

AbstractDike intrusions are often associated with surface deformation and propagating swarms of earthquakes. These are understood to be manifestations of the same underlying physical process, although rarely modeled as such. We construct a physics‐based model of the 2014 Bárðarbunga dike, by far the best observed large dike ( 0.5 km ) to date. We constrain the background stress state by the total dike deformation, the time‐dependent dike pressure from continuous GPS and the extent of the seismic swarm, and the spatial dependence of frictional properties via the space‐time evolution of seismicity. We find that the geodetic and earthquake data can be reconciled with a self‐consistent set of parameters. The complex spatial and temporal evolution of the Bárðarbunga seismicity can be explained by dike‐induced elastic stress changes on preexisting faults, constrained by observed focal mechanisms. In particular, the model captures the segmentation of seismicity, where only the newest dike segment is seismically active. Our results indicate that many features of the seismicity result from the interplay between time‐dependent magma pressure within the dike and stress memory effects. The spatial variability in seismicity requires heterogeneity in frictional properties and/or local initial stresses. Modeling suggests that the dike pressure drops during rapid advances and increases during pauses, which primarily causes the segmentation of the seismicity. Joint analysis of multiple data types could potentially lead to improved, physics‐based eruption forecasts.

Stress memory effect in viscoelastic stagnant lid convection

Stress memory effect in viscoelastic stagnant lid convection

Evaluation of Crack Formation in Concrete and Basalt Specimens under Cyclic Uniaxial Load Using Acoustic Emission and Computed X-Ray Tomography

The paper discusses the use of acoustic emission, stress-memory effect, and X-ray computed microtomography (μST) to detect the onset of destruction of specimens of concrete and basalt which are widely used in construction. It is shown that the most informative parameter is acoustic emission activity based on which the onset of the formation of a main crack can be identified. The geometry of the crack is determined using computed X-ray tomography.

Surface Wave Velocity-Stress Relationship in Uniaxially Loaded Concrete

The deterioration of concrete due to excessive loading, freezing and thawing, corrosion of reinforcement, or alkali-silica reaction (ASR) begins with subtle changes in its microstructure and microcracking. The sonic surface wave velocity measured on prismatic concrete specimens under uniaxial compression was found to be highly stress-dependent. At low stress levels, the acoustoelastic effect and the closure of existing microcracks results in a gradual increase in surface wave velocities. At higher stress levels, concrete suffers irrecoverable damage: the existing microcracks widen and grow together and new microcracks form. This progressive damage process leads first to the flattening and eventually the drop in the velocity-stress curves. Measurements on specimens undergoing several loading cycles revealed that the velocities show a stress-memory effect. Comparing the velocities measured during loading and unloading, the effects of stress and damage on the measured velocities could be differentiated. The stress dependency of surface wave velocity proved to be direction-dependent. The velocity increases and decreases the most when measured parallel and perpendicular to the loading axis, respectively.

Stress triggering and stress memory observed from acoustic emission records in a salt mine

SUMMARY Some of the most interesting questions in geosciences are whether results from laboratory experiments can be applied to processes in the earth crust and whether in situ studies with high spatio-temporal resolution can bridge the gap between laboratory work and seismology. In this study, acoustic emission (AE) activity caused by stress changes due to the backfilling of a cavity in an abandoned salt mine is studied to answer questions regarding (1) the dependence of AE event rates, event distribution and b-value on the stress state, (2) the stress memory effect of rock (Kaiser effect), (3) the possibility to detect significant changes in the system like the initiation of macrocracks and (4) the possibility to estimate future activity from previous AE records. The large number of events studied (>3 × 10 5 ) allows a spatial resolution of the order of 1 m and a temporal one on the order of 1 hr. Stress changes are created due to the thermal expansion and contraction of the rock mass in response to the temperature changes caused by the backfilling. A roughly 20 × 50 × 50 m section of the mining complex just above the backfilled cavity is well covered by a network of 24 piezo-electric receivers and poses an optimal volume for the study. Results of a 2-D finite element thermoelastic stress model are in agreement with the spatio-temporal AE event distribution. In addition to the initial upward migration of the AE event front, which correlates with the calculated stress field, the rock salt exhibits a pronounced Kaiser effect for the first few thermal loading cycles throughout the whole study region. The deviation from the Kaiser effect during later loading cycles seems to be caused by the initiation of a planar macroscopic crack, which is subsequently reactivated. AE activity tends to concentrate along this macrocrack. Calculated b-values decrease before and increase after the supposed initiation of the macrocrack supporting this explanation. In intact rock volumes not subjected to macrocracking a linear relation between the maximum event rate and the calculated absolute Coulomb stress increase is observed. This indicates that future maximum AE event rates can be estimated from expected loading. AE activity during stress loading cycles is most prominent in regions with Coulomb stress maxima indicating possible shear cracking that has the potential to create macrocracks. Strong bursts of AE activity observed during thermal unloading phases are concentrated in regions for which the minimum principal stress becomes tensile. These regions exhibit significantly higher b-values than those active during thermal loading. We interpret these weak events with tensile microcracking.

The evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from Mt. Etna volcano

Volcanic edifices, such as Mt. Etna (Italy), are commonly subject to repeated cycles of stress over time due to the combination of magma emplacement from deep reservoirs to shallow depths and superimposed tectonic stresses. Such repeated stress cycles lead to anisotropic deformation and an increase in the level of crack damage within the rocks of the edifice and hence changes to their elastic moduli, which are a key parameter for reliable modelling of deformation sources. We therefore report results of changes in elastic moduli measured during increasing amplitude cyclic stressing experiments on dry and water-saturated samples of Etna basalt. In all experiments, the Young's modulus decreased by approximately 30% over the total sequence of loading cycles, and the Poisson's ratio increased by a factor of approximately 3 ± 0.5. Microseismicity, in terms of acoustic emission (AE) output, was also recorded throughout each experiment. Our results demonstrate that AE output only re-commences during any loading cycle when the level of stress where AE ceased during the unloading portion of the previous cycle is exceeded; a manifestation of the Kaiser stress-memory effect. In cycles where no AE output was generated, we also observed no change in elastic moduli. This result holds for both mechanical and thermal stressing. Our results are interpreted in relation to measurements of volcano-tectonic seismicity and deformation at Mt. Etna volcano.

An acoustic emission study of damage development and stress-memory effects in sandstone

As part of a study of damage development and stress-memory effects, we have carried out a series of laboratory acoustic emission (AE) experiments on dry Darley Dale sandstone under triaxial compressive loads. In particular, we studied the shape of damage surfaces in stress space. Like the yield surface in the theory of plasticity, a damage surface is defined as the locus of points in 3D stress space beyond which additional permanent damage develops. The shape of a damage surface thus provides a means of characterising the state of damage corresponding to the state of stress to which the material has previously been subjected. In our experiments, which were limited to the cross-section of stress space where σ 2 = σ 3 = P c (P c being the confining pressure), the points of the damage surface were indicated by the onset of AE. The damage surface in (P c, σ 1)-space corresponding to an initial stress state (P c i, σ 1 i ) is almost linear in the region where P c > P c i . In the region where P c < P c i the gradient of the damage surface becomes clearly larger. We compare the experimental results with predictions based on a 2D model of secondary microcrack (wing-crack) formation from frictional surfaces. According to this model, the damage surface is predicted to consist of two linear parts connected by a vertex (or “knee”) located at the point (P c i, σ 1 i ). The comparison shows that the model, although relatively simple, explains many features of the experimentally observed damage surfaces. The results also have implications in terms of a stress-memory effect. If the initially applied stress state (P c i, σ 1 i ) is not known, then it might in principle be derived from the position of the vertex in an experimentally measured damaged surface.

Anisotropic crack damage and stress-memory effects in rocks under triaxial loading

We present and analyse the results from tests performed on sandstone cubes in which the bulk acoustic emission (AE) and the ultrasonic P and S wave velocity changes in the three principal directions were monitored and measured simultaneously with the stress and strain as samples were deformed in three orthogonal directions independently. This combination of measurements has enabled us to directly link AE to the formation of new crack damage. From uniaxial cyclic stressing experiments the existence of the Kaiser stress-memory effect was confirmed based on the AE data and the velocity data from directions normal to the uniaxial stress direction. Furthermore, the effect was found to occur in each principal stress direction independently, regardless of whether or not stresses were applied along orthogonal axes. This suggests that the crack damage formed during stressing is highly anisotropic, with the new microcracks formed during each stress cycle having minor axes parallel to the minor principal compressive stress direction. The observed effects have been modelled in terms of the elastic closure of preexisting cracks and the formation of new highly-oriented dilatant cracks. The dilatant cracks produce AE. By modelling these two separate processes we have demonstrated a clear quantitative correlation between the AE output and the new dilatant crack damage formed during deviatoric stressing. We believe our results confirm the potential of the use of the Kaiser effect to determine crustal stresses from measurements on oriented core plugs taken from borehole cores.